Geomechanical controls on fault and fracture distribution with application to structural permeability and hydraulic stimulation

Transcription

1 CSPG Luncheon Calgary February 5 th 2015 Geomechanical controls on fault and fracture distribution with application to structural permeability and hydraulic stimulation Scott Mildren - Ikon Science

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4 Australian Perspective Source: Gloucester Coal Seam Gas Project, Community Information Fact Sheet, no. 8, October 2008, AGL website, viewed 9 February 2011,

5 Australian Perspective Source: US Department of Energy

6 Contents 1. Introduction 2. Stresses On Planes 3. Stress Determination 4. Mechanical Stratigraphy (Part 1) 5. A Cheesy Interlude 6. Mechanical Stratigraphy (Part 2) 7. Natural or Drilling Related Fractures? 8. Conclusions

7 Introduction

8 Why Do We Bother? Oilprice.net

9 Why Do We Bother? Effects of oil price drop Reduction in company value ExxonMobil and Chevron both down 6% in last 6 months Halliburton down 40% Smaller companies with % reductions ranging between the two Companies need to secure loans Secure loans by increasing reserves Shift to development over exploration

10 How Do We Do It? Geomechanics can play an important role Increase reserves by. Increase volume Mapping migration pathways, seal integrity, pore pressure distribution Increase recoverable % Optimising hydraulic fracturing, sweep efficiency, reservoir characterisation Lower development costs Lower NPT, better well locations and minimise hydraulic fracturing

11 What does stress have to do with it? s Hmax Non-Sealing Faults (423 North Sea faults) Flood Directionality (>80 field cases) s Hmax Rate Correlations (8 field areas, >0.5 million well pairs)

12 What does stress have to do with it? 30 cm Fracture Aperture 0.25 mm 30 cm 30 cm Matrix Permeability 1 md Ave. Permeability 1 md Matrix Permeability 1 md Ave. Permeability md

13 What does stress have to do with it? Structural permeability (faults or fractures) can significantly impact on permeability. Permeability of a fault or fracture is related to the stresses that are acting on it and the strength of that feature. If we can determine the stresses and their relationship to the strength we can better predict permeability.

14 Stresses On Planes

15 The Stress Components Earth s surface is a free surface (no shear stresses) and therefore the vertical stress is a principal stress constraining the other two principal stresses to the horizontal plane. Sv Shmin SHmax

16 Stresses on a Surface Sv SHmax Shmin

17 Stresses on a Surface Normal Stress (s n ) Shear Stress ( )

18 Stress Determination

19 The Stress Components Sv Weight of the overburden SHmax Shmin

20 Borehole Stresses s H s H

21 Borehole Stresses Borehole Breakouts (Compressional) Drilling Induced Tensile Fractures (Tensional)

22 Mechanical Stratigraphy AZIMUTH AZIMUTH 0-360

23 Horizontal Stress Magnitudes Component from vertical load Tectonic component E

24 Stress Determination There exists an interdependent link between pore pressure, rock properties and geomechanics. Each of these elements needs to be understood to determine stress magnitudes.

25 Mechanical Stratigraphy (Part 1)

26 Mechanical Stratigraphy Low Tectonic Strain e h = (x-dx)/x Dominant term s hmin s V Low Tectonic Strain Controlled by Poisson s ratio Sand Shale Sandstone (or steel) = High E, Low Shale, Coal (or rubber) = Low E, high

27 High Tectonic Stress Australian Plate High Tectonic Stress CSG High stress sands Low stress coals Breakout preferentially occurs within sands

28 Mechanical Stratigraphy High Tectonic Strain e h = (x-dx)/x Dominant term s hmin s V High Tectonic Strain Controlled by Young s Modulus Sand Shale Sandstone (or steel) = High E, Low Shale, Coal (or rubber) = Low E, high

29 Low Tectonic Stress Lower tectonic stress within North American Plate Shale gas Low stress sands Higher stressed shales Breakout preferentially occurs within shales

30 Mechanical Stratigraphy Ainsa Quarry turbidites, North Spain Shale 2m Sand Centre for Integrated Petroleum Research, Norway & University of Aberdeen Note the stiff sand layers, intercalated with the soft shale layers

31 Gamma Ray Lithology Young s modulus E Poisson ratio Mechanical Stratigraphy Ainsa Quarry turbidites, North Spain 2m 2m Centre for Integrated Petroleum Research, Norway & University of Aberdeen Note the stiff sand layers, intercalated with the soft shale layers How does the mechanical stratigraphy affect stress, strength and rock failure?

32 Mechanical Stratigraphy

33 Hydraulic Fracture Propagation A classic kitchen sink experiment: Hubbert and Willis, 1957 Wellbore Fracture Gelatin filled Perspex tube Completed Interval Least Principal Stress Gelatin Least principal stress determines orientation of tensile fracture

34 Hydraulic Fracture Propagation Vertical fracture in stratified gelatin Fracture Wellbore Fractures can propagate along a plane-of-weakness. Here the gelatin detaches along a layer. Completed Interval Fractures propagate further in some strata than in others Fractures are planar are they?

35 A Cheesy Interlude

36 A Little Bit Of Cheese

37 A Little Bit Of Cheese

38 A Little Bit Of Cheese

39 A Little Bit Of Cheese

40 A Little Bit Of Cheese

41 A Little Bit Of Cheese

42 A Little Bit Of Cheese

43 Mechanical Stratigraphy (Part 2)

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46 Infillings of calcite and bitumen within interbedded dolostones, limestones, siliceous shales and mudstones of the Monterey Fm (Sibson, 1996)

47 Permeability Network s 1 s 3

48 Structural Permeability

49 Stresses on a Surface Normal Stress (s n ) Shear Stress ( )

50 Assessing Fracture Permeability P shear = σ n + 2T τ μ P hybrid = σ n 4T2 τ 2 4T ΔP P tensile = σ 3 + T Mildren et al (2005)

51 Fracture Modes Relationship between stress and strength that describes the occurrence, mode and orientation of failure s n

52 Infillings of calcite and bitumen within interbedded dolostones, limestones, siliceous shales and mudstones of the Monterey Fm (Sibson, 1996)

53 Assessing Fracture Permeability DP [MPa]

54 Fault Risk and Migration Pathways

55 Natural or Drilling Related Fractures?

56 Borehole Stresses s H s H

57 Natural vs Drilling Related Fractures What is a natural feature? Any feature that exists prior to drilling What is an induced feature? Any feature created as a result of drilling or testing

58 Natural vs Drilling Related Fractures Borehole breakout DITF

59 Natural vs Drilling Related Fractures Breakouts Natural Fractures/Fault Compression Tension

60 Natural vs Drilling Related Fractures Natural Drilling Enhanced Natural Fractures/Fault Compression Tension

61 Natural vs Drilling Related Fractures Drilling Enhanced Fractures or Inclined DITF? Compression Tension

62 Fracture Classification

63 Structural Interpretation 100m Mostly continuous fractures and faults Mostly discontinuous fractures Low fault density

64 Conductive Fractures Discontinuous wellbore Continuous around the wellbore Full Wellbore Dominant strike direction oriented approximately 150 N and secondary populations striking east-west, and approximately 060 N Discontinuous population has an east-west striking population not reflected in continuous and full wellbore fractures.

65 Fracture Permeability Upper Lynott Formation DP [MPa] DP [MPa] Cohesive model Non-cohesive model

66 Conclusions

67 Conclusions Mechanical properties play a large part in governing the way rocks behave under stress. High vs low tectonic stress environments. Dramatic geomechanical differences between formations within individual wells. Fracture distribution, orientation and mode are controlled by mechanical stratigraphy and stress distribution. Stresses can dramatically impact on structural interpretation of image logs.

68 Thank you Any Questions? Dr. Scott Mildren