Evaluation of a Wettability Modifier on Improving Oil Recovery in Fractured Reservoirs

Abstract

Abstract Enhanced Oil Recovery (EOR) methods using injection of cost-effective, water-soluble chemical additives (e.g., surfactants and mutual solvents) have great potential for increasing oil recovery from low-permeability fractured reservoirs. In a previous paper (Alghunaim et al., 2021), we presented experimental results pertaining to the efficacy of using a 1% solution of 3-pentanone (a mutual solvent) and separately a 1% non-ionic surfactant solution injected in four unfractured Permian Basin carbonate cores saturated with a low-salinity brine. The experiments indicated that we produced substantial amounts of oil from the four non-fractured Permian Basin San-Andres cores with permeability ranging from 2.67 mD to 17 mD, and porosity from 7.4% to 12.14%. In the experimental study pertaining to this paper, we used a fractured and an unfractured sandstone core to demonstrate oil recovery potential of 3-pentanone. The main factors that affect oil recovery from fractured reservoirs are preferential flow through fractures that provide large surface areas, matrix rock heterogeneity, and rock wettability. The wettability modifying agents reduce both the interfacial tension between oil and water and the water-oil contact angle to enhance oil recovery. The laboratory assessment included measurements of interfacial tension, rock wettability alteration, and incremental oil recovery beyond waterflood. To quantify the efficacy of 3-pentanone, coreflooding experiments included injecting this mutual solvent both in an unfractured core and a fractured core in a Colton sandstone from Central Utah. The effects of changing concentration of 3-pentanone and duration of soaking period before injecting water were also investigated. The results showed that the oil recoveries from the unfractured core and fractured core at the end of the flooding tests were 59.85% and 64.28%, respectively with the incremental oil recovery of 7% and 22%, respectively. The incremental oil recovery from 3-Pentanone can be explained by the combination of various mechanisms that includes a slight reduction in interfacial tension, alteration of rock wettability from water-wet to strongly water-wet (contact angle reduced from 38° to 18°) and ketone partitioning into the oil phase with a reduction in oil viscosity and increased oil mobility. The increase in enhanced oil recovery by ketone solution in the fractured core is probably due to the increase in mass transfer surface area between the fracture and the rock matrix. The 3-pentanone solution provides an operationally simple, environmentally friendly, and cost-effective EOR method in low-permeability formations.