Trapping vs. Breaching Seals in Salt Basins: A Case History of Macaroni and Mt. Massive, Auger Basin, Gulf of Mexico
Selim S. Shaker
Geopressure Analysis Services (G.A.S), Houston, TX
Prior to testing the Mt. Massive prospect at the Garden Banks block 600, the seismic anomalies and the structural positioning relative to Macaroni Field at Garden Banks block 602, all pointed to a low risk prospect. Testing results of well #1 Garden Banks 600 were disappointing, as most of the targeted objectives were wet sands.
The geopressure profile and sealing capacity at site 602 show a different compartment setting than site 600. A ridge of salt below the Macaroni structural setting offers an explanation for the effective seals at the targeted strata and resulting entrapment of commercial hydrocarbons. However, the salt wall that bounds the southwestern flank of the Auger basin, at the Mt. Massive prospect, is responsible for breach of seals.
The complex interaction between salt and its’ surrounding sediments makes risk assessment of a prospect or play concept a challenge. Geopressure compartmentalization in the Tertiary-Quaternary salt basins of the Gulf of Mexico is created mainly by the principal stresses resulting from interaction between the sediment’s load and salt tectonics. Salt emplacement and displacement history, in relation to the surrounding sediments, sheds light on the possible sealing integrity.
Predicted pore pressure in the shale beds, in relation to the measurable pressure in the reservoir type sand facies, is the backbone of assessing entrapment and sealing capacity. Moreover, defining the fracture pressure envelope in relation to the effective stress window allows estimation of the column height of the hydrocarbon in the trap, i.e. retention capacity.
AAPG Search and Discovery Article #90032©2004 GCAGS 54th Annual Convention, San Antonio, Texas, October 10-12, 2004