Water enhanced borehole breakout formation in granite at elevated temperatures

ABSTRACT: To better understand the behavior of crystalline reservoir rocks at enhanced geothermal conditions, a series of triaxial experiments was conducted on Sierra White Granite at conditions from ambient to 150 °C. Triaxial tests were conducted at 17.2 MPa effective pressure and a constant displacement rate of 3.31x10-6 s-1 on right circular cylinders machined to have a simulated borehole in the center of the sample. Samples were instrumented with acoustic emission pins to monitor damage development during deformation, and post-test samples were imaged using X-ray computed tomography. The configuration of the sample allowed for fluids to be injected into the simulated borehole and remain isolated from the confining medium. Deionized water was injected into the wellbore for three different temperature conditions and compared against a dry borehole at ambient temperatures. Experiments show that the presence of water and elevated temperatures weaken the borehole, and higher temperature are associated with changes in fracture morphology. Elevated temperature tests have increasingly diffuse, broad fracture networks compared to ambient conditions.