Summary

The evaluation of thermal-recovery processes requires relative permeability functions, as well as information about the effects of temperature on these functions. There are significant challenges encountered when estimating relative permeability from laboratory data, such as the accuracy of measurements and generalized assumptions in the interpretation techniques. A novel method is used here to estimate relative permeability and capillary pressure from in-situ aqueous-phase saturation profiles obtained from X-ray computerized tomography (CT) scanning during high-temperature imbibition experiments. Relative permeability and capillary pressure functions are interpreted simultaneously, including possible nonequilibrium effects. Results obtained show a systematic shift toward increased water-wettability with increasing temperature for diatomite reservoir core. The measured changes in relative permeability are linked to the effect of temperature on the adhesion of oil-coated fines to rock surfaces and, ultimately, to rock/fluid interactions.

Introduction

An understanding of the effects of temperature on wettability and relative permeability functions is essential to optimize and forecast the results of diatomite thermal-recovery projects. Most of the controversy regarding the effect of temperature on relative permeability is caused by the mechanisms involved in rock-wettability change that are dependent on both fluid and rock characteristics. A secondary, and equally important, problem is the technique used to process the data, such as oil recovery, phase saturation, or pressure, as well as data interpretation in the form of relative permeability curves.

This paper re-examines the influence of temperature on rock/fluid interactions and heavy-oil relative permeability of diatomite from a core-level experimental and a pore-level perspective. We find experimentally and theoretically that fine particles are released from pore walls under conditions of elevated temperature, high pH, and moderate to low aqueous-phase salinity. The release of fines correlates with changes in relative permeability curves toward greater water-wetness. The mechanism of fines release provides new understanding of a mode of wettability alteration at elevated temperature.

This paper is organized as follows. First, a synopsis of the literature is presented, followed by a discussion of recent developments in the understanding of wettability alteration. Second, the experimental method and the relative permeability interpretative methodology are outlined. Third, relative permeability results interpreted from field core samples at temperature are presented. Discussion and conclusions round out the paper.

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