A. Curtis Huffman1, David J. Taylor2
(1) U.S. Geological Survey, Denver, CO
(2) U.S.G.S, Denver, CO
ABSTRACT: Basement faulting and overlying fractured reservoirs, San Juan basin, New Mexico and Colorado
Analysis of available 2-D reflection seismic data along the eastern and northwestern margins of the San Juan basin reveals a close relationship of Laramide-age basement involved faulting with fracture orientation in the vicinity of several fractured Mancos Shale oil fields. Both of these margins are interpreted as Laramide right-lateral wrench systems with strong basin-ward thrust components. The motion on these faults produced overlying monoclines that included much of the Upper Cretaceous part of the section and a predominance of fracturing parallel to the monoclinal trend. The generally east-west regional extensional regime predominant since Rio Grande rifting has kept this array of longitudinal fractures open.
High-resolution seismic data along the northern margin of the basin demonstrates the presence of multiple thrust and back-thrust faults distributing the basin margin thrusting within the thick Upper Cretaceous Mancos Shale. The Mancos Shale of the Puerto Chiquito field along the eastern basin margin is also fractured by thrust and back-thrust faults but these can be shown to be within a flower structure overlying a right lateral basement wrench fault. We interpret the fracturing in the Verde field on the Hogback monocline along the northwestern basin margin to have resulted from a similar mechanism but the data available to us are not sufficient to demonstrate this conclusively.
AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado