Geopressure Compartmentalization in Keathley Canyon, Deep Water, Gulf of Mexico

S. S. Shaker
Houston, TX

In the Gulf of Mexico, several salt related basins have attracted exploration. Keathley Canyon Block 255 Well #1 (TD 21550’) has tested one of these basins. Extensive geological and Repeated Formation Tester data were collected from this well. Integration of the geopressure profile and the structural setting demonstrates two distinctive main compartments.

A hydrodynamically active compartment exists between the sea floor and the Hyalinea balthica shale section. This phenomenoncould be responsible for the drilling problems and shallow water flow in these relatively young basins. Therefore, entrapment of commercial hydrocarbon in this upper section is unlikely.

A hydrostatically geopressured main compartment extends between the upper effective seal of Hyalinea balthica to the Pliocene section at the base of the basin. This geopressured thick section shows a progressive pressure profile with depth and can be divided into five mini-compartments. Four of these mini-compartments show effective seals (S 1,S2, S4 & S5). On the other hand, on both sides of the incompetent seal (S3), pore-pressure gradient remains in the same hydrostatic envelope. This also suggests communication between C2 and C3 and exploration targets in the C3 are high risk.

Lithology of both seals and reservoir has a direct impact on the geopressure profile progression with depth. Onthe other hand, structural setting is responsible for pore pressure differential between the seal and reservoir (Centroid concept). Drilling on the crest of high relief closure can be a challenging mission in deep water exploration.

AAPG Search and Discovery Article #90901©2001 GCAGS, Annual Meeting, Shreveport, Louisiana