McElroy field, located in the Permian Basin, is a typical example of a complex carbonate reservoir. Discovered in 1926, McElroy field has been under waterflood since the early 1960s. However, maximizing oil recovery is still a major challenge in this field. We have applied a rock-typing workflow based on conventional well logs and core data to incorporate both depositional and diagenetic attributes for characterizing the heterogeneity within the McElroy field. The resulting rock-type distribution may be used to ultimately enhance future development and oil production in the McElroy field.
The applied rock-typing workflow consists of several sequential steps. Firstly, the depositional rock types were described and consolidated in the core domain for the purpose of propagation into the well-log domain. Next, reservoir typing was conducted to identify controls on reservoir properties. This analysis indicated that diagenetic overprint has the dominant influence on fluid flow in the McElroy field. In a subsequent step, pore types were classified by clustering attributes of Gaussian function fits to the pore-throat-radius distributions derived from mercury injection capillary pressure (MICP) measurements. The identified depositional rock types and pore types were populated in the core and the well-log domains applying a supervised model trained using the k-Nearest Neighbors algorithm (KNN).
Computed tomography (CT) scan imaging techniques correlated to log-derived estimates of porosity were used to predict vuggy porosity in the well-log domain. Assessment of vuggy porosity using CT-scan image analysis showed that the separation of sonic porosity and density-neutron porosity is not a reliable tool for estimating vuggy porosity in gypsum-bearing reservoirs. All of the generated geological and petrophysical data were integrated to define the petrophysical rock types that control the reservoir's dynamic characteristics. Validation of the petrophysical rock types by dynamic injection profiles confirmed earlier assertions that fluid flow in this field is dominantly controlled by diagenetic modifications. Finally, we studied the distribution of the identified petrophysical rock types to establish trends for fieldwide spatial distribution of petrophysical rock types. The spatial trends of petrophysical rock types in the field serve to identify the potential for future development opportunities in the McElroy field.