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Performance Monitoring of Mature Oil Reservoirs Using Cased Hole Formation Resistivity (CHFR) Logging Data

Hamada GM, El Mahdy OA and Chandran M

Determining hydrocarbon and water saturation behind casing plays a major role in reservoir management. Saturation measurements over time are useful for tracking reservoir depletion, enhancing recovery strategies and diagnosing production problems such as water production that is one of the main challenges facing oil and gas producers. It is necessary to manage water production to enhance oil production. In order to identify watered out zones, traditionally thermal decay time logging (TDT) and carbon/oxygen (C/O) logging are used, these tools have shallow depths of investigation and their effective application is limited in low porosity and salinity. With the introduction of cased hole formation resistivity technology (CHFR) a new dimension has been added to cased hole evaluation. A deep reading formation resistivity can now be obtained through steel casing that means no effect of borehole fluid invasion on measurements as it has been the case with pulsed neutron tools.

In cased hole evaluation, cased hole resistivity finds it utility in two circumstances; as a first resistivity measurement in old and new wells to assess the formation in present conditions, or as a time-lapse technique to describe temporal behaviour of reservoir dynamic and reservoir fluids movements to mainly detect bypassed oil zones and water invaded zones. Four case studies of mature reservoirs suffer from water production problems attributed to different geological and reservoir conditions. In all cases, the remedial work over operations based on the cased hole resistivity results have allowed a significant enhancement of the oil production and the implementation of an optimum field management strategy.