How Pore-Scale Attributes May Be Used to Derive Robust Drainage and Imbibition Water Saturation Model
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SPWLA Distinguished Speaker Series. The use of fluid pressure measurements and resistivity-derived water saturation models to predict a free water level depth often has limited applications in reservoirs experiencing complex saturation histories. However, the Almond formation at the Wamsutter field presents some characteristics (i.e., unchanged subsurface structure after hydrocarbon charge) that make a saturation-height modelling exercise worthwhile.
Composite drainage capillary pressure (Pc) curves are built by combining stressed mercury intrusions with the centrifuge Pc when wetting phase saturations are lower than 40%. Composite imbibition Pc curves are constructed by combining stressed mercury extrusion tests with counter current imbibition-derived maximum gas trapped saturation.
Preliminary observations in tens of wells show that the reference resistivity-derived water saturation can be fitted by drainage saturation-height functions in the majority of the Almond section. Some upper Almond shoreface bars display anomalously high water sat which could be explained by imbibition of water due to trap leaking or by reservoirs being not fully charged.
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German Merletti is Field Study Petrophysicist at BP. His current role with the Unconventional Reservoirs Technology team includes developing and implementing new workflows for characterizing tight-gas reservoirs in North America and the Middle East. German has been covering a variety of petrophysical and geophysical roles with Repsol-YPF for 8 years in Argentina and the last 10 years with BP in Houston. He holds a BSc in Geological Sciences from The National University of Cordoba (Argentina) and an MSc in Seismic Petrophysics from UT Austin. German is completing a doctoral thesis focused on integration of petrophysical, sedimentary and petrographic facies also in UT Austin.