(1) Schlumberger, Ridgefield, CT
(2) Schlumberger, Jakarta, Indonesia
(3) Schlumberger, Clamart, France
ABSTRACT: Reservoir Monitoring with Cased-Hole Formation Resistivity
Monitoring hydrocarbon saturation changes in cased holes has traditionally been determined by pulsed neutron logging tools. When used in time-lapse applications, changes in reservoir fluid saturation can be monitored over time and the progress of water flood or gas injection programs can be evaluated. Many clients would like to use resistivity devices to complement pulsed neutron logs because they offer a much greater depth of investigation and higher dynamic range in low porosity formations. Until recently, the use of resistivity devices for this purpose has been restricted to fibreglass cased wells. Limitations of this approach include the added cost of the fibreglass casing, collapse of the fibreglass casing during cementing, and incomplete characterisation of other logging tools for this environment.
The recent introduction of the Cased Hole Formation Resistivity Tool (CHFR*) provides a deep resistivity measurements in steel cased wells. The CHFR has been undergoing field-testing in many fields world-wide and has made over 45 jobs in a variety of casing sizes. The ability to measure formation resistivity through steel casing adds a new dimension to reservoir monitoring by allowing the evaluation of fluid saturation further away from the well bore and less affected by mud filtrate and acid. The measurement also has a greater dynamic range in low porosity or low salinity formations. When integrated with Sigma and Carbon/Oxygen logging, the identification of swept zones, flow barriers, or bypassed oil, the movement of fluid contacts, and the estimation of residual oil saturation can be achieved with greater accuracy and confidence.
*Mark of Schlumberger
AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado