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The AAPG/Datapages Combined Publications Database

Wyoming Geological Association

Abstract


Gas Resources of Wyoming; 40th Annual Field Conference Guidebook, 1989
Pages 199-208

Seismic Detection of Upper Dakota Sandstones on the Moxa Arch, Green River Basin, Wyoming, Using Amplitude Versus Offset Data

C. Dean Lausten

Abstract

Cretaceous upper Dakota marine barrier island bar sandstones are prolific gas and condensate producers on the northern end of the Moxa Arch, within the Green River Basin, in Sweetwater County, Wyoming. An important field is the Blue Forest complex with projected reserves of 200 Bcf of gas and 7 million Bbl of oil. The average production depth for the field is 11,000 ft (3353 m). The present areal extent of the field is approximately 36 mi2 (93 km2). The bar sandstones are draped across a broad southeast plunging nose and pinch out to the northwest causing the trap. There are tens of townships flanking the Moxa Arch which have few, if any, wells drilled to the Dakota. There is potential for significant gas reserves on trend with the Blue Forest complex and in geologically similar environments on the Moxa Arch.

The stratigraphic variability of the upper Dakota section coupled with scant well control causes the prediction of the presence or absence of bar sandstone accumulations to be a problem. The seismic method is the logical technique to use to search for these sandstone accumulations. However, in the past there have been problems identifying the presence of sandstone on conventionally acquired and processed seismic data, because the responses of the sandstone and no sandstone cases are very similar.

The development of amplitude versus offset technology has provided a method to distinguish thick sandstone from thin or no sandstone on carefully prepared, ray-traced forward models. These models, constructed to simulate field recorded data with extremely long offsets, demonstrate that the response of the thick sandstone case at far offsets is substantially different from the thin or no sandstone case. Carefully processed seismic data, acquired with parameters chosen by examination of the models, agrees well with the model templates.

Several undrilled areas along seismic lines exhibit a response similar to the thick sandstone cases. The technique should prove valuable for the identification of sandstone accumulations away from existing well control.


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