The paper describes a new model and computer simulation technique for hydraulic fracture in layered media, and its application to laboratory experimental data. Field and laboratory observations show that an initially circular crack (or notch) in a layered media can often turn into a highly elongated fracture. Such fracture containment is often assumed, rather than modeled directly. In the method presented here the simulation of the phenomenon is based on a model of elliptical crack propagation in a 3D layered poro-elastic body. The global Griffith-type fracture criterion and an anisotropic fracture toughness parameter (specific fracture energy of rock) are employed. A computer code based on the proposed model is then used to describe a laboratory hydraulic fracture experiment. The large block hydraulic fracture experiment in a layered material (diatomite) is described. The computer simulations with appropriately selected characteristics of the model give results in reasonable agreement with the experimental measurements. Possible applications of the model are discussed.
IINTRODUCTION
The present work is concerned with the primary features of hydraulic fracture processes in stratified rock materials. As field and laboratory experiments show, an initially small radial crack (or notch) can often grow significantly more in one direction that results in noticeably non-circular (an oval) geometry. The reason for such crack growth behavior may be fracture anisotropy of the layered medium. There are three apparent causes of a non-circular fracture growth: 1) a non-uniform traction on the crack face, 2) an anisotropy of fracture toughness, and 3) heterogeneity of the fracture toughness resulting from layered structure of the rock.
This paper describes a new model for hydraulic fracture in layered media, and its application to a laboratory hydraulic fracture test. The model is developed tirst, followed by a description of the experiment. Computer simulation results of the test are then described, and conclusions drawn.
