Vertical Seismic Profile Applications for Definition of Reservoir Heterogeneity—South Texas, Vicksburg and Frio Sandstones: A Secondary Gas Recovery Project
S. G. Zinke, L. A. Jirik, R. P. Langford, R. J. Finley, 1991. "Vertical Seismic Profile Applications for Definition of Reservoir Heterogeneity—South Texas, Vicksburg and Frio Sandstones: A Secondary Gas Recovery Project", The Integration of Geology, Geophysics, Petrophysics and Petroleum Engineering in Reservoir Delineation, Description and Management, Robert Sneider, Wulf Massell, Rob Mathis, Dennis Loren, Paul Wichmann
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Approaches to defining the distribution of unrecovered natural gas resources in mature fields are being developed and tested as part of the Secondary Gas Recovery Project, a program supported by the Gas Research Institute, the U.S. Department of Energy, and the State of Texas. The study emphasizes integrated geological, geophysical, petrophysical and engineering assessments of potential reservoir compartmentalization. Selected clastic reservoirs in South Texas have been studied in cooperation with Mobil Exploration and Producing U.S., Inc., Oryx Energy Company, and Shell Oil Company. Vertical seismic profiles (VSP's) have been used to help delineate reservoir sandstones and define structural complexities.
Gas reservoirs of the middle Frio Formation (Oligocene) along the Vicksburg fault zone at Seeligson field (Jim Wells County) consist of fluvial, channel-fill and associated splay sandstones that can be identified using well log correlation and facies analysis. Floodplain and levee mudstones vertically and laterally separate the reservoirs. Production and pressure data confirm lateral reservoir discontinuities. Offset VSP's, having close (30 ft) geophone stations, allow resolution of boundaries of composite channel systems defined using log data. Multi-offset VSP's providing continuous interwell coverage were utilized to interpret fluvial channel boundaries in the 19C-04 reservoir. Forward modelling corroborates the interpretations.
McAllen Ranch field (Hidalgo County) produces from overpressured deltaic reservoirs of the Oligocene Vicksburg Formation. Shingled, southeastward-tapering wedges of the Vicksburg depositionally overlie a basal decollement of the Vicksburg growth fault zone, resulting in complex interplay between sedimentation and tectonism. Gas production is from the shelf-edge, deltaic sandstone packages within the lower Vicksburg.