Study on Chemical Combination Formulations for High Temperature and High Salinity Carbonate Reservoirs

Abstract

AbstractChemical flooding technique is one of effective EOR (Enhanced Oil Recovery) ways to improve the oil recovery for mature oilfield in China. It is usually applied successfully in low temperature and low salinity sandstone reservoirs, such as Daqing oilfield (45°C, 5,100 mg/L) and in Changqing oilfield (50°C, 4,700 mg/L). However, it is great challenges to develop chemical EOR formulations for the high temperature and high salinity carbonate reservoir. On the one hand, the high temperature and high salinity condition may cause decomposition of the conventional chemical agents with poor long-term stability. On the other hand, the oil types and compositions, rock surface property and pore structure are all different for sandstone and carbonate reservoirs. Therefore, it is necessary and important to development low cost and high efficiency chemical formulations for high temperature and high salinity carbonate reservoirs.In this paper, the betaine surfactant has been synthesized with cheap raw material of fatty acid, and its functional group of hydroxyl propyl sulfo hydrophilic group can improve the heat resistant and salt tolerant abilities; the star-polymer has been developed and the introduction of multi-functional monomer can inhibit the hydrolysis at high temperature and high salinity conditions. The new SP and ASP chemical formulations have been developed, and show good properties for high temperature and high salinity carbonate reservoir. The SP chemical formulations of the betaine and star-polymer show good heat resistant and salt tolerant capability. It could achieve ultra-low interfacial tension (less than 1.0×10-2mN/m) with temperature range from 30°C to 95°C, or salinity range from 5,000 mg/L to 220,000 mg/L.The effect of alkalis on interfacial tensions were studied, including Na2CO3, Na2SiO3, Na3PO4 and Na2B4O7. The ASP combination formulas with Na2B4O7 showed the best interfacial properties.The SP and ASP chemical formulations had good long term stability, and could maintain ultra-low IFT within 180 days, and the viscosity retention rates were greater than 90%.The dynamic adsorptions of this betaine were less than 1.0 mg/g rock, which can meet the requirement of field applications.After water flooding, the oil recoveries of the SP and ASP formulations increased about 22% (OOIP, Original Oil In Place) and the oil displacement efficiencies of chemical combination flooding reached to 75%.Excellent properties of chemical formulations with the sulfobetaine and star-polymer indicate that this EOR technology can be applied in high temperature and high salinity carbonate reservoir with or without alkaline.