An Electrical Analog Facility for Hydrocarbon Reservoirs

Abstract

Abstract A user-friendly type chart has been constructed as an aid to the petrophysical evaluation of water saturation. It provides a basis for the inter-reservoir comparison of electrical character in terms of adherence to, or departures from, Archie conditions in the presence of significant shaliness or low formation-water salinity. The chart describes a continuum of electrical behavior for both water and hydrocarbon zones. In this respect, it is a generalization of earlier approaches that were necessarily restricted to the water zone. This extension is achieved by adopting a generalized geometric factor, the ratio of formation resistivity to water resistivity, regardless of the degree of hydrocarbon saturation. The type chart relates normalized geometric factor to formation-water conductivity, "shale" conductivity and (irreducible) water saturation. The approach has been benchmarked using data from comprehensively studied reservoirs. The application of the method is described with particular reference to rock types, scale effects, core sampling levels and net reservoir criteria. The use of the type charts is illustrated for reservoir units that show different levels of non-Archie effects. The deliverables include reservoir classification, for interpretation strategy and optimum core-data acquisition, and reservoir characterization in terms of analog porosity and saturation exponents. The principal benefit is a reduction in the uncertainty associated with the well-log analysis of water saturation at an early stage in the appraisal/development process when adequate characterizing data are not available.