In December 1979, a 6,500 acre (2,631 ha.) farm-in prospect in the Maverick basin in Texas was offered to Shell as a potential field for heavy oil production using steam injection. Preliminary economic models from a limited data base were insufficient to evaluate this potentially profitable prospect. A test well was drilled and 100 ft (30 m) of the shallow Upper Cretaceous San Miguel sand (at about 2,000 ft or 610 m) was conventionally cored to obtain accurate data.

From the core description, thin-section, and grain-size analysis, the San Miguel basal sand is interpreted as a barrier-island deposit with the upper zone reworked by a transgressive marine cycle. Petrographic analysis indicated early calcite cementation in a complex pattern in the gross sand interval. Natural fracturing is present in the reservoir. The heavy oil is highly viscous with an extremely low API gravity. The relation of heavy oil to grain morphology was shown by SEM photographs.

The log and core data indicated 45 net ft (14 m) of oil sand. However, oil saturations and gross sand quality were inadequate to meet minimum requirements for a profitable project.

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