PLT-Calibrated Permeability: A Breakthrough in Carbonate Reservoir Characterization

Tuesday, 12 January 2010 Read 9765 times
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A step change improvement can be made to the predictive accuracy of a carbonate reservoir flow simulator by using PLT calibrated permeability to construct the geologic model. The improvement is most dramatic in carbonate reservoirs exhibiting problematic "excess permeability" due to fractures and vuggy porosity. The more realistic characterization of reservoir heterogeneity results in improved predictions of water or gas breakthrough performance, which leads to better reservoir development planning.

Estimating effective permeability at the reservoir scale has been a long-standing challenge in carbonate fields. The carbonate depositional and diagenetic history can be very complex, which can lead to permeability that is difficult to characterize. Vuggy or fractured intervals can have permeability significantly higher than the matrix permeability measured in core plugs. This “excess permeability” may control reservoir flow paths but is difficult or impossible to predict from static well-log transforms that are calibrated to matrix permeability.

In the Tengiz field, a giant carbonate reservoir in western Kazakhstan, a method has been developed to calculate apparent permeability on the basis of flow rate from production-logging tools (PLTs). Incorporating this flow-calibrated permeability into the Earth model offers an elegant solution to the long-standing problem of the best method to incorporate dynamic PLT data into a reservoir model.

Recently, a reservoir model built with apparent permeability resulted in more-realistic heterogeneity and a step-change improvement over previous methods in which only static log-based permeability transforms were used to populate the Earth model. Fewer changes were required to calibrate the full-field reservoir model. History matching to pulse tests showed that this model has a much-improved prediction of the interwell connectivity. Models containing apparent-permeability data have provided higher-confidence estimates of the future movement of gas injection from the Tengiz platform.

Biography:

Michael J. Sullivan, SPE, is the Reservoir Surveillance Coordinator for the Tengiz field in Kazakhstan. Previously, he worked as a petrophysicist at ChevronTexaco E&P Technology Company in Houston. Sullivan had previous assignments as an openhole petrophysicist and as a cased-hole petrophysicist for Chevron in Angola. He has held a variety of positions in petroleum and production engineering since 1979. Sullivan has authored several papers, including a recent Distinguished Author Series article on this topic in the July 2007 JPT

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