--> Abstract: Sedimentology/Petrology of Fall River Formation, Wyoming: Outcrop and Subsurface Study, by B. K. Boyee; #91017 (1992).

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ABSTRACT: Sedimentology/Petrology of Fall River Formation, Wyoming: Outcrop and Subsurface Study

BOYEE, BRENT K., EarthFax Engineering, Inc., Salt Lake City, UT

The Lower Cretaceous Fall River Formation of the southeastern Powder River basin, Wyoming, records an ancient fluvial-dominated deltaic system. Meandering streams supplied sediment to a northward and northwestward prograding delta system. Vertical and lateral facies relationships reveal two episodes of deltaic progradation. The second progradation was the more extensive.

Reservoir sandstones of the Buck Draw field are predominately fluvial-dominated distributary channels. These reservoir sandstones directly overlie an area of anomalously thin Lakota Formation sediments. A subtle topographic low on the top of the Lakota likely affected distribution of Fall River distributary channel sandstones. Interdistributary bay and delta-front deposits provide updip permeability barriers, which allowed hydrocarbons to accumulate in an updip convexity of the distributary channel trend. This identification of specific facies comprising the reservoir sandstones and permeability barriers, and knowledge of factors affecting distribution of these deposits provide an exploration model.

Post-depositional diagenetic processes had a greater effect on reservoir quality of these sandstones than primary depositional processes. Compaction and precipitation of quartz overgrowths were the two most important diagenetic events, destroying virtually all primary porosity. Silica cementation and chemical compaction were less extensive in the fluvial-dominated distributary channel facies than in the delta front facies, thus the higher porosities in the distributary channel facies. Dissolution of unstable mineral phases did not develop to a degree that significantly enhanced porosity. Natural fractures and tension gashes are primarily responsible for hydrocarbon production from the Buck Draw field.

 

AAPG Search and Discovery Article #91017©1992 AAPG Rocky Mountain Section Meeting, Casper, Wyoming, September 13-16, 1992 (2009)