A STUDY OF GAS BUBBLE FORMATION MECHANISM DURING FOAMY OIL DEPLETION EXPERIMENT

Solution gas drive is an effective way to yield oil recovery in some heavy oil reservoirs and is also identified as foamy oil, which shows the characteristics of low gas-oil production ratio, high production rate, and exceeds oil recovery prediction. Although many laboratory investigations and field observations were published, the mechanism of gas bubble motion remained an essential issue. In this study, a sandpack study is designed to investigate a foamy oil displacement mechanism by CT scanning. According to oil and gas production during the entire process, there are three stages corresponding to compressibility single oil flow, foamy oil flow, and channel gas flow. Combining oil saturation images and their histograms, the limit of minimal gas generation saturation and the critical gas saturation for gas phase to flow can be confirmed and a series of formulas is created to identify the size and volume of bubbles. The results indicated that the foamy oil stage takes the major contribution to the whole process, and gas presents as disconnected bubbles in this stage to better use the expansion energy of gas until the gas saturation broke through the critical gas saturation to form a continuous gas phase, which decreases the oil recovery.