Importance of Fines in Smart Water Enhanced Oil Recovery (SmW-EOR) for Chalk Outcrops

Abstract

In SmW-EOR it is generally believed that precipitation of brines must be avoided since it can have a negative impact on the SmW sweep efficiency. But substitution of Mg 2ϩ by Ca 2ϩ on calcite surfaces (a well-accepted phenomenon) can change the brine combination and enhance the possibility of fine formation at speciation. Considering this phenomenon we analyze the possibility of fines formation and its influence in SmW-EOR.To calculate the brine speciation and the amount of precipitate formed at different pressure and temperature conditions, we use the Extended UNIQUAC model for 61 SmW-EOR experiments reported in literature. Both the amount of available soluble SO 4 2-(aq) in the solution and the amount of CaSO 4 precipitation has been calculated and correlated to the corresponding oil recovery.Brine speciation after considering the substitution of Ca 2ϩ by Mg 2ϩ on chalk mineral surfaces showed possible precipitation of CaSO 4 in most of the brine solutions. The amount of CaSO 4 (s) precipitate formed, increased with temperature and consequently the dissolved soluble SO 4 2 -(aq) decreased. Increased concentration of Ca 2ϩ ,Mg 2ϩ or SO 4 2-ions compared to Sea Water-(SW) also enhanced the amount of precipitate formed. Increasing NaCl concentrations increased the solubility of SO 4 2-and Ca 2ϩ in SmW and decreased the amount of precipitate formed. The amount of precipitate formed in the pore space (after the substitution of Mg 2ϩ on calcite surface) consistently correlated to the increased oil recovery observed in various experiments. While in several cases additional oil recovery did not correlate to the amount of soluble SO 4 2-present in the SmW at equilibrium. These results together suggest that the substitution reaction on the mineral surface followed by solid fines formation is the fundamental reason behind the observed EOR. These results indicated that the observed wettability alteration in chalks may not be the primary cause but an additional effect of SmW-EOR.This study shows how Extended UNIQUAC model can be used as a rigorous mathematical tool for understanding of the SmW-EOR in chalk. It also quantitatively explains a series of previous experiments reported in the literature and shows the importance of fine formation in SmW-EOR, both through correlation between modeling and experiments.

Using Reaktoro for mineral and gas solubility calculations with the Extended UNIQUAC model

“…▪ Prediction of thermal properties and phase behavior of aqueous electrolyte systems (Thomsen et al, 1996). Over the past almost four decades, the extended UNIQUAC model has been further enhanced, extended, parameterized, and applied to various aqueous electrolyte systems and engineering applications (Aronu et al, 2011;Arrad et al, 2016Arrad et al, , 2017Arshad et al, 2016Arshad et al, , 2017Awan et al, 2010;Barzegar-Jalali et al, 2020;Bonalumi et al, 2016;Chakravarty et al, 2015bChakravarty et al, , 2015aChokradjaroen et al, 2012;Christensen & Thomsen, 2003Corrêa et al, 2023;Corrêa, Hao, et al, 2022;Darde et al, 2009Darde et al, , 2011Darde, Maribo-Mogensen, et al, 2012;Eftekhari et al, 2017;Faramarzi, Kontogeorgis, et al, 2009;Faramarzi, Kontogorgis, et al, 2009;Figueroa et al, 2016;Fosbøl et al, 2009aFosbøl et al, , 2009bFosbøl et al, , 2013García et al, 2005bGarcía et al, , 2006bGaspar, Arshad, et al, 2014;Gaspar et al, 2016;Gomis et al, 2022;Haghtalab & Peyvandi, 2012;Hashemi et al, 2020;Hingerl et al, 2014;Iliuta et al, 2000Iliuta et al, , 2002Kontogeorgis et al, 2022;Kovalenko et al, 2011;…”

Pore-Scale Investigation of the Ion-Tuned Water Effect on the Surface Properties of Limestone Reservoirs

“…Second, fines can be formed during the fluid flow due to salt precipitations. It was reported 70 that these newly formed CaSO 4 fines can contribute significantly to oil recovery. This mechanism provides an explanation for more efficient recovery by SW3Ca brine.…”