--> The Role of Conventional Core and Electric Log Analyses in Evaluation of Perforation Strategy; Grand Isle 43 Field, Gulf of Mexico, by D. B. Schafer, H. W. Posamentier, and R. L. Spaeth, Jr.; #90986 (1994).

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Abstract: The Role of Conventional Core and Electric Log Analyses in Evaluation of Perforation Strategy; Grand Isle 43 Field, Gulf of Mexico

Daniel B. Schafer, Henry W. Posamentier, Robert L. Spaeth, Jr.

Conventional core and electric log analyses integrated with depositional system analysis, has led to the conclusion that an insufficient perforation strategy has been employed at Grand Isle 43 Field, offshore Louisiana, Gulf of Mexico. Rather than perforation of entire pay zones, only the upper few feet of many pay sands were perforated, and the entire interval was assumed to have been drained. This strategy assumed that there existed no significant

permeability barriers within the pay sands. An integrated study incorporating detailed well-log correlations and analyses of rock fabric and clay mineralogy suggested an offlapping, or shingled, stratal geometry comprising alternating reservoir sandstones and non-reservoir mudstones. This study confirms the presence of permeability barriers to flow resulting in compartmentalization of the reservoir.

Rock properties were compared between rocks previously identified as pay and non-pay to accurately determine if all the reservoir quality rock was being perforated. A large percentage of the non-perforated zones that have commonly been counted as non-pay exhibit very good porosities (23-32%) and permeabilities (7-2700 md). Additionally, thin section and x-ray data confirm that good quality reservoir rock has not been perforated for production or counted as pay in the overall volumetric calculation.

Detailed core analyses suggest that reservoir sandstones occurring within the lower parts of reservoir sands (delta front) were too thin to be clearly resolved on electric logs but nonetheless contained oil. Because such oil-bearing sandstones commonly have not been identified as pay they have not been incorporated into volumetric calculations and hence development strategy. These observations, integrated with the revised depositional model, are being incorporated into a re-evaluation of reserves and further assessment of development opportunities in this field.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994