Multifracture initiation from a series of noncircular convex wellbores

Abstract

In this study, a numerical model is proposed based on the dual toughness and strength criterion for fracture initiation to determine the fracture initiation location and initiation pressure. In the model, hydraulic fractures emanate from a noncircular convex wellbore, which is considered as a jointed cross between an ellipse and a circle. Numerical studies were performed to explore the behaviors associated with fracture initiation under different stress combinations. The results indicate that the initiation pressure is sensitive to the geometric parameters of the wellbore. The initiation location is mainly controlled by the wellbore shape under a near-equal stress state characterized by the ratio of deviation (S) to mean (P) stresses (S/P < 0.10); if S/P > 0.50, the initiation location is dominated by the stress state. For an intermediate stress state (0.10 ≤ S/P ≤ 0.50), the initiation location is affected by both the stress state and wellbore shape; multiple fractures are easier to initiate in the presence of a noncircular wellbore and tend to develop into an X shape. In addition, X-shaped fractures prefer externally expanded wellbores. The subsequent propagations of the X-shaped fractures were also modeled, and these fractures exhibited a strong near-well tortuosity.