Sedimentology and Reservoir Characteristics of the Lower Triassic (Smithian) Sinbad Formation, San Rafael Swell, Utah
Scott Ritter, Colton Goodrich, and Caleb Osborn
The Sinbad constitutes the maximum flooding and turn-around phases of the thick depositional (approximately 200 m) sequence that includes the underlying Black Dragon Formation and at least part of the overlying Torrey Formation. Vertically, the Sinbad Limestone comprises three units, each characterized by a distinctive association of sedimentary facies: (A) a basal storm-influenced, open-marine unit comprised of mixed mollusk-dominated skeletal/non-skeletal limestone microfacies (B) a medial storm-dominated, restricted-marine unit comprised of hummocky crossbedded siliciclastic/peloidal microfacies, and (C) a capping peritidal crossbedded oolitic dolograinstone unit. Lateral variation is most pronounced in the medial unit, where storm-deposited beds thin and pinch out over lateral distances of one to a few tens of meters. Individual beds and microfacies display a large degree of lateral homogeneity and regional persistence in the lower and upper stratigraphic units. Diagenetic fabric elements indicate that the Sinbad Formation was altered by marine, meteoric, and burial diagenetic processes. The upper member of the Sinbad has been pervasively dolomitized throughout the study area. All three units have been replaced by dolomite in section 2 in the southeastern part of the San Rafael Swell. Hydrocarbon-lined interparticle and separate vug (largely molds) pores (1-5%) characterize the skeletal-oolitic limestones with permeability ranging from 0-100 md. Low permeability/porosity characterizes the middle silicilastic unit. The best reservoir qualities (permeability 400 md) occur in portions of the dolomitized oolitic grainstones that form the upper 2 to 3 m of the Sinbad Limestone.
AAPG Search and Discovery Article #90169©2013 AAPG Rocky Mountain Section 62nd Annual Meeting, Salt Lake City, Utah, September 22-24, 2013