Extrapolation of Gas Reserve Growth Potential: Development of Examples from Macro Approaches

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1992

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An analysis of infield completions and reserve growth potential was made in Tertiary non-associated gas reservoirs in South Texas. Infield well completions were defined from a concurrent GRI project involving macro-scale prediction of reserve growth. This report validates 78 percent, or 5.6 Tcf, of a high-end infill estimate of 7.2 Tcf for nine stratigraphic units in South Texas. This is a significant resource volume given the historical expectation that natural gas can be efficiently drained with widely spaced wells (1 or 2 per square mile) in conventional reservoirs.

Groups of infield completions, or reservoir sections, from Frio, Vicksburg, Wilcox, and Miocene reservoirs were examined using geophysical well logs and production and pressure analyses. Seven reservoir-section types that contributed to the macro reserve growth estimate were evaluated. About 20 percent of the estimate consists of gas volumes extrapolated using consolidated reservoir groups, cycled reservoirs, and reservoirs with invalid data. Additional gas volumes in the estimate were extrapolated from reservoir sections representing rate acceleration. The estimate also includes reservoir volumes from the low-permeability Wilcox Lobo trend, where limited drainage radii lead to expected reserve growth. Volumes that represent within-reservoir reserve growth and volumes that represent shallower- or deeper-pool reservoirs determined not to be in pressure communication with preceding completions in a reservoir section formed most of the macro reserve growth estimate.

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