Abstract
Location and trap type of Cretaceous oil and gas fields in the D-J Fairway of Nebraska are related to the occurrence of 12 Permian salt zones. Salt distribution is controlled by the configuration of evaporate basins, truncation at a sub-Jurassic unconformity, and post-Jurassic subsurface dissolution. The Sidney Trough, which marks the eastern (regionally updip) limit of Cretaceous oil production in western Nebraska, is a rootless salt-dissolution collapse feature, whose location and origin is controlled by an abrupt linear facies change from thick, porous Lyons Sandstone to Leonardian salt. Eastward gravity-driven groundwater flow within the Lyons occurred in response to hydraulic gradient and recharge along the Front Range Uplift following Laramide orogeny. Dissolution of salt at the facies change caused collapse of overlying strata, producing fractures through which cross-formational flow occurred. Younger salts were dissolved, enhancing relief across the regional depression and subsidiary synclines. Timing of post-Jurassic dissolution influenced entrapment within D and J sandstone reservoirs. Where Early Cretaceous (pre-reservoir) dissolution occurred, structure at the D and J sandstone level is relatively simple, and stratigraphic traps predominate. Where Late Cretaceous - Tertiary (post-reservoir) dissolution occurred, structure is more complex, formation waters are more saline, oil and gas are localized on dissolution-inducedmore » anticlines, and per-well reserves are significantly higher.« less
Published Version
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