Aqueous Ketone Solution for Wettability Alteration in High-Salinity-High-Temperature Carbonate Reservoirs

Abstract

Abstract Enhanced oil recovery (EOR) has been studied for high-salinity high-temperature (HSHT) carbonate reservoirs, but their thermodynamic conditions, brine chemistry, and petrophysical properties tend to pose various technical challenges for both gas- and chemical-based EOR. This paper presents an experimental study of aqueous solution of 3-pentanone for EOR in a carbonate reservoir with a brine salinity of 224,358 ppm at a reservoir temperature of 99°C. The short dialkyl ketone was previously studied as a sole additive to injection brine for rapid wettability alteration in oil-wet carbonate rocks without affecting the water/oil interfacial tension; however, it had not been tested under HSHT conditions. The main objective of this research was to investigate the impact of 3-pentanone on convective oil displacement in oil-wet carbonate rocks under HSHT conditions. First, aqueous stability was confirmed for mixtures of 3-pentanone and two brines: formation brine (FB) with a salinity of 224,358 ppm and injection brine (IB) with a salinity of 54,471 ppm at reservoir temperature. Quantitative proton nuclear magnetic resonance (1H NMR) analysis was used to determine the solubility of 3-pentanone in FB and IB. Spontaneous and forced imbibition experiments were conducted to assess imbibition enhancement in oil-aged Texas Cream carbonate cores by a solution of 3-pentanone in IB (3pIB) and compared with IB. Afterward, corefloods with oil-aged carbonate cores were performed by injecting IB followed by 3pIB as a tertiary flooding scenario and also by injecting only 3pIB as a secondary flooding scenario. Analysis of the spontaneous imbibition and coreflooding results was assisted by history-matched numerical models where capillary pressure and relative permeability curves were obtained. These data were further used to infer wettability alteration potential of 3-pentanone solution. Because of the markedly different solubilities of 3-pentanone in injection brine (1.1 wt%), formation brine (0.3 wt%), and oil (first-contact miscible), material balance analysis of corefloods was performed to understand the transport of 3-pentanone through varying salinities from injection brine (54,471 ppm) and resident brine (224,358 ppm) while being mixed with in-situ oil. Spontaneous and forced imbibition tests confirmed the wettability alteration of oil-aged carbonate rocks by 1.1-wt% 3pIB. This was further supported by the slope analysis of temporal recovery data as well as analyzing history-matched capillary pressure and relative permeability data. Coreflooding results showed increased oil production rate and reduced residual oil saturation by 3pIB. Relative permeability data, through Lak and modified Lak wettability indices, also indicated a wettability alteration toward more water-wetness by 3-pentanone solution.