Thomas D. Fouch, 1985. "Oil- and Gas-Bearing Upper Cretaceous and Paleogene Fluvial Rocks in Central and Northeast Utah", Recognition of Fluvial Depositional Systems and their Resource Potential, Romeo M. Flores, Frank G. Ethridge, Andrew D. Miall, William E. Galloway, Thomas D. Fouch
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Rocks formed from mineralogical ly complex sediments deposited in fluvial and fluvial-lacustrine depositional settings are known from much of the world. However, relatively few of the rocks have been successfully explored for oil and gas because of the failure to adequately understand the complex lenticular reservoir units that generally characterize continental rocks. It has become increasingly obvious with new studies of hydrocarbon-bearing nonmarine rocks that in the absence of an understanding of the units sedimentologic and mineralogic rock properties, correlation of beds, and identification of genetic units and depositional facies using drill-hole logs may be inaccurate. In addition, reservoir properties of mineralogically complex rocks calculated from logs are frequently misinterpreted, and potential reservoirs may he damaged during drilling, stimulation, or completion activitites.
Abrupt changes in rock type and bedform geometry cause lenticular shaped reservoir units; variable quality within the reservoir is largely due to post-depositional mineral alteration, and induced irregularities of bedding surfaces. Oil and gas accumulations in fluvial rocks commonly occur in a complex of lens-shaped reservoirs, each with a separate hydrocarbon/water contact. Moreover, the pattern of reservoirs may be arranged in such a manner that within a sandstone unit that is continuous between drill holes, water-bearing rock occurs down structural dip from a gas/oil-bearing reservoir. Reservoirs are frequently separated by a permeability barrier of densely cemented sandstone in which the distribution of cement is at least partially controlled by sedimentary features.
The purpose of this paper is four-fold: 1) to provide a brief description of the sedimentologic and