Over a three-well program the FORGE drill teams reduced well times by more than half, with instantaneous ROP increased over 400% in the thick granite pay zone. At the same time, record footage per bit was increased over 200%. The physics-based, limiter-redesign workflow utilized is described, along with specific changes in design and operational practices. Both are expected to yield similar results in any hard rock, geothermal or similar operations.
In 2020, the U.S. Department of Energy (DOE) funded a group at Texas A&M University to develop physics-based practices for the geothermal industry, similar to those that have enabled large gains for many operators in the petroleum industry. Wells in the Frontier Observatory for Research in Geothermal Energy (FORGE) were used to develop and test the workflow and practices. The effort began with sixteen hours of training for all team members, including drilling management. Changes were made in the daily workflow, such as periodic parameter testing, real time recognition and response to the common drilling dysfunctions, limiter identification, and daily discussion of the physics of each limiter and the immediate response required that included remote support personnel. The continual daily emphasis on identification of limiters, combined with training in how each limiter physically worked, created an enabling environment for change
Some of the key performance limiters addressed in these FORGE wells included previously held beliefs about limitations on WOB with PDCs, modifications to reduce BHA whirl, use of high WOB to suppress bit whirl, identification and avoidance of resonant RPM, BHA design and drilling practices to reduce the amplitude of borehole patterns to improve weight transfer, and the use of high spurt loss fluid (water) to achieve brittle rock failure. It was eventually possible to increase WOB to the structural limit of the bits (i.e., 68k lbs on 10-5/8" PDC). The bit vendor was engaged continually in daily analysis of digital data and dulls, and bits were redesigned to redistribute cutter wear, increase aggressiveness, and improve life through the increased use of shaped cutters. A significant finding was that contemporary PDC cutters remained relatively unworn for long distances in the FORGE granite regardless of WOB used, if the team is trained to manage dysfunction The mechanism through which the cutters eventually fail is discussed, along with operational and design practices to further extend the run lengths.
This paper is intended to serve as a reference, with the basic concepts, science, and real-time practices an operator may consider in developing its physics-based, limiter-redesign workflows.