Laboratory-scale study of hydraulic fracturing in heterogeneous media for enhanced geothermal systems and general well stimulation

Abstract

The primary objectives of this research were to experiment with hydraulic fracturing in the laboratory to gain additional understanding of the fracturing process in unconventional rocks having low natural permeability and heterogeneous structures. Focus topics of this research included experimentation with a mechanical impulse hydraulic fracturing method, measurement of critical state hydraulic fracture aperture, laboratory scale modeling of EGS, and an investigation of grain-scale effects on 3D hydraulic fracture geometry. Fractured materials included acrylic, concrete, granite and limestone with specimen sizes up to 300x300x300 mm[superscript 3] cubical blocks. Fracturing fluids included water, brine, oil and epoxies. Applied boundary conditions varied between experiments from unconfined to true-triaxially confined with heating applied in some instances. Data collected during experiments included pressures, flow rates, acoustic emissions (AE), temperatures, strains and video with intended future application for calibration of models. Cross-sections were cut through the test specimens after hydraulic fracture stimulation to investigate and measure fracture geometry at both the grain-scale and macro-scale. Procedures for using the true-triaxial apparatus and associated control systems developed for this project are detailed in appendices to guide future use of the equipment. Supplemental data and results from the hydraulic fracture of 13 specimens are also included.