Design and Characterization of a Heterogeneous Sample for Fracture Branching Studies

ABSTRACT: Reservoir performance and the economic production of hydrocarbons and geothermal energy are closely linked to the permeability of hydraulic and natural fractures in rock formations. Key mechanisms to enhance fracture permeability include hydroshearing, proppant placement, and fracture branching and curving. This paper focuses on fracture branching, specifically on the design and preparation of samples with controlled heterogeneity for fracture branching experiments, which is the foremost step in conducting repeatable and reliable tests. To achieve this, we designed two molds for heterogeneous sample casting using urethane rubber, aluminum tubing, and a pan. While urethane rubber mold offers convenience, we found that an aluminum gridded frame combined with boundary material and rubber columns provides greater flexibility and facilitates easier demolding. A heterogeneous sample, consisting of weak and tighter layers, was cast in the second mold by mixing plaster and water at different ratios. The measured hydro-mechanical properties of the sample include dry density, Young's modulus, Poisson's ratio, uniaxial compressive strength, uniaxial tensile strength, porosity, permeability, and specific fracture energy. The presented sample or its modifications can be applied to various experimental geomechanical studies, improving our understanding of fracture mechanics and enhancing control over hydraulic fracturing.