Hydraulic Fracture Crossing Natural Fracture at Nonorthogonal Angles: A Criterion and Its Validation

Abstract

Summary Hydraulic-fracturing treatments have become an indispensable part of well completion in shale gasfield development. Shale formations often contain natural fractures, and complex hydraulic-fracture networks may form during a treatment. The complex fracture network is strongly influenced by the interaction between the hydraulic fracture and the pre-existing natural fractures. A criterion has been developed to determine whether a fracture crosses a frictional interface (pre-existing fracture) at nonorthogonal angles. This criterion is an extension of the one for orthogonal crossing originally developed by Renshaw and Pollard (1995). The dependence of crossing on the intersection angle is shown quantitatively using the extended criterion. The fracture is more likely to turn and propagate along the interface than to cross it when the angle is less than 90°. The validation of the criterion using laboratory experiments for various angles is described and discussed. When applied to laboratory experiments, good agreement between the criterion and experiments is observed for a wide range of angles. The criterion can be used to determine whether hydraulic fractures cross natural fractures under particular field conditions, and it has been incorporated in a hydraulic-fracture model that simulates hydraulic-fracture propagation in a naturally fractured formation.

On the numerical simulation of crack interaction in hydraulic fracturing

“…This relation is shown in experimental results [5,6] and is described with a crossing criterion by Gu et al [8]. In this example, we compare our numerical results with the crossing criterion.…”

“…The tendency of crossing or diversion for various friction coefficients based on the crossing criterion from Gu et al [8] is also shown in Fig. 15.…”

“…Our results are in the proximity of μ = 2.0 and μ = 1.5. Rocks typically do not possess such a high friction coefficient [8]. It is likely that we overestimate the magnitude of the friction due to our penalty friction law.…”

“…15 The numerical results whether fluid diversion, crack arrest or fracture crossing occurs due to varying interaction angles and stress differences are shown with the point markers. The crossing criterion from Gu et al [8] for various friction coefficients is shown with the lines. The region right of a line indicates crossing numerical aspects such as the size of the time-step and mesh resolution.…”

“…The possibility of the fracture to divert into the natural fracture is not considered in this study. The criterion has been validated and extended by means of experiments for non-orthogonal angles by Gu et al [8] by solving the criterion numerically.…”