Implementation of Thermal Lattice Stimulation Technique in 315°C Geothermal Reservoir to Increase Fracture Complexity

Abstract The Thermal Lattice stimulation technique was implemented in two stages during the stimulation of the geothermal reservoir of Newberry, OR. The stages were pumped in January 2025, at rock temperature of 315°C and at depth of 9593 ft – 9675 ft. The reservoir at that depth is mainly basalt-basaltic andesite with elastic modulus of 55-60 MPa and fracture gradient of 0.9 psi/ft. The implementation consisted of several pulsating stages with long shut-ins. Each stage included pressure pulsation cycles applied below fracture propagation pressure, comprising of 20 pulses over 5 minutes, ramping from 500 psi to an ISIP of 6000 psi. The stimulation sequence was designed to create complex fractures originating from a primary tensile fracture and propagating through intersecting natural fractures. Fracture complexity and enhancement of the reservoir creation were assessed using multiple diagnostics, including pressure fall-off analysis via the MFrac simulator, Distributed Temperature Sensing (DTS) within the treatment well, and surface micro seismic monitoring via 20 shallow boreholes (20 ft deep). Transmissivity (kh/μ) increased from an initial value of 79 md-ft/cp to a post-treatment value of 574 md-ft/cp. Leak-off volumes were calculated through material balance, and conductivity enhancements and were validated through laboratory tests conducted on volcanic rock samples. Laboratory studies on volcanic rocks, including granite and basalt, support the field's observations. Cyclic injections conducted in the lab resulted in up to an eightfold increase in transmissivity—but only when preceded by initial tensile failure. In contrast, hydro-shearing alone produced only marginal improvements. These results indicate that initiating tensile fractures followed by subcritical pulsation is critical for enhancing fracture conductivity in igneous formations. The technique demonstrates significant potential for improving the thermal contact surface area. Power output simulations predict sustained generation of more than 10 MW/day over a 15-year operational period, assuming consistent reservoir behavior and well integrity.