Abstract
We investigate the effect of different saturation histories relevant to various oil displacement processes (including secondary and tertiary gas injections) on three-phase gas/oil/brine relative permeabilities of water-wet sandstone. It is found that three-phase water (wetting phase) relative permeability is primarily a function of water saturation and shows no dependency upon saturation history. Three-phase gas (nonwetting phase) relative permeability is also a function of gas saturation as well as the direction of gas saturation change. Three-phase relative permeability to oil (intermediate-wetting phase) appears to depend on all phase saturations, and saturation history have no significant impact on it. Three-phase oil relative permeability shows weak sensitivity to initial oil saturation prior to gas injection. The functional forms of oil relative permeability with saturation, particularly at low oil saturations, are also examined. It is observed that, at high oil saturations where networks of oil-filled elements govern oil flow, oil relative permeability exhibits a quartic form with oil saturation whereas, at low oil saturations where flow is believed to be controlled by layer drainage, it shows a quadratic form . The quadratic form of three-phase oil relative permeability is consistent with the theoretical interpretation of layer drainage at the pore scale.
Highlights
The concurrent flow of three fluid phases, e.g., oil, gas, and brine, occurs frequently in petroleum reservoirs and during nonaqueous phase liquid (NAPL) migration in aquifers thereby warranting detailed studies of the process
We investigate the effect of different saturation histories on three-phase gas/oil/brine relative permeabilities of water-wet consolidated Bentheimer sandstone and on the stability of spreading oil layers and residual oil saturation
Since all the experiments were performed under the capillary-dominated displacement regime, viscous pressure drops may have played negligible role in trapping of nonwetting fluid during imbibition. This is consistent with the trends reported by Oak [1990] for Berea with a nitrogen/brine/dodecane fluid system and with the contact angles used by Piri and Blunt [2005b] to predict those trends
Summary
The concurrent flow of three fluid phases, e.g., oil, gas, and brine, occurs frequently in petroleum reservoirs and during nonaqueous phase liquid (NAPL) migration in aquifers thereby warranting detailed studies of the process. This multiphase flow property is a manifestation of complicated pore-level displacement physics as well as fluid-fluid and solid-fluid interactions and characteristics It can be either measured in the laboratory using representative rock-fluid systems or estimated using empirical correlations or physically based pore-scale models. Three-phase flow in porous media: A review of experimental studies of relative permeabilities, submitted to Reviews of Geophysics, 2013) reveals that there is a limited number of well-characterized studies on this subject over the past decades. This is mainly because laboratory measurements of threephase relative permeability are almost prohibitively difficult, costly, and time-consuming. Despite the difficulties involved, the recent surge in interest for better understanding of fundamentals of threephase flow as well as advances in experimental science and technology have led to renewed efforts in laboratory determination of three-phase relative permeability
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