Temperature-resistant and salt-tolerant mixed surfactant system for EOR in the Tahe Oilfield

A new temperature-resistant and salt-tolerant mixed surfactant system (referred to as the SS system) for enhancing oil recovery at the Tahe Oilfield (Xinjiang, China) was evaluated. Based on the analysis of the crude oil, the formation water and rock components in the Tahe Oilfield, the long-term thermal stability, salt tolerance and the ability to change the wettability, interfacial activity and oil washing efficiency of the mixed surfactant system were studied. The system contains the anionic surfactant SDB and another cationic surfactant SDY. When the total mass concentration of the SS solution is 0.15 wt%, m(SDB)/m(SDY) ratio is 1 to 1, and excellent efficiencies are achieved for oil washing for five kinds of Tahe Oilfield crude oils (more than 60%). In addition, after adding cationic surfactant, the adsorption capacity of the surfactant is further reduced, reaching 0.261 mg/g. The oil displacement experiments indicate that under a temperature of 150 °C and a salinity of 24.6 × 104 mg/L, the SS system enhances the oil recovery by over 10% after water flooding. The SS anionic–cationic surfactant system is first presented in the open literature that can be successfully applied to obtain predictions of Tahe Oilfield carbonate reservoirs with a high temperature and high salinity.

THE EFFECT OF HARDNESS AND TEMPERATURE ON INTERFACIAL TENSION OF INDIVIDUAL AND MIXED SURFACTANT SYSTEM

Surfactant flooding is one of the chemical enhanced oil recovery (CEOR) techniques that can be used to improve oil recovery. The surfactant injection reduces the oil-water interfacial tension and mobilizes residual oil towards the producing well. In this paper, the performance of alkyl ether carboxylate (AEC) and calcium lignosulfonate (CLS) in individual and mixed surfactant systems were investigated based on their ability to reduce the interfacial tension through a spinning drop method. The interfacial tensions of individual and mixed surfactant systems in different brine systems were measured against decane at 25°C and 98°C. The results show that the individual and mixed surfactant systems in 3.5 wt.% NaCl brine has a significant reduction in interfacial tension at 98°C. In contrast, the presence of hardness in 2.5 wt.% NaCl and 1.0 wt.% MgCl2 brine reduces the interfacial tension of the individual AEC surfactant system and mixed surfactant system significantly at 98°C except for the individual CLS system. Meanwhile, the interfacial tension of mixed surfactant system decreases with increasing surfactant concentration in two brine systems and at 98°C. The findings show the significant application of the AEC and CLS surfactant mixture considering the harsh reservoir conditions for the chemical enhanced oil recovery application.

CdSe Quantum Dots to Quantum Rods: Transition Studies and Evaluation of Sensitivity as Transducers for Biosensing Glucose

Background: The estimation of glucose level in the blood serum, has been widely used as a clinical indicator of diabetes. Optical and electrochemical sensing of glucose widely uses Glucose Oxidase (GOD) enzyme, as the catalyst for glucose oxidation, which releases hydrogen peroxide (H2O2). Optical biosensors are superior to their electrochemical counter-parts as they are resistant to electromagnetic interference, easier to fabricate into a microdevice and require low power supply. The quantum-dot-based biosensors work on the phenomenon of fluorescence quenching following the release of H2O2. Methods: The CdSe nanoparticles are prepared in two series by room-temperature microemulsion method. In series A, only AOT surfactant is used to synthesize spherical CdSe nanoparticles. In series B, the mixed surfactant system of AOT and lecithin is used to synthesize anisotropic CdSe. The morphology and crystallography is studied as the CdSe shape changes from spherical to rod-like. As the CdSe nanoparticles are studied from spherical to rod-like morphology, the transducing sensitivity of these nanoparticles is evaluated with respect to glucose biosensing. The effects of size and shape are studied, based on the fluorescence quenching by H2O2 solutions. The sensitivity of proposed nanoparticles, is evaluated as a function of size, shape, surface area and number concentration of CdSe nanoparticles. Results: The spherical CdSe nanoparticles are found to increase in size as R(water-to-surfactant ratio) is increased from 4 to 12, in series A. Also, the aspect ratio of CdSe nanoparticle is found to increase from 4.2 to 12.8 as the ratio of AOT to lecithin is varied from 1:0.5 to 1:3. The decrease in sensitivity index is seen with increasing surface area for both series A and B. The sensitivity is decreasing again with increasing maximum dimension of the CdSe nanoparticle in the dispersion. While the trend is reverse in case of the number concentration for CdSe nanoparticles synthesized in series B. Conclusion: From the data presented, it can be safely concluded that the sensitivity indices for series A are better than those for series B, for the same values of a) the total surface area of CdSe nanoparticles, b) total number concentration, and c) maximum dimension of CdSe nanoparticles. Also, the single surfactant system (series A) is simple, cheaper and more reproducible to synthesize the CdSe nanosheres, as compared with the mixed surfactant system forming CdSe quantum rods (series B). With these points, it is reasonable to report that CdSe spherical QDs are better candidates for glucose biosensing, as compared to CdSe quantum rods.