ABSTRACT

Lavaca Bay Field, located in Calhoun County, Texas, produces gas from the Frio barrier/strandplain Sandstone of the San Marcos Arch play. The productive downdip part of the Frio Formation in Lavaca Bay Field is divided into 5 depositional sequences that are subdivided into 26 sandstone/shale units, 20 of which are proven gas-productive reservoirs. Well-log parameters, including net sandstone thickness, relative spontaneous potential deflection, resistivity, and the product of net sandstone thickness and relative spontaneous potential were contoured, then integrated with structure maps and production history, to identify separate reservoir compartments. Detailed analysis of one reservoir within the field, Unit 2 of Sequence IV, serves as an example to illustrate these mapping methods.

The Unit 2 of Sequence IV reservoir is divided into five compartments defined by log-derived parameters and production. Two of these compartments contain two or more stacked beach-ridge sandstone bodies that together contain two prospective infill well locations and one prospective recompletion location. The remaining three compartments contain a single beach-ridge sandstone body. Two of these compartments contain one recompletion target each. The third compartment is relatively small and is adequately drained by an existing well. Similar analysis of all 26 reservoirs in Lavaca Bay Field yields 10 proposed infill well locations, each of which individually targets from 2 to 8 separate reservoir compartments, and 30 prospective recompletion targets.