Abstract

Suntura Field is a lower Clear Fork (Leonardian) ramp-margin strat trap along the NW margin of the Midland Basin. It was discovered by Great Western Drilling Co. using seismic stratigraphic and attribute methods (Welch and Gogas, 2003). Geomodeling and reservoir simulation were performed by iReservoir.com to prior to initiation of a fieldwide waterflood. The geologic component of the integrated reservoir study included:

• Facies description and interpretation of 337 ft of available core (Suntura 2 and Suntura 6);

• Extend cored facies to uncored wells using 19 FMI logs;

• Petrographic evaluation of facies, microfacies, pore types and diagenesis;

• Integration of core data into sequence stratigraphic framework used to define internal stratigraphy of the Lower Clearfork interval at Suntura field;

• Integrate facies and stratigraphic findings into the GOCAD geomodel for simulation;

• Determine the role of high-permeability facies as potential waterflood thief zones.

The two cores represent a composite section through parts of Zones B-D. Facies 1–7 vary from deeper water facies (1) to shallow, variably restricted inner lagoon deposition behind a shoal complex (facies 7). Re-establishment of the carbonate factory after a sea level fall is recorded by the mixed carbonate and siliciclastic mudstones of facies 15.

Carbonate environments were probably exposed in areas far up-dip from Suntura field, but no evidence of subaerial exposure was noted in the cores. The absence of peritidal and tidal flat facies at Suntura field is important. Shallowing-upward high frequency cycles terminate in shoal or back-shoal / Inner lagoon facies rather than at peritidal / supratidal facies, producing sub-tidal-dominated cycles that tend to be fairly heterogeneous along depositional strike, with shoals occurring as more localized sand bodies rather than a continuous belt of high-energy deposits. This observation is important for field-scale lateral heterogeneity. While readily recognizable in cores, subtidal cycles are often difficult to recognize on well logs in uncored wells because they lack the elevated gamma ray signatures more common among dolomitized peritidal / supratidal deposits.