The Phase Behavior Study of Air-foam Flooding in Changqing Ultra-Low Permeability Reservoirs

Abstract

For phase change characteristics of air foam flooding in Changqing ultra-low permeability reservoirs,  experiments were performed with the air and the gas-phase oxidation of P-X diagram under reservoir conditions using the PVT high pressure physical device and gas chromatograph. The phase behavior of crude oil and air bubbles after multiple contacts was determined by PVT simulation and the phase equilibrium model. The critical temperature and critical pressure of crude oil were determined to be 424.4? and 9.85MPa. Results show gas dissolved in crude oil after oxidation was strong in the air under the same pressure. Because the foam system and crude oil emulsification during contact have produced multiple contact oxidation, the effect was less than that in air and oil, resulting in a relatively small oxidation of C2-C6, while the oxidation of C7-C16 was relatively more. Furthermore, the trend of gas phase composition approaching C2-C6 was relatively slow, while oil phase composition was closer to C7+, due to the increase in the C7-C16 component. The study provides important insight for miscible flooding and non-miscible flooding applications, as well as for gas injection project design.