Youyi Zhu

The research progress in the alkali-free surfactant-polymer combination flooding technique

Abstract Alkali-free surfactant-polymer SP flooding can avoid scaling, strong emulsification and corrosion caused by alkali, thus reduce the investment and operating cost. It is a new chemical flooding technology for Enhanced Oil Recovery (EOR) with a promising application prospect. The main problems of SP flooding are as follows: shortage of industrialized surfactant product with high performance, weak theoretical research on oil displacing mechanisms and main influencing factors, unsound evaluation methods, lack of pilot tests, and high technical risk. The main factors that affect the oil displacement efficiency of SP flooding are displacing fluid viscosity, interfacial tension, and emulsification strength of SP system. The high viscosity of SP flooding formula system is an important guarantee of EOR process. The lower the interfacial tension, the higher the oil recovery degree is. The emulsify ability of SP system can significantly affect efficiency of oil displacing. SP flooding process has obtained certain effects in pilot tests but there are still some problems. The formula adaptability and quality stability of surfactant product should be improved, the injection program should be optimized, and the field monitoring and process tracking and regulation should be strengthened.

Stability of Polymer and Surfactant Mixture Enhanced Foams in the Presence of Oil Under Static and Dynamic Conditions

Three different types of foaming agents including hydrocarbon surfactant TQ01, partial fluorinated surfactant BF01, and per-fluorinated surfactant QF01 exhibited good foaming ability and foam stability under 95°C high temperature and 32,325 ppm salinity conditions. The oil-tolerance ability order with respect to Malaysia Off-shore (MOS) crude oil for surfactant TQ01, BF01, and QF01 is TQ01 < BF01 < QF01. Introduction of polymer into the foam formula could significantly increase foam stability. Different polymers show different abilities of increasing foam stability. Spreading coefficient and entering coefficient are close to zero for surfactant BF01 foaming system and much less than zero for surfactant QF01 foaming system, so the oil-resistance ability of foam generated by surfactant QF01 is the strongest. For surfactant TQ01 foaming system, the calculated spreading coefficient and entering coefficient are greater than zero; therefore, the TQ01 foam system is more sensitive to MOS crude oil and its oil-resistance ability is the poorest. Core flooding test indicated that using the 0.4% BF01 and 0.2% YH1096 combined foaming formula could increase the pressure drop across the porous media significantly, indicating that strong foam was generated in the presence of MOS crude oil. GRAPHICAL ABSTRACT

A Novel Hydroxylpropyl Sulfobetaine Surfactant for High Temperature and High Salinity Reservoirs

Reservoirs with high temperature and high salinity are widely distributed in various countries, which contribute an important percentage of oil output in the world. Pilot tests show that chemical flooding technique is one of effective EOR (Enhanced Oil Recovery ) ways to improve the oil recovery for mature oilfields. The key technology of chemical flooding is to develop high efficiency surfactants with low cost. In this paper, the betaine surfactant has been synthesized with cheap raw material of fatty acid, and its functional group of hydroxylpropyl sulfo hydrophilic group can improve the heat resistant and salt tolerant abilities of the surfactant. The surfactant was characterized by Infrared Spectra, Raman Spectra and Element Analyzer. The analytical data show that the surfactant is consistent with the designed molecular structure, hydroxylpropyl sulfobetaine. The interfacial tension between the sulfobetaine solution and crude oils achieve ultra-low values ( less than 1.0×10-2 mN/m ) with temperature range from 30 °C to 90 °C, or salinity range from 20000 mg/L to 120000 mg/L, when the surfactant concentrations are from 0.05 wt% to 0.3 wt%. The parameters of hydroxypropyl sulfobetaine show that it is a suitable candidate for the oil-displacing agent due to its good long-term stability (within 180 days), low critical micelle concentration ( 4.74×10-5 mol/L ), low dynamic adsorptions ( 0.44-0.72 mg/g ), good injectivity and mobility. Oil recoveries increased 20 % - 24 % ( OOIP, Original Oil In Place) after water flooding, with both weak alkali ASP and alkali-free SP formulations combined the sulfobetaine. And the oil displacement efficiencies of weak alkali ASP or alkali-free SP flooding have reached to 73 % - 76 %. Excellent properties of the hydroxypropyl sulfobetaine indicate that it is a promising surfactant, which can be applied in reservoirs with high temperature and high salinity.

Effect of Main Factors on Oil Recovery of Surfactant-Polymer Flooding

Alkali-free surfactant-polymer combination flooding (SP flooding) can avoid side-effects encountered in alkali-surfactantpolymer (ASP) combination flooding, such as scaling and corrosion damaged the lifting system, strong emulsification resulted in produced liquid treatment problems and high cost of water handing. It can reduce the operation cost and be applied in oilfield easily. However, the oil displacement mechanism of SP flooding is not fully understood. In this paper, the main factors on enhancing oil recovery of SP flooding such as viscoelasticity, interfacial tension, emulsification and wettability of rocks surface were studied based on the Berea core oil displacement tests. The results of SP flooding physical simulation tests showed that: (1) High viscoelasticity of SP flooding was an important factor contributing higher oil recovery. When the ratio of viscosity of the displacement fluid to that of oil was more than 2, the higher oil recovery could be obtained by SP flooding. (2) The lower the interfacial tension, the higher the incremental oil recovery. When the interfacial tension of oil and water decreased to 5×10-3mN/m level, almost the highest incremental oil recovery of SP flooding could be obtained. Compared with the SP flooding system of solely high viscosity, more than 7-15% incremental oil recovery could be obtained by that of both lower interfacial tension and high viscosity (3) When emulsification intensity increased, the incremental oil recovery of SP flooding increased accordingly. Compard to the weak emulsification SP system, more than 6-11% incremental oil recovery could be obtained by means of enhancing emulsification ability. (4) Oil recovery of SP flooding at water-wet core condition was higher than that at intermediate-wet or oil-wet one. Studies on main factors for oil displacement efficiency of SP flooding are very important for the formula optimization of SP system, and they will provide foundation for scenario design of field tests and applications of SP flooding.

Effects of Calcium Ions on the Solubility and Rheological Behavior of a C22-Tailed Hydroxyl Sulfobetaine Surfactant in Aqueous Solution

Effects of calcium ions (Ca2+) on the solubility, aggregate structure, and rheological behavior of a C22-tailed zwitterionic surfactant, erucyl dimethyl amidopropyl hydroxyl sulfobetaine (EHSB), have been investigated in aqueous solution. In comparison with sodium ions (Na+), Ca2+ ions exhibit a much higher efficiency in decreasing the Krafft temperature (TK) of EHSB. Specifically, contrary to Na+ ions which have no obvious effect on the rheological properties of the EHSB solution, Ca2+ ions increase the viscosity of the EHSB solution at lower EHSB concentration, and enhance its elasticity at higher EHSB concentration. Moreover, Ca2+ ions raise the temperature needed for the elastic-to-viscous transition of the EHSB solution at higher concentration. At lower EHSB concentration, the hydrophobic interaction between the ultralong hydrocarbon chains induces a tighter packing of the hydrophobic chains by forming a more stretched configuration, while at higher EHSB concentration, the electrostatic attraction between Ca2+ ions and the sulfonate groups of EHSB induces a tighter packing of the headgroups by forming Ca2+-mediated bridges among the EHSB headgroups. Besides, the above interactions may strengthen the hydrogen bonding of OH groups and/or of C═O amide groups, which in turn facilitates the compact packing of the surfactant molecules in aggregates and promotes the growth and entanglement of wormlike micelles. Thus, the EHSB solution shows Ca2+-dependent rheological behaviors. The solubility and rheological properties of the ultralong chain surfactant solution can be simultaneously improved with the addition of divalent Ca2+ ions.