Possible Continuous-Type (Unconventional) Gas Accumulation in Lower Silurian "Clinton" Sands, Medina Group, and the Tuscarora Sandstone in the Appalachian Basin: A Progress Report of 1995 project activities

Robert T. Ryder, Kerry L. Aggen, Robert D. Hettinger, Ben E. Law, John J. Miller, Vito F. Nuccio, William J. Perry, Jr., Stephen E. Prensky, John R. SanFilipo, and Craig J. Wandrey

Open-File Report 96-42

DOWNDIP LIMIT OF WATER PRODUCTION

Another diagnostic characteristic of continuous-type (basin-centered, deep basin) gas accumulations is the absence or near absence of producible formation water (Masters, 1979; 1984). Masters (1979; 1984) further reports that water-deficient, gas-saturated sandstone reservoirs in continuous-type gas accumulations are replaced updip by water-saturated sandstones that control entrapment. These zones of predominantly gas-saturated/little producible water and gas-bearing/water-saturated sandstones, as well as an intervening transition zone, can be interpreted from resistivity logs (Masters, 1979; 1984). Analogous zones of low-water, gas-saturated zones flanked by updip high-water saturated oil-and gas-bearing zones are noted by Davis (1984) and Zagorski (1991) in the Appalachian basin. Based on 33 control points, Davis (1984) suggests that the change from gas-saturated "Clinton" sands with little producible water to gas-bearing "Clinton" sands with high water saturation occurs abruptly westward (updip) across a north-northeast trending line through eastern Ohio. In contrast, Zagorski (1991) -- using resistivity logs across two short dip-oriented sections in northwestern Pennsylvania and adjoining Ohio-- suggests that the updip change from gas-saturated Medina Group sandstones to water-saturated sandstones is very transitional.

A map showing wells that produce or have produced water from the "Clinton" sands, the Medina sand, Medina Group sandstones, and the Tuscarora Sandstone was started for this project. In addition to showing the distribution of Lower Silurian sandstones that have high water saturations, this map may help to locate the probable updip limit of the adjoining continuous-type gas accumulation. The compilation of such a map is hindered by several factors. First, not all States require operators to document the character and quantity of water produced from oil and gas wells. Second, produced water that is reported is not always identified by stratigraphic interval. Thirdly, water-bearing parts of the Clinton/Medina interval may be intentionally cased and cemented and, thus, are not reported. Compilation of water data to date consists of recording relevant data from PI's weekly Appalachian Basin Report and plotting it by hand on a 1:500,000 scale map. Other data sources for this compilation are State Agency production files and published articles. The map is still too preliminary to indicate any definite patterns and resistivity logs have not been evaluated for evidence of high-water saturation.

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