Solution gas drive is an effective way to yield large oil recovery in some heavy oil reservoirs,and it is also identified as foamy oil. Due to the high viscosity of heavy oil that prevents gas bubbles to move,bubbles do not form a continuous gas phase compared with those in conventional oil reservoirs. Although many laboratory investigations and field observations were published around this phenomenon,the mechanism of gas bubble motion remained an essential issue. In this study,a sandpack study is designed to investigate foamy oil displacement mechanism by CT scanning. According to oil and gas production during the entire process,there are 3 stages corresponding to compressibility single oil flow,foamy oil flow and channel gas flow and foamy oil flow accounts for the major recovery. Combining oil saturation images and their histograms,the size and volume of bubbles is determined. Gas bubbles are formed in the foamy oil flow stage,and the quantity of bubbles increases exponentially with depletion pressure decreasing. When it enters into gas channelling flow stage,a continuous gas phase develops. Analyzing oil saturation images of inlet and outlet sections turn out that the low oil saturation regions expand together near the inlet but shows a dispersed distribution at the outlet,which indicates that free gas phase may formed near the inlet and gas bubbles are not connected and foamy oil energy is still effective to enhance oil recovery at the outlet.
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