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Evaluation Techniques for ThinlyBedded Sandstones
Petrophysics
Jan van der Wal, Senergy
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Outline
• What are Thin Beds?
• Part 1: Evaluation Techniques
• Part 2: Revisiting Normalised Qv of Juhasz
• Example
(NL: Spekkoek)
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• Introduction
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Introduction
Thin Beds Concept
• What are ‘Thin Beds’?
• Laminations of sand and shale, with..
• .. beds so thin that logs do not read true properties.
• Why do we care? In Thin Beds..
• .. conventional evaluation can miss pay,
• .. phi & perm are too low,
•
.. resistivity reads too low, and• .. saturation height functions give too low HC.
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Introduction
When to Apply?
• Consider
• Bed thickness
• Shale percentage, ~50 %?
---
• Laminated, or dispersed?
• Depositional Environments, can we model it?
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Introduction
What is Thin?
• Depends on logging tool as well, < 1m?
Thomas Stieber paper
Sabah
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Introduction
What is Thin?
• Porosity• Old logs < 0.5-1 m
• High res < 0.4 m?
• Resistivity• Old indution < 2m
• Recent < 0.8m?
R
c o r r
Bed Thickness
R meas
2
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Techniques
Vshale from Images
• Core Photos in XLS• detailed Sand flag
(0,1)
• Smooth to logresolution (por
~1ft, res 1m)
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Techniques
Vshale from Image Logs Conductive Dark
Resistive Light
NEU/DEN/SON
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Techniques
Vshale from NMR (1/2)
• Assumes ClayBoundFluid relates to Vshale
• Shale volume
• Vshale = (CBFV/ClayPhiShale)
•
Vshale = (BFV/PhiShale)• Complications:
• dispersed components with additional BF
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Techniques
Vshale from NMR (2/2)
• Clay bound
• Laminated: Cap.BF
and FFV
• Clean sand
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Techniques
Vshale from 3D-res
• 2000’s, revived thin beds
• Tensor Model
• Horizontal and Vertical, or
• Parallel Conductivity and Serial Resistivity
Res HOR
+
R e
s V E R
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Techniques
Volumetric / Probabilistic
• Probabilistic
• Allows for more components, glauconite?
• Cementation?
• Requires more input curves
• Deterministic: Thomas Stieber (1975)
• Input: Phi and Vsh,
• Outputs: Phi_sand, Vsh_lam, Vsh_disp
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Techniques
Core Porosity – of sands!
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Techniques
Saturation from core
• Dean Stark
• Capillary Pressures
1. Get Swirr.
2. What is max Rsand?
3. Optimize shale model
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Techniques
Saturation - Height Function
• Derive SHF from thick beds
• Apply to thin beds
• But is rock quality the same?
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Techniques
Summary – part 1
• Fairly common, also in North Sea
• Vshale: Cuttings, Core, Image logs, NMR, 3D-res
• NTG curve
• Porosity: Core Phi <-> sand lamination• Porosity of sand
• If Resistivity still problematic -> SHF
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• Part 2. 3D resistivity workflow
•
Thomas Stieber• Conductive dispersed components
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3D-resistivity workflow
Case Study data – where is the HC?
Vshale
OriginalPublication
Neutron &
Density Deep Res
Case Study, Clavaud, 2005
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3D-resistivity workflow
steps
•Aim: properties of sand lamination
1. Thomas Stieber (1975)
• Φ, Vsand, Vsh.disp
2. Resistivity of the sand lamination• 3D-res 2000’s
• Rsand
3. Saturation computation (SwRT)
• Juhasz 1981
kfl
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3D-resistivity workflow
Thomas Stieber Definitions
•Shale (not clay)
• Shale types:
i i i kfl
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3D-resistivity workflow - Step 1
Thomas & Stieber, 1975
•
2 endpoints + 1
P o r o s i t y
Volume of Shale
Clean Sand
‘Pure Shale’
3D i i i kfl S 2
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3D-resistivity workflow - Step 2:
Resistivity of Sand Laminations 3D-res
• 2a) Tensor Model
• Horizontal and Vertical, or
• Parallel Conductivity and Serial Resistivity
•
2b) Anisotropy Model• Smart Tensor Model;
• Inputs Thomas Stieber
Res HOR
+
R e s V E R
3D i i i kfl S 3
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3D-resistivity workflow - Step 3
Saturation Calculation
•
Which equation?• Conventional (deterministic)
• Laminated Shaly sand eqs:•
Poupon, Indonesia, Simandoux
• Thin Beds (dispersed clay/shale in sandlamination)
• Dispersed Shaly sand eqs:
• Dual Water, Waxman Smits, Normalised Qv Juhasz
sh
shn
w
m
w
sh
t
R
V S
R
V
R
11
Poupon, parallel conductor
3D i ti it kfl
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3D-resistivity workflow
Saturation from Resistivity
• Waxman Smits equation
• For waterleg assume SWT = 1, (and a*=1):
Shale corrArchie
3D i ti it kfl
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3D-resistivity workflow
Waxman Smits in Xplot
Y = a X + b
Slope B
Y =
X =
(cousin of Pickett-plot)
3D i ti it kfl
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3D-resistivity workflow
Juhasz
• Juhasz: if no core Qv available,• Qv = f(Vshale)
1/Rw_shale
=
shale conductivity
+
1/Rw
100%Shale
1/Rw ~
C o n d u c t i v i t y
Qv_shale
1/Rw_shale
3D i ti it kfl
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3D-resistivity workflow
Juhasz Normalised Qv
• Juhasz: Qv = f(Vsh), or Qv = f(Phi), f(1/Phi)
• Qv = f(1/Phi, Vsh) = f(RPD), (similar to ~Qvn)
• Relative Porosity Difference
• Assume Qv = RPD*C, substitute
3D i ti it kfl
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3D-resistivity workflow
To better pick BC
1/Rw
RPD
Slope B*C
= CWA
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3D resistivity workflow
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3D-resistivity workflow
Data Example
BC Rw
3D resistivity workflow
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3D-resistivity workflow
RPD in Thin Beds?
• RPD of Bulk not good enough
• => RPD of Sand lamination (RPDs)
• RPDs = f(1/PHIs, Vsh.disp), or
POROSITY POROSITYV h l N t & H V R &
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CPI with eval
BVirr
H20HC
POROSITY
Conv
POROSITY
Conv &
Par.Cond.
POROSITY
Thin Beds &
3D-Res
Vshale
Original
Publication
Neutron &
Density
H+V Res &
Parallel
Conductor
Case Study, data of Clavaud
3D resistivity workflow
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3D-resistivity workflow
Summary
• In case of: 3D resistivity, no core, water leg
• Optimise Thomas Stieber with Tensor Model
• Resistivity Sand from Anisotropy model• Relate Qv to RPD
• Compute RPD for sand lamination only
•
New Xplots for picking Rw and ‘BQv’
R f
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References
• Cao-Minh, C., Clavaud, J., Sundararaman, P., Froment, S., Caroli, E., Billon, O., Davis, G. & Fairbairn, R., GraphicalAnalysis of Laminated Sand-Shale Formations in the Presence of Anisotropic Shales, 2008, PETROPHYSICS, Vol 49,
No. 5, October 2008, pp. 395 –405.• Clavaud, J. B., Nelson. R., Guru, U. K. and Wang, H., 2005, Field Example of Enhanced Hydrocarbon Estimation in
Thinly Laminated Formation with a Triaxial Array Induction Tool: A Laminated Sand- Shale Analysis with AnisotropicShale, SPWLA 46th Annual Logging Symposium, June 26-29, 2005.
• Juhasz, I., 1981, Normalised Qv. The Key to Shaly Sand Evaluation using the Waxman-Smits Equation in the Absenceof Core Data. SPWLA 22nd Annual Logging Symposium, June 23rd-26th, 1981.
• Passey, Dahlberg, Sullivan, Yin, Brackett, Xiao, Guzman-Garcia, 2006,Petrophyscial Evlauation of HydrocarbonPore-Thickness in Thinly Bedded Clastic Reservoirs, AAPG Archie Series, No 1
• Stromberg S., Nieuwenhuijs R., Blumhagen, C., Edwards, J., Ramamoorthy R., Herold, B., 2007, Reservoir Quality,Net-to-Gross and Fluid Identification in Laminated Reservoirs from a new generation of NMR logging tools.Examples from the Gharif Formation, Southern Oman. Transactions of the SPWLA 1st Annual SPWLA Middle EastRegional Symposium April 15- 19.
• Thomas, E. C., Stieber, S. J., 1975, The distribution of shale in sandstones and its effect on porosity. Transactions ofthe SPWLA 16th Annual Logging Symposium, June 4-7, 1975.
• Van der Wal, J., Stromberg S., 2012, Correcting the water saturation calculation for dispersed clay in thinly
bedded sandstones, Revisiting the Normalised Qv Equation of Juhasz, Transactions of the SPWLA 53rd
Annual Logging Symposium• Waxman, M.H. & Thomas, E. C., 1974. Electrical Conductivities in Shaly Sands-I. The Relation between
Hydrocarbon Saturation and Resistivity Index; II. The Temperature Coefficient of Electrical Conductivity. J. Pet Tech.213-23. Trans., AIME, 257.
• Worthington, P.F., 2000, Recognition and evaluation of low-resistivity pay, Petroleum Geoscience, Vol 6 2000 (aspublished in Geological Society London, one-day seminar Hidden Hydrocarbons, 2001)
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• Backup
L i
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Logging programs
• Dip meter
• Image logs
• NMR
• 3D resistivity
• High resolution, Consider slow logging
• See AAPG Archie series No 1
Conclusions
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Conclusions
• Workflow can be based on log data only
• New form of Norm Qv of Juhasz applied to thin beds
• Qv estimate refined
• Conventional: low HC
•Conventional with 3D res (Parallel Res): more HC
• Thin Beds with 3D res: most HC
What is RPD?
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What is RPD?
•Middle East for Carbonate stringers (PDO)
• Shaliness indicator
• Combines 1/PHIT and Vshale (~ Neu-Den separation)
• RPD= (Neu + Co – PhiT)/ PhiT
• How to get ‘Co’ • Use ND overlay
• For clean sand: RPDs ~ 0
•
Clean but conduct: RPDs > 0
What if no 3D resistivity available?
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What if no 3D resistivity available?
• Make cases for vertical resistivity
• Check with Thomas Stieber
• Simplest: Rv = Rh * C
• Better: Rv = Rh * C * Vsh_lam, or
• Rv = Rh + C * Vshl * (Rh – RshH)• Rv = Rh + (C* Vshl / ((1/RshH – 1/Rh))
What is Parallel Conductor model?
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What is Parallel Conductor model?
• Ct = Vsand * Csand + Vsh.lam * Cshale, or
• 1/ RT = Vsand / Rsand + (1-Vsand) / Rsh.hor
Res HOR
When to apply Thin Beds
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When to apply Thin Beds
• Neutron Density Data
• Intermediate GR?
• Dispersed, Laminated,
or Both?
3
<
D e n s i t y
>
2
3 < Neutron > 2
GR
When to apply Thin Beds
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When to apply Thin Beds
• Conductive dispersed shale?
3
<
D e n s i t y
>
2
3 < Neutron > 2
DeepRes
What if you do have core?
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What if you do have core?
• Are plugs of the sand lamination?
• Porosity:• Calibrate Clean Sand endpoint to match the high porosity
• Optimise input PHIT
• Calibrate BC & RPD to match the predicted QV curve
Depositional Environments
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Depositional Environments
Fluvial systems (1/2)
100m
Static Model
(25x25x0.5)
Dynamic Model
(100x100x10)
8m
Arbroath, Scotland
Introduction
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Introduction
Also in North Sea
Sele and Forties
Article:Turbidite reservoirs of the Sele Formation, Central North Sea: geological challengesfor improving productionM. HEMPTON, J. MARSHALL, S. SADLER, N. HOGG, R. CHARLES and C. HARVEY
From Abstract• Fields: Forties, Nelson, Montrose –Arbroath, Scoter, Pierce, the Gannet cluster, Guillemot A, Mirren and Merganser, Phyllis, Starling and
Blane are under appraisal/development.
• ‘Forties’ submarine fan system sourced from feeder channels in northwest andwest.
From 3D seismic & wells:
• Near sources (updip): thicker, higher N/G, and more channelized.
• Downdip: thinner, finer grained and stacked lobes and minor channels (controlled by accommodation space and salt movement).
Introduction
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Introduction
Depositional Environments
Techniques
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Techniques
Bed Thickness vs Occurrence
• Altered carbon cycling and coupled changes in Early Cretaceousweathering patterns: Evidence from integrated carbon isotope andsandstone records of the western Tethys
• Ulrich Georg Wortmanna, , , Jens Olaf Herrleb, , Helmut Weissertb
Bed Thickness
N r o f B e d s t h i c k e r t h a n
h
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• Where (and when) should we expect Thin
Beds issues?
How much shale
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Sw vs computed Sw
• Theoretical parallel conductor modelVshale 0.15;
PhiShale 0.18; ShaleRes 3.09;
PhiSand 0.2; SandRes from Archie
Techniques
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q
Rock quality
• Does NTG correlate to bed-thickness?
• Does bed-thickness correlate with quality?
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• Geo Models
Depositional Environments
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The 20th SPE Bergen One Day SeminarApril 10th 2013 | Bergen, Norway
p
Scale - Fluvial systems
100m
Static Model
(25x25x0.5)
Dynamic Model
(100x100x10)
8m
Arbroath, Scotland
Depositional Environments
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The 20th SPE Bergen One Day SeminarApril 10th 2013 | Bergen, Norway
p
Good news: Turbidites
(image fromgeo ExPro)
Kota KinabaluSabah,
Oligocenedeepwater,among mostsand-richoutcrops
How much shale
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The 20th SPE Bergen One Day SeminarApril 10th 2013 | Bergen, Norway
Shale vs Sw
• In ideally laminated,more than 10% of shale
is problem
Model:
• Sw = 20% in sands
• Assumed perfect
(theoretical) parallel
conductor model
Workflow
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The 20th SPE Bergen One Day SeminarApril 10th 2013 | Bergen, Norway
Workflow
• Conventional
• Vshale
• Porosity
• Saturation
• Thin Beds
• Vshale
• Porosity
• Sand Phi & Shale
• Rsand & Saturation
Techniques
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The 20th SPE Bergen One Day SeminarApril 10th 2013 | Bergen, Norway
Vshale from Core (2/2)
•
Calibrate traditionaltechniques (GR, ND)
to downscaled (i.e.
smoothed) core
sand/shale flag
calcite
calcitecalcite
Introduction
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The 20thSPE Bergen One Day Seminar
April 10th 2013 | Bergen, Norway
When to apply Thin Beds
• Neutron Density Data
• Intermediate GR?
• Dispersed, Laminated,
or Both?
3
<
D e n s i t y
>
2
3 < Neutron > 2
GR
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