Lithology, porosity and water saturation were evaluated as part of a field-wide reinterpretation of log and core data for the Hemlock Reservoir, McArthur River Field, Cook Inlet, Alaska. To identify the conglomerates and sandstones which comprise this reservoir, a new method was developed for estimating the fraction of rock framework which is conglomerate. The method is based on the observation that, in this reservoir, the replacement of sand by nonporous pebbles results in poorer sorting and an overall decrease in porosity. Comparisons between core- and log-derived conglomerate estimates were used to calibrate and test the method.

The reservoir properties of conglomerates and sandstones in the Hemlock Formation differ significantly, and while depositional factors have most likely resulted in a heterogeneous distribution of conglomerates and sandstones, the core data are too sparse to resolve this distribution. A map of the log-derived conglomerate fraction is sufficiently controlled to provide detailed information on reservoir heterogeneities; trends on this map are consistent with depositional models for the Hemlock Formation. The conglomerate map was integrated into the waterflood management of the field; for wells from one platform this resulted in a greater than two fold increase in incremental oil production per dollar spent on reperforations.

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