Hydrologic Characterization of the Saline Frio Formation, Victoria County, Texas Gulf Coast: A Case Study

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1987

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Pressure data gathered from drillstem tests (DSTs) and bottomhole pressure measurements in onshore oil and gas wells along the Texas Gulf Coast were used for evaluating pressure regimes and their influence on the migration potential of formation fluids. The data were used to construct potentiometric surfaces and residual potential surfaces and to assess the effects of depressurization caused by hydrocarbon production.

This technique was utilized for preliminary geohydrologic characterization of the Frio Formation of the Texas Gulf Coast. Included in this report are the results of such an analysis for Victoria County, Texas, as a sample case study. Pressure data were evaluated for reliability, and a screening and classification system was applied to closely monitor the quality of data used for generating potentiometric surfaces. Preceding the hydrologic analysis, steps were taken to review the available geologic information in the context of Tertiary Texas Gulf Coast formations.

An evaluation of the regional pressure-depth plots reveals multiple overlapping pressure regimes. Also indicated is an area of extensive depressurization attributable to hydrocarbon production. The potentiometric surfaces also reflect depressurization that results in local variations in flow directions and a general trend of flow toward the oil and gas fields. Potentiometric surfaces for the deeper sections of the Frio reflect the high equivalent hydraulic heads in the geopressured region.

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