Northwest Asphalt Ridge tar sand deposit well logging and coring comparison

Quantitative well logging techniques were performed on four wells used to conduct a small scale tar sand steamflood and four additional wells used to provide reservoir data for the design of a fourth field experiment near Vernal, Utah. The purposes of this study were to: summarize and present the log derived information; determine how accurately the log data matched 3 the core data; and estimate values for Rw in the Rimrock Sandstone Member. A gamma, sidewall neutron, density, SP, induction and caliper log suite was utilized in determining porosity and water saturations. A sonic log was utilized in determining the elastic rock properties; pressure velocity, shear velocity, Young's modulus and Poisson's ratio. Carbon/oxygen logs were also run to determine hydrocarbon saturation. The density log was determined to be the best logging source of porosity. Crossplotting and shale corrections did not improve the porosity quality. Formation water resistivity was estimated from the Archie equation using the core porosity and water saturations and using the induction log formation resistivity. Generally, good porosity information was determined from the density log. Water saturations were acceptable but did not match the core data as well as desired. Elastic rock properties derived from the sonic logs also matched core derived values. Carbon/oxygen logs have proven to be a good method of detecting changes in formation oil saturation. Oil saturation values derived from the carbon/oxygen log may be conservative due to a lack of a clean unsaturated sandstone zone to use as a reference point.