--> Abstract: Pore Pressure Profiles in Deep Water Environments: Case Studies from Around the World, by Stephen O'Connor, Richard E. Swarbrick, Phill Clegg, and David T. Scott; #90078 (2008)

Datapages, Inc.Print this page

Pore Pressure Profiles in Deep Water Environments: Case Studies from Around the World

Stephen O'Connor, Richard E. Swarbrick, Phill Clegg, and David T. Scott
GPT, Durham, United Kingdom

Deep water sandstone reservoirs are commonly observed to be isolated within shale-dominated sequences. Pore pressure profiles through such sequences are based on both direct measurements in the reservoirs, and estimation based on porosity and shale properties in the non-reservoir section. Profiles from clastic sequences of deep marine shales with associated, thin reservoirs, reveal an overburden/lithostatic parallel increase of pressure beneath a fluid retention depth (near top overpressure). The depth to the fluid retention depth is largely controlled by clay content. Many deep water shales have high clay content, explaining the shallow onset of overpressure, which adds the additional drilling hazard of shallow water flows in this environment. Thick reservoir sections reveal local hydrostatic-parallel profiles creating variable transition zones into adjacent shales. At temperatures greater than about 100oC, however, there is a tendency for pressure profiles to converge with the overburden/lithostat, creating narrower drilling margins and more likelihood of seal breach. Lithostatic parallel profiles can be used locally for pore pressure prediction, provided that reservoirs are not able to drain laterally or vertically to the surface, and remain at temperatures less than about 100oC. Care must also be taken where the reservoir has a large structural relief, as lateral transfer may enhance crestal pressures. Pressures in many deep water reservoirs can be used to assess risk failure, particularly for stratigraphic traps. Examples will be used from Nile Delta, Gulf of Mexico, SE Asia and West African basins.

 

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas