Pacific Section AAPG Convention

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Application Of Pseudo-Cp Curves Derived From Pks Core Data To Estimation Of Original Sw In Heavy Oil Reservoirs


A companion paper presented at this conference discusses the derivation of pseudo-capillary pressure curves from PKS core data in heavy oil reservoirs, for use in the calculation of original Sw where laboratory Cp measurements are either inadequate or not available and resistivity-based Sw does not provide the necessary information. This method has been applied in several fields, examples of which are shown. In each case, permeability was calculated from a log transform calibrated to core data, and height above the OWC (used as a proxy for the FFL) was calculated for each reservoir depth level in each fault block. Field 1 has never been produced so current Sw is probably very close to original Sw. Formation waters are fresh to brackish, wet legs may not have the same water chemistry as oil-bearing sands, and no information on field Rw is available. The pseudo-Cp curves were used to construct a permeability-referenced model to derive Sw, which compares favorably to core So. The other field examples are from reservoirs which have been in production for decades, first on primary and then on cyclic steam. Original formation waters were likely low to moderate salinity and variable both laterally and vertically, and steam injection has reduced the TDS in some zones. Heat has affected some wells, but log max recorded temperature is not a reliable indicator for where the heat is and how it may influence the deep resistivity measurement. Wells available for a reservoir study span several decades and represent the fields at different stages of depletion. No Cp measurements were available, and original Sw was needed for OOIP. Sw from pseudo-Cp curves compared to core and time-of-logging Sw show significant depletion in some zones, moderate depletion in others, and appear to be a reasonable estimate for original Sw.