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Preliminary Investigation of the Aptian Section as a Potential Unconventional ‘Shale Gas' Reservoir in the Downdip Mississippi Interior Salt Basin, Mississippi, USA

Hackley, Paul; Enomoto, Catherine; Lohr, Celeste D.; Scott, Krystina R.; Valentine, Brett J.; Dulong, Frank T.; Alimi, Hossein; Bove, Alana M.

Previous work by the U.S. Geological Survey (USGS) has shown that the Lower Cretaceous (Aptian) Pearsall Formation is potentially an important unconventional ‘shale gas' reservoir in the Maverick Basin of south Texas, where thermal maturity is in the dry gas window. However, our reconnaissance studies showed that regional thermal maturity of the Aptian section is lower northeast of the San Marcos Arch and thence eastward to the Florida panhandle, and total organic carbon content is low (<1%). This study evaluates ‘shale gas' prospectivity of the Pearsall-equivalent section (Rodessa and Pine Island Formations) in the downdip Mississippi Interior Salt Basin of southern Mississippi, where reconnaissance indicated thermal maturity of the Aptian section approaches the wet gas/condensate window. Using a regional structure map for top of Pearsall-equivalent strata, wells penetrating the Pine Island Formation at depths of 12,000-15,000 ft below surface across southern Mississippi were evaluated. Wireline electric logs showing tops of the Pine Island Formation (approximately 100-400 ft thick) and underlying Sligo Formation were correlated in a 15-well cross-section extending approximately 200 mi east-southeastward from Adams County MS on the west to Jackson County MS on the east. In some wells, a James Limestone interval of 100-200 ft was identified by a more negative spontaneous potential (SP) and higher resistivity log values whereas the Pine Island was identified by higher SP and lower resistivity. Pine Island cuttings samples were collected from these 15 wells from the Mississippi Office of Geology in Jackson, MS. Cuttings typically had a gross lithology of 70-90% gray to medium-dark gray to black lime mudstone and siltstone, with 10-30% of cuttings consisting of light-gray to yellow, green, and red lime mudstone and siltstone. Sixty cuttings samples were high-graded by selecting dark-gray to grayish black cuttings fragments for organic petrography, vitrinite reflectance, X-ray diffraction mineralogy, and geochemical screening analysis. A limited amount of core was available from the Pennzoil No. 1 Piazza, Jefferson Co., and 3 samples were selected for thin section preparation. Results from this work will be used to improve future USGS resource assessments in the onshore Gulf Coast region and can be applied to modeling studies and other research in the Mississippi Interior Salt Basin where thermal maturity, organic content and mineralogical data are necessary.


AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013