An Assessment of the Factors Affecting Hydraulic Fracture Containment in Layered Rock: Observations from a Mineback Experiment

Abstract

In situ experiments, which were accessible for direct observation by mine-back, have been conducted to determine the effect that geologic discontinuities, elastic properties, and in situ stress differences have on hydraulic fracture propagation and the resultant overall fracture geometry. Vertical fractures were observed to terminate only in regions of high minimum horizontal in situ stress. Fracture growth into a higher (by a factor of 5 to 15) elastic modulus region was preferred to propagation into a region of higher (by a factor of 2) stress. Geologic discontinuities did not arrest the lateral or vertical propagation of hydraulic fractures. However, hydraulic fracture growth was affected by discontinuities, because fracture-fluid leakoff occurred along intersecting discontinuitiDS which the hydraulic fractures crossed, and thereby reduced the total extent of the hydraulic fractures. The results of the mineback experiment clearly indicate that differences in the minimum horizontal in situ stress between the reservoir rock and adjacent layers is the most critical factor affecting hydraulic fracture containment.