In this paper, we present the drilling and completion results for Injection Well 34A-22 and Production Well 34-22, two horizontal geothermal wells that were drilled and completed successfully at the Blue Mountain field in northern Nevada. The wells were designed as an injection and production well pair to deliver flow rates of approximately 1250 gpm. The well paths targeted static reservoir temperatures between 350 °F to 400 °F, as required for commercial production at the Blue Mountain power plant facility. The geologic setting at Blue Mountain is representative of many areas throughout the Basin and Range Province with high quality geothermal resource potential. The lateral sections of the wells targeted the Grass Valley formation, a Mesozoic metasedimentary formation comprised predominantly of interbedded phyllite and quartzite, as well as intrusive diorite and dikes and sills. The horizontal wells were placed in a southern reservoir compartment believed to have relatively few large-scale faults and low intrinsic permeability. A major project highlight was the ability to successfully drill fully horizontal, large diameter hole sections along the curve and lateral sections of both wells. While building the curve from vertical to horizontal, we were able to achieve target build rates of 10 degrees per 100 ft. The production laterals were drilled with a 9 7/8” hole size to accommodate 7” production casing and permanent fiber optic cables. Injection Well 34A-22 was stimulated with a 16-stage plug-and-perf hydraulic stimulation treatment with proppant. A total of approximately 267,000 bbl (11.2 million gal) of slickwater fluid and 7.3 million lbs of proppant were pumped during the stimulation treatment. The stimulated reservoir volume geometry was characterized using several independent reservoir diagnostics approaches, including microseismic monitoring, fiber optic strain sensing, pressure transient analysis, and offset well pressure monitoring. The dimensions of the stimulated reservoir volume were estimated to be roughly 1800 ft x 3000 ft x 750 ft, which is sufficient to meet the reservoir performance requirements of this project. Both horizontal wells were drilled from the same pad. Optimal placement of the lateral on Production Well 34-22 required building a complex, three-dimensional curve with a significant amount of back-build and lateral step-out, representing a significant de-risking step for future projects where drilling multiple wells from a single pad may be required. By completing this project successfully, we have demonstrated that currently no technical barriers exist to drilling horizontal wells and completing them with a multistage stimulation treatment approach in hard rock, high-temperature geothermal formations.

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