Propagation characteristics and aperture evolution of hydraulic fractures in heterogeneous granite cores

Abstract

Hydraulic fracturing is assumed to be a potentially important technology for the improvement of heat exchange rate in the exploitation and stimulation of geothermal resources. The propagation characteristics and aperture evolution of hydraulic fractures in enhanced geothermal system (EGS) are very important for the evaluation and optimization of field fracturing operation. In this article, we employed a series of hydraulic fracturing experiments with heterogeneous granite cores. The experimental monitoring demonstrates the different stages in fracturing treatment in granite cores, including initiation, propagation, and closure stages. The results indicate that, with the increase of confining pressure, the breakdown pressure increases, the maximum fracture width decreases, and the closure of fracture increases. The injection rates do not affect the breakdown pressure obviously. In addition, the fracture morphology was also illustrated by the detection using microscope and X-ray computer tomography (CT). Based on the observation of fractures and the experimental monitoring results, a pre-proposed model was employed to calculate the fracture aperture during fracturing treatment process. The results emphasize the dominant role of fracture closure in the evolution of fracture evolution process. Larger confining pressure results in larger closure proportion, the closure proportion of the fracture aperture even can exceed 90% when confining pressure is 30 MPa.