Stress analysis of hydraulic fracturing operations in layered granular media

The paper deals with the determination of basic two- and three-dimensional stress distribution patterns in infinite single- and multi-layered, granular media during hydraulic pressure grouting. A majority of previous publications have tended to concentrate on simplified direct methods in which the vicinity of crack tip is defined with a large number of finite elements. Due to the inherent singular characteristics of strains in the vicinity of the crack tip, the present method superimposes the results of highly refined crack tip elements on the results of coarser, but conventional, finite element system. Two dimensional finite element models simulating hydraulic fracturing conditions are given using STRUDL II and NASTRAN computer programs. Corresponding experimental model results for validation of analytical model for far field and crack tip stresses are also presented. In addition, three dimensional finite element model representations for vertical and horizontal fracture configurations are investigated. Analysis of hydraulic fracture criteria is based on the stresses near the fracture zone. The results are compared with the selected previous work.