Reservoir Stress-Sensitivity

Report
Reservoir StressSensitivity
BGD Smart
JM Somerville
M Jin
Reservoir Stress-Sensitivity
• Reservoir properties and therefore
behaviour influenced by changes in
stress
• Caused by either changes in pore
pressure or temperature, or
combination
• Properties = permeability,
dimensions, integrity
Stress-Sensitivity Scales
• Near wellbore
– permeability – (stress skin cf skin caused by
invasion)
– failure
• Increasingly distant from the wellbore
– permeability
• Whole reservoir
– permeability, directional floods
• Field
– compaction, subsidence, seal alteration
Stress-Sensitivity Scales
• Near wellbore – Influenced by UBD
– permeability – (stress skin, no skin
caused by invasion)
– failure
• Increasingly distant from the
wellbore
– permeability
Reservoir Stress-Sensitivity: a
multi-disciplinary challenge
More
Realistic
Reservoir
Model
Better
Decisions
Reservoir Stress-Sensitivity: a
multi-disciplinary challenge
More
Realistic
Reservoir
Model
Stress Sensitivity
Better
Decisions
Better Decisions Re:•
•
•
•
•
•
•
•
•
•
Reserves
Well design
PI
Well locations
Production strategy
Reservoir management (inc 4D seismic)
Seal integrity
Compartmentalisation
Facilities
Efficacy of UBD technology and methodology
All impacting recovery factor and
costs
HWYH-399
Key:
Breakout
from CBIL(A)
Drilling-induced
tension
from STAR
HWYH-394
Key:
Drilling-induced
tension cracks
Bed boundary
Fracture
Unclassified,
possible
stylolite
All from STAR
The Conceptual Model
• The reservoir consists of blocks or
layers of intact rock bounded by
discontinuities
• The reservoir is stressed in an
anisotropic manner
• The whole system exhibits
hysteresis
Thinly-bedded interval in the Annot Sandstone.This interval
is underlain and overlain by more ‘massive’ sandstones.
The
Reservoir
Discontinuities
“Intact” Rock
Boundary and Local Stresses
within the Reservoir
sv
Reservoir
sh
sH
sv
sv
sh
Boundary or
Regional Stresses
sH
sv
sh
Local
Stresses
sh
Intact Rock Properties
(stress-sensitive values where appropriate)








Ambient porosity and permeability
Elastic constants E and v
Biot’s coefficient
Failure (Fracture) Criteria
Vp and Vs velocities
Vp anisotropy at ambient conditions
Permeability at reservoir stress
conditions
Palaeomagnetic trial
s1
s2
e1
e2
P and S
waves
Fluid
flowing at
pressure
s2
Stress-Sensitive
Values of:•
•
•
•
•
Elastic Moduli
Biot’s Coefficient
Permeability
Vp,Vs
Failure Criterion
s1
Tests with Specimen in Triaxial Cell
s1
s1
e1
Failure
s2 = constant
s2
s2
s1
Single State Triaxial Testing
e1
s1
x
x
x
x
s2’’’’
s1
x
s2’’’
x
s2’’
x
Tan = Triaxial
Factor
x
s2’
e1
Failure Criterion - Triaxial Factor
s2
s1
x
s 2’
x
s2’’
x
s2’’’
x
s2’’’’
s1
x
x
x
Tan = Triaxial
Factor
x
e1
s2
Multi-Failure State Triaxial Testing
P Wave Velocity at 27.5MPa versus Porosity
9000
Series1
UT MN 1307
P Wave Velocity (m/s)
8000
HRDH 704
7000
HWYH 325
HWYH 394
6000
HWYH 399
5000
4000
3000
2000
y = -111.63x + 6753
1000
R2 = 0.7776
0
0.0
5.0
10.0
15.0
20.0
25.0
30.0
Porosity (%)
Vp at 27MPa vs Porosity
35.0
Modulus of Elasticity at 27.6MPa versus Porosity
Series1
UT MN 1307
HRDH 704
HWYH 325
HWYH 394
HWYH 399
120.00
M odulus of Elasticity (GPa)
100.00
80.00
60.00
y = -1.7701x + 68.839
40.00
R = 0.5076
2
20.00
0.00
0.0
5.0
10.0
15.0
20.0
25.0
Porosity (%)
Young’s Modulus at 27
MPa vs Porosity
30.0
35.0
Angle of Internal Friction versus Porosity
70
Series1
Angle of Internal Friction
UT MN 1307
60
HRDH 704
HWYH 325
50
HWYH 394
HWYH 399
40
30
20
y = -1.3045x + 49.54
R2 = 0.7722
10
0
0.0
5.0
10.0
15.0
20.0
25.0
30.0
Porosity (%)
Angle of Internal Friction
vs Porosity
35.0
Sampling Rationale - Intact Rock
Wireline Log
Rock
Mechanics
Property
Correlation
Sample
Core, then
Test
Petrophysical
Property
Populating Model - Intact Rock
Correlation
Synthetic
Rock
Mechanics
Log
Convert
Reservoir
Characterisation
Model into a
Geomechanical
Model
The Process
• Populate the Conceptual Model with
properties and data
• So create a Geomechanical Model of the
reservoir (plus surrounding rock)
• Impose process-induced changes on the
Geomechanical Model using analytical or
numerical solutions
• Numerical offers more realism than analytical
– hence coupled modelling
Coupled Modelling
More realistic simulation
results
Fluid Flow Simulator
Change in Pore
Pressure, Temperature,
Saturations
Change in Permeability
Change in Effective
Stresses
Rock Movements, Change
in Stress and Strain
Stress-Analysis
Simulator
Reservoir and o/b
stresses, strains and
displacements
Enhanced 4D Seismic
Interpretation/Reservoir
Management
Fluid Flow Simulator
Change in Pore
Pressure, Temperature,
Saturations
Change in Effective
Stresses
Differentiating Filter
(Synthetic)
Saturation-Related
changes in Impedance
Change in Permeability
Stress-Related changes
in Impedance
Rock Movements, Change
in Stress and Strain
Changes in Velocity
and Density
Stress-Analysis
Simulator
More realistic simulation
results
Fluid Flow Simulator
Change in Pore
Pressure, Temperature,
Saturations
Change in Effective
Stresses
Enhanced 4D Seismic
Interpretation/Reservoir
Management
Differentiating Filter
(Synthetic)
Saturation-Related
changes in Impedance
Change in Permeability
Stress-Related changes
in Impedance
Rock Movements, Change
in Stress and Strain
Changes in Velocity
and Density
Stress-Analysis
Simulator
Reservoir and o/b
stresses, strains and
displacements
Example 1
UKNS, Perm Stress
Sensitivity
(ECLIPSE coupled with
VISAGE)
Production Prediction: permeability
reduction
The diagram
shows the
absolute
reduction (k1k18). The
maximum
reduction in
permeability is
in the central
part of the field
(ECLIPSE Output)
0.39000
k/k0
Perm
sensitivity
modelled with
hysteresis
0.39500
0.38500
Series1
0.38000
0.37500
0.37000
42000 44000 46000 48000 50000
mean stress (kPa)
Stress Sensitive
Permeability with hysteresis
0.39500
k/k0
0.39000
Injection in Miller
induced
unloading
0.38500
Series1
0.38000
Depressurisation in
Miller
0.37500
0.37000
42000 44000 46000 48000 50000
mean stress (kPa)
Injection in South Brae
induced unloading in
Miller Field
Comparison of GOPR Predictions
Oil
Production
Rate is
sharply
reduced
because the
permeability
reduction in
the area
causes a
reduction in
BHP and
leads to a
increase in
gas
production
(ECLIPSE Output)
Horizontal Ground Displacements - 1
Horizontal Ground Displacements - 2
Horizontal Ground Displacements - 3
Stress Ratio vs. time
Between
wells
Close to well
Ds 3 3 - Dq / Dp
k=
=
Ds 1¢ 3 + 2 Dq / Dp
Stress Status in p-q terms (anisotropy)
close to wells
far from
wells
Stress Path Distribution
Permeability Stress Path Sensitivity
p-q-k 3D
MOBIL "U"- Field: Unconsolidated Sand
40
#C4C2P6
q (MPa)
#C4C4P1A
100
#C4C2P4
30
20
#C4C5P1
k
MATLA
B
10
100-200
0-100
N/A(UCMS)
1
S52
<= 40.0
<= 45.0
<= 50.0
<= 55.0
<= 60.0
<= 65.0
S46
<= 70.0
<= 75.0
<= 80.0
<= 85.0
S43
> 100.0
S37
S34
S31p
S28
S25
S22
S19
S16
S13
S10
S7
S4
q
61
58
55
52
49
46
43
40
37
34
31
28
25
22
19
16
13
7
10
S1
4
<= 100.0
k/k0
%
<= 95.0
S40
1
<= 90.0
S49
90-100
80-90
70-80
60-70
50-60
40-50
30-40
20-30
10-20
0-10
S55
S43
S49
S58
S55
<= 35.0
51
S52
Normalised Permeability Contours
<= 30.0
S46
S37
S58
k(%):
q
41
S40
P'
S31
K stress path sensitive for Unconsolid Sand
S34
Mean Ef f ectiv e Stress, p' (MPa)
21
31
S25
50
S28
40
S19
30
S22
20
S13
10
S16
0
S7
0
11
S10
S1
0
S4
Differential Stress,
#C4C2P2
61
Excel
Compaction and
subsidence
FE MGV 6.1-02 : H E R IOT-W A TT U N IV E R S ITY
21-JA N -2000 10:53 compac05.cgm
Model: MOD L01
L005: TIME /MON TH S * * * * * * *
N odal D IS P LA C E Y
Max/Min on model set:
Max = .504E -3
Min = -.461E -1
Compaction in
1987
1
Y
FE MGV 6.1-02 : H E R IOT-W A TT U NIV E RS ITY
.2E -1
.15E -1
.1E -1
.5E -2
0
-.5E -2
-.1E -1
-.15E -1
-.2E -1
-.25E -1
-.3E -1
-.35E -1
-.4E -1
X
21-JA N -2000 11:10 compac18.cgm
Z
Model: MOD L01
L018: TIME /MON THS * * * * * * *
N odal DIS P LA C E Y
Max/Min on model set:
Max = .194E -1
Min = -.339E -1
2
Y
Z
X
.2E -1
.15E -1
.1E -1
.5E -2
0
-.5E -2
-.1E -1
-.15E -1
-.2E -1
-.25E -1
-.3E -1
-.35E -1
-.4E -1
Compaction IN 1995
in which the result of
injection is shown
Example 2
UKNS, Seismic StressSensitivity
(ECLIPSE, VISAGE, HWU software)
Features of a 2D flow model grid
embedded
for coupled geomechanical simulation
Overburden
Faults
Caprock
Sideburden
Gas
, Water
in the flow model grid
Well
Displaced shape of the geomechanical
model
Surface subsidence
Typical location of shear
strain on faults
Differential compaction
across faults in reservoir
(VISAGE Output)
Mean effective stress distribution at the end of
the simulation
Unperturbed stress field
(constant gradient)
Perturbed stress field
above and below reservoir
Apparent deepening of reservoir
due to decreasing pore pressure
Localized effects
at faults
(VISAGE Output)
Time-lapsed compressional acoustic
impedance
Changes in overburden/caprock
due to stress redistribution
Changes in reservoir
Top of caprock
due to pore pressure decline
Initial gas-water contact
Changes in reservoir
due to fluid movement
(VISAGE Output)
Initial Modelling: Before Production Begins
Time Lapse Model: Saturation Changes Only
Time Lapse Model: Saturation + Stress
Time-lapsed seismic trace model
Reflector at
top of
caprock
Perturbations at reflector
event due to fluid change
effects
Reservoir
top
Reservoir
base
Pull-up in reflector event
due to stress change
effects
Where are we now?
• Extreme examples of reservoir
stress-sensitivity accepted: Ekofisk,
HP/HT, Gulf of Mexico, Angola?
• The processes required exist in
usable form
• Non-uniform levels of commitment
• What about the more subtle
reservoirs?
Technical Challenges
•
•
•
•
•
•
Discontinuity distributions
Discontinuity properties
Rel perm stress-sensitivity
In situ stress state
Coping with anisotropy
Seamless software
Organisational Challenges
• Realising the full value of the
data we already have
• Cost vs value of the process
• Coping with multi-disciplinarity
Is this too much to ask for?
Better
performance
Fully
owned
decisions
Shared
belief
Shared
analysis
Decision Making
• Straight from the geomechanical model,
aided possibly by some calcs, e.g.
– fracture density = well locations for max PI
– subsidence = yes or no
• With the aid of coupled modeling, e.g
– improvement of appraisal
– impact of perm sensitivity = recovery, GOR etc
– Ground movements and subsidence = threat
to wells and facilities
– 4D seismic enhancement = better management
Thank You
What do we want to
achieve today?
• Overview of the main tasks of the project
• Select candidate reservoirs for study
• Set up communications
• Agree next meeting date 17th August?
Hysteresis
K
Increasing Stress
Hysteresis
K
Increasing Stress
Hysteresis
K
Increasing Stress
UBD site history very important
Effective
Stress
around the
wellbore
Failure Level
Time
Drilling Completion
Production
Building the Geomechanical Model
*Structure and anisotropy analysis from Seismic
MultiDisciplinary
Tasks
assembling
data for
Model
*Published and proprietary studies
Basin process simulations
*Geomechanical Core Analysis
*Log analysis
*Geomechanics of fracture genesis
*Genetic Units expertise
Analogue studies
Characterise Structural Setting of the Reservoir
Creation of the
Geomechanical Model
Characterise Reservoir Rocks
Characterise Reservoir Faults &
Fractures
Reservoir Geomechanical Model
Stress-Sensitive
Coupled Modelling
Deliverables
feedback to
improve
characterisation
Stress-Sensitive
Reservoir Modelling
and Coupled
Simulations (Ground
movements, Fluid
Flow and 4D seismic)
Better Decisions Reservoir Management
feedback to
improve
characterisation

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