The hybrid impact of modified low salinity water and anionic surfactant on oil expulsion from carbonate rocks: A dynamic approach

Experimental investigation of the sequence injection effect of sea water and smart water into an offshore carbonate reservoir for enhanced oil recovery

This study explores enhanced oil recovery (EOR) strategies, with a focus on carbonate reservoirs constituting over 60% of global oil discoveries. While "smart water" injection proves effective in EOR for carbonate reservoirs, offshore application challenges arise due to impractical volumes for injection. To address this, we propose a novel continuous injection approach, systematically investigating it on a laboratory scale using the Iranian offshore reservoir, Sivand. Thirty-six contact angle tests and twelve flooding experiments are meticulously conducted, with key ions, potassium, and sulfate, playing pivotal roles. Optimal wettability alteration is observed at 4 times potassium ion concentration in 0-2 times sulfate concentrations, driven by ionic strength and charge interactions. Conversely, at 3-5 times sulfate concentrations, the optimal contact angle shifts to 2 times potassium ion concentration, suggesting a mechanism change linked to increasing sulfate ion ionicity. A significant wettability alteration, evidenced by a 132.8° decrease, occurs in seawater with a twofold concentration of potassium ions and a fivefold concentration of sulfate ions. Micromodel experiments introduce an innovative alternation of smart water and seawater injections. The first scenario, smart water followed by seawater injection, reveals negligible post-seawater injection oil recovery changes. In contrast, the second scenario yields a maximum recovery of 7.9%. The first scenario, however, boasts superior overall sweep efficacy, reaching approximately 43%. This research expands understanding of smart water and seawater injection in EOR, presenting a viable solution for optimizing offshore carbonate reservoir recovery. The insights contribute to evolving EOR methodologies, emphasizing tailored strategies for varying reservoir conditions.

Study on anionic-nonionic mixed surfactant for enhanced oil recovery in a hypersaline reservoir

Hypersaline reservoirs are characterized by high salinity and high calcium and magnesium concentration. In order to enhance oil recovery of the hypersaline reservoirs, a specialized ternary mixed surfactant system composed of nonionic alkanolamide surfactants and anionic surfactant was developed in this study. Through careful analysis and optimization, lauric acid diethanolamide (LDEA), octanoic acid diethanolamide (ODEA), and sodium dodecyl sulfonate (SDS) were identified as promising candidates for the surfactant compounding system, and formed a ternary surfactant system composed of LDEA, ODEA, and SDS with the mass ratio of 4.64 : 0.66 : 1.00. Experimental results revealed that the interfacial tension of the system was consistently below 10-2 mN m-1 and could even reach ultra-low levels (10-3 mN m-1) under conditions of calcium and magnesium ion content of 2000 mg L-1, surfactant concentrations ranging from 0.05 to 0.3 wt%, temperature ranging from 50 to 80 °C, and salinity ranging from 20 000 to 50 000 mg L-1. Furthermore, the mixed surfactant system exhibited favorable wetting capacity and emulsifying power. The static adsorption capacities of the mixed surfactant on oil sands were less than 2 mg g-1. This study offered a novel strategy for the actual exploitation of reservoirs with high calcium-magnesium and high salinity.

Effect of the Type and Concentration of Salt on Production Efficiency in Smart Water Injection into Carbonate Oil Reservoir Rocks

Smart waterflooding is one of the most practical emerging methods of enhanced oil recovery in carbonate reservoirs. In this study, the effect of salt type and its concentration in smart water on oil recovery from a carbonate reservoir rock is investigated. A series of experimental measurements, including zeta potential (ZP), interfacial tension (IFT), and contact angle (CA), were conducted to examine the effect of ions on the oil/brine/rock interaction. IFT, ZP, and CA were also used as screening methods to select effective solutions for flooding experiments. The results of the study show that synthesized brines containing sodium acetate and potassium acetate salts have a significant effect on the reduction of IFT; however, rock surface wettability due to such brines is insignificant. The presence of organic salts in the injected water can alter the properties of the fluid and rock surface, leading to improved oil recovery. The salts can reduce the interfacial tension between the oil and water phases, making it easier for the water to displace and mobilize trapped oil. This effect is particularly beneficial in reservoirs with high oil-water interfacial tension as it enhances the capillary forces and improves the sweep efficiency. Smart water with sodium acetate (MSW.NaOAc) caused a 7% increase in oil production in the tertiary injection process due to IFT and CA reduction. The secondary injection of MSW.NaOAc led to an oil production efficiency of 76%, which is 10% higher than that of the secondary injection of seawater (SW), confirming the effectiveness of acetate ions in enhancing oil recovery. Doubling the concentration of sulfate ions in modified SW (MSW.NaOAc.2S) caused a 19% increase in oil production in tertiary injections after SW flooding. The secondary injection of MSW.NaOAc.2S produced a 13% increase in the recovery factor compared to SW flooding in the secondary mode. The main driving mechanism for oil mobilization was found to be wettability alteration, which is supported by the analyses of CA and ZP. This study confirms that the salt type and concentration present in a brine solution play a vital role in the movement of trapped oil in carbonate reservoirs.