YI Xiangyi, ZHANG Ziwei, XIA Tao, DAI Yating, WU Yuanqin
The emulsion of crude oil and spent acid after acid fracturing treatment brings many troubles to production, such as increasing the loads of pump and pipe, causing corrosion and wax precipitation of pipe, and so on. Therefore, before trial-production we should find a way to break the emulsion which is made of residual acid and crude oil and then dehydrate it. In order to measure the demulsification effect and time of the mixed emulsion, demulsification experiments of emulsion of crude oil and three different spent acids with different concentrations are conducted in the laboratory. The spent acids include gelled acids, cross-linked acids, insitu gelled acids which are widely used in the field. Through analyzing all the impact factors, the results show that the demulsification efficiency of gelled acid is the best, followed by cross-linked acid, and the efficiency of in-situ acid is the worst. At the simulated bottom hole temperature of 90℃, the dehydration rate after demulsification of emulsion of crude oil and spent gelled acids is over 98%. The lower the acid concentration is, the better the demulsification efficiency will be. This feature is most obvious when in-situ acids are used. The longer the time taken, the better the demulsification efficiency will be. But the demulsification ends after 90 min.The demulsification is fast and the dehydration rate is high at high temperatures. However, with the production of the well, crude oil flows to the bottom hole from the reservoir and the temperature declines, so the dehydration rate may decrease.