Characteristics of discrete and basin-centered parts of the Lower Silurian regional oil and gas accumulation, Appalachian basin: Preliminary results from a data set of 25 oil and gas fields
U.S. Geological Survey Open-File Report 98-216
Appendix B
Athens gas field (A)
| Location: | Crawford County, Pennsylvania (Lake Canadohta and Centerville 7½ min. quads) |
| Discovery date: | 1974; shut in until 1980 |
| Depth (ft): | 4,900 to 5,100 |
| Hydrocarbon type and GOR: | Gas and local associated oil |
| Structural setting: | Regional southeast-dipping homocline with local anticlinal noses; northwest-southeast trending Tyrone-Mount Union lineament crosses the southwestern corner of the field |
| Stratigraphic name of reservoir: | Medina Group; Grimsby Formation and Whirlpool Sandstone |
| Trap: | Stratigraphic; no recognizable updip pinchout of sandstone reservoirs; updip reservoir limits are defined by a loss of gas-filled porosity (i.e. updip Medina Group sandstones produce small amounts of water and gas); this configuration of reservoir and trap is explained by paleostructure with a cemented gas/water contact that is later tilted |
| Porosity: | F ave = 3.25%, range 1.6 to 7.3%; secondary (dissolution) porosity is dominant; F = 3.01, 5.55, 6.04 % also reported |
| Permeability: | Kave = 1.4 mD, range <0.1 to 177mD (high value caused by drilling-induced fracture)( K ave < 1 mD, range < 0.1 to 0.6 mD if high value removed); K = 0.0368, 0.139, 0.159 mD also reported |
| Natural fractures: | Vertical fractures (18 to 40 cm long and 0.5 to 1 mm wide) and local horizontal fractures are reported in a core; outcrops of Upper Devonian strata above the Athens field show dominant joint sets trending N40 to 70° E and N40 to 70° W |
| Diagenetic features: | Reservoirs consist of a variety of quartzose, lithic, and feldspathic arenite whose diagenetic history includes formation of authigenic clay, cementation (silica and dolomite), dolomitization, and dissolution of cements and grains |
| Water saturation and volume/salinity of produced water: | Sw (ave) = 39.7%, range 22 to 73 %; water production is minimal; for 320 days in 1981 and early 1982, 270 barrels of water was produced with 20,474 MCF of gas (rate of 13 BW/MMCFG) |
| Gas/water and oil/water contacts: | A gas/water contact is difficult to define because of the long gas-to-water transition zone |
| Reservoir pressure: | 1,125 to 1,272 psi (0.26 psi/ft) |
| Bottom-hole temperature: | 110° F (in nearby wells in Washington County) |
| Well spacing: | 40 acres |
| Ultimate production (EUR per well): | |
| References: | Laughrey (1984); Pennsylvania Oil and Gas Oil and Gas Association—Gas Advocacy Committee (1980); Rodgers and Anderson (1984) |
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