科研之友
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摘要
The amount of synthetic surfactants required for a surfactant flood can be minimized by the addition of an alkali. An alkali reduces surfactant adsorption on sandstone and carbonate rocks, and generates in-situ surfactant with acidic crude oils. Many reservoirs, especially carbonates, contain gypsum (or anhydrite), which is sparingly soluble in water. In such cases, a conventional alkali such as sodium carbonate cannot be added to alkaline-surfactant-polymer (ASP) formulations because it precipitates as CaCO3 on interacting with gypsum (or anhydrite). In this study, we test ammonia as an alkali to perform ASP floods in carbonate cores containing gypsum. The concentration of calcium ions in the presence of gypsum when ammonia is used as alkali can be as high as 2000 ppm, depending on the brine salinity and composition. Therefore, surfactant and polymer selection study was performed to identify suitable candidates under high calcium concentrations. Oil recovery experiments were performed in carbonate cores containing gypsum, using ammonia as the alkali. PHREEQC, the USGS geochemical simulator, was used for reactive transport modeling and was found to be an effective tool for designing these corefloods. High pH propagation and good oil recovery was observed in the ASP coreflood performed in a carbonate core containing gypsum. Addition of sodium sulfate in injection brines decreased gypsum dissolution. Gypsum dissolution was also lower at higher temperatures and lower NaCl concentrations. The surfactant retention in the ASP coreflood using ammonia, however, was found to be about the same as that of the SP coreflood, even though a high pH propagation was observed during the ASP coreflood. A good agreement was observed between the measured concentration of the effluent ions from the corefloods and the PHREEQC simulations.
- 出版日期2016-11-15
