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Torrington field (North) is productive from the Lower Cretaceous "J" sandstone in the Wyoming portion of the Denver basin. The trapping mechanism is stratigraphic, with reservoir sandstones enveloped laterally and updip by shale-dominated lithofacies. The field has produced 13,000 bbl of oil from two wells since its discovery in late 1981. However, production can be increased by development based on recognition of features comprising the "J" sandstone depositional system.
Three major sedimentary environments and their associated facies, characteristic of a meandered fluvial system, occur within the "J" interval in the area: abandoned channel, point bar(s), and interfluvial plain. Production at both Torrington (North) and Torrington is from reservoir development within point bar deposits. Cores of the "J" point bar at Torrington (North) show that it is comprised primarily of very fine to fine-grained quartzarenites and sublitharenites. Dominant framework grains are quartz and lithic fragments which are cemented by quartz overgrowths and authigenic clays (primarily kaolinite). Sedimentary structures observed in the cores include burrowing and bioturbation, high-angle plane-parallel cross-bedding, discontinuous wavy shale laminae, climbing ripples, and tr ncated laminae. Although excellent hydrocarbon shows occur from the base to the top of the point bar, production appears to be confined to thin intervals of medium-grained quartzarenite found near the middle of the vertical sequence. This may be due to flow regime size sorting which affected differential clay diagenesis within the point bar.
Petrophysical reservoir characteristics of the "J" sandstone were established through examination of X-ray diffraction, scanning electron microscopy, thin-section petrography, and conventional core analysis data. Microporosity development and geometry also affect production.
Field extension locations and an exploratory drill site have been established as a result of this study.
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