--> --> Characterizing outcrop growth faults, slump blocks, mud volcanoes and other sedimentary deformation features for use as reservoir analogues for observed features in targeted reservoirs in the Green River Formation, Uinta Basin, Utah

AAPG Rocky Mountain Section Meeting

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Characterizing outcrop growth faults, slump blocks, mud volcanoes and other sedimentary deformation features for use as reservoir analogues for observed features in targeted reservoirs in the Green River Formation, Uinta Basin, Utah

Abstract

Sand dominated clastic deposits form an important component of the rapidly developing Green River horizontal play in the Uinta Basin of NE Utah. Reservoir quality within the Green River is highly variable, with one cause being sedimentary deformation compartmentalizing clastic reservoirs, creating discontinuities and degrading intergranular porosity and permeability values. This occurs within fluvial and marginal lacustrine sandstone facies of the Flagstaff, Castle Peak and Douglas Creek Members of the Green River Formation. In many cases, well and seismic data demonstrate stratigraphic discordance that is interpreted to be related to sedimentary deformation shortly after burial. Evidence includes sudden thickening or thinning of reservoir units with undeformed strata above and below these features, stratigraphic zones of pervasive deformation (seismites?) and proximity to concurrently active faulting. These features appear to partition these sandstone reservoirs, making their characterization important for operators in the Uinta Basin. On the eastern flank of the Uinta Basin, there exists a large series of growth faults, slump blocks, mass transport deposits, mud volcanoes and diapirs, all related to fluvial sandstone deposits in a near shore settings of ancient Lake Uinta. Studied intervals include the Uinta A, Douglas Creek and Lower Black Shale informal members of the Green River Formation. The deformed sandstone blocks exhibit brittle deformation in the form of micro faults and minor brecciation, with limited ductile deformation. Dark oil shales acted as undeformed glide planes on which these blocks moved. These blocks range in size from 100 yards to nearly a quarter mile across and display everything from gently dipping rotations to being nearly overturned. Mud volcanoes and diapirs are often in close spatial association to the blocks, and deformed intervals will sometimes stack vertically, with undeformed lacustrine mudstones in between. Geographically, the deformed blocks appear to cluster in paleo valleys and along main-stem fluvial deposits. It is expected that a better characterization of these deformed deposits with allow for more accurate modeling of similarly deformed reservoirs within the active Green River oil play.