This paper presents the results of a series of injection experiments carried out on basaltic tuff cores from the Newberry geothermal field. A combination of triaxial and injection experiments were performed on the cores to characterize their goemechanical properties and to better understand their response to stimulation treatment. Fluid flow was maintained across the samples throughout the experiments while stress, strain and acoustic emissions were recorded. Rock deformation and acoustic emissions data were analyzed, and the locations of events were shown to correlate with the fracture location in the samples. Some experiments were conducted at elevated temperatures to investigate the rock response to thermal stimulation. Data clearly shows increased AE activity and deformation with cold fluid injection into heated samples compared to isothermal injection.
Enhanced geothermal systems (EGS) are expected to be a significant source of energy generation in the years to come. EGS development relies on creation of conductive pathways for fluid flow and heat exchange. Optimization of the reservoir development process such as drilling and stimulation can benefit from core testing. This paper describes a rock characterization and core testing program for a portion of the core from well GEO- N2, drilled at Newberry geothermal field. This well is located about 2.8 km from the western rim of the Newberry volcano caldera in Oregon, U.S.A. The paper describes tests to measure various petrophysical and geomechanical parameters for these core sections. Some of the experiments on have been performed under heated conditions.
The cores from the GEO N2 had a diameter of 0.0635 m (2.5 inches) and their length to diameter ratios varied from 1.5:1 to 2:1. Mineral composition and pore scale characterization were performed using XRD and thin sections on the core. A variety of laboratory tests have been conducted on the plugs to determine rock strength (triaxial and injection tests), velocity data (shear and compressional), elastic properties, acoustic emissions and stress-dependent porosity and permeability.