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TP00-091 Advanced Wellbore Stability Model (WELLSTAB-PLUS) Dr. William C. Maurer.

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Presentation on theme: "TP00-091 Advanced Wellbore Stability Model (WELLSTAB-PLUS) Dr. William C. Maurer."— Presentation transcript:

1 TP Advanced Wellbore Stability Model (WELLSTAB-PLUS) Dr. William C. Maurer

2 TP 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

3 TP Typical Occurrences of Wellbore Instability in Shales soft, swelling shale brittle-plastic shale brittle shale naturally fractured shale strong rock unit

4 TP Cost of Wellbore Instability Problems $500 million/year, before 1992 G.M. Bol, SPE SPE European Petroleum Conference $92 million, BP 1997 $38 million, BP 1998 first quarter J. Kijowski, BP-Amoco Downhole Talk, Issue 80

5 TP Wellbore Stability Problems 8 8High Torque and Drag 8 8Bridging and Fill 8 8Stuck Pipe 8 8Directional Control Problem 8 8Slow Penetration Rates 8 8High Mud Costs 8 8Cementing Failures and High Cost 8 8Difficulty in Running and Interpreting Logs

6 TP Wellbore Failure Mechanisms MAURY et al., 1987

7 TP Effect of Borehole Pressures

8 TP PWPW PWPW  max  min High Support PressureLow Support Pressure Effect of Mud Support Pressure on Rock Yielding

9 TP Rock Failure

10 TP Rock Failure Mechanisms PLASTIC BRITTLE

11 TP Rock Yielding around Wellbores Laboratory Tests Rawlings et al, 1993 Isotropic StressesAnisotropic Stresses

12 TP Change In Near-Wellbore Stresses Caused by Drilling  V (overburden)  Hmin  Hmax  Hmin  Hmax P w (hydrostatic) Before Drilling In-situ stress state After Drilling Lower stress within wellbore

13 TP Stress Concentration around an Open Wellbore PwPw PoPo  Hmin  Hmax zz   rr zz rr  r

14 TP Strength vs Stress Identifying the Onset of Rock Yielding Shear Stress Shear Strength r´r´ Effective Compressive Stress Stable Stress State q´q´ r´r´ Shear Stress Shear Strength r´r´ Effective Compressive Stress Unstable Stress State q´q´ r´r´ q´q´ Min Stress Max Stress q´q´

15 TP Effect of Pore Fluid Saturation

16 TP Effective Stresses Partioning of Total Stress between Mineral Grains and Pore Fluids PoPo    ´ =  -  P o  ´ - effective stress  - total stress P o - pore pressure  - Biot Coefficient (  1 for weak, porous rocks)

17 TP Effective Rock Stress  z =  o - p f  o = Overburden Stress  z = Matrix Stress p f = Pore Fluid Pressure

18 TP Effect of Near-Wellbore Pore Pressure Change on Effective Stresses Shear Stress No Yield Yield Shear Strength Effective Compressive Stress r´r´ ´´ r´r´ ´´ P o increase

19 TP

20 TP MEI Wellbore Stability Model: (mechanical model, does not include chemical effects) 8Linear elastic model (BP) 8Linear elastic model (Halliburton) 8Elastoplastic Model (Exxon) 8Pressure Dependent Young’s Modulus Model(Elf)

21 TP Mathematical Algorithms 8Dr Martin Chenervert(Un. Texas) 8Dr. Fersheed Mody(Baroid) 8Jay Simpson(OGS) 8Dr. Manohar Lal(Amoco) 8Dr. Ching Yew(Un. Texas)

22 TP Stress State on Deviated Wellbore   zz rr zz   zz   

23 TP

24 TP (BP) Linear Elastic Model

25 TP

26 TP (Halliburton) Linear Elastic Model

27 TP

28 TP (Exxon) Elastoplastic Model

29 TP

30 TP

31 TP

32 TP

33 TP (Elf) Pressure Dependent Young’s Modulus

34 TP

35 TP Shale Borehole Stability Tests Darley, 1969 DIESEL DISTILLED WATER

36 TP Montmorillonite Swelling Pressure Powers, ,000 60,000 40,000 20, th3rd2nd1st SWELLING PRESSURE, psi kg/cm 2 LAYERS OF CRYSTALLINE WATER

37 TP Shale Water Adsorption Chenevert, WEIGHT % WATER WATER ACTIVITY - a W DESORPTION ADSORPTION

38 TP Shale Swelling Tests Chenevert, 1970 TIME - HOURS LINEAR SWELLING - % Activity of Internal Phase

39 TP Effect of K+Ions on Shale Swelling Baroid, 1975 Ca++ K+ Na+ Cs+ Na+ Ca++ Li+ K+ Rb+ Cs+ Na+ Mg++ Na+ 10A° Na

40 TP Effect of Swelling Strains on Wellbore Stability Soft, Swelling Shale Hole Closure due to Swelling Strains Most Likely Scenario for Soft Reactive Shales in Low Stress Settings

41 TP North Sea Speeton Shale Specimen Exposed at Zero DP to Drilling Fluid Drilling Fluid: Ionic Water-Base (CaCl 2 Brine) Activity = 0.78

42 TP North Sea Speeton Shale Specimen Exposed at Zero DP to Drilling Fluid Drilling Fluid: Oil-Base Emulsion (Oil with CaCl 2 Brine) Activity = 0.78

43 TP 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

44 TP Principle Mechanisms Driving Flow of Water and Solute Into/Out of Shales Force Flow Fluid (water) Solute (ions) Hydraulic Gradient (P w  P o ) Chemical Potential Gradient (A mud  A shale ) Hydraulic Diffusion (Darcy´s Law) Advection Diffusion (Fick´s Law) Chemical Osmosis H2OH2O H2OH2O H2OH2O H2OH2O t1t1 t2t2 t3t3 P r Other Driving Forces: Electrical Potential Gradient Temperature Gradient H2OH2OH2OH2O H2OH2OH2OH2O H2OH2O H2OH2O H2OH2O

45 TP 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 A w ) Low concentration of dissolved molecules or ions ( = High A w )

46 TP Effect of Osmotic Flow on Near-Wellbore Pore Pressure for a Balanced Bottomhole Pressure Condition Osmotic flow from mud to shale Pore Pressure Decrease Osmotic flow from shale to mud r a mud a shale PP r PWPW P fm PWPW P Pore Pressure Increase

47 TP Water Acitivity in Salt Solution Salt Concentration, % w/w Water Activity CaCl 2 NaCl KCl Water Activity in Brine at Room Temperature

48 TP A Critical Issue: How Efficient Are Shale ²Membranes² ? Laboratory Measurements, Chenevert, 1998 Membrane Efficiency of Speeton Shale when Exposed to Various Water-based Fluids de-ionized water 0.78 a w CaCl a w CaCl a w KCOOH 0.78 a w Glycerol Osmotic Membrane Efficiency

49 TP

50 TP Limitations of Existing Models 8Do not handle shale hydration 8Very complex 8Input data not available 8Limited field verification 8Cannot field calibrate

51 TP Mathematical Algorithms 8Dr Martin Chenervert(Un. Texas) 8Dr. Fersheed Mody(Baroid) 8Jay Simpson(OGS) 8Dr. Manohar Lal(Amoco) 8Dr. Ching Yew(Un. Texas)

52 TP Mechanical/Chemical Property Input

53 TP Help Information as Clicking Question Mark

54 TP Pore Pressure Input/Predict

55 TP Pore Pressure Prediction via Interval Transit Time Log Data

56 TP In-Situ Stresses Input/Predict

57 TP Correlation to Determine Horizontal Stresses

58 TP Output Windows

59 TP Safe Mud Weight vs Well Inclination

60 TP Wellbore Stability Design (through Mud Weight-Inclination diagram)

61 TP Safe Mud Weight Distribution by Azimuth

62 TP Near-Wellbore Stresses Distribution

63 TP Mohr Diagram

64 TP Wellbore Stress Distribution

65 TP Propagation of Swelling Pressure

66 TP Effect of Concentration of Salt in Mud

67 TP Effect of Membrane Efficiency

68 TP Too large inclination Wellbore Stability Design (continued)

69 TP Wellbore Stability Design (continued) Decrease inclination

70 TP Wellbore Stability Design (continued) Too high mud weight

71 TP Wellbore Stability Design (continued) Decrease mud weight

72 TP Not enough salinity Wellbore Stability Design (continued)

73 TP Increase salinity Wellbore Stability Design (continued)

74 TP Wellbore Stability Design (through Mud Weight-Salinity diagram) Too low mud weight

75 TP Wellbore Stability Design (continued) Increase mud weight

76 TP Wellbore Stability Design (continued) Not enough salinity

77 TP Increase salinity Wellbore Stability Design (continued)

78 TP Wellbore Stability Design (continued) Low Value Membrane Efficiency

79 TP Wellbore Stability Design (continued) High Value Membrane Efficiency

80 TP Field Calibration

81 TP Field Calibration (continued)

82 TP Effect of Concentration of Salt in Mud

83 TP Multi-Depth Data/Calculation Display

84 TP Microsoft Word Report

85 TP Microsoft PowerPoint Presentation

86 TP Project Tasks 8Distribute Wellbore Stability Model (WELLSTAB) 8Develop Enhanced Model (WELLSTAB-PLUS) 8Add time dependent feature to model 8Hold workshops 8Conduct field verification tests 8Write technical reports

87 TP Field Verification Goals 8Determine model accuracy 8Improve mathematical algorithms 8Field calibrate model 8Make models more user-friendly 8Convert wellbore stability from an art into a science

88 TP Benefits  Accelerate Technology Implementation  Affordable Software  Compound R & D Funds  Technical Interchange  Unbiased Information  Schools and Forums

89 TP

90 TP


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