Session 1 log-analysis

Abdelrahman Elkhateeb

Cairo University

12/08/2016Abdelrahman Elkhateeb www.facebook.com/formation.evaluation 2

*Petrophysics is the study of rock properties and their interactions with fluids (gases, liquid hydrocarbons, and aqueous solutions)

*The petrophysicist is the link between the subsurface disciplines

*Petrophysics is the science that integrates many valuable data together to have quantitative formation evaluation based on conventional/advanced logs and core analyses

*Log analysis vs. petrophysics

Log Analysis

Different Inputs Certain Outputs

GR Resistivity Porosity ɸ


𝑆#𝑉%&

Borehole Sketch

12/08/2016Abdelrahman Elkhateebwww.facebook.com/formation.evaluation 4

Schlumberger

What We Provide...


Is it Complicated?!! J


*A 24/7 job

*Presence of hydrocarbon is your call

*Wells/lithology could be very complicated

*Tough to learn in most companies

*Skill shortage in the industry

*Too much to learn

*What to start with?

*Where/How to start?

…........BUT, is it worth really?

A Shed of Light...


*Everyone takes the petrophysicist outputs to use

*You are the link between the geologist and the RE

*You learn how to manage, work under stress and how to provide only what is accepted

*You manage the LWD and wireline operations

*You are dealing with data no one literally see or use

*You are dealing with new technology, that makes you always think

*Your output is seen at all management levels

Log Example


This log is drawn by hand for presentation purposes only

What To Do (Simply)?


*Estimate clay volume

*Calculate the porosity

*Read the resistivity

*Calculate water saturation

REMEMBER!!The key for log interpretation is to understand how to read the log

How to Read the Log?



Clay Volume Calculation


*A simple equation using GR log is used to evaluate the clay volume

*The neutron/density could be used to calculate the clay volume with the same equation

*The softwares use different evaluation appraoches, a bit complicated, depending on the inputs used

*Porosity tools or even resistivity could be used to evaluate the clay volume

𝑮𝑹 𝐥𝐨𝐠 ,𝑮𝑹𝒄𝒍𝑮𝑹𝒔𝒉,𝑮𝑹𝒄𝒍

= shV

Density Porosity Calculation


* The density log is the most robust porosity tool

* The porosity is calculated using simple equation:

∅𝑫 =𝝆𝒎𝒂 − 𝝆𝒍𝒐𝒈𝝆𝒎𝒂 − 𝝆𝒇𝒍

* Matrix density differs by lithology* L.ST: 2.71 g/cc* S.ST: 2.65 g/cc* Dol.: 2.847 g/cc

* The 𝝆𝒇𝒍 is the density of the fluid saturating the rock immediately surrounding the BH, (usually mud filtrate)....SLB

* The tool is affected by washouts, rugose holes and high tension

Density Porosity Chart


27 p.u.

*Determine the porosity from the density log value of 2.4 g/cc for a dolomite reservoir?

Sonic Porosity Calculation


* The sonic log is the reflecting primary porosity only

* The porosity is calculated using simple equation:

* Matrix density differs by lithology*S.ST: 55.5-51.3 µs/ft (18000-19500 ft/s)*L.ST: 47.6-43.5 µs/ft (21000-23000 ft/s)*Dol.: 43.5-38.5 µs/ft (23000-26000 ft/s)

* The tool is used for seismic tie, CMT job evaluation and secondary porosity evaluation

∅< =∆>?@A,∆>BC∆>D?,∆>BC

Sonic Porosity Chart


10.5 p.u.

*Determine the porosity from the sonic log value of 70 µs/ft for a sandstone reservoir?

34 p.u.

Calculating Total Porosity


* With 3 inputs, the porosity could be the average of them

* For Gas Intervals

ϕFGϕ<GϕH

I=Tφ

φT =FLMNOGHLMNO

P

Density-Neutron Crossplot


g/cc2.38=bΡ0.165=NФ

0.20

L.St or S.S ??

Porosity-Resistivity Pick



Water Resistivity (Rw)


* This is a key parameter in saturation calculation

* Rw is evaluated through different methods:

* Reversed Archie Method

* Pickett Plot

* Formation Water Salinity

* The uncertainty in the Rw value affects the saturation profile near the contact dramatically


Rw From Pickett Plot


*Pickett plot is very important tool to detect the water resistivity

*It should be used as a confirmation for the reversed Archie method with more accuracy

*The m value is the slope of the line

*(m) value is crucial in carbonates

*The core data is usually needed to vary (m) parameter, otherwise the default value is used

Salinity Value From Slb Chart


*Easily used to detect the Rw and salinity using the formation temperature

*The salinity should not change across different locations/wells in the same structure

*The Rw changes with temperature/depth

*The formation salinity could vary significantly from formation to another

Calculating Water Saturation


*There are several models for Sw calculations*Two main reservoirs exist; clean and shaly reservoirs*The clean formations are evaluated with Archie equation

*Shaly reservoirs use different models depend on the clay distribution *Schlumberger/Laminated sand-shale simplified model is one

simple model to evaluate the shaly sands

1𝑅a=

∅P𝑆𝑤P

1 − 𝑉cde ∗ 𝑎𝑅𝑤+𝑉cde𝑅%&

𝒂∗𝑹𝒘Ф𝒎∗𝑹𝒕= n )W(S

Log Example



The Effective Porosity (Oil)


*In oil bearing reservoirs, the effective porosity curve is divided into three curves, the bulk volume of water (BVW), movable oil and residual oil.

Residual Oil

Movable Oil

Bulk Volume Water

0.5 0effФ

The Effective Porosity (Gas)


*In gas bearing reservoirs, the effective porosity curve is divided into three curves, the bulk volume of water, the movable fluids and the gas.

0.5 0effФ

Residual Gas

Movable Hydrocarbon

Bulk Volume Water

Sw-BVW Relationship


*Bulk Volume of Water is the volume of the water relative to the total bulk volume of the rock.

*Water saturation is the amount of water in the pore spaces.

Sw= BVW/ ϕ

ϕ* wBVW = S

References


*Schlumberger Chartbook 2009

*Schlumberger Log interpretation principles and applications 1989

Abdelrahman Elkhateebwww.facebook.com/formation.evaluation

Session 1 log-analysis

Presentations & Public Speaking

Transcript of Session 1 log-analysis