Oral defense (modified)

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Oral defense (modified)

  1. 1. Simulation Study of The Effect of Well Spacing, Permeability Anisotropy, and Palmer and Mansoori Model on Coalbed Methane Production Ismail Zulkarnain Harold Vance Department of Petroleum Engineering. Texas A&M University 25 th July, 2005
  2. 2. Outline 2 <ul><li>Objectives </li></ul><ul><li>US coalbed Methane Resource </li></ul><ul><li>CBM and Conventional Natural Gas Reservoirs </li></ul><ul><li>Reservoir Characteristics of Coals </li></ul><ul><li>Adsorption and Desorption Phenomena </li></ul><ul><li>Dual Porosity Model </li></ul><ul><li>Simulation Data </li></ul><ul><li>Well Spacing Effect </li></ul><ul><li>Permeability Anisotropy </li></ul><ul><li>Palmer and Mansoori Theory </li></ul><ul><li>Conclusions </li></ul>
  3. 3. Objectives <ul><li>Study the effect of interference between wells on the </li></ul><ul><li>reservoir performance coalbed methane production. It </li></ul><ul><li>also is known as well spacing effect on coalbed </li></ul><ul><li>methane production. </li></ul><ul><li>Study the effect of well configuration on an anisotropic coal bed methane reservoir. </li></ul><ul><li>Study the effects of Palmer and Mansoori Theory </li></ul><ul><li>(Matrix Shrinkage Effect and Cleats Compression </li></ul><ul><li>Effect) on the reservoir performance of coal bed </li></ul><ul><li>methane (CBM). </li></ul>3
  4. 4. CBM in the United States <ul><li>Early CBM wells were drilled to release gas as a safety measure prior to coal </li></ul><ul><li>mining operations. </li></ul><ul><li>Increase in natural gas prices in he 1970’s encouraged intensive research efforts </li></ul><ul><li>and federal tax credits catalyzed CBM exploration and development to produce </li></ul><ul><li>CBM for profit. </li></ul>From Kentucky Geological Survey 4
  5. 5. US Coalbed Methane Resource 5 “ Coalbed methane activity is increasing in the U.S., the world leader in reserves and production, due to recent high gas prices and dwindling conventional gas supplies” Walter B. Ayers
  6. 6. US Coalbed Methane Resource 5 Proved Reserves 18,743 bcf US Production (2003) 1600 bcf 8% of US dry gas production
  7. 7. Sandstones and Coal Reservoirs Surface Area of Coals are in the range of; 2,150 – 3,250 ft 2 /g (SOURCE: Marsh (3), 1965) <ul><li>Large Internal Surface Area of Coal </li></ul>6 If average surface area of coal is 2700 ft 2 /g, 16 gram of coal has surface area equal to a football field area. 295ft x 147 ft Surface Area Can EQUAL Micro-particle of Coal A block of Coal
  8. 8. CBM and Conventional Natural Gas 7 Typical Conventional Natural Gas CBM Depth 150 to 3000m 150 to 1500m Water Rates may increase during production Rates typically decreases during production life Well Spacing Normally, 1 well per square mile but density may be increased 2 to 8 wells per square mile Gas Storage Stored in macropores or fractures Stored as adsorbed gas on the coal matrix
  9. 9. Reservoir Characteristics of Coal <ul><li>Matrix (micro pores) </li></ul><ul><li>Fracture/Cleats (macro pores) </li></ul><ul><ul><ul><li>Face Cleats (continuous throughout the reservoir) </li></ul></ul></ul><ul><ul><ul><li>Butt Cleats (discontinuous, terminated at an intersection) </li></ul></ul></ul>8
  10. 10. Reservoir Characteristics of Coal 9
  11. 11. Coalbed Recovery Mechanism <ul><li>3 Stages in Primary Recovery; </li></ul><ul><ul><li>Dewatering: to reduce cleat pressure </li></ul></ul><ul><ul><li>Stable Prod. Stage: Methane desorbing from matrix and flowing to the cleat </li></ul></ul><ul><ul><li>Decline Stage: Methane and water flow to the well bore </li></ul></ul><ul><ul><li>All the flow is in fractures </li></ul></ul><ul><ul><li>Fractures are 100% saturated with water </li></ul></ul>10 q g , q w
  12. 12. Schematic of Coalbed Methane Well 11 PUMP GAS COAL WATER CEMENT OVERBURDEN Water (Sand, shale, and thinner coal beds) PUMP MAY BE SET IN COAL RATHER THAN IN RAT HOLE
  13. 13. Adsorption and Desorption (Sorption) in Coal 12
  14. 14. Langmuir Theory of Single Molecule Adsorption 13
  15. 15. Reservoir Mechanism 14 Coalbed Adsorption Phenomenon
  16. 16. Reservoir Mechanism 15
  17. 17. Adsorption Phenomena <ul><li>Physical adsorption between methane and the coal solid molecules </li></ul><ul><li>involves intermolecular forces (Van der Waals forces) </li></ul><ul><li>Adsorption is instantaneous </li></ul><ul><li>Equilibrium adsorption model </li></ul><ul><ul><ul><li>Gas adsorption/desorption is pressure dependent </li></ul></ul></ul><ul><ul><ul><ul><li>LANGMUIR ISOTHERM </li></ul></ul></ul></ul>16 Adsorption
  18. 18. Langmuir Equation <ul><li>Relationship used to represent the sorption mechanism </li></ul><ul><li>in coal bed methane reservoir is given as: </li></ul>(Seidle et al, 1990) Where ; V(p) = gas content ( scf/ft 3 ) V L = Langmuir volume ( scf/ft 3 ) (Saturated monolayer volume) p = gas pressure ( psi ) p L = Langmuir pressure (Pressure at half of the Langmuir volume) www.hycal.com (2004 CIPC Session 31) 17
  19. 19. Langmuir Adsorption 18 <ul><li>Matrix may be “undersaturated” if gas is not available </li></ul><ul><li>at initial conditions </li></ul><ul><li>Desorption pressure is less than initial pressure </li></ul><ul><li>(p d < p i ) </li></ul><ul><li>Desorption pressure determines the adsorbed gas </li></ul><ul><li>content </li></ul><ul><li>Desorption pressure is analogous to bubble point </li></ul><ul><li>pressure for oil </li></ul>
  20. 20. Langmuir Sorption Isotherm “ Single layer sorption theory” Developed in 1916 by Irving Langmuir Gas Concentration, scf/ton Pressure, psi 19 <ul><li>Isotherm is used to </li></ul><ul><li>predict the release of </li></ul><ul><li>gas from the reservoir </li></ul><ul><li>as pressure is reduced. </li></ul><ul><li>Isotherm is based on </li></ul><ul><li>the theory that simply </li></ul><ul><li>states that the rate of </li></ul><ul><li>molecules arriving </li></ul><ul><li>and adsorbing on </li></ul><ul><li>the solid surface </li></ul><ul><li>should equal the rate </li></ul><ul><li>of molecules </li></ul><ul><li>leaving the surface </li></ul>Theoretical Isotherm; P i = P d ; p d = p m Undersaturated Isotherm; P i > P d ; p d = p m P d
  21. 21. Dual Porosity Model (Coalbed modeling) Warren and Root (paper SPE 426 ) <ul><li>Analogous to Warren and Root Model </li></ul><ul><li>Modeling two interconnected systems </li></ul><ul><ul><ul><li>Coal matrix and Permeable rock fractures </li></ul></ul></ul>20 Fracture Cell, “f” Matrix Cell, “m” Actual Reservoir Model Reservoir Matrix Fracture Matrix Fracture Warren & Root Coal Bed Methane Initial Gas Storage Free gas in pores OR Fractures(Cleats ) Adsorbed to coal OR Free gas in fractures Matrix / fracture flow “ Pseudo Steady State Model” Darcy’s Law Fick’s Law (Diffusion)
  22. 22. Diffusive Flow of Gas in CBM Reservoirs <ul><li>Fick’s law of diffusion is given as: </li></ul><ul><li>Diffusion of gas out of the coal matrix can be expressed by a </li></ul><ul><li>simple diffusion equation: </li></ul><ul><li>Driving force for this mode of transport is a concentration </li></ul><ul><li>gradient between the matrix and the cleat. </li></ul>21 Average gas concentration in the matrix Concentration in the outer surface of the coal
  23. 23. Simulation Details <ul><li>Construct a dual porosity simulation model using CMG to </li></ul><ul><li>simulate the process of primary production from a single </li></ul><ul><li>coal seam. </li></ul><ul><li>Model consists of </li></ul><ul><ul><ul><li>21 * 21 * 1 grid system </li></ul></ul></ul><ul><ul><ul><li>1 producing well </li></ul></ul></ul>22 Producer
  24. 24. Simulation Details 23
  25. 25. Relative Permeability Curves 24
  26. 26. Well Spacing Effect 25
  27. 27. 80 acre spacing
  28. 28. 40 acre spacing
  29. 29. 80 acre spacing
  30. 30.
  31. 31. 20 acre spacing
  32. 32. 80 acre spacing
  33. 33. Well Spacing Effect Comparison of an 80 acre well and a 40 acre well 27
  34. 34. Simulation scenarios 28 y = 1866.76 ft x = 1866.76 ft 80 acre-Isotropic Reservoir A y = 1320 ft x = 1320 ft 40 acre-Isotropic Reservoir B
  35. 35. Gas rate (scf/day) per well basis 29
  36. 36. Water rate (bbl/day) per well basis 30
  37. 37. Comparison of 80 acre spacing, 40 acre spacing, 20 acre spacing, and 5 acre spacing on an 80 acre reservoir 31
  38. 38. 32 Reservoir model y = 1866.76 ft x = 1866.76 ft Isotropic-Square Reservoir System 80 acre
  39. 39. Simulation scenarios 33 80 acre reservoir with 20 acre spacing A B C D 80 acre reservoir with 80 acre spacing 80 acre reservoir with 40 acre spacing 80 acre reservoir with 5 acre spacing
  40. 40. Gas rate (scf/day) per field basis 34
  41. 41. Water rate (scf/day) per field basis 35
  42. 42. RF Gas (fraction) per field basis 36
  43. 43. RF Water (fraction) per field basis 37
  44. 44. RF Water (fraction) per field basis 38
  45. 45. Permeability Anisotropy 39
  46. 46. 40 Problem Statement <ul><li>Coalbed methane is a naturally fractured reservoir. </li></ul><ul><li>Coalbed methane reservoir is consisted of the face </li></ul><ul><li>cleats (continuous fractures) and the butt cleats </li></ul><ul><li>(discontinuous fractures). </li></ul><ul><li>The existence of the face cleats and the butt cleats </li></ul><ul><li>causes the permeability anisotropy in coalbed methane </li></ul><ul><li>reservoirs. </li></ul>
  47. 47. 41 Problem Statement y x Anisotropic - Reservoir System Permeability in x-direction is higher than permeability in y-direction Butt Cleats Face Cleats
  48. 48. 42 Reservoir model y = 1866.76 ft x = 1866.76 ft Anisotropic-Square Reservoir System (k X =1 md and k Y =0.01 md)
  49. 49. 43 Effect of well configuration on anisotropic reservoir <ul><li>Scenario A </li></ul><ul><li>The reservoir is 80 acre area. The reservoir has 4 </li></ul><ul><li>wells. Each of the well has the same drainage </li></ul><ul><li>area, 20 acre. Each of the well is located in the </li></ul><ul><li>center of square reservoir area. </li></ul>
  50. 50. 44 Effect of well configuration on anisotropic reservoir <ul><li>Scenario B </li></ul><ul><li>The reservoir is 80 acre area. The reservoir has 4 </li></ul><ul><li>wells. Each of the well has the same drainage </li></ul><ul><li>area, 20 acre. Each of the well is located in the </li></ul><ul><li>center of rectangular reservoir area. Placement of </li></ul><ul><li>wells is aligned to the direction of lower </li></ul><ul><li>permeability direction. </li></ul>
  51. 51. 45 Effect of well configuration on anisotropic reservoir <ul><li>Scenario C </li></ul><ul><li>The reservoir is 80 acre area. The reservoir has 4 </li></ul><ul><li>wells. Each of the well has the same drainage </li></ul><ul><li>area, 20 acre. Each of the well is located in the </li></ul><ul><li>center of rectangular reservoir area. Placement of </li></ul><ul><li>wells is aligned to the direction of higher </li></ul><ul><li>permeability direction. </li></ul>
  52. 52. Gas rate (scf/day) per field basis 46
  53. 53. Water rate (scf/day) per field basis 47
  54. 54. RF Gas (fraction) per field basis 48
  55. 55. RF Water (fraction) per field basis 49
  56. 56. Tabulated results (Well configuration) 50
  57. 57. Palmer and Mansoori Theory 51
  58. 58. <ul><li>Palmer and Mansoori theory models low pressure k rebound in coals: </li></ul><ul><ul><li>At higher pressures, k decreases with pressure due to compaction (cleats compression) </li></ul></ul><ul><ul><li>At lower pressures, k increases with pressure due to matrix shrinkage during gas desorption. </li></ul></ul>52 Palmer and Mansoori model
  59. 59. 53 Cleats compression k Overburden pressure coal matrix fracture (a) Before cleats compression (b) After cleats compression
  60. 60. 54 Matrix shrinkage Width of cleats after shrinkage Coal matrix after shrinkage Width of cleats before shrinkage Coal matrix before shrinkage Fractures/cleats Coal matrix Coal matrix Coal matrix k
  61. 61. 55 Palmer and Mansoori model Cleats Compression Matrix Shrinkage
  62. 62. 56 Palmer and Mansoori model
  63. 63. 57 Palmer and Mansoori model
  64. 64. 58 Palmer and Mansoori model It has an implication on the gas production:
  65. 65. Sensitivity Analysis on Palmer and Mansoori Model Parameters 59
  66. 66. Sensitivity Cases <ul><li>Young’s Modulus, psia </li></ul><ul><ul><li>500,000 psia, 750,000 psia, 1,000,000 psia, 1,500,000 psia, 2,000,000 </li></ul></ul><ul><ul><li>psia, 3,000,000 psia, 4,000,000 psia, and 5,000,000 psia, </li></ul></ul><ul><li>Poisson’s Ratio, fraction </li></ul><ul><ul><li>0.1, 0.2, 0.3, 0.4, 0.5, </li></ul></ul><ul><li>Strain Maximum, dimensionless </li></ul><ul><ul><li>0.001, 0.005, 0.01, 0.02, 0.05, 0.1 </li></ul></ul>60
  67. 67. Young’s modulus 61
  68. 68. 62 Young’s modulus
  69. 69. 62 Young’s modulus, E
  70. 70. 62 Poisson Ratio, ν
  71. 71. 62 Bulk modulus, K
  72. 72. 62 Young’s modulus, E
  73. 73. 62 Young’s modulus, E
  74. 74. 63 Young’s Modulus
  75. 75. Poisson’s Ratio 64
  76. 76. Poisson’s Ratio 65
  77. 77. 66 Poisson’s Ratio
  78. 78. Strain Maximum 67
  79. 79. Strain Maximum 68
  80. 80. 69 Strain Maximum
  81. 81. Conclusions <ul><li>Well Spacing </li></ul><ul><li>Interference between wells creates beneficial effect on coalbed methane production. The more interference is created, the higher the production is. </li></ul><ul><li>Interference between wells accelerates the dewatering stage. </li></ul><ul><li>The closer well spacing, the higher and earlier peak gas rates. Closer well spacing results in higher cumulative gas production. </li></ul>70 <ul><li>Permeability Anisotropy </li></ul><ul><li>The existence of face cleats and butt cleats creates permeability anisotropy in coalbed methane reservoir. </li></ul><ul><li>Placement of wells should be considered based on the existence of permeability anisotropy. </li></ul><ul><li>Wells aligned or placed along the lower permeability direction results the higher gas production and cumulative gas production. </li></ul>
  82. 82. Conclusions <ul><li>Palmer and Mansoori Theory </li></ul><ul><li>We observe that Palmer and Mansoori model should be considered and included in the modeling and simulation of coalbed methane performance. </li></ul><ul><li>The higher the Young’s Modulus is the higher the gas rate and cumulative gas production is. </li></ul><ul><li>The higher the Poisson’s Ratio is the lower the gas rate and cumulative gas production is. </li></ul><ul><li>The higher the strain maximum is the higher the gas rate and cumulative gas production is. </li></ul>71
  83. 83. Nusantara Archipelago, Indonesia-Southeast Asia Thank You
  84. 84. Simulation Study of The Effect of Well Spacing, Permeability Anisotropy, and Palmer and Mansoori Model on Coalbed Methane Production Ismail Zulkarnain Harold Vance Department of Petroleum Engineering. Texas A&M University 25 th July, 2005
  85. 85. <ul><li>CMG shows that mass transfer rate from matrix cell “m” bounded by a set of fracture associated with a fracture cell “f” can be expressed as : </li></ul>Diffusive Flow of Gas <ul><li>Where; </li></ul><ul><li>Vol = Bulk Volume </li></ul><ul><li>Shape = Shape factor (matrix-fracture interface area per unit volume) </li></ul><ul><li> </li></ul><ul><li>Diffus(k)= Diffusion value (COAL-DIF-COMP) </li></ul><ul><li>S g A-mod = gas saturation in the matrix (default = 1) </li></ul><ul><li>C(k,gas,m) = Concentration of component ‘k’ in gas phase of matrix cell “m” </li></ul><ul><li>C(k,gas,f) = Concentration of component ‘k’ in gas phase of fracture cell “f” </li></ul>
  86. 86. RF Gas (fraction) per well basis
  87. 87. RF Water (fraction) per well basis
  88. 88. Tabulated Result
  89. 89. Young’s modulus
  90. 90. Young’s modulus
  91. 91. Poisson’s ratio
  92. 92. Poisson’s ratio
  93. 93. Strain maximum
  94. 94. Strain maximum
  95. 95. Reservoir Model 30 ft 1866.76 ft 1866.76 ft
  96. 96. Transformation (Wattenbarger and Arrevallo) Simulation: Isotropic-Rectangular Reservoir System (k = 0.1) x = 590.32 ft y = 5903.2 ft b y = 1866.76 ft x = 1866.76 ft Anisotropic-Square Reservoir System (k X =1 md and k Y =0.01 md) a
  97. 97.
  98. 98.
  99. 99. Dual Porosity (Warren and Root) (a) (b)
  100. 100. Diffusion and Flow of Methane (a) (b) (c)
  101. 101. Scenario A y-direction/low permeability x-direction/high permeability
  102. 102. Scenario B y-direction/low permeability x-direction/high permeability
  103. 103. Scenario C y-direction/low permeability x-direction/high permeability

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