Effect of Solvent on Steam Recovery of Heavy Oil

Abstract

SPE 14223Summary. Solvents and light' ends of cmdes ze frequently used as difuen& to facilitate pumping and pipeline kmspotion of heavy cmdes. The use of solvent done for in-situ recovery of heavy oil tends to be limited because of its high cost; however, the usc of solvent as an additive to steam processes has been tested both in the laboratory and in the field. The results of these tests are mixed. fn this study, we use numerical experiments to defineate the recovery mdanism of a steam-slug process when solvents are present. A gocd understanding of the mechanism will help provide an interpretation of the conditions under which solvents can improve steam oil recovery. The study focuses on the use of small quantities of solvent-i. e., no more than 10% of the steam volume. IntroduatlorrSteam injection is widely used for heavy-oil recovery. Using small amounts of ,solvent (fess than 10% of steam volume) with steam has pOtentiaJ io increase oil recove~. While solvent is known to benefit oif mcove~by reducing oil viscosity, the use of small amounts is insufficient to affect a significant volume of oif. In this simulation study, we found that a smafl amount of solvent can im. prove sweep by creating a mobility transition zone. When coinjected with steam, the vaporized solvent travels with steam and condenses in the cooler regions of the reservoir. R then mixes with oil, creating a transition zone of Iower-vismsity fluid between the steam and the heavy oif. The mobiMy ratio of the displacing and displaced fluids is improved, thus suppressing viscous fiigering and improti!ng sweep.The placement of the solvent in &e resemoir is crucial to the process performance because it determines the location of the hansition zone. The solvent placement is controlled by the injfxtion procedure and the solvent volatihiy. For example, when solvent is injected before steam, or a heavy soIvent witi low voladlity is coinjected with steam, incremental recovery is poor because of inadequate transition-zone generation in the reservoir.Although deftition of solvent volafll~depends on reservoir pressure and temperamre, fight solvmts generally include C02, ethane, propane, amd other gases, while heavy solvents generally include hydrocarbon liquids in the C 16to Cm range. Naphtha will be considered a medium solvent. Light solvents give earlier recovery and~eater recovery efficiency in km of less solventloss. Medium solvents give tie most improvement @ total oif production at somewhat higher solvent loss. Heavy solvents do not improve recovery. Previous WorkThe useof various solvents in conjunction with steam has been reporkd in the literature. Balier, Farouq .4di and Snyderl studied naphtha injection before steam injection in a two-dimensional (2D) vertical mcdcl Elfed with tar sand. Naphtlm was found to be highly effective in opening a steam flow path in a homogeneous sandpack but broke through quickIy in a pack with a highly permeable channel, AIikban and Famuq .41i2 further studied the steamdrive solventslug process in a linear celf model pac...

Modeling and measurement of thermo-physical properties for Athabasca bitumen and n -heptane mixtures

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Light- and Heavy-Solvent Impacts on Solvent-Aided-SAGD Process: A Low-Pressure Experimental Study

“…Naphtha has been demonstrated to improve recovery, mainly by reducing bitumen viscosity and thereby improving recovery in the water-swept portions of the reservoir, making moreefficient use of the drive energy provided by the CO 2 or ethane. Shu and Hartman (1988) conducted a series of simulation studies to investigate the effect of solvent type and concentration. They categorized the solvents into light, medium, and heavy solvents, according to their respective volatility (high, medium, and low) under reservoir conditions during thermal recovery.…”

Effects of Solvent Properties and Injection Strategies on Solvent-Enhanced Steam Flooding for Thin Heavy Oil Reservoirs with Semi-Analytical Approach

“…Thus, it is assumed that the diffusion coefficient is proportional to the contact area in a limited distance beyond the edge of the steam front, as illustrated in Figure 3b. The limited distance is defined as the effective operating thickness of the solvent, which is determined by the volatility of solvent; 5. medium solvents (C 6 -C 12 ) are considered to provide the greatest increase in total oil production because they can both travel with the steam in a vaporized phase and condense in the cooler regions of the reservoir and diffuse in the crude oil [21]. Light solvents (CO 2 , C 1 -C 5 ), which have considerably higher volatility, are believed to transport further into the reservoir and thus increase the operating thickness when co-injecting with medium solvents.…”