Print this pageMeasuring Formation Resistivity through Casing at Elk Hills Field
D. E. Sharbak
Occidental of Elk Hills Incorporated, Tupman,
CA
Occidental of Elk Hills recorded formation resistivity through casing
in ten wells at the Elk Hills Field, Kern County, California. Two types
of 
tools
were used to record the data. This case history describes the
tools and theory used to make the measurements. The data are compared
to open hole logs to validate the technique. The data are also
applied to reservoir monitoring and surveillance questions. The new
technique required some confirmation of the accuracy and precision
of the measurement. The logs illustrate the effects of borehole size,
cement thickness, open perforations, casing corrosion and casing
scale. One log in particular compares a cased hole resistivity just after
completion to the open hole induction resistivity. Despite the high
signal-to-noise ratio, sufficient precision can be obtained to match
open hole resistivity data. The study applies the logs to determine
gas, oil, and water contacts in the 26R Reservoir. The data appears
to reveal the contacts even in the presence of scale and open perforations.
Another surveillance application in the Main Body B reservoir
identifies water breakthrough in an existing waterflood. The
lower resistivities are consistent with scale buildup in the same intervals.
Reservoir monitoring is an important issue at Elk Hills Field.
The resistivity data could improve the performance of an existing
waterflood, and determine moving oil-water, gas-oil contacts. Reservoir
monitoring is difficult in existing wells because of the shallow
investigation of typical cased hole logging tools. The through casing
resistivity technique measures across a five-foot radius from the wellbore,
allowing resistivity to be measured beyond the invaded zone.
The results of this study show good agreement with open hole data
but mixed success in application. Since reservoir monitoring is a significant
and common issue, subsequent application and improvement
of this technique is expected to continue.
AAPG Search and Discovery Article #90904©2001 AAPG Pacific Section Meeting, Universal City, California
