Print this pageShallow Gas Accumulations within Parasequences of the Transgressive Systems Tract in the Grand Isle/West Delta Fields, Offshore Louisiana
SUTER, JOHN R., KEN ABDULAH, WAYNE ORLOWSKI, PATTY TRAVIS, PETE GLAGOLA, JIM YOUNG, DAVID NATSO, and WILLIAM FINLEY
The Grand Isle and West Delta fields, offshore Louisiana, have produced over 500 MMBOE and 2 TCF of gas since 1955. Recently, attention has been given to shallow gas accumulations within Late Pliocene and Pleistocene sands. These sands lie at depths of less than 1700m, have gas columns on the order of only 6m, and have produced 100 BCF of gas. A detailed sequence stratigraphic and structural reconnaissance study was carried out over the Grand Isle and West Delta fields, aimed at understanding the factors controlling the gas accumulations within this shallow section (500m -1700m). The study, covering 900 square kilometers and 32 OCS blocks, was based on 87 exploration wells, and 2D and 3D seismic data.
The interval is characterized by periods of major deltaic progradation followed by fluvial incision and bypass, and subsequent transgression. These repetitive periods of deposition appear to be related to fourth-order eustatic cycles. Gas accumulations within this Late Pliocene-Pleistocene interval are typically associated with shallow-marine parasequences of the transgressive systems tract. These areally limited parasequences are encased by highstand shales, creating stratigraphic and combination traps. Sands within the incised valleys, that were cut during lowstands, are typically wet except Where syn- and post-depositional faulting, and structuring, produced three-way/fault and four-way dip closures. The extensive incised-valley systems, together with major normal faults, provide the pathways for the migrating gas.