Robert L. Horine¹, William H. Mills¹, Vanessa J. Sturrock¹, Mike Anthony²
(1) BP Amoco Exploration, Houston, TX
(2) Marathon Oil Company, Lafayette, LA

Abstract: Structural controls on sedimentation and hydrocarbon charge in the Troika Field - Deepwater Gulf of Mexico

Three of the most prolific wells in the Deepwater Gulf of Mexico are in the Troika Field. The Troika S-10 reservoir is capable of sustaining very high production rates, over 30,000 BOPD, because of a unique combination of structure and stratigraphy. The interaction of sedimentation and salt withdrawal produced optimum conditions for oil production.

Salt movement influenced the structure of the Troika Field before, during, and after deposition of the reservoir sequence. Initial salt evacuation created an elongate minibasin that was closed on the seaward end. Turbidite flows entering this basin experienced flow stripping, leaving behind a thick (250’-600’) clean sand. This sediment loading caused further salt withdrawal, forcing the axis of the minibasin and of the deposition to migrate laterally. Eventually, all of the salt was evacuated from the southern end of the field, welding the reservoirs to the underlying section. Further evacuation of salt from the northern end of the field caused the reservoir to tilt, creating a trap with 2500’ of structural closure.

Ongoing structural movement also influenced the hydrocarbon accumulation in the reservoir. Well and seismic data indicate the reservoir tilted after filling, spilling some reserves and creating a paleo-oil/water contact at the north end of the field. Welding of the reservoir section created a blind limb of the structure from which oil was unable to displace the water. This resulted in a perched water table south of the crest of the structure.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana