Download - WELLBORE STABILITY.pdf
TP00-09 1
Advanced Wellbore Stability Model
(WELLSTAB-PLUS)
Dr. William C. Maurer
TP00-09 2
DEA-139 Phase I
DEA Sponsor: Marathon Duration: 2 Years Start Date: May 1, 2000 End Date: April 30, 2002 Participation Fee: $25,000/$35,000
TP00-09 3
Typical Occurrences of Wellbore Instability in Shales
soft, swelling shale
brittle-plastic shale
brittle shale
naturally fractured shale
strong rock unit
TP00-09 5
Wellbore Stability Problems
High Torque and Drag
Bridging and Fill
Stuck Pipe
Directional Control Problem
Slow Penetration Rates
High Mud Costs
Cementing Failures and High Cost
Difficulty in Running and Interpreting Logs
TP00-09 7
Effect of Borehole Pressures
TP00-09 8
PW PW
smax smax
smin smin
High Support Pressure Low Support Pressure
Effect of Mud Support Pressure on Rock Yielding
TP00-09 10
Rock Failure Mechanisms
PLASTIC BRITTLE
TP00-09 11
Rock Yielding around Wellbores Laboratory Tests
Rawlings et al, 1993
Isotropic Stresses Anisotropic Stresses
TP00-09 12
Change In Near-Wellbore Stresses Caused by Drilling
sV (overburden)
sHmin
sHmax sHmin
sHmax
Pw (hydrostatic)
Before Drilling In-situ stress state
After Drilling Lower stress within wellbore
TP00-09 13
Stress Concentration around an Open Wellbore
Pw
Po
sHmin
sHmax
sz sq
sq
sr
sz
sr
s
r
TP00-09 14
Strength vs Stress Identifying the Onset of Rock Yielding
Shear
Str
ess
sr´
Effective Compressive Stress
Stable Stress State
sq´
sr´
Shear
Str
ess
sr´
Effective Compressive Stress
Unstable Stress State
sq´
sr´
sq´
Min Stress
Max Stress
sq´
TP00-09 15
Effect of Pore Fluid Saturation
POROUS ROCK SOLID ROCK
Pf = Fluid Pressure
so=sz so=sz+pf
TP00-09 18
Effect of Near-Wellbore Pore Pressure Change on Effective Stresses
Sh
ear
Str
ess
No Yield
Yield
Effective Compressive Stress
sr´ sq´ sr´ sq´
Po increase
TP00-09 19
TP00-09 20
MEI Wellbore Stability Model: (mechanical model, does not include chemical effects)
Linear elastic model (BP)
Linear elastic model (Halliburton)
Elastoplastic Model (Exxon)
Pressure Dependent Young’s Modulus Model(Elf)
TP00-09 21
Mathematical Algorithms
Dr Martin Chenervert (Un. Texas)
Dr. Fersheed Mody (Baroid)
Jay Simpson (OGS)
Dr. Manohar Lal (Amoco)
Dr. Ching Yew (Un. Texas)
TP00-09 22
Stress State on Deviated Wellbore
s3
s2 sz sr
tqz b q
tzq
sq
a
s1
TP00-09 23
TP00-09 24
(BP) Linear Elastic Model
TP00-09 25
TP00-09 26
(Halliburton) Linear Elastic Model
TP00-09 27
TP00-09 28
(Exxon) Elastoplastic Model
TP00-09 30
TP00-09 31
TP00-09 33
(Elf) Pressure Dependent
Young’s Modulus
TP00-09 34
TP00-09 35
Shale Borehole Stability Tests Darley, 1969
DIESEL DISTILLED WATER
TP00-09 36
Montmorillonite Swelling Pressure Powers, 1967
80,000
60,000
40,000
20,000
0 4th 3rd 2nd 1st
5000
4000
3000
2000
1000
0
SW
ELLIN
G P
RESSU
RE, psi
kg/c
m2
LAYERS OF CRYSTALLINE WATER
TP00-09 37
Shale Water Adsorption Chenevert, 1970
0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00
5
4
3
2
1
0
WEIG
HT %
WATER
WATER ACTIVITY - aW
DESORPTION
ADSORPTION
TP00-09 38
Shale Swelling Tests Chenevert, 1970
TIME - HOURS
LIN
EAR S
WELLIN
G -
%
.01 0.1 1.0 10
0.4
0.3
0.2
0.1
0
-0.1
1.00
0.91 0.88 0.84 0.75
0.25
Activity of Internal Phase
TP00-09 39
Effect of K+Ions on Shale Swelling Baroid, 1975
Ca ++
K+
K+
K+
Na+
Cs+
Na+
Ca++
Li+
K+
Rb+
Cs+
Na+
Mg++
Na+
10A°
Na+
- -
- -
-
- -
-
-
-
- - -
-
-
TP00-09 41
North Sea Speeton Shale Specimen Exposed at Zero DP to Drilling Fluid
Drilling Fluid:
Ionic Water-Base
(CaCl2 Brine)
Activity = 0.78
TP00-09 42
North Sea Speeton Shale Specimen Exposed at Zero DP to Drilling Fluid
Drilling Fluid:
Oil-Base Emulsion
(Oil with CaCl2 Brine)
Activity = 0.78
TP00-09 43
North Sea Speeton Shale Specimen
Exposed at Zero DP to Drilling Fluid
Drilling Fluid:
Non-Ionic Water-Base
(Methyl Glucoside in
Fresh Water)
Activity = 0.78
TP00-09 44
Principle Mechanisms Driving Flow of Water and Solute
Into/Out of Shales
Force
Flow
Fluid (water)
Solute (ions)
Hydraulic Gradient (Pw Po) Chemical Potential
Gradient (Amud Ashale)
Hydraulic Diffusion
(Darcy´s Law)
Advection
Diffusion
(Fick´s Law)
Chemical Osmosis
H2O
H2O H2O
H2O t1
t2 t3
P
r
Other Driving Forces: Electrical Potential Gradient Temperature Gradient
H2O H2O
H2O H2O
H2O H2O
H2O
+ -
-
-
+
+
+
-
TP00-09 45
Osmotic Flow of Water through Ideal Semi-Permeable Membrane
Ideal Semipermeable Membrane - permeable to water - impermeable to dissolved molecules or ions
Water flow direction High concentration
of dissolved molecules or ions ( = Low Aw )
Low concentration of dissolved molecules
or ions ( = High Aw )
TP00-09 49
TP00-09 50
Limitations of Existing Models
Do not handle shale hydration
Very complex
Input data not available
Limited field verification
Cannot field calibrate
TP00-09 51
Mathematical Algorithms
Dr Martin Chenervert (Un. Texas)
Dr. Fersheed Mody (Baroid)
Jay Simpson (OGS)
Dr. Manohar Lal (Amoco)
Dr. Ching Yew (Un. Texas)
TP00-09 52
Mechanical/Chemical Property Input
TP00-09 53
Help Information as Clicking Question Mark
TP00-09 54
Pore Pressure Input/Predict
TP00-09 55
Pore Pressure Prediction via Interval Transit Time Log Data
TP00-09 56
In-Situ Stresses Input/Predict
TP00-09 57
Correlation to Determine Horizontal Stresses
TP00-09 58
Output Windows
TP00-09 59
Safe Mud Weight vs Well Inclination
TP00-09 61
Safe Mud Weight Distribution by Azimuth
TP00-09 62
Near-Wellbore Stresses Distribution
TP00-09 63
Mohr Diagram
TP00-09 64
Wellbore Stress Distribution
TP00-09 65
Propagation of Swelling Pressure
TP00-09 68
Too large inclination
Wellbore Stability Design (continued)
TP00-09 69
Wellbore Stability Design (continued)
Decrease inclination
TP00-09 70
Wellbore Stability Design (continued)
Too high mud weight
TP00-09 71
Wellbore Stability Design (continued)
Decrease mud weight
TP00-09 72
Not enough salinity
Wellbore Stability Design (continued)
TP00-09 73
Increase salinity
Wellbore Stability Design (continued)
TP00-09 74
Wellbore Stability Design (through Mud Weight-Salinity diagram)
Too low mud weight
TP00-09 75
Wellbore Stability Design (continued)
Increase mud weight
TP00-09 76
Wellbore Stability Design (continued)
Not enough salinity
TP00-09 77
Increase salinity
Wellbore Stability Design (continued)
TP00-09 78
Wellbore Stability Design (continued)
Low Value Membrane Efficiency
TP00-09 79
Wellbore Stability Design (continued)
High Value Membrane Efficiency
TP00-09 80
Field Calibration
TP00-09 81
Field Calibration (continued)
TP00-09 86
Project Tasks
Distribute Wellbore Stability Model (WELLSTAB)
Develop Enhanced Model (WELLSTAB-PLUS)
Add time dependent feature to model
Hold workshops
Conduct field verification tests
Write technical reports
TP00-09 87
Field Verification Goals
Determine model accuracy
Improve mathematical algorithms
Field calibrate model
Make models more user-friendly
Convert wellbore stability from an art into a science
TP00-09 89
TP00-09 90