Research on Mechanisms of Alkaline Flooding for Heavy Oil

To investigate mechanisms of alkaline flooding for heavy oil, we designed three flooding systems, including NaOH, diethylamine, and compound alkali (a mixture of NaBO2 and Na2CO3; NaBO2/Na2CO3 = 2:1 by weight) and evaluated their performances for Binnan heavy oil by sandpack flooding tests. Results indicated that the displacement efficiency of alkaline flooding depended upon the concentration and type of alkali. Displacement efficiency increased with the increase of the alkaline concentration and basicity. It was relative to the type of emulsion generated by alkaline solutions to a certain degree but independent of the interfacial tension between alkaline solution/heavy oil. Although water-in-oil (W/O) emulsion may appear when heavy oil was mixed with some alkaline solutions in the phase test, not all of them could exhibit well performance in the sandpack flooding test. To further elucidate the mechanisms of alkaline flooding for heavy oil, it was compared to the water flooding process in a glass-etched microscopic model, and a conclusion was drawn that the penetration of alkaline solutions in crude oil was the main mechanism to improve sweep efficiency during alkaline flooding and W/O emulsion was just the derived result of alkaline solutions penetrating and not the basic reason for enhanced oil recovery (EOR) by alkaline flooding.