Water Saturation Determination Using Empirical Resistivity/BVW Correlation Methods: Montney Unconventional Petroleum Play, Western Canada

Summary The determination of water saturation (Sw) is a fundamental goal in the petrophysical evaluation of both conventional and unconventional reservoirs. Unconventional reservoir rocks, however, pose challenges for common petrophysical evaluation methods (e.g., Archie method) that rely on standard logging suites due to many diverse geological factors, including low porosity and permeability, significant contents of clay and organic matter, and complex pore structure. Specialized downhole logs, such as those from nuclear magnetic resonance (NMR) and dielectric tools, provide other methods for determining Sw, but they are seldom widely available. In most unconventional petroleum plays, well log analysts are necessarily required to evaluate legacy wells with standard logging suites of various vintages. In the Montney unconventional petroleum play, a simple approach to Sw determination involving the empirical correlation of bulk volume water (BVW) from full-diameter core samples to deep resistivity from depth-matched downhole logs has proven to be effective for evaluating wells with deep resistivity and porosity logs. Here, we update the resistivity/BVW relationship developed for 15 wells in an earlier study with core and log data from an additional 19 wells. The updated relationship has practical utility in comparative multiwell petrophysical evaluations. Additionally, we introduce a modified resistivity/BVW method for the evaluation of individual wells whereby the estimated water resistivity (Rw) at in situ salinity and temperature is used to anchor the resistivity/BVW correlation at 100% BVW. This modification allows the resistivity/BVW method for Sw determination to be customized to specific geological settings within the Montney unconventional petroleum fairway.