Geopressure Progression - Regression: An Effective Risk Assessment Tool in Gulf of Mexico Deep Water

By

SHAKER, SELIM S.

Geopressure Analysis Services (G.A.S.), Houston, TX

In the Tertiary – Pleistocene clastic sediments, compaction disequilibrium is the primary cause of geopressure compartmentalization in the deep water of Gulf of Mexico. A sealed compartment is the key for exploration success in any play concept. Estimating the shift of pore pressure envelopes associated with successive compartments helps in predicting objectives risk.

The actual pressure measurements (i.e. RFT’s and MDT’s) in reservoir type sections show a cascade profile with depth in the geopressured (abnormal) column. The sealing and retention capacities are functions of this pressure envelopes shift. A correlation was found between the progressive – regressive shift and exploration success in some of these deep- water wildcats.

Substantial hydrocarbon accumulations were found where a considerable progressive shift (> 1000 psi) is recorded i.e. Green Canyon 908 #2, 72 #A-1, 506 #1; Mississippi Canyon 211 #1, 809 #1, 546 #1; and Viosca Knoll 1001 #1. Marginal reserves or wet reservoirs were found where small shift (< 1000 psi) is noticed i.e. Garden Banks 142 #1, 543 #1, 248 #3; Green Canyon 908 #2; Mississippi Canyon 809 #1; and Keathley Canyon 255 #1.

On the other hand, where pressure envelopes show regression behavior, the target reservoirs were deemed unsuccessful i.e. Mississippi Canyon 211 #1 and Viosca Knolls 1001 #1 and 912 #1.

Bore-hole location in relation to the structural position of each objective needs to be considered before making a conclusive assessment. Study of this correlation on a basin to basin basis helps the evaluation of seal integrity, compartmental communication and potential hydrocarbon trapping.