This paper describes the theory of cased hole formation resistivity measurements and presents examples demonstrating the diversity of their use. Resistivity behind casing has many applications, from evaluating formations in new wells to monitoring water influx and bypassed hydrocarbons in producing wells. These robust deep-resistivity measurements can be combined with data from traditional cased hole and openhole evaluation tools to provide a comprehensive formation evaluation from behind casing.
Example A highlights the use of these measurements in the successful completion of a new Cook Inlet offshore well. Traditional openhole logs were not obtained because of hole conditions and the borehole environment, which also limited traditional cased hole evaluation techniques such as sigma and carbon-oxygen logging. The new resistivity measurements were instrumental to the successful completion of this well as an oil producer with low water cut.
Examples B and C, from wells in a mature field, demonstrate the use of the measurements to identify water influx and encroachment, which is vital for reservoir monitoring. Both wells produced water from high-permeability thief zones, which prompted profile modification to limit water production and enhance off-take from zones with lower permeability. The new cased hole resistivity measurements provided valuable data, not available from traditional production logs, to assess sweep efficiency, which will be used to guide recompletion or sidetrack decisions.