Ohio shale gas

Ohio shale is located in the Appalachian basin, and the United States is the first to produce commercially valuable natural gas in this petroleum system. The Ohio shale belongs to the Upper Devonian in the western Appalachian Basin (Figure 6- 14), but the strata in some areas are more complicated due to the changes in the sedimentary environment of the basin (Roen, 1993). The middle-upper Devonian shale stratum has a distribution area of about 33 1520 km2, exposed along the basin edge, with a deposition thickness of about 5,000 ft, of which the black shale rich in organic matter is about 5000ft (Dewitt et al., 1993). Hunter and Young( 1953) studied 3,400 wells in Ohio shale, among which 6% wells produced 1055 cubic feet/day, and the rest wells produced little gas after completion, with an average of only 6 1 1,000 cubic feet/day ... 1994.

Fig. 6- 14 middle Devonian-lower Mississippi shale stratigraphic map of west Appalachian basin (according to Moody et al., 1987).

Curtis and Faure( 1997, 1999) pointed out that the fault boundary and depression of the sub-basin controlled the organic matter related to algae derivatives in Ohio shale. Due to the lack of water circulation and limited oxygen supply, the sub-basins are anoxic and the organic matter is preserved. The preserved algae cause the concentration of organic matter and the discharge of oxygen, and the algae material is even preserved at the edge of the sub-basin, which provides an important material source for shale gas. Figure 6- 15 describes the distribution of kerogen with TOC value, and the Ohio shale in the lower Huron is the main source rock. The study of vitrinite reflectance shows that all organic matter in the lower Huron member is basically mature, which is beneficial to hydrocarbon generation. Organic matter is mainly kerogen II (Curtis and Faure, 1997, 1999). The closed area of TOC isoline shown in Figure 6- 15 is the main gas producing areas in West Virginia, Eastern Kentucky and Southern Ohio (American Natural Gas Research Institute, 2000). From the west to Big Sandy, Kentucky near the border of West Virginia, the proportion of black shale, organic matter content and natural gas production gradually increased to the maximum, which is consistent with the test results of TOC maximum and kerogen content.

Fig. 6- Distribution map of total organic carbon content (TOC) of Ohio shale in the lower part of Huron Formation (according to CurtisandFaure, 1997)