Experimental Study of Hydraulic Fracture - Interface Interaction

摘要

Hydraulic fracturing experiments were performed to study the propagation of fluid-driven cracks across slanted frictional interfaces. The interfaces separated dissimilar materials and loading was biaxial. Hydraulic fractures were initiated by means of 1/4-in. (0.6 cm) oil injection tubes embedded approximately 2 in. (5.1 cm) from the interface. Cracks generally propagated in the direction of the maximum applied load, intersecting the interface at either 30 or 60 degrees. A total of 16 tests were completed with normal stresses on the interfaces ranging from 550 to 1540 psi (3.8 to 10.6 MPa). Shear stress varied from 260 to 950 psi (1.8 to 6.6 MPa). A crack typically crossed an interface when the normal stress exceeded 1260 psi (8.7 MPa), regardless of which material it originated in. Two- and three-dimensional finite element models of the blocks indicated that a condition of plane stress prevailed at the outset of testing. They also showed that, for a given total boundary load, stresses on the interface were generally insensitive to the details of load distribution. However, concentrated stresses at the injection point proved to be substantially different from what would be calculated by assuming a uniform internal stress field in the block. (ERA citation 09:035168)