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Technical Paper: Accurate Oil Saturation Determination and Monitoring in a Heavy Oil Reservoir
Paper 46245
Abstract
The ability to determine oil saturation changes through time in the Kern River field is critical to heat management and optimization of reserves depletion. The Kern River reservoir is a complex multi-layered fresh water braided river deposit undergoing varying stages of thermal recovery. In the past, the practice had been to selectively core when new well locations were identified. An alternative to open hole core saturation measurements is the Carbon Oxygen Ratio (COR) log, which yields accurate and repeatable data that can be used to identify and monitor reserves depletion.
In this field, time-lapse 4D oil saturation images are being generated from a grid of several hundred observation wells. Over 360,000 feet of COR data have been acquired. The project is realizing accuracies comparable to core data -- bore out from a database containing 36,000 feet of core. In 1993, nine observation wells were drilled and cored. After casing was cemented in place, the wells were logged immediately to reduce uncertainties associated with subsequent production. Full field monitor logging was implemented in 1996 and again in 1997. Small changes in the COR oil saturation measurement over time are being monitored with a measurement precision of +/- 3.2 saturation units (su) with a confidence level of 95%. The highly accurate and precise data were made possible in part by reservoir conditions, well bore conditions, and a process improvement program incorporating all major steps from acquisition to data processing. A shared database tracked progress and monitored quality throughout the project. The project deliverables were in digital form only.
Log-to-core data comparisons, steps to determine precision and accuracy, as well as time-lapse 4D images showing reservoir dynamics, will be discussed.
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