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Sour gas is widely distributed in the Big Horn, western Wind River, and greater Green River basins, and the eastern part of the Overthrust belt in Wyoming. In adjacent parts of Idaho and Utah, available data to evaluate the probable occurrence of sour gas diminished rapidly west of the Wyoming border. Principal geologic and geochemical factors in the formation of sour gas include (1) hydrocarbon reactions with sulfates in source and reservoir rocks and formation fluids, (2) thermal desulfurization of crude oil at temperatures in excess of 100°C (212°F) and depths of 3,000 m (9,842 ft) or greater, and (3) catagenic decomposition of kerogen to form CH4 and H2S at temperatures of about 350°C (662°F) and depths of 7,000 m (22,965 ft) r more.
Sour gas is found with an increasing probability of occurrence from the Chugwater Formation (Triassic) to the Madison Group (Mississippian). It also occurs in lower Paleozoic rocks, but the few reported occurrences preclude estimation of its resource potential at this time. Based on both surface and subsurface evidence, sour gas is closely associated with carbonate-evaporite sequences from cyclic depositional environments from subtidal through supratidal-sabkha that are present in western Wyoming from the Mississippian through the Triassic. In the three basins and the Overthrust belt, sour gas resources are estimated to have a mean volume of 20 to 27 tcf, with a 95 to 5% probability range of 7.5 to 56 tcf. The distribution by basin is estimated to be the following: Big Horn, 17%; west rn Wind River, 13%; greater Green River, 45%; and eastern Overthrust belt, 25%.
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