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.
© 2006. Society of Petroleum Engineers
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History
- Original manuscript received:
15 November 2004
- Revised manuscript received:
17 February 2006
- Manuscript approved:
1 March 2006
- Version of record:
20 June 2006
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