ABSTRACT: Evaluation of Untested Stratigraphic Traps in a Pleistocene Canyon-Fill Complex, Offshore Louisiana
James E. Geitgey
Eugene Island Block 390, located approximately 100 mi offshore Louisiana, was acquired by ARCO Oil and Gas Company in 1983 to test upper Pleistocene amplitude anomalies located on the faulted northwest flank of a diapiric salt structure. Although drilling has established the presence of oil and gas in the objective section, an attempt to delineate further reserve potential on the block was made by evaluating additional amplitude anomalies located downflank in an adjacent syncline.
Seismic stratigraphic analysis indicates that the anomalies are located within the confines of an erosionally incised submarine canyon complex, approximately 3 mi wide and 500 ft deep. A number of high-amplitude events located in the upper part of the fill complex are interpreted to represent relatively coarser grained sandstone bodies, in contrast to the fine-grained material that represents the majority of the fill. In map view, these high- amplitude events are axially elongated, dip-trending bodies that were deposited laterally adjacent to one another.
In the deepest parts of the ARCO 1 well, stratigraphically below their original objective, approximately 50 net ft of oil-saturated but very low-permeability silt and shale were encountered. Examination of the well location on seismic data indicates that the ARCO 1 well was drilled into in the canyon flank, updip from and laterally adjacent to the high-amplitude events. The interpretation is that the low permeability oil saturated sections seen in the ARCO 1 well is representative of the depositional transition into the seal facies. Therefore, the highest amplitude events located downdip of the ARCO 1 well are thought to represent stratigraphically trapped hydrocarbons reservoired within canyon-fill sands, an interpretation supported by positive amplitude vs. offset analysis results.< P>
AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990