GAS PRODUCTION FROM THE CHATTANOOGA SHALE IN SOUTHERN KANSAS: FIRST TRIES AND INITIAL DATA FOR POSSIBLE FUTURE RECONNAISSANCE STUDIES

Two wells (#1-34 Spriggs, #1-16 McGrath) drilled by Metro Energy Group in Barber County, Kansas in 2005 tested Devonian-Mississippian Chattanooga Shale [~65 ft thick (20 m); ~4900 ft depth (1495 m)] for shale gas. Sidewall samples from the Spriggs well from zones with >120 API gamma ray units assayed at 43 scf/ton (1.34 cc/gr); those with <120 API units registered 23 scf/ton (0.72 cc/gr). Samples from the McGrath well assayed respectively 22 and 18 scf/ton (0.69, 0.56 cc/gr). Desorption rates were strong at first and then drastically dropped in a few days. The McGrath well produced for four months, with a rapidly dropping rate. Production was wet gas [(1-(C1/ΣCn) ≈ 25%], with methane δC¹³ = -43 ‰ and δD = -170 ‰, indicating thermogenic origin. Plugging of microporosity by heavier hydrocarbons is hypothesized as the reason for the poorly sustained production.

The extensive logging suite that was run in these wells allowed a close integration to be made between wireline petrophysical measurements and both the shale formation characteristics and adsorbed and free gas content. The interpretation models were developed as a potential aid to the analysis of the Chattanooga Shale in other wells in southern Kansas that have a conventional logging suite. A compositional model that used inputs of gamma-ray, bulk density, neutron porosity, and photoelectric factor logs was used to predict volumetric proportions of clay, quartz, pyrite, kerogen and effective porosity. The kerogen estimates were then related to adsorbed gas, while shale and effective porosities were incorporated with resistivity in a shaly sand model to predict free gas. The application of these calibrated models to logs from wells in the area that penetrate the Chattanooga Shale offers some promise as a regional reconnaissance method to locate prospective gas sites.