Eclipse Pvti Refernce Manual

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PVTi

Reference Manual

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PVTi Reference Manual

Table of Contents3

Table of Contents

List of Figures ..... ...................................................................................................................................................................7

List of Tables ...... ...................................................................................................................................................................8

Chapter 1 - New developments........................................................................................................ 9Developments for 2007.1 .......................................................................................................................................................9

Developments for 2005A ......................................................................................................................................................10

Developments for 2004A ......................................................................................................................................................11

Chapter 2 - The Most Asked Questions About PVTi.................................................................... 15

Introduction......... .................................................................................................................................................................15

Chapter 3 - Introduction ................................................................................................................. 27

General information..............................................................................................................................................................27

Chapter 4 - Getting started............................................................................................................. 31

Starting PVTi ...... .................................................................................................................................................................31

Chapter 5 - Tutorials ....................................................................................................................... 32

Overview............. .................................................................................................................................................................32

Fluid Properties Estimation...................................................................................................................................................34

Creating a fluid system.........................................................................................................................................................37

Simulating experiments ........................................................................................................................................................43

Fitting an equation of state to experimental results ..............................................................................................................50

Exporting ECLIPSE Black Oil PVT tables.............................................................................................................................54

Converting a black oil run to compositional..........................................................................................................................58

Workflow Tutorial .................................................................................................................................................................61

Multiphase Flash .................................................................................................................................................................69

Exporting an ECLIPSE Thermal model ................................................................................................................................73

Data analysis and quality control..........................................................................................................................................77Removing contamination from samples................................................................................................................................84

Converting old projects to the current version ......................................................................................................................87

Chapter 6 - Reference section....................................................................................................... 89

General information..............................................................................................................................................................89

Main PVTi window ................................................................................................................................................................90

The PVTi main module .........................................................................................................................................................91

The fluid model ... .................................................................................................................................................................98

COMB - Compositional Material Balance ...........................................................................................................................112

Simulation using PVTi ........................................................................................................................................................117

Regression in PVTi.............................................................................................................................................................126

Exporting keywords ............................................................................................................................................................133

VFP module........ ...............................................................................................................................................................138Utilities ................ ...............................................................................................................................................................144

Batch system and keywords...............................................................................................................................................152

Error handling ..... ...............................................................................................................................................................165

Chapter 7 - Keywords ................................................................................................................... 167

PVTi keywords.... ...............................................................................................................................................................167

Keywords A-D..... ...............................................................................................................................................................168

ACF: Acentric factors......................................................................................................................................................... 169

ACHEUH: A-coefficient for Cheuh-Prausnitz BICs............................................................................................................ 170


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4 PVTi Reference ManualTable of Contents

ALLDRY: Dry Gas Tables for Each Sample ...................................................................................................................... 171

BIC: Binary interaction coefficients .................................................................................................................................... 172

BLACKOIL: Start of the BLACKOIL section....................................................................................................................... 174

CALVAL: Specify calorific values....................................................................................................................................... 175

CHARACT: Components to be characterized.................................................................................................................... 176

CNAMES: Component names ........................................................................................................................................... 177

COATS: Blackoil tables...................................................................................................................................................... 178

COMB: Start of the COMB section .................................................................................................................................... 179COMBINE: Group existing components ............................................................................................................................ 180

CORRACF: Splitting correlation for ACFs ......................................................................................................................... 181

CORRCP: Splitting correlation for critical properties ......................................................................................................... 182

DRYGAS: Dry gas tables................................................................................................................................................... 183

DEADOIL: Dead oil tables ................................................................................................................................................. 184

DEBUE: Select output to debug file................................................................................................................................... 185

DEBUG: Select output to debug file................................................................................................................................... 186

DEFBIC: Default binary interaction coefficients ................................................................................................................. 187

DEGREES: Temperature convention ................................................................................................................................ 188

DIFFERENTIAL: Blackoil tables ........................................................................................................................................ 189

DREF: Reference densities ............................................................................................................................................... 190

Keywords E-K ..... ...............................................................................................................................................................191

ECHO: Insert PVI file into PVP file ...................................................................................................................................... 192

EOS: Defines the required Equation of State ..................................................................................................................... 193EOSOUT: EoS data for ECLIPSE 300................................................................................................................................. 194

EXP: Experiments .............................................................................................................................................................. 195

EXPIND: Set Status of Experiments .................................................................................................................................. 200

FIT: Perform fit by regression ........................................................................................................................................... 201

FRAC: Specify plus fraction data ........................................................................................................................................ 202

FRAGOR: Blackoil tables..................................................................................................................................................... 203

FVFREF: FVF reference conditions.................................................................................................................................... 204

GI: Define GI nodes for E200 tables ................................................................................................................................. 205

GROUP: Start of the GROUP section.................................................................................................................................. 206

GRBYALL: Start of the GROUP section.............................................................................................................................. 207

GRBYMIX: Start of the GROUP section.............................................................................................................................. 208

GRBYSAM: Start of the GROUP section.............................................................................................................................. 209

GRPBYWGT: Grouping by molecular weight ........................................................................................................................ 210

HYDRO: Define component as hydrocarbon or non-hydrocarbon....................................................................................... 211KVTABLE: Request K-value table for ECLIPSE 300 output ............................................................................................... 212

Keywords L- O .... ...............................................................................................................................................................213

LBC: Lohrenz-Bray-Clark viscosities.................................................................................................................................. 214

LBCCOEF: Set non-default LBC coefficients ...................................................................................................................... 215

LIVEOIL: Live oil tables .................................................................................................................................................... 216

LNAMES: Specify library names.......................................................................................................................................... 217

MAXIT: Max. number of regression iterations.................................................................................................................... 218

MAXSTEP: Maximum step size allowed in regression ........................................................................................................ 219

MDP: Data for Whitson splitting .......................................................................................................................................... 220

MESSAGE: Echo message to file and screen...................................................................................................................... 221

MINDELP: Minimum pressure difference ........................................................................................................................... 222

MINSTEP: Minimum step limit allowed in regression ......................................................................................................... 223

MIX: Mix samples .............................................................................................................................................................. 224

MODSPEC : Denotes start of the run specification section .................................................................................................. 225MODSYS : Start of the MODSYS section ........................................................................................................................... 226

MOSES : Blackoil tables..................................................................................................................................................... 227

MW : Specify molecular weights......................................................................................................................................... 228

MWS : Define plus fraction mole weight for CMF splitting.................................................................................................. 229

NCOMPS : Specify number of components ..................................................................................................................... 230

NEWPVI : Request new output PVI file ............................................................................................................................ 231

NEWPVO : Request new output PVO file......................................................................................................................... 232

NOECHO : No insertion of PVI file into PVP file ................................................................................................................ 233

OBS : Specify observations.............................................................................................................................................. 234


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Table of Contents5

OBSIND : Specify observation weights ............................................................................................................................ 235

OMEGAA/B: Specify EoS omega values........................................................................................................................... 237

OPTIONS : Set various program options ......................................................................................................................... 238

OUTECL3 : Start of the OUTECL3 section ...................................................................................................................... 240

Keywords P- S.... ...............................................................................................................................................................241

PARACHOR : Define parachors........................................................................................................................................... 242

PCRIT : Critical pressures................................................................................................................................................ 243

PEARCE : Blackoil tables................................................................................................................................................. 244PEDERSEN : Specify Pedersen viscosities..................................................................................................................... 245

PRCORR : Peng-Robinson correction ............................................................................................................................. 246

PSEUCOMP : Start of the PSEUCOMP section.................................................................................................................. 247

RECOVERY : Liquid production for recovery estimates................................................................................................... 248

REGRESS: Start of the REGRESS section....................................................................................................................... 249

REGTARG : Regression target ........................................................................................................................................ 250

RTEMP : Reservoir temperature for ECLIPSE Compositional......................................................................................... 251

RUNSPEC : Denotes start of the run specification........................................................................................................... 252

SALINITY : Specify sample salinity ................................................................................................................................. 253

SAMPLE : Specify fluid sample........................................................................................................................................ 254

SAMPLES : Specify fluid samples.................................................................................................................................... 255

SAMPLES : Specify fluid samples.................................................................................................................................... 256

SAMTITLE : Specify titles of fluid samples....................................................................................................................... 257

SAVCOMP : Save compositions ...................................................................................................................................... 258SCT : Defines Semi-Continuous Thermodynamics split................................................................................................... 259

SG : Specify specific gravity............................................................................................................................................. 260

SIMULATE : Start of the SIMULATE section.................................................................................................................... 261

SPECHA-D: Specify specific heat capacity coefficients.................................................................................................... 262

SPLIT : Start of the SPLIT section................................................................................................................................... 263

SSHIFT : Dimensionless volume shifts for PR3 ................................................................................................................ 264

STCOND : Standard conditions......................................................................................................................................... 265

SYSTEM : Start of the SYSTEM section........................................................................................................................... 266

Keywords T - Z ... ...............................................................................................................................................................267

TBOIL : Specify boiling points.......................................................................................................................................... 268

TCRIT : Specify critical temperatures............................................................................................................................... 269

THERMX : Thermal expansion coefficient for volume shifts............................................................................................... 270

TITLE : Specify run title ................................................................................................................................................... 271

TLOW : Define lowest temperature for VFP tables ............................................................................................................ 272TREF : Specify reference temperatures............................................................................................................................ 273

UNITS : Specify unit conventions..................................................................................................................................... 274

VAR : Specify regression variables ................................................................................................................................... 275

VCRIT : Specify volumes.................................................................................................................................................. 278

VCRITVIS : Specify volumes for LBC viscosity calculations ........................................................................................... 279

VERSION : Version of PVTi .............................................................................................................................................. 280

VFP : Start of the VFP section.......................................................................................................................................... 281

WAT100 : Output water properties .................................................................................................................................... 282



WATVFP : Output water properties .................................................................................................................................... 285

WETGAS : Wet gas tables.................................................................................................................................................. 286

WHIT : Defines Whitson splitting....................................................................................................................................... 287

WHITSON : Blackoil tables ................................................................................................................................................ 288X/YMFVP: XMFVP and YMFVP ECLIPSE tables.............................................................................................................. 289

ZCRIT : Specify critical Z-factors...................................................................................................................................... 290

ZCRITVIS : Specify critical Z-factors for LBC calculations.............................................................................................. 291

ZI : Specify sample composition...................................................................................................................................... 292

ZMFVD : Composition versus depth table ......................................................................................................................... 293

Chapter 8 - Technical Description ............................................................................................... 294

Overview............. ...............................................................................................................................................................294


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6 PVTi Reference ManualTable of Contents

Theoretical background of PVT ..........................................................................................................................................295

Equation of state. ...............................................................................................................................................................316

Basic laboratory experiments..............................................................................................................................................338

Regression ......... ...............................................................................................................................................................347

Output for ECLIPSE simulators ..........................................................................................................................................353

Analysis techniques ............................................................................................................................................................371

Recommended PVT analysis for oil reservoirs...................................................................................................................372

Recommended PVT analysis for gas condensate reservoirs .............................................................................................377Consistency tests and correlations .....................................................................................................................................381

Fluid Properties Estimation.................................................................................................................................................384

Regression in PVT analysis................................................................................................................................................386

Wax and asphaltene precipitation in PVTi ..........................................................................................................................394

Cleaning samples contaminated with oil-based mud..........................................................................................................398

Mixing and recombination of samples.................................................................................................................................400

ECLIPSE Thermal Export Module ......................................................................................................................................401

Appendix A - Units........................................................................................................................ 409

Units.................... ...............................................................................................................................................................409

Appendix B - Symbols.................................................................................................................. 413

Symbols .............. ...............................................................................................................................................................413

Appendix C - Bibliography........................................................................................................... 415

Appendix D - Index ....................................................................................................................... 421


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List of Figures7

List of Figures

Figure 5.1 .......... Fingerprint Plot .......................................................................................................................................40

Figure 5.2 .......... Phase Plot ..............................................................................................................................................41

Figure 5.3 .......... The plotted simulation results .................................................................................................................46

Figure 5.4 .......... Plot of Oil FVF, Viscosity and Rs versus pressure for the output black oil property tables ....................56Figure 5.5 .......... Phase Diagram for Schrader Bluff Fluids ...............................................................................................70

Figure 5.6 .......... The phase envelope plot. .......................................................................................................................78

Figure 5.7 .......... The main display shows messages indicating the quality of the data.....................................................79

Figure 5.8 .......... The main plot window after zooming in ..................................................................................................80

Figure 5.9 .......... The plot of k values versus pressure. .....................................................................................................81

Figure 5.10 ........ The Hoffman-Crump plot ........................................................................................................................82

Figure 5.11 ........ Hoffman-Crump-Hocott plot. ...................................................................................................................83

Figure 5.12 ........ The original sample, the cleaned sample and the estimated contaminant.............................................85

Figure 6.1 .......... The main PVTi window ...........................................................................................................................91

Figure 6.2 .......... Fingerprint Plot .....................................................................................................................................109

Figure 6.3 .......... Phase plot.............................................................................................................................................110

Figure 6.4 .......... Ternary Plot .........................................................................................................................................111

Figure 6.5 .......... Main display after performing material balance ....................................................................................113

Figure 6.6 .......... COMB module - vapor versus pressure plot ........................................................................................114Figure 6.7 .......... The VFP module...................................................................................................................................138


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8 PVTi Reference ManualList of Tables

List of Tables

Table 5.1 The Fundamentals panel .........................................................................................................................35

Table 5.2 Component and fluid definitions...............................................................................................................37

Table 5.3 Program Options data..............................................................................................................................39

Table 5.4 Constant Composition Expansion experiment at 220o F (* indicates bubble point pressure)..................44Table 5.5 Differential Liberation Experiment at 220o F (* indicates bubble point pressure).....................................47

Table 6.1 List of library components ........................................................................................................................95

Table 6.2 Observation data....................................................................................................................................123

Table 6.3 Set PVTi Program Options panel...........................................................................................................145

Table 6.4 Keywords for introducing sections .........................................................................................................156

Table 6.5 RUNSPEC keywords .............................................................................................................................156

Table 6.6 SYSTEM keywords ................................................................................................................................157

Table 6.7 SPLIT keywords.....................................................................................................................................158

Table 6.8 GROUP keywords..................................................................................................................................159

Table 6.9 COMB keywords ....................................................................................................................................159

Table 6.10 SIMULATE keywords.............................................................................................................................160

Table 6.11 REGRESS keywords .............................................................................................................................160

Table 6.12 BLACKOIL keywords .............................................................................................................................161

Table 6.13 PSEUCOMP keywords ..........................................................................................................................162Table 6.14 OUTECL3 keywords ..............................................................................................................................162

Table 6.15 VFP keywords........................................................................................................................................163

Table 6.16 APITRACK keywords.............................................................................................................................163

Table 6.17 Error codes ............................................................................................................................................165

Table 7.1 Output indices ........................................................................................................................................185

Table 7.2 Output indices ........................................................................................................................................186

Table 7.3 Required data for experiments...............................................................................................................195

Table 7.4 Keyword arguments ...............................................................................................................................196

Table 7.5 Restrictions for EXP keyword arguments...............................................................................................198

Table 7.6 Component Types..................................................................................................................................211

Table 7.7 Equation of State omega values ............................................................................................................237

Table 7.8 Default limits for variables......................................................................................................................276

Table 8.1 Alkanes ..................................................................................................................................................297

Table 8.2 Napthenes..............................................................................................................................................298Table 8.3 Aromatics ...............................................................................................................................................298

Table 8.4 Physical properties.................................................................................................................................299

Table 8.5 Multi-component (ii) mixtures.................................................................................................................299

Table 8.6 CVD Report............................................................................................................................................308

Table 8.7 Equation of State coefficients ................................................................................................................318

Table 8.8 Equation of State constants ...................................................................................................................319

Table 8.9 Parameter estimation data. N is the number of experimental points .....................................................335

Table 8.10 Parameter Values for Pure Component Viscosity Correlation ...............................................................335

Table 8.11 Physical Properties of Methane and Decane.........................................................................................336

Table 8.12 PVTi defaults for Fluid Property Estimation ...........................................................................................385

Table A.1 Units.......................................................................................................................................................410

Table A.2 Constants...............................................................................................................................................411

Table A.3 Conversion factors .................................................................................................................................411


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PVTi Reference Manual New developments

Developments for 2007.19

Chapter 1

New developments

Developments for 2007.1

Maintenance of this application is continuing until further notice.


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10 New developments PVTi Reference ManualDevelopments for 2005A

Developments for 2005A

Maintenance of this application is continuing until further notice.


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Developments for 2004A11

Developments for 2004A

ECLIPSE Thermal Export facility

For the 2003A version of PVTi a new ECLIPSE Thermal support module was available where

you were able to interactively develop a correlation which accurately predicted K-values for

each component in a given fluid. For the 2004A version this module has been extended to a full

export facility where you can write out files that are suitable for use as PVT input for ECLIPSE

Thermal. The motivation behind this is so that, just as you can export files to use as PVT input

for ECLIPSE BlackOil and ECLIPSE Compositional, they will now be able to do the same for

ECLIPSE Thermal.

PVTi will export a series of keywords when an export for ECLIPSE Thermal is performed. For

a workflow description and brief summary of these keywords see "Compositional Data for

ECLIPSE Thermal" on page 367. For a more technical outline of how the exported keywords

are used in ECLIPSE Thermal see "ECLIPSE Thermal Export Module" on page 401.

Export for API Tracking option in ECLIPSE

BlackOil

The API Tracking facility enables ECLIPSE BlackOil to model the mixing of different types of

oil, having different surface densities and PVT properties.

Without the API Tracking facility, the presence of different types of oil in the reservoir could be

handled with the aid of PVT region numbers. Oil in PVT region 1 would have its properties

determined from PVT table number 1, and so on. However, this method cannot model the

mixing of oil types. Oil flowing from region 1 into region 2 would appear to take on the

properties associated with region 2.

The API Tracking facility essentially replaces the concept of PVT regions for oil. The PVT

tables used for determining the oil properties are selected at each time step according to the

average API of the oil in each grid block (or to be more precise, its average surface density).

For a overview of the workflow involved to export PVT tables suitable for use in ECLIPSE

BlackOil with the API Tracking option turned on see "Export for API Tracking option in

ECLIPSE BlackOil" on page 134. For a more technical description of the API Tracking model

in ECLIPSE as well as an explanation of how PVTi calculates suitable PVT tables see "Model

for API Tracking option in ECLIPSE BlackOil" on page 364.

Batch Mode

For the 2004A version of PVTi the batch mode has undergone a significant revamp. Over the

last few years the user interface of PVTi has evolved rapidly and the existing batch mode facility

no longer adequately supports more recent functionality. There have been 3 significant

modifications to the PVTi batch mode:

1 The way a batch mode is executed has changed. The new way to launch a batch mode run

on a PC is to use the command $pvti -batch filename where filename is the

name of your PVTi project. See "General information" on page 152 for more details on

running batch mode with other platforms.


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Developments for 2004A13

2 HEATVAPS.

This keyword is used to store the Heat of Vaporization at the standard temperature for each

component.

Sections

There is a new section called APITRACK. This is used when preparing batch files if the APITracking export facility is to be made use of in batch mode. It is essentially the same as the

BLACKOIL section but has an extra keyword called SAMPLES, which records the samples for

which PVT tables will be exported.

Manual

1 The section "The Most Asked Questions About PVTi" on page 15 has been updated with

questions regarding the Batch Mode, ECLIPSE Thermal Export and API Tracking

functionality.

2 A number of the tutorials have been amended - in particular the tutorial entitled “Using the

ECLIPSE Thermal Support Module” has been replaced by a tutorial called "Exporting an

ECLIPSE Thermal model" on page 73.


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14 New developments PVTi Reference ManualDevelopments for 2004A


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PVTi Reference Manual The Most Asked Questions About PVTi

Introduction15

Chapter 2

The Most Asked Questions

About PVTi

Introduction

This section has been designed as a reference section so that you can quickly access information

about common problems encountered with PVTi without having to spend time looking through

the manual for the relevant section. The questions in this section have been constructed using

the most common support issues and also the InTouch database. Cross-references are provided

where necessary so that readers can access the appropriate parts of the manual for more detailed

information on a particular topic if required.

The questions are:

• "What is PVTi used for? Why do we need it?" on page 16

• "Where do I start? How do I set up a project within PVTi?" on page 16

• "How do I create an experiment along with a series of observations?" on page 17

• "What are the data limitations in PVTi?" on page 18

• "What is the Fluid Properties Estimation facility in PVTi?" on page 19

• "How do I perform regression on multiple fluid samples?" on page 19

• "What regression parameters should I choose?" on page 21

• "What is the difference between normal regression, special regression and automatic (PVTi

selects) regression?" on page 20

• "How does PVTi support gas condensate simulation?" on page 22

• "Can Black Oil tables be extended above the liquid bubble point in PVTi?" on page 22

• "Can PVTi be used if you know the composition of a fluid but do not have any

observations? And vice-versa?" on page 22

• "What black oil correlations are available in PVTi?" on page 23

• "How do I generate the asphaltene phase envelope using PVTi?" on page 23

• "How does PVTi support ECLIPSE Thermal?" on page 24

• "How do I Use PVTi’s Batch Mode?" on page 25


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16 The Most Asked Questions About PVTi PVTi Reference ManualIntroduction

• "How Can I Export PVT Tables to use the API Tracking Functionality in ECLIPSE

BlackOil?" on page 25

What is PVTi used for? Why do we need it?

PVTi is a compositional PVT equation-of-state based program used for characterizing a set offluid samples for use in our ECLIPSE simulators.

We need PVTi because it is vital that we have a realistic physical model of our reservoir fluid

sample(s) before we try to use them in a reservoir simulation. PVTi can be used to simulate

experiments that have been performed in the lab on a set of fluid samples and then theoretical

predictions can be made of any observations that were performed during a lab experiment, in

order that we can test the accuracy of our fluid model.

Any differences between the measured and calculated data are minimized using a regression

facility which adjusts various Equation of State parameters. This ‘tuned’ model is then exported

in a form suitable for one of our ECLIPSE simulators.

What is especially important to note when using the ECLIPSE Compositional simulator is that

PVTi and ECLIPSE Compositional use the same flash algorithm. This is vital as the flash has been used to simulate the experiments and predict values for experimental observations and is

therefore inherent within the fluid model itself which has been exported by PVTi. If ECLIPSE

Compositional used a different flash then the fluid model exported by PVTi would no longer be

valid.

Where do I start? How do I set up a project within

PVTi?

Defining a Fluid Sample

If you want to open a new project then start PVTi as instructed in "Getting started" on page 31

for your machine-type and choose a filename. PVTi starts; recognizes that it has a new project

and immediately opens the Fundamentals panel. This panel has been specifically designed to

make setting up a new project as easy as possible. Simply fill in the Components and ZI

columns with the component names and mole fractions respectively, which is the minimum

required to have a project within PVTi.

To fill in the component names simply type the standard shorthand names for the components

in your fluid, for example, C1, N2, CO2, H2S, IC5, etc. For more information on shorthand

names and component types see "Component types" on page 102. The mole fractions can be

entered as fractions or percentages by selecting the appropriate option on the panel. Also,

weight fractions/percentages can be entered for the components instead of mole fractions/

percentages.

Your Mole/Weight data must add up to 1 if entering as fractions and up to 100 if entering as

percentages. If they do not then PVTi asks you if you want it to renormalize your data when you

close the Fundamentals panel. If you want to add some components then select No,- otherwise

select Yes.

Warning If you try to perform operations on a fluid with incorrectly normalized mole/

weight fractions then the operation may fail.


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Introduction17

Once the Fundamentals panel has been completed you will see have a sample called ZI on the

tree view on the left-hand side of the main window.This is the fundamental sample for the

project and the name ZI cannot be changed.

Creating Other Fluid Samples

Other fluid samples can be created in a project by selecting Edit | Samples | Name... . Simplytype in the name of the new fluid sample you want to create. The composition information can

then be entered for this fluid by selecting the Edit | Samples | Compositions... option.

Additional fluid samples to the project must always be subsets of the ZI sample in terms of the

component names, for example you cannot have a C8 component in an additional fluid sample

called OIL if C8 was not defined in the ZI sample. If you open the Edit | Samples |

Compositions... panel you can see why this has to be the case in PVTi.

Note Just because a component is defined in the ZI sample it does not mean there has to be

any of it there. It only has to be defined in the ZI sample to be used in other fluid

samples. If the mole fraction of a C8 component in the ZI sample is set to be 0.0 then

the C8 component can then be use in the OIL sample and the mole fractions set as

required.

Once at least one fluid sample (the ZI sample) has been defined then any experiment supported

within PVTi can be simulated as well as operations such as phase plots, fingerprint plots and

splitting.

For more information on creating fluid samples see "Defining Samples" on page 107.

How do I create an experiment along with a series

of observations?

Creating Experiments

To create an experiment select the Edit | Experiments... option and the experiment Entry panel

opens. The existing experiments are listed and you can edit them by selecting one of them and

clicking the next button. To create a new experiment click add in the top left of the panel and

select the experiment you wish to create. Choose the fluid sample you want to perform the

experiment on and then navigate through the panels by filling in the required information and

then clicking next, which takes you to the next panel. The information generally consists of

temperature and/or pressure information but not always, it depends on the experiment.

Once an experiment has been created an experiment button, along with an experiment name,

appears below the fluid sample which the experiment was performed on.

Creating Observations

If there are no observations at all for a particular experiment then to create one you need to select

the Edit | Observations... option and the Observations panel appears.

On the Experiments column on the left-hand side there is a list of all the experiments that are

available within PVTi and * symbols are next to the ones that you currently have defined within

your project.


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If one of these experiments is selected then in the Experiment List column a list of all the names

of the experiments of that type in your project appears for example, BUBBLE5, DEW3, DL1.

If one of these is selected then all the possible observations available within PVTi for that type

of experiment are displayed in the Observation Type column. Again observation types with a

* next to them means that there are values already defined for this particular experiment in your

project. Simply click on one to see and edit the values. To create a new observation select the

one you want and then click on the + button on the top left of the panel. Values and weights canthen be entered for the observation.

Note Currently defined observations for an experiment can be edited in the Observations

folder on the experiment Entry panel.

For more information on creating and editing experiments/observations see "Simulation using

PVTi" on page 117 and/or the tutorial "Simulating experiments" on page 43.

What are the data limitations in PVTi?

Pre-2003A

Up to and including the 2002A_1 release (pre-2003A) the following data constraints were

present in PVTi:

• 50 fluid samples

• 50 components per fluid sample* (see below)

• 50 experiments per fluid sample

• 300 observations per experiment

Note *When a splitting operation was performed it was possible to have more than 50

components (up to 100 in fact) but the components had to be grouped back so that therewere less than 50 before any experiment simulation could take place.

2003A

These pre-2003A data constraints have been present in PVTi for 4 to 5 years and, in-line with

the huge increase in computing power in the last few years, we have decided to enhance the data

constraint capability of PVTi so that the following is now available:

• 100 fluid samples

• 100 components per fluid sample* (see below)

• 100 experiments per fluid sample

• 300 observations per experiment

Note It is now possible to read in, save, split and group with fluids containing up to 100

components. However, the limit is still 50 components for any functionality involving

the EoS flash.


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Introduction19

What is the Fluid Properties Estimation facility in

PVTi?

The Fluid Properties Estimation (FPE) facility in PVTi is designed so that it can be used when

you have minimal data at your disposal, at the well-site for example. In this scenario, a full lab

analysis of multiple fluid samples from the reservoir has not yet been performed. Typically, just

a single sample would be available and minimal fluid behavior known for example, saturation

pressure at a particular temperature.

Specifically, the FPE facility assumes that a single fluid sample with compositional information

is available which includes a single plus fraction (for example C7+) component of which the

weight fraction is known. Typically, this weight fraction data is fairly accurate but the mole

weight, which is used to characterize the critical properties of the plus fraction, is not. The FPE

functionality allows you to perform a quick look simulation that regresses on the mole weight

of the plus fraction, and keep the weight fraction constant, in order to fit to a saturation pressure

observation at a particular temperature.

The FPE facility is available in the top right-hand corner of the fundamentals panel whenever a

new project is created. Alternatively it can be accessed using the Edit | Properties Estimation

(FPE)... option. For more information on this facility see "Fluid Properties Estimation" on

page 384. For an example of how it works see the tutorial "Fluid Properties Estimation" on

page 34.

How do I perform regression on multiple fluid

samples?

General

The fluid samples that PVTi performs regression on is determined by the structure of the tree

view on the left-hand side. By default, PVTi performs a regression on every experiment which

has observations defined, even if there are multiple fluid samples, each with their own

experiments. The reason for this is that, within a project, all fluid samples are considered to be

relevant to each other and so the same fluid model should be applied to all samples, even if the

compositional make-up of each sample is different

Note If two of your fluid samples are not relevant to each other for example they come from

different wells/reservoirs then a separate project should be created for each one.

Disabling Experiments/Observations

You can prevent PVTi from including an experiment in the regression by right-clicking on theexperiment and selecting Don’t use in Regression. A cross appears on the experiment

indicating it is not currently available within the regression facility.

You can disable an observation so that it is not used within the regression by again right-clicking

and selecting Don’t use in Regression. Alternatively, by right-clicking and selecting Set

Weight and then entering zero the observation is also not included in the regression.


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Note If an experiment is disabled then, as you would expect, all the observations are

automatically disabled.

Regression Weights

In general there will be a set of values in an observation. For example, if we have a differentialliberation (DL) experiment defined then a viscosity observation would have a value for each

pressure. We have two types of weight: there are single weights for each value of an observation

and global weights that apply to every value in an observation.

By right clicking on an experiment observation the global weight can be set. As mentioned

above, by setting this to zero none of the values in the observation would be used. Alternatively,

you may want to set a global weight for an experimental observation particularly high, for

example, matching the bubble point of a fluid is normally very important if one wants to ensure

that it is a single-phase liquid at the temperature and pressure of the reservoir.

Or maybe you do not trust the accuracy of a particular observation value, for example an oil

formation volume factor (FVF) value in a DL experiment.You may then not want to use a global

weight as all the other observation values look ok. In this case setting a single-value weight to

a very low value helps you match all the other values in the observation during regression as therogue, inaccurate value no longer inhibits convergence.

Both the single-value and global weights for an experimental observation can be set in the

Observations panel by selecting the Edit | Observations... option, highlighting the

appropriate observation and then simply typing in your chosen weights.

For a good example of how to use the regression facility, see the tutorial "Fitting an equation of

state to experimental results" on page 50.

What is the difference between normal regression,

special regression and automatic (PVTi selects)

regression?

There are 3 types of regression: normal, special and automatic. The difference between them

depends entirely on what kind of variables are being regressed on.

Normal regression parameters are equation of state variables relating to a particular component,

for example, critical pressure, , critical temperature, , acentric factor, . and the binary

coefficients. The full set of normal regression variables can be viewed using the regression

panel using the Run | Regression... panel. Select normal as the regression type and then click

variables - the upper table shows the single-valued normal regression parameters for each

component and the lower panel shows the binary coefficients table. For more information on

setting normal regression see "Setting normal variables" on page 127.

Special regression parameters are global Equation of State variables, for example, the thermal

expansion coefficient or the Cheuh-Prausnitz A factor for binary coefficients. There may also

be some splitting parameters available as special regression variables depending on whether a

multi-feed split has been performed on the plus fraction. See "Multi-feed Split (also called semi-

continuous thermodynamic (SCT) split)" on page 106 for more details on this facility. For more

information on setting special regression variables see "Setting special variables" on page 129.

P c T c ω


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Introduction21

The automatic regression facility or PVTi Selects as it is called on the Regression panel

attempts to choose the best normal variables to regress on for you before actually doing the

regression and reporting the answer. It should be noted that there is no substitute for a good

engineer in the sense that one should not just use this automatic facility all the time in the belief

that PVTi will do all the work. For example, the automatic facility will not use special variables

to regress on and so it is up to you to decide whether this would be necessary or not.

However the automatic facility can still be a useful tool in obtaining a good match to PVT data.The way the algorithm chooses the regression parameters is essentially based on 2 criterion. No

parameters are allowed to have more than a 90% correlation on any other parameter. Secondly,

no parameter is allowed to have less than 1% of the sensitivity of the most sensitive parameter

For a detailed discussion of the automatic regression algorithm see "A consistent methodology

that can be applied automatically" on page 389.

For more general information on the regression facility see "Regression in PVTi" on page 126.

What regression parameters should I choose?

It should be noted that there are no concrete rules for getting a good match to observations

relating to multiple fluid samples, but there are some general guidelines of what is often a goodidea, and what you should definitely not do.

Library components tend to have properties that are very well known and any of these will not

normally be good choices of regression variables. Properties of non-library components and

characterized components are much less well known and these are often good choices. In

general, the following set of variables are normally good things to initially regress on:

• and of any non-library component.

• and of any component with mole weight of C7 or heavier (as these are effectively

mixtures of different molecule types and so may differ from library values).

• and of any component with mole weight C7 or heavier. Again because these are

mixtures.

• No binary inter-active coefficients because of the risk of over-fitting.

• No viscosity-specific parameters, again because of the risk of over-fitting.

The variables mentioned above are all normal regression variables. The following set of special

regression variables can also often prove useful to get a match between samples:

• Do a multi-feed split to split the plus fraction into 2 or 3 pseudo-components. The ,

SCTMW and K w parameters, which control the splitting are then very good choices.

• The Cheuh-Prausnitz A binary parameter if using Cheuch-Prausnitz binaries.

• The mole weight of a plus fraction (if no split on the plus fraction has been performed).

For a detailed explanation of why some of the above are good and bad choices for regression parameters, see "Regression in PVT analysis" on page 386. There are also more specific

guidelines for choosing regression parameters depending on whether one is dealing with an oil

reservoir, see "Recommended PVT analysis for oil reservoirs" on page 372 - or a gas-

condensate reservoir, see "Recommended PVT analysis for gas condensate reservoirs" on

page 377.

Finally, for a tutorial illustrating the use of the normal and special regression facilities in a

typical workflow see the new "Workflow Tutorial" on page 61.

P c T c, ω

P c T c, ω

Ω A Ω B

α


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How does PVTi support gas condensate

simulation?

Gas condensate simulation is modeled in PVTi using the Constant Volume Depletion (CVD)

experiment. In most gas condensate reservoirs liquid does reach a high enough saturation to

become mobile as the pressure drops. Thus, gas and oil, to a good approximation, do not move

with respect to each other and so the CVD experiment models this behavior very well. Other

experiments that tend to be used for gas condensates are the dew point and constant composition

expansion experiments. For more information see "Gas condensate systems" on page 340.

A common failing when analyzing gas condensate reservoirs is to attempt to establish an

equation of state representation without a through examination of the data on which it is to

based. Things to check in the data are the characteristics of the heavy components (use a

fingerprint plot), material balance information and other information such as K-values and Z-

factors. Once you are happy with the data that you will try to match there is a recommended

procedure, in terms of regression, which will work for most gas condensates. For a detailed

description on how to model gas condensates see the section entitled "Recommended PVT

analysis for gas condensate reservoirs" on page 377.

Can Black Oil tables be extended above the liquid

bubble point in PVTi?

Yes. You should make sure that the DL/CVD experiment you simulate in PVTi covers the full

range of pressure values you are likely to encounter within your reservoir. If ECLIPSE BlackOil

encounters a pressure outside the range in the black oil table you exported from PVTi then it

will have no choice but to try to extrapolate to estimate properties such as gas-oil ratio (GOR)

and formation volume factor (FVF). The extrapolation used is linear and uses the appropriate

quantities at the two highest pressures in the exported black oil table.

However, this extrapolation can sometimes run into difficulties as is common in any problemwhen you are trying to gain information about unexplored parameter space. The normal error is

that ECLIPSE throws up negative compressibilities for your fluid. If this happens then be sure

to check your black oil tables covered the appropriate range of pressures.

For a thorough description of the black oil model used by PVTi and how the tables are extended

above the bubble point see "Blackoil model" on page 353.

Can PVTi be used if you know the composition of

a fluid but do not have any observations? And

vice-versa?

You know the fluid composition

If you have compositional information about the fluid, but no observations, then you can do

anything you want within PVTi except use the Regression facility. This is because the

Regression facility tries to minimize the differences between lab observations and PVTi’s

theoretical predictions and this is not a sensible operation if no observations are defined.


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Introduction23

In fact, in PVT laboratories engineers tend to use the default fluid model (one that has not been

regressed on) for a given equation of state in PVTi to give them a ‘ball-park’ answer for their

particular experimental observation. This can give them some idea as to how to set their

experiment up as they now have information on the kind of answers they might expect to

measure.

You have observationsIf you have observations but no compositional information at all then PVTi does have the

facility to convert black oil tables into a fully compositional model. To do this you must have

black oil tables that were exported by PVTi using the 2002A release or later. The tutorial entitled

"Converting a black oil run to compositional" on page 58 will explain this workflow in more

detail.

Note If you have black oil tables exported from before and including 2001A_2 PVTi, or you

have no black oil tables at all then, unfortunately, PVTi will not be able to construct the

compositional model for you. !

What black oil correlations are available in PVTi?

PVTi is a compositional PVT program and at the moment does not support black oil correlations

within its functionality.

It can however export a black oil model, using the compositional model tuned by the user within

PVTi to a DL or CVD experiment, for the ECLIPSE BlackOil simulator by generating tables of

Rs, FVF, etc. as a function of pressure for a given reservoir temperature. To export a black-oil

model select File | Export Keywords... . If you want to export a black oil table from a DL

experiment then you generally use the Oil Reservoir... menu option and if you have a CVD

experiment then the Gas Reservoir...option is appropriate. For more information on exporting

keywords see the section entitled "Exporting keywords" on page 133.

How do I generate the asphaltene phase envelope

using PVTi?

Just like a phase curve has single phase regions for the vapor and liquid and a 2-phase region an

asphaltene phase envelope may exist for your fluid. The asphaltene phase envelope partitions

off a region in pressure-temperature space where an asphaltene phase exists, analogous to the

two-phase region in a standard phase curve.

The upper line partitioning a region in pressure-temperature space where an asphaltene phase

does and does not exist is called the Asphaltene Disappearance Pressure (WDP) line. The lower

line is called the Asphaltene Appearance Pressure (WAP) line. In PVTi 2003A both curves aresupported, whereas in PVTi 2002A/2002A_1 just the functionality for the appearance line is

available.

Unlike a standard phase curve though where, as long as you do not have a fluid consisting of a

single pure component, there will always be a two-phase region, this is not the case in terms of

an asphaltene phase envelope. Asphaltene may never be present no matter what temperature and

pressure your fluid is at.


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Introduction25

For more detailed information on the new thermal module see "ECLIPSE Thermal Export

Module" on page 401. For workflow information and a summary of the exported keywords see

"Compositional Data for ECLIPSE Thermal" on page 367.

How do I Use PVTi’s Batch Mode?

The batch mode facility is accessed from the command line (if using a PC) using the command

‘$pvti -batch filename.pvi’ where filename is the rootname of your project. If using

a UNIX machine then use the command ‘@pvti -batch filename.pvi’. The

recommended way to prepare a file for use in the batch mode is as follows:

1 Open the project file in interactive mode which you wish to use.

2 Save the file using the File | Save (concise)... menu option.

3 Load this new ‘concise’ file back into PVTi and open the Set PVTi Program Options

panel by doing Utilities | Program | Options.... Set the last option Write Keywords for

Batch Mode to Yes.

4 Now perform the required workflow in interactive mode that you wish the batch mode to

reproduce e.g. simulation of experiment, splitting, grouping, export, etc.

5 When you have performed the workflow save the file using File | Save...

6 The saved file is now suitable for running in batch mode.

For a comprehensive review of the new batch mode functionality see "Batch system and

keywords" on page 152.

How Can I Export PVT Tables to use the API

Tracking Functionality in ECLIPSE BlackOil?

PVTi now has the capability to export multiple PVT Tables for use in ECLIPSE BlackOil’s APITracking. Without the API Tracking facility, the presence of different types of oil in the

reservoir could be handled with the aid of PVT region numbers. Oil in PVT region 1 would have

its properties determined from PVT table number 1, and so on. However, this method cannot

model the mixing of oil types. Oil flowing from region 1 into region 2 would appear to take on

the properties associated with region 2

Just like exporting a standard black oil table a depletion experiment must be defined in order to

do API Tracking export. The workflow is as follows:

1 Use the File | Export Keywords | API Tracking option in ECLIPSE BlackOil... menu

option to open the Export Panel for API Tracking.

2 Select the samples you wish to use in the export and move them to the Use box.

3 Choose the keywords you wish to export. Normally the Live Oil (PVTO) and Dead Gas(PVDG) keywords are used with the API Tracking option.

4 Select whether you wish to export a gas table for each sample or just a single gas table.

5 Select whether you wish to plot the tables in PVTi.

6 Select whether you wish to write to tables using full double precision numbers.

7 Select the separator you wish to use for the export.

8 Select the units you wish to export the table in.


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PVTi should then write the tables to a file and show them in the output display. This file is then

suitable to use as the PVT input for an API Tracking run in ECLIPSE BlackOil. For a similar

description of the API Tracking workflow see "Export for API Tracking option in ECLIPSE

BlackOil" on page 134. For a technical description of the API Tracking model in ECLIPSE as

well as an explanation of how PVTi calculates suitable PVT tables see "Model for API Tracking

option in ECLIPSE BlackOil" on page 364.


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PVTi Reference Manual Introduction

General information27

Chapter 3

Introduction

General information

The PVTi program is an Equation of State based package for generating PVT data from the

laboratory analysis of oil and gas samples. The program may be used through an interactive

menu system or run in a batch mode. An interactive session can be saved as a batch input file,

which contains commands to reproduce the interactive operations. Alternatively, a batch input

file can be run from an interactive session.

Equations of state and viscosity correlation

Four equations of state are available, implemented through Martin’s generalized equation. This

enables the Redlich-Kwong, Soave-Redlich-Kwong, Peng-Robinson and Zudkevitch-Joffe

equations to be used. Two 3-parameter extensions of the Peng-Robinson Equation of State are

also available, one based on a Peneloux et al. volume shift, the other being an implementation

of the Schmidt-Wenzel Equation of State 2-parameter Peng-Robinson. The Soave-Redlich-

Kwong Equation of State similarly has a three-parameter extension.

Viscosities may be calculated using a method by Pedersen et al. based upon a corresponding

states comparison with methane, or by the Lohrenz-Bray-Clark method.

Fluid definition

Multiple fluid samples can be defined by specifying components as one of three types. Library

components require only that the appropriate component mnemonic be entered. Characterized

components define properties of plus fractions from a limited set of information. Finally all the

properties of a component can be defined, a facility which can be used selectively to edit the

properties of existing components.


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28 Introduction PVTi Reference ManualGeneral information

It is possible to group the components to reduce or pseudoise the fluid system (make a fluid

definition of the system using pseudo components), or to split the plus fraction into more

components, preserving molecular weight and mole fraction. Multiple samples having different

plus fraction properties, say mole weight and specific gravity, can be characterized by splitting

the plus fraction into two or more pseudo-components of fixed properties but variable

composition.

Fingerprint plots of mole fraction against molecular weight, or phase diagrams, are available.

Material balance checks

A compositional material balance can be performed on any gas condensate or volatile oil for

which a laboratory constant volume depletion or differential liberation experiment has been

performed. This can be used to estimate liquid compositions and hence K -values. The calculated

quantities can then be used to estimate the quality and consistency of the laboratory data.

Additionally, tests on recombination of separator data can be performed and estimates of

reservoir recovery can be made.

Simulation of experiments

Experiments may be performed on the fluid systems defined using the equation of state model.

Possibilities are:

• saturation pressures

• flash calculations

• constant composition expansions

• constant volume depletions

• differential liberations

• swelling tests

• multi-stage separator simulations.

Other experiments available are:

• composition versus depth

• vaporization test

• multiphase flash

• critical point

• saturation temperature

• first contact miscibility

• multiple contact miscibility (condensing and vaporizing).

• wax appearance temperature

• asphaltene appearance pressure


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30 Introduction PVTi Reference ManualGeneral information


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PVTi Reference Manual Getting started

Starting PVTi 31

Chapter 4

Getting started

Starting PVTi

Windows platforms

ECLIPSE Program Launcher

1 Start the ECLIPSE Program Launcher.

2 Click on the PVTi button.

3 Select the version and working directories as required.

Command line

1 Type the command $PVTI in a command prompt window.

UNIX platforms

1 Type the command @pvti at the command prompt.


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PVTi Reference Manual Tutorials

Overview 32

Chapter 5

Tutorials

Overview

Eclipse Pvti Refernce Manual

Documents

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