ABSTRACT: Predicting pore pressure in very deep-offshore: a case study from Astrid Marin Block, offshore Gabon

Poix, Olivier¹, A. Delepoulle², G. Butteux³, M. Vialla³, J. Coleman⁴, I. Burnet⁴, and F. Milla³
(1) TOTALFINA, Paris la Defense, France
(2) TOTALFINA, N/A 
(3) TOTALFINA 
(4) UNOCAL

This paper presents one of the challenges that the Astrid Gabon Team has faced in anticipating the drilling of a wildcat well by more than 2500 m of water depth. This well is the first exploration well in the very deep offshore of Gabon in the TOTALFINA operated Astrid Marin Block. This paper focus on the pre-drill pore pressure prediction work realised by the Astrid Gabon Team to try to better anticipate possible shallow pressure hazards and deeper overpressures.

Astrid Marin is very large frontiers block (about 300 times the size of a typical Gulf of Mexico's block). Only 2D seismic coverage was available to realise the pre-drill prediction. The prediction mostly relies on extracted interval seismic velocities using a special velocity processing called "INVEL" which was developed by TOTALFINA and CGG. This processing gives a relatively high vertical resolution velocity profile that can then be used to predict the pore pressure using a classical pore pressure prediction approach.

This paper discusses the specific approach used by the Astrid Gabon Team. This specific approach is dictated by the uncertainties associated with very deep-water depths and the lack of offset wells for calibration. In this paper the team comments on the availability of the data, their relevance, the calibration as well as the quantification of the uncertainties associated with pore pressure prediction in this very deep offshore setting.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia