Exploration and Development of Hydrocarbons from Low-Permeability Chalks—an Example from the Upper Cretaceous Niobrara Formation, Rocky Mountain Region
Published:January 01, 1986
Richard M. Pollastro, Peter A. Scholle, 1986. "Exploration and Development of Hydrocarbons from Low-Permeability Chalks—an Example from the Upper Cretaceous Niobrara Formation, Rocky Mountain Region", Geology of Tight Gas Reservoirs, Charles W. Spencer, Richard E. Mast
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Chalk beds of the Upper Cretaceous (Coniacian-Campanian) Niobrara Formation were deposited in a shallow epicontinental seaway in the Western Interior of the United States during a major global sea-level rise. Biogenic gas is produced from the thermally immature, organic-rich chalk beds of the Niobrara in the eastern part of the Denver basin in eastern Colorado, northwestern Kansas, and southwestern Nebraska. These chalks have high porosity and low permeability. Accumulations of shallow gas are not controlled by major structural closures but by local, faulted, low-relief domal structures, or noses. Fracture stimulation, primarily with the use of foam treatments, is necessary to make gas production from these wells economically feasible.
Westward and at greater depth in the basin, however, oil is produced from much tighter, naturally fractured chalk beds that are thermally mature and capable of thermogenic oil generation.
The reservoir properties (mainly porosity and permeability) and types of hydrocarbons produced in the chalk of the Niobrara Formation from a given location within the basin are primarily controlled by diagenetic processes. Maximum burial depth (with associated differential pressure and temperature history) is the main controlling factor in reservoir quality. Thus, reservoir characteristics and source-rock potential of the Niobrara can be predicted from an understanding of the post-Niobrara depositional and thermal history of the region coupled with research that has identified systematic diagenetic changes.
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Geology of Tight Gas Reservoirs
Tight gas reservoirs occur in low-permeability, gas-bearing formations that are present to some extent in all gas-producing basins worldwide. This is the first volume to bring together data on tight reservoirs for a variety of basins and different geologic settings. The papers in this volume discuss characteristics of some of the most significant tight gas areas in the United States; however, these data are equally applicable to many other recognized and unrecognized tight gas provinces in other nations. In general, tight reservoirs in the United States are grouped into tight gas sandstones and eastern Devonian shales. The Devonian shale sequences are dominantly marine shale but include some siltstone and sandstone. Tight gas sandstone formations of other than Devonian age are present throughout the United States and consist primarily of fluvial and marine sandstones and siltstones. In addition, gas also occurs in low-permeability marine carbonate reservoirs. The 14 papers in this volume cover such topics as: coal-bed methane and tight gas sands interrelationships; gas-bearing shales in the Appalachian basin; exploration and development of hydrocarbons from low-permeability chalks; and geologic characterization of low-permeability gas reservoirs.