Abstract: An Integrated Approach to Identifying Natural Gas Reservoir Compartments Using 3-D Seismic, Depositional Facies Analyses, and Production Tests: Examples From Middle Frio Fluvial Reservoirs, Stratton Field, South Texas

Raymond A. Levey, Bob A. Hardage, Robert J. Finley

To target incremental gas resources in a 50-yr-old gas field in the onshore Gulf, we used an integrated approach to identify natural gas reservoir compartments. From a 7.5-sq mi, 3-D seismic volume, we analyzed infield drilling and recompletions in the middle Frio Formation, Stratton field, south Texas. Data were also acquired from VSPs that were depth sampled for seismic thin-bed calibration, depositional facies analyses of well logs, production history, and static and transient pressure tests. Because the Frio reservoir section we imaged is not severely faulted, reservoir compartments indicated by

well tests were thought to he caused by stratigraphic and diagenetic variability. Numerous seismic thin beds in these vertically stacked reservoirs produce an average 1 bcf of gas per completion, sometimes with multiple completions per well at depths of 5000-7000 ft in reservoirs <15 ft thick. A reflection amplitude slice map from the 3-D seismic survey (calibrated to the VSP data) illustrates structural variability and shows that depositional variability controls sandstone distribution. Color displays of 3-D seismic reflection amplitude data indicate subtle stratigraphic compartment boundaries when supported with geologic and engineering data. Calibrated 3-D slice maps showing channel meander-belt sandstones can detect reservoirs <250 ft wide and <15 ft thick, suggesting tha reservoir geometry is consistent with compartment dimensions determined from pressure test data. These data sets illustrate the integrated approach required to successfully target incremental oil and gas resources by calibrated imaging of the interwell space.

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