The present study investigates the aqueous stability of polyethylene glycol and oleic acid-based anionic surfactants through the dynamic light scattering (DLS) and zeta potential methods, for application in enhanced oil recovery (EOR). Polyethylene glycol dioleate sulfonate (PDOS) surfactant solutions were prepared in concentrations of 0.05, 0.1, 0.3, 0.5, and 1 wt% in deionized water. Aqueous stability of PDOS was assessed by measuring the droplet size over five days, using nano particle analyzer HORIBA SZ-100 at 25 o C. Results show that good aqueous stability of PDOS was achieved at concentrations of 0.1 to 1 wt%, but with the droplet size becoming unstable at the lowest concentration of 0.05 wt%. The polydispersity indices were classified into polydisperse distribution type recorded as 0.3 to 0.5 at concentrations of 0.05 and 0.1 wt% and 0.2 at concentrations of 0.3 to 1 wt%. The critical micelle concentration (CMC) of PDOS was 0.3% and the interfacial tension of PDOS surfactant above the CMC was around 10-3 dyn/cm. The zeta potential of PDOS surfactant without the addition of salt in concentrations of 0.05, 0.1, 0.3, 0.5, and 1 wt% was highly stable up to-96.8,-90.5,-89.6,-82.3, and-64.4 mV, respectively. With the addition of salt they were moderately stable at a concentration of 1 wt%. The conductivity increased with increasing concentration. The zeta potential of PDOS with the addition of salt was moderately stable in a concentration of 1%. Although PDOS with concentration of 0.05% showed a high value of zeta potential with the addition of salt, there is no guarantee that the PDOS surfactant solution will be stable for five days.
The formation of microemulsion in the injection of surfactant at chemical flooding is crucial for the effectiveness of injection. Microemulsion can be obtained either by mixing the surfactant and oil at the surface or injecting surfactant into the reservoir to form in situ microemulsion. Its translucent homogeneous mixtures of oil and water in the presence of surfactant is believed to displace the remaining oil in the reservoir. Previously, we showed the effect of microemulsion-based surfactant formulation to reduce the interfacial tension (IFT) of oil and water to the ultralow level that suffi cient enough to overcome the capillary pressure in the pore throat and mobilize the residual oil. However, the effectiveness of microemulsion flooding to enhance the oil recovery in the targeted representative core has not been investigated.In this article, the performance of microemulsion-based surfactant formulation to improve the oil recovery in the reservoir condition was investigated in the laboratory scale through the core flooding experiment. Microemulsion-based formulation consist of 2% surfactant A and 0.85% of alkaline sodium carbonate (Na2CO3) were prepared by mixing with synthetic soften brine (SSB) in the presence of various concentration of polymer for improving the mobility control. The viscosity of surfactant-polymer in the presence of alkaline (ASP) and polymer drive that used for chemical injection slug were measured. The tertiary oil recovery experiment was carried out using core flooding apparatus to study the ability of microemulsion-based formulation to recover the oil production. The results showed that polymer at 2200 ppm in the ASP mixtures can generate 12.16 cP solution which is twice higher than the oil viscosity to prevent the fi ngering occurrence. Whereas single polymer drive at 1300 ppm was able to produce 15.15 cP polymer solution due to the absence of alkaline. Core flooding experiment result with design injection of 0.15 PV ASP followed by 1.5 PV polymer showed that the additional oil recovery after waterflood can be obtained as high as 93.41% of remaining oil saturation after waterflood (Sor), or 57.71% of initial oil saturation (Soi). Those results conclude that the microemulsion-based surfactant flooding is the most effective mechanism to achieve the optimum oil recovery in the targeted reservoir.
Most of Indonesia’s oil field has been producing the oil for long period of time. For this reason, enhanced oil recovery (EOR) method becomes the most promising method to improve oil production for the country. Chemical flooding, especially polymer flooding is the simplest and the most commonly applied chemical enhanced oil recovery technique, since it can be used after water flooding process. Screening is considered the first step in evaluating and selecting potential polymers for reservoirs. Therefore, this paper aims to select partially Hydrolyzed Polyacrylamide (HPAM) base polymers to find suitable polymer for a targeted mature reservoir in Indonesia. A polymer screening study was carried out on 3 HPAM polymers to identify a potential candidate which can withstand reservoir conditions. These are Kerui, Zekindo, and FP 3630S. Initially, a comprehensive rheological (viscosity, shear rate) study was conducted at various polymer concentrations (500 - 2500 ppm) and brine to investigate the polymers. Then, filtration and screen factor test was conducted at various concentrations (1000 - 2000 ppm). Then, a thermal stability test was conducted at anaerobic condition and 140 °F for 2 months. Finally, for oil recovery used core flooding test. Based on the result of the test, FP 3630S with a concentration of 2000 ppm was chosen for the core flooding test. The test was designed in 3 steps: At first, water injected into the sample, followed by polymer-solvent at 2000 ppm concentrated of 1 PV, the finally injected by water. The results of core flooding showed oil recovery of 28.93 % OOIP. Finally, this study was performed to develop screening criteria and to correlate oil recovery prediction. HIGHLIGHTS One of the efforts to increase old field production is by choosing the right type of polymer to be injected Polymer screening was carried out through testing stages, namely rheology, filtration and screen factor, thermal stability, and core flooding Selected one type of polymer that meets all the qualifications of the screening tests GRAPHICAL ABSTRACT
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