Scott M. Stookey¹, Ronald C. Surdam¹, Ronald S. Steel¹

(1) University of Wyoming, Laramie, WY

ABSTRACT: Sequence Stratigraphy and Reservoir Quality of the Frontier Formation, Riverton Dome, Wyoming

Located six miles south of Riverton, Wyoming, in the Wind River Basin, Riverton Dome is a mature oil and gas field situated on the most basinward structure of the Beaver Creek-Big Sand Draw fold trend. Most of the natural gas production from it occurs within a few sandstones of the Upper Cretaceous Frontier Formation. Seven Frontier sandstone benches are generally identified. Primary reservoirs occur in the First, Third, and Fifth Frontier sandstones. Sandstones within these reservoirs are considered tight gas sandstones (k < 0.1 md). Sequence stratigraphic, lithologic, and petrologic techniques were combined to more accurately characterize these three hydrocarbon reservoirs at Riverton Dome and surrounding areas.

Analysis of cross sections and facies associations indicate that the Frontier Formation is composed three third-order systems tracts. These systems tracts consist of prograding shoreface sandstones at the base, succeeding fluvial deltaic sandstones, and delta front sandstones at the top.

Petrographic analyses reveal that the Fifth Frontier sandstones have the highest reservoir quality. Relatively early emplacement of calcite cement in the Fifth Frontier sandstone preserved primary porosity, and subsequent dissolution of calcite cement created abundant secondary porosity, which approaches 18% in some samples. Open fractures enhance the reservoir quality in the Fifth Frontier sandstone and are particularly important for production from the First and Third Frontier sandstones, where porosity and permeability are commonly less than 10% and 0.1md. Natural fractures with apertures less than 170m are commonly open and have fracture permeabilities averaging 425 md.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado