Porosity, Permeability, Overpressure and Effective Stress Evolution in the Auger Basin, Gulf of Mexico

Gao, Baiyuan; Flemings, Peter

The Auger Basin is located about 345km southwest of New Orleans. We model porosity, permeability, overpressure and effective stress evolution in the Auger Basin from late Pliocene to the present. The RFT tests show the in-situ pressure in the O, P and Q sand is about 72.8~82.6MPa in the Auger field and about 98.5~100.7Mpa in the Macaroni field. We construct compression model based on the lab experiments and field pressure observations. In the lower effective stress interval (equal or less than 20MPa), the porosity and effective stress relationship is constrained by the experiments results from CRS (constant rate of strain) tests. In the higher effective stress interval (higher than 20MPa), the porosity effective stress relationship is based on the available RFT tests. The permeability model for each layer is assigned as a function of mudstone fraction. The results show that when the tilting permeable reservoirs are encased low permeability mud-rich layers, at the base of the reservoirs, the high overpressured fluid is drained from the surrounding mud-rich stone into the high permeable reservoirs. Compared to the adjacent mudstone, mudstone surrounding the bottom of the tilting reservoirs has a higher effective stress, lower porosity and lower permeability. On the contrary, at the crest of the tilting reservoirs, the fluid is expelled from the reservoir into the mudstone. The mudstone surrounding the crest of the reservoirs has lower effective stress, higher porosity and higher permeability than the adjacent mudstone at the equivalent depth. This study illustrates the regional flow field within the sedimentary basins and help to understanding the change of porosity, permeability and effective stress as the basin evolves.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013