Building Up Steam, A Progressive Approach to Drilling Volcanic Geothermal Formations

Abstract

There are several challenges for polycrystalline diamond compact (PDC) drill bits when drilling through volcanic and interbedded applications. Roller cone (RC) bits have historically been used in geothermal applications. However, low rate of penetration (ROP), bearing life, and repairability limitations have halted progress in performance and economic gains. This paper presents game-changing PDC technology that addresses the limitations of previous conventional drill bits in a challenging geothermal application. A reimagining of drill bit body geometries, the latest in shaped cutter technology, and durable backup elements were lab tested and customized on an unconventional drill bit chassis to maximize ROP, improve durability, and reduce downhole torque variation. The initial design phase focused on identifying and overcoming these key challenges. The second phase was to field test the new drill bit in the target application and compare it to offset runs, including roller cone, hybrid, and conventional fixed cutter bits. Key performance indices such as ROP, durability, steerability torque generation/variation, and cost per meter (CPM) were considered when evaluating the new design's performance. Initial testing in the 16-in. section showed promising results in the field. Higher-than-average ROP and excellent interval resulted in the lowest cost per meter run. In addition, the drill bit complemented the bottomhole assembly (BHA) design well, as minimal effort was needed to keep the trajectory as planned. The delta torque generation was lower than conventional PDC bits whilst displaying higher ROP than roller cone alternatives. The improved durability of the new design also allowed it to be run multiple times without repair, which was not possible with previous bits due to bearing hours or durability issues. This was always a challenge through the volcanic formations seen in this application. In remote locations that do not have facilities to repair drill bits, the ability to run multiple times without the need to repair is critical. The operator saved costs by not needing to transport the bit and repair any PDC cutters or secondary components after multiple runs. This outstanding run validated the benefits of the new design in terms of both technical and economic perspectives.