Extensional Fault System Evolution and Reservoir Connectivity Darrell W. Sims Center for Nuclear Waste Regulatory Analyses (CNWRA), Southwest Research Institute, San Antonio, Texas, U.S.A. Alan P. Morris Department of Earth and Environmental Science, University of Texas at San Antonio, San Antonio, Texas, U.S.A. David A. Ferrill Center for Nuclear Waste Regulatory Analyses (CNWRA), Southwest Research Institute, San Antonio, Texas, U.S.A. Rasoul Sorkhabi 1 Technology Research Center, Japan National Oil Corporation, Chiba, Japan ABSTRACT S andbox analog modeling experiments provide new insights into the effects of fault geometry on reservoir connectivity. During progressive distributed exten- sion, three phases of fault system evolution are apparent. In Phase I, geo- metrically simple faults nucleate rapidly at a large number of sites throughout the deforming region. This is followed by Phase II, in which faults link and increase in trace length. Phase III is characterized by a quasi-steady-state nucleation and linkage of faults. Reservoir connectivity has many components; here, we focus on fault- controlled connectivity, which can be viewed from two complementary perspectives: rock mass connectivity (continuity of rock between and around faults) and fault network connectivity. Which of these perspectives is adopted depends on whether faults cutting the reservoir act as barriers to flow (e.g., in highly porous sandstone reservoirs) or conduits for flow (e.g., in fractured carbonate reservoirs). We use two measures of fault-controlled connectivity: (1) a fault density measure derived from the number of intersections 5 Sims, D. W., A. P. Morris, D. A. Ferrill, R. Sorkhabi, 2005, Extensional fault system evolution and reservoir connectivity, in R. Sorkhabi and Y. Tsuji, eds., Faults, fluid flow, and petroleum traps: AAPG Memoir 85, p. 79 – 93. 79 1 Present address: Energy & Geoscience Institute, University of Utah, Salt Lake City, Utah, U.S.A. Copyright n2005 by The American Association of Petroleum Geologists. DOI:10.1306/1033717M853132