Petrography and diagenesis of the bitumen-and heavy-oil-bearing White Rim Sandstone Member of the Cutler Formation (Permian), Tar-Sand Triangle area, southeastern Utah

The Permian White Rim Sandstone Member of the Cutler Formation in the Tar Sand Triangle area of southeastern Utah hosts one of the largest tar sand and heavy oil accumulations in the United States. Major diagenetic events include pervasive calcite cementation, calcite and feldspar dissolution, and subsequent growth of authigenic kaolinite, quartz, illite, and minor iron-bearing carbonate. Hydrocarbons migrated into the secondary porosity created by the dissolution of calcite and detrital feldspar, and into remaining primary porosity. Biodegradation of the oil, possibly by meteoric water flushing during uplift, has resulted in low API gravities. Kaolinite is the authigenic phase that conceivably could result in recovery problems during enhanced reservoir stimulation. Kaolinite can be dislodged and mobilized by recovery fluids under high flow rates, only to clog pores and block pore throats, resulting in decreased effective permeability. Potentially, the most serious recovery problem would result from thermal stimulation, during which kaolinite has been known to react with quartz and ions in solution to form smectite. In the presence of fresh water (steam), smectite swells to seriously decrease reservoir porosity and permeability.