Seismic data Interpretation On Dhodak field Pakistan

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I (Jamal Ahmad) presented this on 21 Feb, 2009 to defend my M.Phil dissertation in Geophysics at QAU, Islamabad, Pakistan. For more information about this, you may contact me directly at jamal.qau@gmail.com.

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Seismic data Interpretation On Dhodak field Pakistan

  1. 2. Geophysical Modeling of the part of Central Indus Basin with the help of Seismic and Well data <ul><li>By: Jamal Ahmad </li></ul><ul><li>(M.Phil Geophysics)‏ </li></ul><ul><li>Supervisor: Dr. Shahid Nadeem Qureshi </li></ul><ul><li>Department of Earth Sciences </li></ul><ul><li>QAU, Islamabad </li></ul>
  2. 3. Objectives <ul><li>To interpret surface structure on satellite image. </li></ul><ul><li>Synthetic seismogram comparison using different wavelets. </li></ul><ul><li>Picking horizons at different levels on seismic section, using synthetic seismogram and well picks. </li></ul><ul><li>Various 3D views of the interpretation </li></ul><ul><li>To interpret lithology using different well logs </li></ul><ul><li>To create cross plots using different well logs </li></ul><ul><li>To analyze sand-shale for various zones </li></ul><ul><li>To estimate water saturation using Pickett-Plot </li></ul><ul><li>AVO-AVA comparison </li></ul><ul><li>AVO-AVA Synthetics </li></ul>
  3. 4. The Dhodak gas field is the Pakistan’s largest gas and condensate producing field. The Dhodak field, with estimates 620Bcf of proven gas reserves and 30million barrels of condensate, is located in the Central Indus basin approximately 15KM North of Safed koh Block . Introduction to Area
  4. 5. Location of study area on surface tectonic map of Pakistan
  5. 6. Basemap of the data used
  6. 7. Divisions of Central Indus basin ( Raza et al, 1989 ) Cross Section along the Central Indus basin (Raza et al, 1989 )
  7. 8. General geology and stratigraphy
  8. 9. Surface geological map (Bakr & Jeckson, 1964 )‏ Surface geological map (sheikh et al, 1989)
  9. 10. Surface structure map and satellite map (Kellogg, 1936)‏
  10. 11. Stratigraphy of the area
  11. 13. Well Correlation along the Zindapir-Dhodak anticlines
  12. 14. Seismic data interpretation
  13. 15. Ricker wavelet Synthetic seismogram created using Ricker wavelet
  14. 16. Klauder wavelet Synthetic seismogram created using Klauder wavelet
  15. 17. Ormsby wavelet Synthetic seismogram created using Ormsby wavelet
  16. 18. Butterworth wavelet Synthetic seismogram created using Butterworth wavelet
  17. 19. Comparison of synthetics using all wavelets
  18. 20. Seismic sections used:
  19. 21. Interpreting well picks on seismic line 795-SK-06 using synthetics of dhodak-01 and 03 Dunghan Pab Sandstone Mughalkot
  20. 22. Interpreting well picks on seismic line 795-SK-06
  21. 23. Interpreting well picks and lithological strip on seismic line 795-SK-06 using Dhodak-03
  22. 24. Interpreting Well picks and lithological strip on seismic line 795-SK-06 using Dhodak-03
  23. 25. Time contour map: Dunghan Limestone
  24. 26. Depth contour map: Dunghan Limestone
  25. 27. Time contour map: Pab Sandstone
  26. 28. Depth contour map: Pab Sandstone
  27. 29. Time contour map: Mughalkot Formation
  28. 30. Time contour map: Chiltan Limestone
  29. 31. Time contour map: Alozai
  30. 32. Isochors map: Chiltan-alozai
  31. 33. Isochors map: Dunghan-Chiltan
  32. 34. RMS Velocities along seismic line: 795-SK-04 Average Velocities along seismic line: 795-SK-04
  33. 35. Fault Model
  34. 36. Time Surface grid at Dunghan level along with faults and well locations
  35. 37. Time Surface grid at Pab Sandstone level along with faults and well locations
  36. 38. Time Surface grid at Mughalkot level along with faults and well locations
  37. 39. Time Surface grid at Chiltan level along with faults and well locations
  38. 40. Time Surface grid at Alozai level along with faults and well locations
  39. 41. A-3D visualization with all interpreted Formations, faults and well locations
  40. 42. B-3D visualization with all interpreted Formations, faults and well locations
  41. 43. Dunghan surface with seismic line:795-SK-06
  42. 44. Dunghan, Chiltan & Alozai Formation along the seismic line: 805-SK-20
  43. 45. 3D-Movie
  44. 46. Interpreted seismic line: 795-SK-04 V ave V int V rms Bulk Modulus Shear Modulus Density Poisson Ratio V s V p
  45. 47. Interpreted seismic line: 805-SK-20
  46. 48. Average Velocities along the seismic line: 795-SK-04 Line:795-SK-04
  47. 49. Interval Velocities along the seismic line: 795-SK-04 Line:795-SK-04
  48. 50. RMS Velocities along the seismic line: 795-SK-04 Line:795-SK-04
  49. 51. Rock Physical properties along the seismic line 795-SK-04
  50. 52. General equations used: <ul><li>K= ρ * ((V P ) 2 -(4/3)*(V s ) 2 )‏ </li></ul><ul><li>Where </li></ul><ul><li>ρ = Density </li></ul><ul><li>V p = Interval Velocity (km/sec)‏ </li></ul><ul><li>V s = Shear Velocity (km/sec)‏ </li></ul><ul><li>K = Bulk modulus </li></ul><ul><li>Shear Modulus= ρ * (V s ) 2 </li></ul><ul><li>Where </li></ul><ul><li>ρ = Density </li></ul><ul><li>V s = shear Velocity (km/sec)‏ </li></ul><ul><li>Density= 0.31 * (V P ) 0.25 </li></ul><ul><li>Where </li></ul><ul><li>V p = Interval Velocity (m/sec)‏ </li></ul><ul><li>Poisson Ratio= (0.5* (V p 2 -2*V s 2 ))/ (V p 2 -V s 2 )‏ </li></ul><ul><li>Where </li></ul><ul><li>V p = Interval Velocity (km/sec)‏ </li></ul><ul><li>V s = Shear Velocity (km/sec)‏ </li></ul><ul><li>Shear Velocity= V p -1.36/1.16 </li></ul><ul><li>Where </li></ul><ul><li>V p = Interval Velocity (km/sec)‏ </li></ul><ul><li>V p has been calculated using acoustic log. </li></ul>
  51. 53. Bulk Modulus along the seismic line: 795-SK-04 Line:795-SK-04
  52. 54. Shear Modulus along the seismic line: 795-SK-04 Line:795-SK-04
  53. 55. Density along the seismic line: 795-SK-04 Line:795-SK-04
  54. 56. Poisson Ratio along the seismic line: 795-SK-04 Line:795-SK-04
  55. 57. Shear Velocity along the seismic line: 795-SK-04 Line:795-SK-04
  56. 58. Primary Velocity along the seismic line: 795-SK-04 Line:795-SK-04
  57. 59. Well Log Interpretation
  58. 60. Well logs displayed for Dhodak-02
  59. 61. Well logs displayed for Dhodak-01
  60. 62. Well logs displayed for Dhodak-01
  61. 63. Well Lathe on Dhodak-03 from 165 SP of the seismic line: 795-SK-05R
  62. 64. Stratigraphic well correlation using four Dhodak wells:3-1-2-7 (S-N)
  63. 66. Sand-Shale analysis along the productive zone of Dhodak-02
  64. 67. Sand-Shale analysis along the Pab Sandstone zone of Dhodak-02
  65. 68. Lithological analysis along the Lower Ranikot zone of Dhodak-02
  66. 69. Lithological analysis along the Pab Sandstone zone of Dhodak-02
  67. 70. Lithological analysis along the Mughalkot zone of Dhodak-02
  68. 71. Lithological analysis along the Parh Limestone zone of Dhodak-02
  69. 72. Petro-Physics
  70. 73. Sonic-Density cross plot for Dhodak-01 with overlay on the generalized Sonic-Density lithological plot.
  71. 74. Sonic-Density cross plot for Dhodak-01 with overlay on the generalized three minerals crossplot.
  72. 75. Sonic-Neutron Porosity cross plot overlaid on the generalized cross plot for lithological interpretation
  73. 76. Sonic-Porosity cross plot overlaid on the generalized cross plot for lithological interpretation
  74. 77. Density-Porosity cross plot overlaid on the generalized cross plot for lithological interpretation
  75. 78. Density-Poisson Ratio cross plot Density-Shear sonic cross plot
  76. 79. Sonic-density cross plot Porosity-Shear Sonic cross plot
  77. 80. Porosity-Density cross plot Porosity-Poisson Ratio cross plot
  78. 81. Sonic-porosity cross plot Poisson Ratio-Shear Sonic cross plot
  79. 82. Poisson Ratio-Vs cross plot Density-Vp cross plot
  80. 83. Vp-Poisson Ration cross plot Vp-Shear Sonic cross plot
  81. 84. Vp-Vs cross plot Vs-Poisson Ratio cross plot
  82. 85. Sonic-Density Cross plot
  83. 86. Plots for Dhodak-02 well
  84. 89. Vp-Vp/Vs cross plot Vp-Vp/Vs cross plot overlay
  85. 90. SP – Volume of Shale cross plot GR-Volume of Shale cross plot
  86. 91. Pickett Plot
  87. 92. AVO/AVA Synthetics
  88. 93. <ul><li>AVO Synthetics: </li></ul><ul><li>AVO Synthetic displays are used to study of the effects of trace offset on reflection amplitude. The AVO (amplitude variation with offset) Synthetics simulates the effects that offset distance has on trace amplitude. The AVO traces displayed are equivalent to a CMP (common midpoint) gather that is used to observe these amplitude variations. </li></ul><ul><li>Trace gathers can also be displayed with NMO (normal moveout) effects applied and offset limited stacks can be generated from the CMP gathers. </li></ul><ul><li>AVA Synthetics: </li></ul><ul><li>AVA Synthetic displays are used to study of the effects of reflection angle on trace amplitude. The AVA (amplitude variation with angle) synthetics program simulates the effects that changing reflection angle (with offset distance) has on trace amplitude. </li></ul><ul><li>The result is an angle sorted gather used to observe these amplitude variations. All gathers are corrected for NMO (normal moveout). </li></ul><ul><li>AVA Synthetics are primarily used as an analytical tool to compare the effects of geology on trace amplitude that are independent of trace offset. In other words, an amplitude effect such as a phase reversal, caused by the same geological conditions of density, velocity and Poisson’s ratio contrast, will generate the same anomaly at the same incidence angle regardless of the depth of the anomaly. </li></ul><ul><li>On an AVA display, the general trace character (variation in amplitude with time) will appear approximately the same as an AVO display, but anomalies (on an AVO display) similar to the one described above will appear at different offsets, rather than at the same angle. This makes the AVA display useful for identifying anomalies that are expected to occur at specific reflection angles. </li></ul>
  89. 94. AVA-AVO comparison
  90. 95. T psv = T pp ((1 + V p / V s ) / 2) Where:T psv is the P-SV travel time.  Tpp is the P-P travel time.  V p /V s is the ratio of P and S average velocities to the reflector Zoeppritz Equation: Shuey 2-term and 3-term equations:
  91. 96. AVO model for Dhodak-02
  92. 97. AVA model for Dhodak-02
  93. 98. AVA model for Dhodak-01 using Zoeppritz equation
  94. 99. AVA model for Dhodak-01 using Shuey02 equation
  95. 100. AVA model for Dhodak-01 using Shuey03 equation
  96. 101. AVO model for Dhodak-01 using Zoeppritz equations
  97. 102. AVO model for Dhodak-01 using Shuey2 equation
  98. 103. AVO model for Dhodak-01 using Shuey 03
  99. 104. <ul><li>Conclusions: </li></ul><ul><li>From surface Geology of the area : </li></ul><ul><li>Eocene strata is exposed at the surface of study area. </li></ul><ul><li>On moving towards the south of the study area, older strata go on exposing up till the Zindapir anticline, where Paleocene-createous strata is exposed on the surface. </li></ul><ul><li>Pop-up structure prevails the whole area. </li></ul><ul><li>Extension of the structure is North-South. </li></ul>
  100. 105. <ul><li>From seismic interpretation : </li></ul><ul><li>There is very small variation in the synthetics, created using various wavelets. </li></ul><ul><li>Normally the throw of these faults is very low (25msec to 80msec), except at few places (e.g. in line 18, there is an about 100msec throw of fault ). </li></ul><ul><li>Velocity of these formations is very high, ranging from 4000m/sec to 7000m/sec. </li></ul><ul><li>Depth converted maps have been prepared using SRD rather than depth from KB. </li></ul><ul><li>Since most of the faults terminates in the Eocene strata, therefore the age of Eocene can be assigned to these faults. </li></ul><ul><li>Chiltan formation is highly fractured and distorted. </li></ul><ul><li>Isochors map between Chiltan and Alozai formations, showing the time thickness in the range of 700msec to 1300msec. Maximum variation is on the southern side. </li></ul><ul><li>Isochors map between Dunghan & Chiltan formations, showing the time thickness in the range of 600msec to 1300msec. Maximum variation is on the southern side. </li></ul>
  101. 106. <ul><li>RMS and average velocity graphs showing continuously increasing trend of velocities. </li></ul><ul><li>3D visualization of the seismic and the other maps, provide the ease in the seismic data interpretation. </li></ul><ul><li>Variation in the velocity lines along the seismic line give hint of the presence of faults. </li></ul><ul><li>Variation in the rock physical properties can directly be co relatable with the structure, interpreted. </li></ul><ul><li>In order to get production from Chiltan Limestone, Dhodak-09 well would have to be deepen for a few meters more. </li></ul>
  102. 107. <ul><li>For well Log Interpretation: </li></ul><ul><li>Some of the well logs have been estimated using the general curve estimation relations. </li></ul><ul><li>Well lathe shows the sharp variation of amplitudes in the lower part. </li></ul><ul><li>Well correlation shows the pinching out in the Eocene strata but linear trend of strata, below it. </li></ul><ul><li>Unit-2 of the Lower Ranikot showing the higher value of porosity and lower values of water saturation. This gives hint of the presence of some hydrocarbon accumulation (Well-01). Similar is the situation with Pab Sandstone. </li></ul>
  103. 108. <ul><li>For Petrophysical interpretation: </li></ul><ul><li>Sonic-Density cross plot showing the increasing trend and the data values fall in the range on the sandstone and lime stone zone. </li></ul><ul><li>The same plot has also been overlaid on the three minerals plot, which showing the data values to be residing in the calcite zone and trending towards sandstone. </li></ul><ul><li>Density-Porosity cross plot shows linear trend of the data values that totally resides in between the zone of Sandstone and Limestone. </li></ul><ul><li>various other cross plots showing the linear trend, in increasing order. </li></ul><ul><li>If a curve estimated from the other curve and plotted against its native curve, the output trend of the data point is linear line. </li></ul><ul><li>Most of the data points lies in the range of 10% to 20 % porosity, for the Impedance-Porosity cross plot. </li></ul><ul><li>There is a linear trend of volume of shale both against SP and GR. </li></ul><ul><li>Pickett plot showing the water saturation lines, with decreasing order, for the Dhodak-02 well, cropped for the reservoir zone. </li></ul>
  104. 109. <ul><li>For AVO/AVA modeling: </li></ul><ul><li>Phase reversal in AVA/AVO gives hint of the presence of some hydrocarbon accumulation. </li></ul><ul><li>The output of the AVO may vary from AVA, for the complex areas, with sharp dipping of horizons and presence of faults. </li></ul><ul><li>Very distortions can be seen in the AVA models as compared to the AVO models. </li></ul><ul><li>Clear phase reversal can be seen for both AVA and AVO models, using the data of Dhodak-01 well. </li></ul><ul><li>There is a very small difference between the output AVO/AVA models, created using Zoeppritz, Shuey2 and Shuey3 equations. </li></ul><ul><li>Shuey3 and Shuey2 equations gives smooth trend for the output AVA model as compared to the AVA model, created using Zoeppritz equation. </li></ul><ul><li>Zoeppritz equation give sharp edges at the reflections of the output AVO model as compared to the AVO models, created using either Shuey2 or Shuey3 equations. </li></ul><ul><li>The results of AVA, created using Shuey2 equation gives more accurate results. </li></ul>
  105. 110. Thanks
  106. 111. Questions.... ?

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