Pore-Level Mechanics of Forced and Spontaneous Imbibition of Aqueous Surfactant Solutions in Fractured Porous Media

Abstract

Water flooding typically recovers about 50% of the original oil in place leaving much oil in the reservoir. Recovery efficiency in fractured reservoirs can be dramatically lower in comparison to conventional reservoirs because water channels selectively from injector to producer leaving considerable oil within the matrix and uncontacted by injected water. An enhanced recovery process is needed to access such oil held in the reservoir matrix. Addition of aqueous surfactants to injection water dramatically reduces oil/water interfacial tension and surfactant may adsorb to oil-wet rock surfaces inducing a shift in wettability that improves the imbibition of water. At the pore level, capillary forces are responsible for oil trapping and generally dominate over viscous and gravitational forces. Because of the reduction in interfacial tension between oil and water with the addition of surfactant, the role of capillary forces on fluid flow can be minimized. When gravity parameters are large enough to give a Bond number (ratio of gravity to capillary forces) greater than 10, gravitational forces become more dominant and oil held with rock matrix by capillarity may be released as a result of buoyancy. In this work, we use experiments conducted in two-dimensional micromodels to investigate the effect of gravity at low interfacial tension. The micromodels have the geometrical and topological characteristics of sandstone and the network is etched into silicon. Porelevel mechanics are observed directly via a reflected-light microscope. A screening study of sulfonate and sulfate surfactants was conducted to choose an appropriate system compatible with the light crude oil (27°API). A variety of flow behavior through the microscope is investigated including forced and spontaneous imbibition. Results are illustrated via pore-level photo and image analysis of microscopic pictures of the micromodel. Forced displacements are conducted at realistic flow rates to maintain a 1 m/day Darcy velocity and at surfactant concentrations of 0.9% to 1.25%. Forced displacement with a horizontal or vertical positioning of the micromodel yields dramatic improvement of recovery for surfactant injection cases. Most of the oil retained after a waterflood was recovered by tertiary injection of surfactant solution. In comparison, about 25% oil saturation remained after a waterflood.

EOR of Spontaneous Imbibition by Surfactant Solution for Tight Oil Reservoirs

“…Gautam et al demonstrated an imbibition model with the presence of fracture fluid flow using the droplet detachment model [19]. Most of the past research concerning the analytical or numerical model of imbibition is based on the nonlinear diffusion equation [20,21,22,23,24]. The numerical model of imbibition considering the effects of surfactant, which are wettability alteration and IFT, were also established [25,26].…”

Impact of Chemical Flood Mode on Oil Recovery in Fractured Carbonates

“…They showed that imbibition of wetting phase from the fracture into the matrix is proportional to the volume of injected water at low injection rates (filling fracture regime) and proportional to the square root of time at high flow rates (instantly-filled fracture regime). Alshehri et al (2009) investigated the improvement of oil recovery in the presence of gravity when IFT is reduced. The experiments were also conducted on silicon micromodels and it was found that oil recovery improved to about 90% (compared to 74% when gravity had no effect) in a scheme using spontaneous imbibition followed by forced imbibition scheme.…”

Study on the Countermeasures and Mechanism of Balanced Utilization in Multilayer Reservoirs at Ultra-High Water Cut Period

“…As water injection methods continue to evolve, oilfields are entering periods of high water cut or even ultra-high water cut stages [1][2][3][4][5][6]. This leads to highly dispersed remaining oil, presenting significant challenges for oilfield development [7][8][9][10].…”