Abstract
Drilling in high speed applications typically requires the use of a turbine or a uniform-rubber thickness motor. While both generate high rotating speeds, both are limited in the output power transferred to the bit. This decreases the drilling potential of the bit, especially impregnated bits, which are designed to handle high speeds and power, thereby producing excellent Rate of Penetration (ROP) in hard rock drilling. Additionally, the per-foot drilling cost for turbines and uniform-rubber thickness motors is significantly higher when compared to traditional drilling motors and in some cases the cost of turbines prevents the introduction of impregnated bits to certain markets.
A new and unique positive displacement motor has proven that the use of turbines and uniform-rubber thickness motors are not the only choices for high speed drilling. This new motor is similar to conventional positive displacement motors in that it consists of a bearing assembly, drive transmission shaft and power section for speed and power generation. However, the power section is a modified 2:3 lobe configuration with special geometry features which minimize the out of balance forces caused by rotor rotation. These special geometry design features are based on the use of a standard round power section tube, meaning the use of specialty manufactured and expensive uniform-rubber power section tubes are not required. The net result is a 2:3 lobe configuration that can rotate at the speeds required for high speed drilling while generating higher output power than existing technology.
Field testing of this new motor design has shown performance that meets or exceeds existing high speed drilling technology with regards to ROP and total drilling time. Drilling locations that require high Weight on Bit (WOB), which frequently causes problems with other technologies, was not a challenge as the new motor design was able to drill-off after multiple high pressure spikes. The overall motor cost was lower than turbines and uniform-rubber thickness motors, benefitting the operator with a lower cost per foot with equal interval drilled. This unique motor design gives operators a new tool to optimize performance in high speed drilling applications.
