AN INTEGRATED SEISMIC AND WELL-LOG SEQUENCE STRATIGRAPHIC STUDY OVER 32 GRAND ISLE/WEST DELTA OCS BLOCKS
JOHN R. SUTER, KENNETH C. ABDULAH, PATTY D. TRAVIS, PETER A. GLAGOLA, JAMES W. YOUNG, DAVID C. WATSO, WILLIAM E. FINLEY, 1996. "AN INTEGRATED SEISMIC AND WELL-LOG SEQUENCE STRATIGRAPHIC STUDY OVER 32 GRAND ISLE/WEST DELTA OCS BLOCKS", Stratigraphic Analysis Utilizing Advanced Geophysical, Wireline and Borehole Technology for Petroleum Exploration and Production, Jory A. Pacht, Robert E. Sheriff, Bob F. Perkins
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A 3-D seismic survey covering some 900 square kilometers and 32 OCS blocks, in the Grand Isle and West Delta area offshore Louisiana, together with well logs from 87 exploration wells, form the basis for a detailed integrated sequence stratigraphic study. The study focused on Plio-Pleistocene, fluvial/deltaic reservoirs that have produced over 100 BCF of shallow gas from the CI, EA, and FJ Sands within the Grand Isle blocks. Typical gas columns within these sands are on the order of 6 meters and, in the past, production rates have been hampered by water coning. Horizontal drilling technology has provided the means to overcome this problem, but it requires a clear understanding of the lateral continuity of the reservoir.
The section studied comprised (in descending order) the B, C, D, and E intervals found at depths ranging from 500 m to 1700 m. These intervals contain a number of reservoir sands, originally designated by lithostratigraphic tops. Each succession has distinctly different characteristics, interpreted as a response to differential accommodation, and is separated by large-scale transgressions/avulsions. The B interval (BT sands) consists of relatively thin highstand deltaic complexes. The C interval contains two incised valley successions (CI, CII sands). The D interval comprises the DR, DB, and DJ successions. The DB succession consists of at least four high-frequency sequences, expressed as stacked, intercutting incised valleys, capped by transgressive parasequences. The DJ interval consists of a series of at least eight complex, sigmoidally offlapping deltaic parasequence sets. These downlap onto the DR deposits, which downlap the underlying EA incised valley sands.
Amalgamated incised valleys reach thicknesses of over 125 m, while individual valley fills reach about 60 m in thickness. The cyclic pattern of incision is related to high frequency Plio-Pleistocene eustatic cycles. Depositional cycles have been interpreted from well-log stacking patterns and integrated with seismic attribute maps to better understand the distribution of sedimentary facies and hydrocarbon accumulations in both time and space.