Since 2011, the Devonian Berea Sandstone in northeastern Kentucky has produced oil where thermal maturity studies indicate that likely source rocks, namely, the Devonian Ohio Shale and Mississippian Sunbury Shale, are thermally immature. Downdip, where source rocks are mature for oil, the Berea Sandstone and Ohio Shale primarily produce gas. To investigate this thermal maturity discordancy, the molecular and isotopic composition of gases from the Berea Sandstone (oil associated) and Ohio Shale (nonassociated) were analyzed to understand the gas generation and migration history.Collected along a northwest-southeast transect in eastern Kentucky, samples range from 1079 to 4602 ft, respectively. All are wet gases with a thermogenic origin (δ13C-CH4 = −53.5‰ to −46.1‰). This is mostly consistent with a reevaluation of thermal maturity in a companion study that expands the area mature for oil. Gas migration is required, however, in updip parts of the Berea play where vitrinite reflectance (VRo) values are less than 0.6%. Southeast regional dip exerts a first-order influence on thermal maturity as gases become drier and isotopically heavier downdip. Correlation of δ13C values for heavier hydrocarbon gases in a natural gas plot with VRo contour spacing demonstrates the influence of nearby source rock thermal maturity on gas composition. Downdip, migration of oil and the attendant increase in permeability relative to gas may account for the dominance of gas production in the Ohio Shale. Migration along with basin uplift after the Alleghany orogeny may have contributed to development of a gas phase that exsolved from oil.

中文翻译：

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肯塔基州东部泥盆纪Berea砂岩的分子和同位素气体组成及其对气体演化的影响

自2011年以来，肯塔基州东北部的泥盆纪Berea砂岩已在热成熟度研究表明可能的烃源岩（即泥盆纪俄亥俄页岩和密西西比州Sunbury页岩）不成熟的情况下生产了石油。Downdip的烃源岩已经成熟，Berea砂岩和Ohio页岩主要产生天然气。为了研究这种热成熟度的不一致性，分析了Berea砂岩（伴有石油）和Ohio页岩（未伴有）的气体的分子和同位素组成，以了解天然气的产生和迁移历史。样本范围分别为1079到4602英尺。所有都是具有热成因的湿气（δ13C-CH4= -53.5‰至-46.1‰）。这与在伴随研究中对热成熟度的重新评估相一致，该研究扩大了石油的成熟面积。但是，在Berea矿的上倾部分中，镜质体反射率（VRo）值小于0.6％时，才需要气体迁移。东南地区的倾角对天然气的成熟度具有第一级的影响，因为气体变得更干燥，且同位素的倾角更大。天然气田中较重烃气的δ13C值与VRo轮廓间距的相关性证明了附近烃源岩热成熟度对天然气成分的影响。下倾角，油的运移以及随之而来的相对于天然气的渗透率增加可能是俄亥俄页岩气产量占主导地位的原因。