Improved Workflow for Evaluation of Thinly
Bedded Sandstones
Revisiting the Normalised Qv equation of Juhasz
Jan van der Wal & Simon Stromberg
www.senergyworld.com
Thin Beds – Introduction
2/19
• 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
Case Study data – where is the HC?
Vshale
Original
Publication
Neutron &
Density
Deep Res
What steps in Thin Bed workflow?
• 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
•
Juhasz 1981
4/19
Definitions
• Shale types:
Step 1
Thomas & Stieber, 1975
6/19
• 2 endpoints + 1
Clean Sand
Porosity
‘Pure Shale’
Volume of Shale
Step 2:
7/19
Resistivity of Sand Laminations 3D-res
• 2a) Tensor Model
• Horizontal and Vertical, or
• Parallel Conductivity and Serial Resistivity
Res HOR
• Smart Tensor Model;
• Inputs Thomas Stieber
+
Res VER
• 2b) Anisotropy Model
Step 3
8/19
Saturation Calculation
• Which saturation equation?
Poupon, parallel conductor
• Conventional (deterministic):
• Laminated Shaly sand eqs:
• Poupon, Indonesia, Simandoux
1  V sh
V
1

  m  S wn  sh
Rt
Rw
R sh

• Thin Beds (dispersed clay/shale in sand lamination) :
• Dispersed Shaly sand eqs:
• Dual Water, Waxman Smits, Normalised Qv Juhasz

Saturation from Resistivity
• Waxman Smits equation
Archie
9/19
Shale corr
• For waterleg assume SWT = 1, (and a*=1):
Waxman Smits in Xplot
Y
10/19
= aX +b
Y=
Slope B
X=
(cousin of Pickett-plot)
Juhasz
11/19
• Juhasz: if no core Qv available,
• Qv = f(Vshale)
~ Conductivity
1/Rw_shale
1/Rw
Qv_shale
100%
Shale
Juhasz Normalised Qv
12/19
• 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
To better pick BC
13/19
= CWA
Slope B*C
1/Rw
RPD
To better pick Rw
14/19
• Terms divided by RPD:
CWA/RPD
Slope 1/Rw
BC
1/RPD
Data Example
BC
15/19
Rw
RPD in Thin Beds?
16/19
• RPD of Bulk not good enough
• We require RPD of sand lamination (RPDs)
• RPDs = f(1/PHIs, Vsh.disp), or
Vshale
Original
Publication
Neutron &
Density
H+V Res &
Parallel
Conductor
POROSITY
Conv
BVirr
HC
Case Study, data of Clavaud
H20
POROSITY
Conv &
Par.Cond.
POROSITY
Thin Beds &
3D-Res
Summary Workflow
18/19
• 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’
Conclusions
19/19
• 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
References
• 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 Anisotropic Shale, SPWLA 46th Annual Logging Symposium,
June 26-29, 2005.
• Thomas, E. C., Stieber, S. J., 1975, The distribution of shale in sandstones and its effect on
porosity. Transactions of the SPWLA 16th Annual Logging, Symposium, June 4-7, 1975.
• Juhasz, I., 1981, Normalised Qv. The Key to Shaly Sand Evaluation using the Waxman-Smits
Equation in the Absence of Core Data. SPWLA 22nd Annual Logging Symposium, June 23rd-26th,
1981.
• Cao-Minh, C., Clavaud, J., Sundararaman, P., Froment, S., Caroli, E., Billon, O., Davis, G. &
Fairbairn, R., Graphical Analysis of Laminated Sand-Shale Formations in the Presence of
Anisotropic Shales, 2008, PETROPHYSICS, Vol 49, No. 5, October 2008, pp. 395–405.
• 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 East Regional Symposium April 15- 19.
• 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.
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?
• Make cases for vertical resistivity
• Check with Thomas Stieber
• Simplest: Rv = Rh * C
• Better: Rv = Rh * C * Vsh_lam, or
• Rv = RH + (RH – RshH)*RatioMax*Vshl
• RV = RH + 1/ ((1/RshH – 1/RH) * Vshl)
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
• Neutron Density Data
GR
3 < Density > 2
• Intermediate GR?
• Dispersed, Laminated, or
Both?
3 < Neutron > 2
When to apply Thin Beds
DeepRes
3 < Density > 2
• Conductive dispersed shale?
3 < Neutron > 2
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