LAUSR

ABSTRACT In order to prevent and eliminate the asphaltene precipitation during gas flooding, the rules of the changes of the pressure under different conditions are systematically studied by the laser solid detection system, the light transmission method, and the P–T phase diagram when the asphaltene precipitation occurs. When the pressure is reducing to a certain value, the penetrating light intensity of the crude oil is markedly decreased, which shows that the pressure at this point is the pressure of the onset of asphaltene precipitation (AOPP). The AOPP value decreases with an increase in the temperature. During gas flooding, the AOPP value increases with an increase in the content of gas in the crude oil, and these two nearly do have a linear relationship. According to the P–T phase behaviors of the gas–crude oil system, with an increase in the content of gas in the crude oil, the asphaltene precipitation envelope curve (APE) is gradually moved up, which shows that the possibility of asphaltene precipitation is much higher. During oil production, for the oil reservoirs with rich asphaltene, the production pressure drop should be kept a small value to ensure that the flowing bottom-hole pressure is higher than AOPP and it is necessary to help complement producing energy timely by using water injection, gas injection, etc. Besides, according to the intersection of T–P curve and APE curve in the P–T phase diagram, the location where the asphaltene precipitation occurs in the wellbore can be roughly predicted. The experimental results can provide the theoretical foundation for taking measures to prevent and eliminate the asphaltene precipitation.