Development of a Downhole Piston Motor Power Section For Improved Directional Drilling: Part I - Design, Modeling Analysis

摘要

Directional drilling can be used to enable multi-lateral completions from a single well pad to improve well productivity and decrease environmental impact. Downhole rotation is typically developed with a motor in the Bottom Hole Assembly (BHA) that develops drilling power necessary to rotate the bit apart from the rotation developed by the surface rig. Historically, wellbore deviation has been introduced by a "bent-sub" that introduces a small angular deviation to allow the bit to drill off-axis with orientation of the BHA controlled via surface rotation. The geothermal drilling industry has not realized the benefit of Rotary Steerable Systems, and struggles with conventional downhole rotation systems that use bent-subs for directional control due to shortcomings with downhole motors. Commercially-available Positive Displacement Motors are limited to approximately 350 F (177C) and introduce lateral vibration to the bottom hole assembly contributing to hardware failures and compromising directional drilling objectives. Mud turbines operate at higher temperatures but do not have the low-speed, high torque performance envelope for use with conventional geothermal drill bits. Development of a fit-for purpose downhole motor would enable geothermal directional drilling. Sandia National Laboratories is developing technology for a downhole piston motor to enable directional drilling in high temperature, high strength rock. Application of conventional hydraulic piston motor power cycles using drilling fluids is detailed. Work is described regarding conceiving downhole piston motor power sections; modeling and analysis of potential solutions; and development and laboratory testing of prototype hardware. These developments will lead to more reliable access to geothermal resources and allow preferential wellbore trajectories resulting in improved resource recovery, decreased environmental impact and enhanced well construction economics.