Numerical Study on Proppant Transport in Supercritical Carbon Dioxide under Different Fracture Shapes: Flat, Wedge-Shaped, and Bifurcated

Abstract

As a new type of waterless technology, supercritical carbon dioxide fracturing has been widely studied by scholars in recent years, and the migration characteristics of the corresponding proppant in supercritical carbon dioxide still need further research. In this paper, the Eulerian–Eulerian computational fluid dynamics method was used to study the transport capacity of supercritical carbon dioxide, and the UDF method was used to simulate the physical parameters of supercritical carbon dioxide. In view of the deficiencies of previous studies, the special cases of wedge-shaped fractures and bypass fractures are considered, and the influence of large-span pressure and temperature on migration is first analyzed in plane fractures, which makes this study more complete. The results show that: (1) compared with slickwater, the proppant transport channel in supercritical carbon dioxide is 30% smaller at 305 K and 10 MPa. (2) The transport capacity of supercritical carbon dioxide increases with the increase of pressure and decreases with the increase of temperature. But when the pressure or temperature is too high, they have little effect on it. (3) In wedge-shaped fractures, the proppant stack height and length increase initially as the shrinkage rate of fracture width (the ratio of the fracture reduced width to the fracture length) increases. However, as the fracture width ratio increases, the maximum proppant stack height decreases in the later stage. (4) In bifurcated fractures, with the increase of bypass angle, the area of proppant in the bypass zone tends to decrease. The width of the bypass inlet has little effect on the proppant settlement in the bypass. This study further understands the migration law of proppant in supercritical carbon dioxide in fractures.