--> ABSTRACT: Effect of Sandstone Detrital Composition on Reservoir Quality Assessment and Prediction, by Salman Bloch; #91019 (1996)

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Effect of Sandstone Detrital Composition on Reservoir Quality Assessment and Prediction

Salman Bloch

Initial composition of sandstones is a key control on reservoir quality. In weakly-cemented sandstones (<10% cement), rigid grain content, rather than grain size, is the main parameter affecting permeability, particularly in the 5,000-10,000 ft depth range. The rigid grain content can be predicted from provenance and depositional-facies calibration data.

In most reservoirs, with the exception of highly cemented sandstones and sandstones with a low rigid grain content, there is a discernible reIationship between initial (Beard-Weyl) and present-day permeability. For a giver burial history, in weakly-cemented sandstones containing more than 85%, rigid grains, facies-controlled permeability contrasts that existed in the original sediments are enhanced. Increasing ductile grain abundance progressively worsens reservoir quality. For example, in moderately-sorted sandstones with more than 15-20% of altered volcanic rock fragments (VRFs permeability is reduced to < 0.1 md, even following a favorable burial history Samples with 10-15% VRFs have permeabilities <5md, whereas samples with <10% VRFs can have high permeability, depending n grain sizes Chemical diagenesis, the effects of which can destroy, preserve or enhance reservoir quality, is also controlled by detrital components, interacting with pore fluids.

A newly-developed systematic approach, based on empirical and "hybrid" models (e.g., ExemplarTM), allows in many instances to accurately predict or assess, prior to drilling, compactional effects, the type and extent of cementation, and occurrence of porosity-preserving coats on detrital grains.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California