--> Abstract: The Effects of Fault Geometries and Slip-Surface Characteristics on 3-D Reservoir Connectivity, by N. G. Lindsay, F. C. Murphy, J. J. Walsh, and J. Watterson; #91004 (1991)

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The Effects of Fault Geometries and Slip-Surface Characteristics on 3-D Reservoir Connectivity

LINDSAY, NICHOLAS G., FINBARR C. MURPHY, JOHN J. WALSH,* and JUAN WATTERSON, University of Liverpool, Liverpool, U.K.

Faults modify reservoir connectivity through (1) the geometrical changes of permeable unit architecture, and (2) the hydraulic characteristics of individual fault surfaces. Both processes have been investigated in a working quarry where outcrop allows fault observations in both cross-section and plan view. The Westphalian sandstone/shale fluvio-deltaic sequence is approximately 50 m thick, with a sandstone/shale rate of approximately 3, with up to 80 faults (displacement range 1 mm to 10 m) on cross sections up to 180 m long. Individual sandstone units, up to 2 m thick, appear on cross sections to have no continuity because each is cut by faults with throws greater than its thickness. When similar units are examined on the quarry floor, fault throws vary laterally from values greater han that of a sandstone unit thickness, to a value less than this thickness and finally to zero at lateral terminations, or fault tips. Connectivity in 3-D is thus maintained in units cut by faults with throws greater than the unit thickness, albeit with greatly increased tortuosity compared with pre-faulting geometry.

In many cases there is no sandstone continuity across fault surfaces, even where throws are less than sandstone thickness, because of shale smears on fault surfaces. The combined effect of shale smears is no apparent sandstone continuity on any section across the quarry but their sealing potential is reduced by lateral fault termination.

Assessment of reservoir performance requires analysis of the fault 3-D geometry and displacement variation and their effect on the sedimentary architecture, together with definition of the hydraulic properties of the fault surfaces.

 

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)