Robert Freedman and Joseph R. J. Studlick
Eastern E&P Operations
Onshore Division
Shell Oil Company
New Orleans, LA
ABSTRACT
In December, 1979, a 6,500-acre farm-in prospect was offered to Shell Oil as a candidate for primary heavy-oil production using steam injection. This paper describes the petrophysical, geologic, and economic considerations which entered into the prospect evaluation. The prospect was the shallow (e.g., 2,000 feet) San Miguel sand in southwest Texas. Preliminary evaluation of the prospect was made using a limited data base provided by the lessor. This evaluation was uncertain due to the lack of accurate knowledge of formation oil saturations and properties. The accurate determination of oil properties is frequently the most difficult problem encountered in the evaluation of a heavy oil prospect. Oil samples are often not easily obtainable due to the limited mobility (e.g., “no flow of oil”) of the crude at reservoir conditions.
In order to obtain the needed data, it was recommended that a test well be drilled, cored and logged. The test well was drilled in April, 1980 and a full suite of conventional logs were obtained over the San Miguel sand. In addition, the Schlumberger NML and EPT tools were logged over the sand. Approximately 100 feet of conventional cores were recovered and analyzed. Analysis of oil samples extracted from the cores revealed an extremely low API gravity and high viscosity crude which hindered development of these oil sands. In addition, other negative factors were present. The log and core data indicated a sand with 45 net feet of oil (NFO), however, the oil saturations and sand quality fell short of the minimum requirements for a profitable project.