AAPG Bulletin, V. 82 (1998), No. 3 (March 1998), P. 387-411.

Fluid Flow in a Faulted Reservoir System: Fault Trap Analysis for the Block 330 Field in Eugene Island, South Addition, Offshore Louisiana¹

Laurel L. Alexander² and James W. Handschy³

©Copyright 1998. The American Association of Petroleum Geologists. All rights reserved.

¹Manuscript received April 29, 1996; revised manuscript received February 7, 1997; final acceptance September 3, 1997.
²Cornell University, Department of Geological Sciences, Snee Hall, Ithaca, New York 14853. Present address: Shell Offshore, Inc., New Orleans, Louisiana 70130.
³Shell E&P Technology Company, Houston, Texas 77001.

Shell Offshore, Inc. (SOI) granted permission to publish this paper. In addition, SOI provided data for the study and funding for publication. We thank John Austin and the Pennzoil Corporation for donating the three-dimensional (3-D) seismic survey, sand structure maps, pressure data, and well logs that were used in this study. Landmark Graphics donated the 3-D seismic workstation and software to the Global Basins Research Network (GBRN). We are indebted to Dietmar Schumacher of Geo-Microbial Technologies, Inc., and Jean Whelan of Woods Hole Oceanographic Institute for providing geochemical data and insight into interpreting the data. Shell E&P Technology Company provided CSP analyses. Reviews by Lawrence Cathles and Teresa Jordan improved this manuscript. We gratefully acknowledge the useful comments provided by AAPG reviewers L. Fairchild and D. Tearpock. Beth Bishop and Teresa Howley provided drafting assistance. This work is part of Laurel Alexander’s 1995 Ph.D. dissertation. The work was supported by the GBRN and DOE grant DC-FC22-93BC14961. 

Abstract

Reservoirs in the Eugene Island Block 330 (EI-330) field are believed to have been filled through a complex pattern of cross-fault spilling through juxtaposed sands, and possible vertical migration up associated growth faults. Fault-plane-section analysis of a major basin-bounding fault shows that given the present configuration of juxtaposed sands, cross-fault flow cannot account for the filling of most EI-330 reservoirs; however, a syntectonic process of across-fault spiral migration of hydrocarbons during active slip on the fault could account for the filling of the reservoirs. Hydrocarbons could have entered the shallow reservoirs about 0.68 Ma, before most of the present downthrown sand-on-shale traps formed.

A Pennzoil three-dimensional seismic survey, shot over the highly faulted eastern anticlinal structure, enabled the detailed mapping of a buried, down-to-the-north fault and the adjacent sands. This buried fault, fault F, divides the main reservoirs of the EI-330 field into two separate fault blocks. Fault-plane-section analysis, combined with pressure and geochemical data from the two fault blocks, reveals that fault F is generally nonsealing to lateral fluid migration between juxtaposed sands of the same age. The fault is sealing to lateral fluid flow in the majority of cases where sands of different ages are juxtaposed. In one case, the capillary pressure differential between two juxtaposed sands was higher than can be attributed to permeability differences of common Gulf Coast sands, suggesting that material in the fault zone is the most likely cause of the lack of fluid flow between the juxtaposed sands.