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Tijerina-Canales-Blucher (TCB) field of Kleberg County, Texas, has produced significant amounts of hydrocarbons from Oligocene Vicksburg sandstones at depths between 8,500 and 11,500 ft. TCB Vicksburg sandstones were deposited in deltaic to shallow-marine environments as evidenced by various sedimentological and biological indicators. Diapirism of Jackson shale coupled with growth faulting generated highly faulted, rollover elongate anticlines. These faulted, elongate highs along with stratigraphic pinch-outs form the main traps in TCB field.
Detailed examination of cores from six different Vicksburg sand-shale intervals aided in delineation of a complex diagenesis related to depositional environment, lithology, burial, and thermal history of the region. The sandstones vary in lithology from lithic to feldspathic lithic arenites and wackes. A volcanic source during Vicksburgian time is indicated by the presence of high percentages of volcanic-rock fragments. This overabundance of labile constituents is the prime factor that resulted in the "jambalaya" of diagenetic complexities.
Porosity in the TCB Vicksburg sandstones is almost entirely secondary and was generated predominantly by the dissolution of feldspars and volcanic-rock fragments. Permeability was greatly enhanced by dissolution of recrystallized clayey matrix and carbonate cement. An overall smectite-illite signature pervades the vertical section, with an extremely well-developed authigenic imprint of highly crystalline chlorite, kaolinite, illite, and many other mineral species superimposed onto the primary signature, especially with depth. The best TCB reservoirs have the largest average grain size and had the greatest amount of feldspars and volcanic-rock fragments prior to diagenesis. Evolution of secondary porosity was directly related to the generation and migration of hydrocarbons through thes reservoirs.
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