Crack morphology of multiple radial well fracturing based on extended finite element method

Key words:  radial well fracturing  induced stress field  interference stress field  orientated propagation  extended finite element method

Abstract:

The technology of radial well fracturing has been applied in various oil fields and proved to be effective, and the crack morphology needs an intensive investigation. In this study, a formation fracturing model was built using the extended finite element method (XFEM) based on fluid-solid coupling equations, and the maximum principal stress criterion and maximum energy release rate criterion were both used as the damage mechanisms of rock materials. The simulation results of three types of well models(i.e. the single radial well, vertical multiple radial wells and horizontal multiple radial wells) were analyzed, and verified by 3D physical experiments in the laboratory. It has concluded that an induced stress field along the radial well during fracturing is the main reason for the propagation major fractures. The distance of orientated fracture can extend to 40 meters. The effect of crack orientated propagation can be improved under vertical multi radial wells fracturing. An interference stress field can be induced at near wellbore under horizontal multi radial well fracturing, and secondary cracks connected with nearby radial wells can be generated in the interference stress field. Also the major fracture propagating along the radial well can be still generated in the zone far away from the wellbore. The combination of the two kinds of fractures can effectively improve the oil drainage area and also can reduce the oil flow resistance near the wellbore. At last the perforation scheme of radial wells is optimized.