Geothermal energy is a renewable source of energy, where heat extraction is preferentially balanced with the reservoir's natural heat recharge rate. The objective of this paper is to present and validate a novel rate of penetration (ROP) model for drilling hard and abrasive formations including granite formations for polycrystalline diamond compact (PDC) bits. The ROP model was developed based on a derived relationship of a threshold weight on cutter (WOC) and its corresponding depth of cut (DOC) for a single cutter. Laboratory data was used to scale the derived single cutter relationship to a full-hole ROP model for PDC bits. The ROP model includes a non-linear correlation for Phase I (inefficient drilling due to low WOB values) and a linear Phase II (efficient drilling) ROP response to WOB. The ROP model was verified using measured drilling parameter data from Utah FORGE well# 58-32 and data from Chocolate Mountains well # 17-8 in Southern California. When compared to oil and gas well drilling, geothermal drilling in granitic formations can be more difficult and complicated due to rock hardness and high temperatures. PDC bits can increase ROP and optimize drilling for these types of hard formations. This paper provides novel insight into the ROP response of PDC bits to drilling operational parameters.
Geothermal energy is a renewable, reliable, and clean source of energy. Geothermal wells typically need to be drilled into intrusive igneous rocks such as granite. Igneous rocks are formed from the solidification and crystallization of magma in the earth's crust. Granite is a plutonic rock that primarily is made up of quartz, feldspar, and micas.
Oil and gas drilling operations rarely include any interval of an igneous or a metamorphic rock formation, while drilling into these types of rocks is an essential part of the extraction of geothermal energy. PDC bits deliver higher ROPs in soft to medium formations and potentially last longer when compared to roller cone bits. In very hard and abrasive rocks, usually, insert-tooth roller cones are more favorable. However, using PDC bits in these types of rocks has been practiced in many laboratories and field applications. PDC bits that were specially designed for drilling granite and quartzite rocks have been studied by researchers in recent years. Several novel cutting structure enhancements have been proposed and demonstrated in recent years to enhance the penetration response and durability of PDC bits.
