Print this pageSub-Salt Pressures — Meeting the Technological Challenges
Sub-salt represents a peculiarly difficult environment for the prediction of pressure. In particular the generally inferior quality of seismic imaging beneath salt provide poor resolution of velocities used in traditional shale-based pressure prediction. Further the estimation of pore pressures from well data, where available, can be hampered by the absence of a sufficiently relevant or extended “normal pressure” section from which to determine a reference “normal compaction trend” used in pressure calculations. Overburden varies widely depending on salt geometry, impacting the generation of fluid pressure from compaction disequilibrium as well as the magnitude of the horizontal stresses. There are workarounds for these issues, including running look-ahead VSPs during drilling operations near base salt to image below salt better, or using 3D basin models to “calibrate” a 3D seismic pressure volume outside salt, and then take the basin model to guide pressure prediction in both reservoirs and shales beneath salt.
Developing a robust geological model of the pressure regime and the expected distribution of pressures remains a proven method in many of the world-wide examples which we will review. This paper will also review the principal areas of exploration/drilling beneath salt worldwide, the geometry and origin of the salt bodies and the individual challenges faced in pressure prediction in each.
AAPG Search and Discover Article #90100©2009 AAPG International Conference and Exhibition 15-18 November 2009, Rio de Janeiro, Brazil