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  1. 2. Geomodels of interpreted seismic data and overlaying attributes provide new ways to analyze structure. <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>ATC </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>
  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. Comparison of synthetics using all wavelets
  14. 16. Seismic sections used:
  15. 17. Interpreting well picks on seismic line 795-SK-06 using synthetics of dhodak-01 and 03 Dunghan Pab Sandstone Mughalkot
  16. 18. Interpreting well picks on seismic line 795-SK-06
  17. 19. Interpreting well picks and lithological strip on seismic line 795-SK-06 using Dhodak-03
  18. 20. Interpreting Well picks and lithological strip on seismic line 795-SK-06 using Dhodak-03
  19. 21. Time contour map: Pab Sandstone
  20. 22. Depth contour map: Pab Sandstone
  21. 23. Time contour map: Chiltan Limestone
  22. 24. Isochors map: Dunghan-Chiltan
  23. 25. RMS Velocities along seismic line: 795-SK-04 Average Velocities along seismic line: 795-SK-04
  24. 26. Fault Model
  25. 27. Time Surface grid at Dunghan level along with faults and well locations
  26. 28. Time Surface grid at Pab Sandstone level along with faults and well locations
  27. 29. Time Surface grid at Mughalkot level along with faults and well locations
  28. 30. Time Surface grid at Chiltan level along with faults and well locations
  29. 31. Time Surface grid at Alozai level along with faults and well locations
  30. 32. A-3D visualization with all interpreted Formations, faults and well locations
  31. 33. B-3D visualization with all interpreted Formations, faults and well locations
  32. 34. Dunghan surface with seismic line:795-SK-06
  33. 35. Dunghan, Chiltan & Alozai Formation along the seismic line: 805-SK-20
  34. 36. 3D-Movie
  35. 37. Interpreted seismic line: 795-SK-04 V ave V int V rms Bulk Modulus Shear Modulus Density Poisson Ratio V s V p
  36. 38. Interpreted seismic line: 805-SK-20
  37. 39. Rock Physical properties along the seismic line 795-SK-04
  38. 40. 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>
  39. 41. Bulk Modulus along the seismic line: 795-SK-04 Line:795-SK-04
  40. 42. Shear Modulus along the seismic line: 795-SK-04 Line:795-SK-04
  41. 43. Density along the seismic line: 795-SK-04 Line:795-SK-04
  42. 44. Poisson Ratio along the seismic line: 795-SK-04 Line:795-SK-04
  43. 45. Well Log Interpretation
  44. 46. Well logs displayed for Dhodak-02
  45. 47. Lithological analysis along the Pab Sandstone zone of Dhodak-02
  46. 48. Petro-Physics
  47. 49. Density-Porosity cross plot overlaid on the generalized cross plot for lithological interpretation
  48. 50. Density-Poisson Ratio cross plot Density-Shear sonic cross plot
  49. 51. Sonic-density cross plot Porosity-Shear Sonic cross plot
  50. 52. Porosity-Density cross plot Porosity-Poisson Ratio cross plot
  51. 53. Sonic-porosity cross plot Poisson Ratio-Shear Sonic cross plot
  52. 54. Poisson Ratio-Vs cross plot Density-Vp cross plot
  53. 55. Vp-Poisson Ration cross plot Vp-Shear Sonic cross plot
  54. 56. Vp-Vs cross plot Vs-Poisson Ratio cross plot
  55. 57. Sonic-Density Cross plot
  56. 58. Plots for Dhodak-02 well
  57. 61. Pickett Plot
  58. 62. <ul><li>Conclusions: </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><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>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 Dunghan & Chiltan formations, showing the time thickness in the range of 600msec to 1300msec. Maximum variation is on the southern side. </li></ul><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>
  59. 63. <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 corelatable 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><ul><li>Some of the well logs have been estimated using the general curve estimation relations. </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>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>Density-Porosity cross plot shows linear trend of the data values that lies 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>
  60. 64. Thanks
  61. 65. Questions.... ?