Summary
Creating uniform multiple fractures is a challenging task due to reservoir heterogeneity and stress shadow. Limited-entry perforation and in-stage diversion are commonly used to improve multifracture treatments. Many studies have investigated the mechanism of limited-entry perforation for multifracture treatments, but relatively few have focused on the in-stage diversion process. The design of in-stage diversion is usually through trial and error because of the lack of a simulator. In this study, we present a fully coupled planar 2D multifracture model for simulating the in-stage diversion process. The objective is to evaluate flux redistribution after diversion and optimize the dosage of diverters and diversion timing under different in-stage in-situ stress difference.
Our model considers ball sealer allocation and solves flux redistribution after diversion through a fully coupled multifracture model. A supertimestepping explicit algorithm is adopted to solve the solid/fluid coupling equations efficiently. Multifracture fronts are captured by using tip asymptotes and an adaptive time-marching approach. The modeling results are validated against analytical solutions for a plane-strain Khristianovic-Geertsma de Klerk (KGD) model. A series of numerical simulations are conducted to investigate the multifracture growth under different in-stage diversion operations. Parametric studies reveal that the in-stage in-situ stress difference is a critical parameter for diversion designs. When the in-situ stress difference is larger than 2 MPa, the fracture in the high-stress zone can hardly be initiated before diversion for a general fracturing design. More ball sealers are required for the formations with higher in-stage in-situ stress difference. The diverting time should be earlier for formations with high in-stage stress differences as well. Adding more perforation holes in the zone with higher in-situ stress is recommended to achieve even flux distribution. The results of this study can help understand the multifracture growth mechanism during in-stage diversion and optimize the diversion design timely.
