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Integration of Seismic Inversion, Pore Pressure Prediction, and TOC Prediction in Preliminary Study of Shale Gas Exploration

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Conventional natural gas is being exploited rapidly to achieve energy security and to satisfy the demand. However, due to the high demand for oil and gas it is becoming more difficult to find sufficient conventional reserves. To anticipate the predicted shortage of gas, we need to explore new, unconventional resources, such as shale gas. Shale gas is shale lithology that has high TOC, is brittle, and is located in the dry gas window zone. This study describes the early exploration of shale gas potential in one block in South Sumatra basin area.

In this study, the integration of geochemical data, rock physics and seismic inversion for characterizing and searching for shale gas potential will be described. The preliminary exploration stage of gas shale play covers sweet spot analysis using the Passey method to create a pseudo TOC in the target formation. Secondly, the overpressure area is mapped to avoid any potential pitfalls. Thirdly, seismic inversion is performed to map the distribution of shale based on the parameters Vp / Vs and map its TOC through conversion from Vp parameter.

As a result, log analysis shows one target zone of potential shale gas with TOC above 1% with a thickness of 100 feet. Integration of pore pressure data, shale distribution and TOC distribution of the target zone shows two potential areas in west, north-south trending, and in the east relatively of the well-X. Both locations can be recommended for the next pilot holes in order to acquire a complete set of new data and to be able to evaluate more intensively.

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Integration of Seismic Inversion, Pore Pressure Prediction, and TOC Prediction in Preliminary Study of Shale Gas Exploration

  1. 1. The Energy Company of Choice Integration of Seismic Inversion, Pore Pressure Prediction, and TOC Prediction in Preliminary Study of Shale Gas Exploration Andika Perbawa (1), Bayu Kusuma (1), Sonny Winardhi (2) PIT HAGI 2012 - 216 (1) Medco E&P Indonesia (2) Institute of Technology Bandung
  2. 2. Halaman 2Halaman 2 • Introduction • Basic theory • Data Availability and Method • Result • Conclusions and Recommendations Outline
  3. 3. Halaman 3Halaman 3 Introduction “Natural gas that cannot be produced at economic flow rates or in economic volumes of natural gas unless the well is stimulated by a large hydraulic fracture treatment, a horizontal wellbore, or by using multilateral wellbores or some other technique to expose more of the reservoir to the wellbore”
  4. 4. Halaman 4Halaman 4 What is Shale Gas ? Source: US Energy Information Administration
  5. 5. 1,275 TCF 862 TCF 774 TCF 681 TCF 485 TCF
  6. 6. Halaman 6Halaman 6 Organic rich shale : TOC > 1.0%, HI > 100 Gas type : Free gas and absorb gas Permeability : Low  need fracture job Maturation : Mature to over-mature zone window (> 1.3 %Ro) Thickness : > 75 ft Kerogen type : Type I and II generates more gas than type III. Mineralogy : More quartz / less clay, brittle shale / more fracture. Storage : Fractures and pores Low recovery efficiency : 8-15% Performance of production : Depend on natural fractures and artificial fracture Characteristics Introduction
  7. 7. Halaman 7 • Rock type, lithology, mineralogy and V-clay estimation • Kerogen estimation and distribution • Fracture orientation • Maturation distribution • Shale distribution • TOC distribution • Reservoir pressure distribution • Brittleness and ductile distribution • Porosity distribution • Permeability distribution • Depositional setting, direction and isopach of shale distribution • Gas saturation and composition estimation • Fluid sensitivity • Volume calculation Key Parameter in Shale Gas Exploration Introduction Materials covered
  8. 8. Halaman 8Halaman 8 Delineate potential shale gas play using available data, then recommend a drilling location to acquire a complete set of new data and to be able to evaluate shale gas resources more intensively Objectives Introduction
  9. 9. Halaman 9Halaman 9 1. Geochemistry • Total Organic Carbon: TOC • Maturation : %Ro , Tmax, LOM • Kerogen type : HI, S2/S3 Data needed to evaluate the potential of shale gas in exploration: Data Availability 2. Petrophysics and Petrography • Mineralogy: XRD, SEM • Permeability • Fracture evaluation • Gas content and capacity (absorbed and free) • Pressure 3. Well Data • GR, spectral GR, Vp, Vs, Density, Neutron, Resistivity, Image log, dip meter, PE, ect. • Core Data • VSP/checkshot 4. Seismic Data • 3D pre-stack seismic data *Red indicates data available for this study
  10. 10. Halaman 10Halaman 10 Workflow Well Data (GR, ILD, Sonic, RHOB, NPHI) Seismic Data (PSTM Pre-Stack) Geochemist Data (Ro, TOC) Sweetspot identification and TOC prediction Rock Physics (S-Wave prediction) Seismic Simultaneous Inversion Shale Distribution Probable Shale Gas Potential Zone Overpressure Identification Overpressure Zone TOC Distribution
  11. 11. Halaman 12Halaman 12 Regional Tectonic Setting Location (After Argakoesoemah, 2005) (Bishop, 2001) Tectonostratigraphy Objective area
  12. 12. Halaman 13Halaman 13 Depositional Environment Ginger and Fielding, 2005 Upper Talang Akar Fm.Lower Talang Akar Fm. Objective area Objective area
  13. 13. TOC Prediction Method Simultaneous Seismic Inversion Pore Pressure Prediction
  14. 14. Halaman 15Halaman 15 Passey (1990) Method: TOC Prediction Method – Theory (1) TOC Prediction Method Simultaneous Seismic Inversion Pore Pressure Prediction Ro transformation to LOM:
  15. 15. Halaman 16Halaman 16 TOC Prediction Method – Application (1) Crossover between DT (green) and resistivity (purple) indicates potential zone -------- DT -------- -------- ILD --------Gamma ray ΔLogR Pseudo TOC Cutoff TOC line (1%) Target Zone Pseudo TOC indicate Upper Talang Akar Fm. as potential zone (TOC ≥ 1%) TOC original TOC prediction Ro ≈ 1.82 % TD: 7680 Ro ≈ 1.42 % Top TAF TOC Prediction Method Simultaneous Seismic Inversion Pore Pressure Prediction
  16. 16. TOC Prediction Method Simultaneous Seismic Inversion Pore Pressure Prediction
  17. 17. Halaman 18Halaman 18 Shear Wave Prediction Method – Theory (2) TOC Prediction Method Simultaneous Seismic Inversion Pore Pressure Prediction Input: Vp, ρ, Vsh, Sw, Ф 𝜶Initial value α=0.01 𝜸 = 𝟏 + 𝟐𝜶 𝟏 + 𝜶 𝝁 𝒅𝒓𝒚 = 𝝁 𝒎(𝟏 − 𝜽) (𝟏 + 𝜸𝜶𝜽) 𝑲 𝒅𝒓𝒚 = 𝑲 𝒎(𝟏 − 𝜽) (𝟏 + 𝜶𝜽) Vsh, 𝝁 𝒄𝒍, 𝝁 𝒒𝒓𝒕𝒛 , 𝑲 𝒄𝒍 , 𝑲 𝒒𝒓𝒕𝒛 , 𝝁 𝒃𝒓, 𝝁 𝒈 , 𝑲 𝒃𝒓 , 𝑲 𝒈 Hashin-Strikman 𝑽 𝒑 (𝜶) = 𝑲 𝒅𝒓𝒚 + 𝟒 𝟑 𝝁 𝒅𝒓𝒚 𝝆 𝑽 𝒑 𝜶 − 𝑽 𝒑 𝒂𝒄𝒕𝒖𝒂𝒍 ≈ 𝒎𝒊𝒏𝒊𝒎𝒖𝒎 yes no𝑽 𝒔 = 𝝁 𝒅𝒓𝒚 𝝆 Update 𝜶 Gassman’s equation (Modified Lee, 2005)
  18. 18. Halaman 19Halaman 19 Validation Method – Application (2) TOC Prediction Method Simultaneous Seismic Inversion Pore Pressure Prediction Good match Good match Velocity actual (ms) Velocitypredicted(ms) Apply to Objective well data Method test in the other well that has Vs Check relationship between prediction and actual data
  19. 19. Halaman 20Halaman 20 Cross plot analysis – Pseudo TOC vs Vp Method – Application (2) TOC Prediction Method Simultaneous Seismic Inversion Pore Pressure Prediction TOC(%) Vp (ft/s) Gamma ray (API) organic shale trend in the upper TAF shale sand trend sand trend
  20. 20. Halaman 21Halaman 21 Cross plot analysis – Gamma Ray vs Vp/Vs Method – Application (2) TOC Prediction Method Simultaneous Seismic Inversion Pore Pressure Prediction 2.1 Vp/Vs Gammaray 86 Vp/Vs < 2.1 = Sandy Vp/Vs > 2.1 = Shaly
  21. 21. Halaman 23 Method – Application (2) Seismic section Well X TELISA MARKER 3 BASEMENT 26 m.a. LOWER TAF 23 m.a. -base inversion window- NESW 21 m.a. UPPER TAF -top inversion window- NE SW 1000 ms 2000 ms 3000 ms
  22. 22. Halaman 24 Simultaneous Seismic Inversion Result: Vp Method – Application (2) TOC Prediction Method Simultaneous Seismic Inversion Pore Pressure Prediction Well-X 1000 ms 2000 ms 3000 ms
  23. 23. TOC Prediction Method Simultaneous Seismic Inversion Pore Pressure Prediction
  24. 24. Halaman 26Halaman 26 Pore Pressure Prediction Method – Theory (3) (Chilingar et. al., 2002) (Reynolds., 2002) Gradient (psi/ft) Equivalent mud-weight (ppg) Geo-pressure characteristic 0.465-0.65 8.95 – 12.51 Soft to mild 0.65-0.85 12.51 – 16.36 Mild > 0.85 > 16.36 Hard (Dutta, 1987) TOC Prediction Method Simultaneous Seismic Inversion Pore Pressure Prediction
  25. 25. Halaman 27Halaman 27 Pore Pressure Prediction Method – Application (3) TOC Prediction Method Simultaneous Seismic Inversion Pore Pressure Prediction Pore Pressure Prediction using velocity data from: 1. DT log/Sonic (purple). 2. Pseudo DT derived from resistivity (red) using Faust (1953) equation. VR=a(Rdeep)c 3. Calibrated velocity stacking (black). After all of velocity data are aligned, apply Eaton’s equation to calibrated velocity stack cube
  26. 26. Halaman 28 Potential Shale Gas Area Result Potential Area
  27. 27. Halaman 29 • Passey’s method shows a sweet spot interval in Upper Talang Akar Fm. • The potential shale gas is about 100 feet thick and has more than 1% of TOC in Upper Talang Akar Fm. • The Lower Talang Akar Fm. has less potential shale gas. • The shale distribution covers a whole objective area (Upper Talang Akar Fm.) • There are several spotty areas that have a medium pressure regime in the north, west and south-east relative to well- X. Drilling needs to be aware. • The two interesting potential shale gas areas (TOC ≥ 1%) are located in the west, trending north-south, and in the east relative to well-X. • Both locations can be recommended for the next pilot holes in order to acquire a complete set of new data and to be able to evaluate more intensively Conclusions
  28. 28. Halaman 30 • Use actual shear wave data to reduce uncertainty. • Use TOC data from Core or SWC for accurate depth location. • Drill a pilot hole in order to acquire a complete set of new data and to be able to evaluate more intensively. • Core Data • SEM • XRD • Geochemist analysis (TOC, Ro, HI, Rock eval, etc.) • Complete well log data (include shear wave data) • VSP • Conduct a 3D data with small bin and narrow inline/xline interval. Perform anisotropic processing and analysis to determine young modulus and bulk modulus cube for brittleness identification. • Conduct coherence, variance, dip-azimuth attribute to determine fracture orientation. Recommendations
  29. 29. Halaman 31 • Argakoesoemah R.M.I., Raharja M., Winardhi S., Tarigan R., Maksum T.F., Aimar A., 2005, Telisa Shallow Marine sandstone As An Emerging Exploration Target In Palembang High, South Sumatra Basin, Proceedings Indonesian Petroleum Association, 30th Annual Convention, Jakarta. • Bishop, Michele. G., 2001, South Sumatra Basin Province, Indonesia: The Lahat/Talang Akar-Cenozoic Total Petroleum System. USGS 99-50-S. USA. • Dutta, N.C., ed, 1987, Geopressure: Society of Exploration Geophysicists Reprint Series 7, 365 p. • Eaton, Ben A., 1975. The Equation For Geopressure Prediction From Well Logs. SPE 50th Annual Fall Meeting, Dallas, TX, September 28 – October 1, 1975. SPE paper # 5544, 11 pp. • Fatti, J. L., P. J. Vail, G. C. Smith, P. J. Strauss, and P. R. Levitt, 1994. Detection of gas in sandstone reservoirs using AVO analysis: A 3D seismik case history using the Geostack technique. Geophysics, 59, 1362–1376. • Faust, L. Y., 1953, A velocity function including lithologic variation, Geophysics, 18, 271-288. • Finnegan, J., 2011, Is Shale Gas a Game Changer in the Global Energy Supply Outlook?, American Century Investment, In-Fly-72552 1107. • Ginger, D., K. Fielding, 2005, The Petroleum Systems and Future Potential of the South Sumatra Basin. IPA05-G-039. • Holditch, S.A., 2007, Unconventional Gas. NPC Global Oil and Gas Study, Texas. • Lee. M.W., 2005, A simple method of predicting S-wave velocity. Geophysics 71, 161-164. • Passey. Q. R., 1990, A Practical Model For Organic Richness from Porosity and Resistivity Logs, AAPG Bulletin V.74, No.12. References

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