--> Abstract: Potential Gas Reservoirs in the Upper Mannville Sandstone, by M. Z. Farshori and C. Schroder-Adams; #91012 (1992).

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ABSTRACT: Potential Gas Reservoirs in the Upper Mannville Sandstone

FARSHORI, M. Z., PanCanadian Petroleum Ltd., Calgary, Alberta, Canada, and C. SCHRODER-ADAMS, Schroder Paleo-Consulting, Calgary, Alberta, Canada

A detailed sedimentological and micropaleontological study of the Upper Mannville sandstone Lower Cretaceous in southern Alberta was conducted in order to understand depositional history, the geometry, reservoir quality, and production performance. Until recently, these tight sandstones have been overlooked by industry as a potential reservoir for gas and bypassed during well completions.

The Upper Mannville sandstones occur as thin sheets and ribbons sandwiched between a regional coal and underlying Ostracod Beds or Glauconitic Sandstone in southern Alberta. Six thin coarsening-upward sedimentary cycles occur and each is overlain by either a thin coal or a soil zone. A typical cycle begins with a scoured base overlain by transgressive lag and/or black shale that grades upward into bioturbated siltstone, then overlain by fine- to medium-grained kaolinitic sandstone. The Mannville sandstone consists mainly of stacked cycles of lenticular sand bodies deposited on beaches, tidal flats, lagoons, bays, and marshland. These cycles are also separated by incised tidal channels representing breaks in sedimentation. Each cycle contains scattered microfossils and abundant trace f ssils that are diagnostic of marginal marine environments. The assemblages consist entirely of agglutinated taxa with primitive test structures. Some samples yielded freshwater organisms such as thecamoebians.

These regressive cyclic sand bodies result from the interplay of sedimentation, tectonics, climatic variations, and local sea level fluctuations. These sands are classified as heterogeneous feldspathic litharenite. They contain zones of low porosity (i.e., 10-15%) and low permeability (0.1-2 md) due to the presence of authigenic kaolinite and calcite cements. As a result, fracturing of the sandbodies is generally required to enhance gas production. The gas-bearing thin reservoir sandstones are widely distributed and roughly cover an area of about 5000 sq. kilometers in the study area.

 

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)