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Time-Lapse Open-Hole Logging in a Heavy-Oil Thermal-Recovery Well

O’SULLIVAN, TERRY, Aera Energy LLC, Bakersfield, CA; JAIME ROIG, Aera Energy LLC., Bakersfield, CA; PETE RICHTER, Schlumberger Oilfield Services, Casper, WY

For wells drilled in heavy-oil steam-recovery projects, open-hole resistivity logs often appear to read too low through heated, oil-bearing intervals. Calculated water saturation values from these logs are highly dependent on the temperature used to represent the volume investigated by the deep resistivity measurement.

When the reservoir temperature is known, a correction can be made to the formation water resistivity using a standard "Arps-type" temperature-resistivity relationship. It is often difficult to evaluate reservoir temperature from open-hole log data. Contact temp.measurements only provide the temperature at the borehole wall, and cased hole temperature logs are only run after completing the well, when it is usually too late to change the completion design. The extent the drilling process affects the volume of rock investigated by the deep resistivity measurement is also unknown.

Comparison of two open-hole logging runs, recorded 5 hours apart with identical tool strings, are reported here. The maximum wellbore temperature increased from 215F to 265F between runs, with almost no effect on the deep resistivity measurement. Significant changes were observed, however, on flushed zone resistivity and on other measurements including the gamma ray and density. These changes are related to the temperature change, but also to an increase in mud cake thickness.

It is encouraging that the deep resistivity measurement seems largely unaffected by the drilling process. The problem of determining the true reservoir temperature from open-hole data remains. One strategy that has been reasonably effective utilizes dielectric logging measurements, which are largely unaffected by temperature, to provide the real-time evaluation data needed for completion decisions.

AAPG Search and Discovery Article #90911©2000 AAPG Pacific Section and Western Region Society of Petroleum Engineers, Long Beach, California