It was an argued issue concerning effects of emulsification in chemical combination flooding process. For example, it may increase oil displacement efficiency. On the other hand, it makes the produced liquid handing to be more difficult. How does emulsification impact on oil recovery and produced liquid handing, and how to control emulsification degree are significant issues that are greatly concerned by engineers.
Effect of emulsification on oil recovery of chemical combination flooding was investigated based on emulsification intensity index quantitative measurements and Berea core flooding experiments. Field tests results domestrated that emulsification could remarkably influence oil recovery and produced water handing process.
Core flooding tests showed that enhanced oil recovery by strong alkaline alkali-surfactant-polymer (ASP) flooding, weak alkaline ASP flooding and surfactant-polymer (SP) flooding was different under the same interfacial tension (IFT), viscosity and slug size conditions. The incremental oil recovery after water flooding was about 23%-25%, 20%-23% and 17%-19% respectively as chemical slug size of 0.5PV. The emulsification intensity indexes for different formula were measured. It indicated that the sequence of emulsification intensity index of the three kinds of flooding systems was strong alkaline ASP flooding > weak alkaline ASP flooding > SP flooding. Core flooding experiments of chemical combination flooding with serial emulsification intensity index showed that incremental oil recovery could be increased by 6%-10% with stronger emulsification degree than that with weaker emulsification index.
ASP flooding field tests in Daqing Oilfield showed the different results in incremental oil recovery between strong alkaline ASP and weak alkaline ASP floodings. Emulsion stability of produced liquid from strong alkaline ASP flooding was stronger than that from weak alkaline ASP flooding. The special de-emulsifier and more complicated liquid treatment process were used in strong alkaline ASP flooding field tests. The cost was much higher than that of weak alkaline ASP flooding.
From the above experiments and field tests results, moderate emulsification is necessary for chemical combination flooding. From the view of overall investment and outcome ratio, weak alkaline ASP flooding may be more favorable for expanding application in oilfield than its counterpart of strong alkaline ASP flooding.