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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 65 (1981)

Issue: 5. (May)

First Page: 1010

Last Page: 1010

Title: Elmworth Gas Field, Alberta, Canada: Depositional Environments and Diagenetic Consideration of Low Permeability Gas Reservoir: ABSTRACT

Author(s): Sun Ho Youn

Article Type: Meeting abstract


Elmworth is a giant gas field in low permeability sedimentary rocks and is considered part of the Deep Basin in Alberta, Canada. Gas production is obtained mostly from conglomerates with unusually high permeability but with some difficulties in producing from lower permeability zones. The study of Falher conglomerate and sandstone (Lower Cretaceous) reveals that this low permeability gas reservoir owes its origin to an unique combination of depositional environments and diagenetic processes.

A detailed study of Falher A and B units shows that sediments were deposited during a regression in the following coastal environments: beach, shore, lagoon-bay, coastal plain, and fluvial. Cyclic patterns of vertical sequences indicate an oscillating shoreline and five such sequences are recognized.

Conglomerate and coarse sandstone occur in beach facies, while fine sandstone rich in detrital clays and organic matter predominates in shore facies. Detrital dolomite is characteristically distributed in shore facies and this is taken to indicate the direction of transport. Conglomerate and sandstone are overlain by carbonaceous shale and coal deposited in a swamp environment.

Vitrinite reflectance data indicate that the sediments were subjected to deep burial and associated important diagenetic processes.

Authigenic minerals are found to be most significant in Falher sediments. Quartz in the form of overgrowths and microcrystalline crystals is most extensively developed in sand-supported conglomerates and mineralogically mature sandstones in various environments. Kaolinite is predominant in most conglomerates and in sandstone, which show high primary porosity and permeability. Illite is more common in sandstone than in conglomerate though this trend is obscured by detrital clays in shoreface sandstone. Carbonate cement, mostly calcite and dolomite, is important, as it reduces porosity drastically. Diagenetic processes are strongly related to the depositional environments and their study is important not only in understanding the nature of the reservoir but in delineating the reservoir uality.

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Copyright 1997 American Association of Petroleum Geologists