A cooperative study with the Delta Drilling Company (Tyler, Texas) provided a unique correlation of experimental tools (induced gamma-ray spectroscopy, digital sonic) and commercial tools (natural gamma-ray spectroscopy, high-resolution dipmeter) with petrophysical/geologic measurements on a whole rock core from the tight gas sandstones of the Upper Jurassic Cotton Valley Group in east Texas.

For example, a SARABAND suite of logs and dipmeter analyses processed according to the major genetic units of sedimentation (barrier bar, tidal delta) demonstrates the dynamic conditions of fluvial and shallow-marine (tidal) systems. Induced and natural gamma-ray spectroscopy with a SARABAND presentation yields a stratigraphic analysis of the clay/non-clay fractions and the lithology. Of growing economic importance, fracture containment boundaries to hydraulic fracturing can be predicted from a mechanical properties log--a combination of SARABAND and digital sonic.

The tight gas sandstones are characteristically well-laminated and bedded lithic sandstones with low porosities (< 10%) and low permeabilities (< 0.1 md). The intergranular pores are lined with diagenetic minerals--quartz overgrowths and calcite, and are filled, lined, and/or bridged with nonexpandable illite, chlorite, and illite/chlorite mixed-layer clay minerals.

The depositional paleoenvironment of the lower section of the Cotton Valley Group is interpreted as a sequence of shallow-marine, organically burrowed, layered, foreshore-shoreface deposits comprising the above-mentioned major genetic sedimentation units, the barrier bar and the tidal delta.

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