Abstract

The Yates Field Unit in Pecos County, near Iraan, TX operated by Kinder Morgan CO2 is currently under CO2 gravity drainage. Discovered in 1926, the field has produced approximately 1.46 Bbl of oil to date. Geologically, the unit is located near the southeastern termination of the Central Basin Platform in the Permian Basin. The primary and most productive reservoir unit is the San Andres formation followed by the Seven Rivers, Grayburg, and Queen formations. The San Andres is a complex dual porosity reservoir replete with numerous separate vug porosity types, fractures, and small caves associated with dolomitization, tectonics, and karst processes, respectively. Since May of 2008, starting from the western field boundary and moving east, Kinder Morgan geologists have logged 42 out of 189 cores and described over 1000 thin sections documenting; lithologies, Dunham carbonate classifications, grain types, sedimentary structures, karst fabrics, porosity types, cement mineralogy, and dissolution horizons (stylolitization). Although the core study is not yet complete, 13 major depositional facies have been identified in the San Andres thus far. Based on facies stacking patterns and significant epikarst or hardground surfaces a preliminary YFU San Andres sequence stratigraphic framework has been established. This framework is complicated and overprinted by multiple stages of dolomitization and karst processes. Complete karst collapse suites are rare in any one YFU core but have been locally documented specifically within the San Andres formation displaying world class oil field karst collapse features.