Abstract

Recent discovery of natural gas in sandstones of the Jackfork Group of southeastern Oklahoma has led to revised interpretations of hydrocarbon potential in the Ouachita thrust province of eastern Oklahoma. Jackfork reservoirs consist of fine to very fine grained, submarine-fan lobe sandstones with low matrix permeability and porosity. Production is dependent upon natural fractures, enhanced in most cases by artificial stimulation. Individual wells have produced at rates of 1.3-5.7 million cubic feet per day and possess estimated reserves in the range of 2.0-7.6 billion cubic feet. Hyperbolic decline suggests gas contribution from the matrix, possibly due to the presence of microfractures. Drilling has concentrated on two subsidiary thrust blocks in the hanging wall of the Ti Valley thrust, southern Latimer County. However, recent outcrop, petrographic, and sedimentological analyses have shown that traditional depositional models of the Jackfork are overly limited and that potential Jackfork reservoirs exist across a broad area to the south of the current play. Such analyses have revealed the existence of thick, medium-coarse-grained channel sequences at a number of localities in the Lynn Mountain syncline. Similar sequences may also exist well to the south, in the Boktukola syncline, where thick sand intervals have been identified. Petrographic study of samples from the Lynn Mountain syncline suggests that channel sequences may have significantly higher reservoir quality than is found in productive Jackfork sandstones to the north. Traditional assumptions postulating low regional hydrocarbon potential for the Jackfork therefore stand in need of revision.

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