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Sequence Stratigraphy and Structural Trap Styles of the Tuscaloosa Trend [Abstract]
The deep Tuscaloosa Trend was discovered in 1975 by Chevron with the Alma Plantation #1 well in False River Field. This discovery initiated a significant drilling effort that resulted in the discovery of several deep fields containing large gas reserves. In 1990, production was declining, and the reservoir pressures were rapidly falling in these prolific fields. A trend-wide re-evaluation was performed by a multi-discipline team at Amoco Production Company with specific emphasis on the producing fields, including Port Hudson, Morganza, Moore-Sams, Judge Digby, False River, Profit Island, Solitude Point, Irene, and Lockhart Crossing. The re-evaluation effort culminated in the acquisition of three new 3-D seismic grids covering Amoco's major fields: Port Hudson, Moore-Sams, Judge Digby, False River, Solitude Point, and Profit Island. The 3-D seismic evaluation revealed new fault patterns and untested fault blocks that the existing wells would not have drained. The seismic interpretation greatly improved the understanding of the spatial patterns and orientations of the faults. Because the seismic cannot image down to the reservoir scale, log evaluation and correlation was incorporated into the 3-D framework to provide a much more defined evaluation of the individual parasequence and reservoir units. To date, the trend re-evaluation has resulted in the drilling of 46 new wells, of which 43 were productive. Continued discovery of deeper reservoirs at Judge Digby Field by BP has added significant reserves.
Sequence stratigraphic analysis was applied to determine a physical chronostratigraphic framework by interpreting sequences, system tracts, and parasequences on well logs, seismic, and biostratigraphy. Depositional systems and lithofacies tracts within system tracts and parasequences were defined and used to analyze existing and prospective reservoirs. Four Tuscaloosa sequences have been identified herein: A,B,C, and D. The re-evaluation of the Tuscaloosa Trend included the evaluation and integration of 1,200 miles of reprocessed 2D seismic data and over 300 well logs. The changes in the regional structural and stratigraphic models were incorporated into the detailed evaluation of the 3-D surveys. The combination of the Lower Cretaceous shelf margin and the deep Louann salt played a significant role in controlling trapping style and deposition, and resulted in three unique strike-trending regions. Within the three unique regions, four structural trapping styles have been identified and defined: 1) unexpanded faulted anticline over salt, 2) expanded and unexpanded faulted anticline over salt, 3) expanded three-way fault closure, and 4) expanded and faulted rollover anticline.
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ACKNOWLEDGMENTS AND ASSOCIATED FOOTNOTES
Barrell Energy, Inc., 22 Ivory Moon Place, The Woodlands, TX 77381
Copyright © 2003 by NOGS (The New Orleans Geological Society)