--> Abstract: Hydraulic Fracturing during the Formation and Deformation of a Basin: Its role in the Dewatering of Low Permeability Sediments, by J. W. Cosgrove; #90942 (1997).

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Abstract: Hydraulic Fracturing during the Formation and Deformation of a Basin: Its role in the Dewatering of Low Permeability Sediments

COSGROVE JOHN W,

The geological expression of hydraulic fracturing is very varied and is controlled primarily by the magnitude of the differential stress and the intrinsic properties of the rock. The orientation and type of fractures that develop within a basin is determined by the state of stress which in turn is controlled by the geological boundary conditions. During the early stages of burial and diagenesis the formation of hydraulic fractures is thought to play an important role in the movement of fluids through low permeability, semi-lithified sediments. Unfortunately, these fractures are not generally preserved and are presumed to heal once the fluid pressure is relieved.

However the low permeability Mercia mudstone of the Bristol Channel basin contains bodies of sand which, during the opening of the basin, were injected along some of the hydraulic fractures in the mudstone preserving them as sedimentary dikes and sills. Field observations indicate that fluid pressures within the mudstone were also very high during basin inversion and that hydraulic fracturing provided a transient permeability which relieved this. The fractures are not visible in most of the mudstone but have been preserved within evaporite rich horizons as a network of satin spar veins. Thus the chance preservation of the sedimentary dikes and satin spar veins shows that at different times during the evolution of the basin, fluids migrated through low permeability units along transient networks of hydraulic fractures. In addition the orientation and spatial organization of these fractures reflect the boundary conditions operating at various stages in the basin history.

AAPG Search and Discovery Article #90942©1997 AAPG International Conference and Exhibition, Vienna, Austria