Geophysics and Geophysical Exploration (지구물리와물리탐사)

Korean Society of Earth and Exploration Geophysicists (한국지구물리·물리탐사학회)
권호 표지
DOI QR코드

DOI QR Code

Overpressure prediction of the Efomeh field using synthetic data, onshore Niger Delta, Nigeria

합성탄성파 기록을 이용한 나이지리아의 나이저 삼각주 해안 에포메(Efomeh) 지역의 이상고압 예측

  • Omolaiye, Gabriel Efomeh (Mosunmolu Limited, The Oceanview Place, Alpha Beach Road, Lekki Peninsula) ;
  • Ojo, John Sunday (Applied Geophysics Department, Federal University of Technology) ;
  • Oladapo, Michael Ilesanmi (Applied Geophysics Department, Federal University of Technology) ;
  • Ayolabi, Elijah A. (Geoscience Department, University of Lagos)
  • Received : 2009.09.10
  • Accepted : 2010.11.17
  • Published : 2011.02.28
Download PDF
⟨ Previous Next ⟩

Abstract

For effective and accurate prediction of overpressure in the Efomeh field, located in the Niger delta basin of Nigeria, integrated seismic and borehole analyses were undertaken. Normal and abnormal pore pressure zones were delineated based on the principle of normal and deviation from normal velocity trends. The transition between the two trends signifies the top of overpressure. The overpressure tops were picked at regular intervals from seismic data using interval velocities obtained by applying Dix's approximation. The accuracy of the predicted overpressure zone was confirmed from the sonic velocity data of the Efomeh 01 well. The variation to the depth of overpressure between the predicted and observed values was less than 10mat the Efomeh 01 well location, with confidence of over 99 per cent. The depth map generated shows that the depth distribution to the top of the overpressure zone of the Efomeh field falls within the sub-sea depth range of 2655${\pm}$2m (2550 ms) to 3720${\pm}$2m (2900 ms). This depth conforms to thick marine shales using the Efomeh 01 composite log. The lower part of the Agbada Formation within the Efomeh field is overpressured and the depth of the top of the overpressure does not follow any time-stratigraphic boundary across the field. Prediction of the top of the overpressure zone within the Efomeh field for potential wells that will total depth beyond 2440m sub-sea is very important for safer drilling practice as well as the prevention of lost circulation.

나이지리아의 나이저 삼각주 분지에 위치한 에포메 지역의 이상고압을 효과적이고 정확하게 예측하기 위해 탄성파 및 시추공 자료를 종합적으로 해석하였다. 정상 공극압 영역과 및 이상 공극압 영역을 평균 및 편차의 원리를 기초로 하여 평균속도 경향성으로부터 도시하였다. 두 경향성 사이의 전이는 이상고압영역의 상부경계면을 나타낸다. Dix 근사식에 의해 구해진 구간속도를 이용하여 탄성파자료로부터 이상고압 영역의 상부경계면을 일정한 간격에서 발췌하였다. 예측된 이상고압 영역의 정확도는 에포메(Efomch)01 시추공의 음파검증 자료를 통해 확인되었다. 이상고압 심도의 예측값과 관측값 사이의 편차는 에포메(Efomch)01 시추공에서는 10m 이하 이며, 99퍼센트 이상의 신뢰도를 갖는다. 이렇게 생성된 심도 단면도는 에포메 지역 이상고압 영역의 상부 경계면이 해수면 아래 2655${\pm}$2 m (2550 ms) to 3720${\pm}$2 m (2900 ms)사이에 분포하고 있음을 보여준다. 이 심도는 에포메01 시추공의 지층평가를 이용하면, 두꺼운 해양성 셰일층에 해당한다. 에포메 지역 내의 아그바다층(Agbada Formation)의 하부는 과도한 압력을 받고 있으며, 이상고압의 상부 심도는 조사 지역에 걸쳐 항상 층서경계와 부합되는 것은 아니다. 에포메 지역에 향후 설치할 심도 2440 m 이상 시추공들에서의 이상고압 영역 상부 경계면 예층은 순환손실의 방지와 보다 안전한 시추를 위해 매우 중요한 정보이다.

Keywords

References

  1. Barker, C., 1972, Aqua thermal pressuring, role of temperature in development of abnormal pressure zones: AAPG Bulletin, 56, 2068-2071.
  2. Barker, C., 1990, Calculated volume and pressure changes during the thermal cracking of oil to gas in reservoirs: AAPG Bulletin, 74, 1254-1261.
  3. Bowers, G. L., 1995, Pore-pressure estimation from velocity data: accounting for pore-pressure mechanisms besides undercompaction: SPE Drilling and Completion, 10, 89-95. https://doi.org/10.2118/27488-PA
  4. Bowers, G. L., 2002, Detecting high overpressure: The Leading Edge, 21, 174-177. doi:10.1190/1.1452608
  5. Bruce, B., 2002, An introduction to this special section 'pore pressure': The Leading Edge, 21, 169-177. doi:10.1190/1.1452606
  6. Dix, C. H., 1955, Seismic velocities from surface measurements: Geophysics, 20, 68-86. doi:10.1190/1.1438126
  7. Dutta, N. C., 1997, Pressure prediction from seismic data: NPF Special Publication, 7, 187-199. doi:10.1016/S0928-8937(97)80016-1
  8. Dutta, N. C., 2002a, Deepwater geoharzard prediction using prestack inversion of large offset p – wave data and rock model: AAPG Bulletin, 21, 193-198.
  9. Dutta, N. C., 2002b, Geopressure prediction using seismic data: Current status and the road ahead: Geophysics, 67, 2012-2041. doi:10.1190/ 1.1527101
  10. Fertl, W. H., 1976, Abnormal formation pressures, Developments in Petroleum Science No. 2: Elsevier.
  11. Gardner, G. H. F., Gardner, L. W., and Gregory, A. R., 1974, Formation velocity and density the diagnostic bases of stratigraphic trap: Geophysics, 39, 770-780. doi:10.1190/1.1440465
  12. LaPorte, N., 2010, A Gulf coast Fisherman's survival story: The Daily Beast Online News June 1, 2010. Available online at: http://www.thedailybeast. com/blogs-and-stories/2010-06-01/life-gets-worse-on-the-gulf-coast/? cid=tag:all5 [verified January 2011].
  13. Martinsen R. S., 1994, Summary of published literature on anomalous pressures: implications for the study of pressure, in P. J. Ortoleva, ed., Basin Compartments and Seals. AAPG, Memoir 61, Tulsa, OK, pp. 27-36.
  14. Mouchet, J. P., and Mitchell, A., 1989, Abnormal pressure while drilling. Elf Aquitaine Manuals Techniques 2: Boussens, France.
  15. Mufson, S., 2010, Gulf of Mexico oil spill creates environmental and political dilemmas: Washington Post, April 27, 2010. Available online at: www. washingtonpost.com/wp-dyn/content/article/2010/04/26/AR201004260 4308.html [verified January 2011].
  16. Osborne, M. J., and Swarbrick, R. E., 1997, Mechanism for generating overpressure in sedimentary basins: A re-valuation: AAPG Bulletin, 81, 1023-1041.
  17. Osinowo, O.O., Oladunjoye, M.A. and Olayinka, A.I., 2007, Overpressure prediction from seismic data: implications on drilling safety: 40th American Geophysical Union, fall meeting 2007, San Francisco, USA
  18. Pennebaker, E. S., 1968, Seismic data indicate depth, magnitude of abnormal pressure: World Oil, 166, 73-77.
  19. Pickett, G. R., 1963, Acoustic character logs and their application in formation evaluation: Journal of Petroleum Technology, 15, 659-667. doi:10.2118/452-PA
  20. Reijers, T. J. A., Petters, S. W., and Nwajide, C. S., 1997, The Niger delta basin. African Basins, in R. C. Selley, ed., Sedimentary Basins of the World 3: Elsevier, pp. 151-172.
  21. Rubey, W. W., and Hubbert, M. K., 1959, Role of fluid pressure in mechanics of overthrust faulting: AAPG Bulletin, 70, 167-206.
  22. Sayers, C. M., Den Boer, L. D., Nagy, Z. R., and Hooyman, P. J., 2006, Wellconstrained seismic estimation of pore pressure with uncertainty: The Leading Edge, 25, 1524-1526. doi:10.1190/1.2405338
  23. Short, K. C., and Stauble, A. J., 1967, Outline of geology of the Niger Delta: AAPG Bulletin, 51, 761-779.
  24. Weber, K. J., and Daukoro, E. M., 1975, Petroleum geology of the Niger Delta: Tokyo 9th World Petroleum Congress Proceedings: 2, pp. 209-221.
  25. Wikipedia, 2010, Free Encyclopedia, 20 August 2010.
  26. Wolinsky, M. A., and Pratson, L. F., 2007, Overpressure and slope stability in prograding clinoforms: Implications for marine morphodynamic: Journal of Geophysical Research, 112, F04011. doi:10.1029/2007 JF000770