Consolidation of Geologic Studies of Geopressured-Geothermal Resources in Texas

The Pleasant Bayou C-zone geopressured-geothermal reservoir is currently undergoing long-term production testing. Using all available deep-well data and building on broad-based previous work, we constructed a detailed geologic characterization of the C-zone reservoir, including sandstone geometry and continuity, porosity distribution, depositional facies interpretation, and structural configuration. This characterization formed the basis for calculating total sandstone volume and effective pore volume of the reservoir and for constructing models for use in numerical simulations. Total effective pore volume of the C-zone reservoir is estimated to be between 6.2 and 6.6 billion barrels. With respect to the test well, one-third of this volume is proximal (within about 3 mi), and two-thirds are remote. Geologically based reservoir volume and models will be useful in predicting long-term well performance and interpreting pressure and production trends during the testing program.

We are monitoring pressures in deep gas wells in Chocolate Bayou field to detect possible changes that can be related to production at the Pleasant Bayou test well. No wells produce gas directly from the C-zone reservoir, but several do produce from thin, overlying sandstones, which may be in contact with the perforated interval. Gas well pressure data are reported semiannually and must be monitored for several years to obtain meaningful trends.

At a depth of 20,200 ft, the DOE Hulin No. 1 well in southwestern Louisiana penetrates a 550-ft-thick sandstone, which is the deepest known Gulf Coast geopressured-geothermal reservoir. Although the lack of deep well control has precluded detailed mapping, regional stratigraphic context and log response suggest that the Hulin reservoir was deposited in a submarine canyon or proximal submarine fan on the lower Miocene continental slope. Testing the Hulin reservoir will offer a unique opportunity for research and resource evaluation.