Robotic Controlled Drilling: A New Rotary Steerable Drilling System for the Oil and Gas Industry

Abstract

Abstract The paper reviews the development of a second-generation rotary steerable drilling tool. The principle of operation is a bendable shaft that points the bit in the opposite direction to the shaft bending direction. This tilting action is a departure from other rotary steerable device concepts that push the bit sideways to change the wellbore trajectory. Combining this tilting action with extended gage bit technology provides maximum effectiveness in torque and drag reduction while reducing vibration and further improving hole cleaning. Important to the tool development was basing the design on lessons learned by others thereby improving both performance and reliability. The paper also discusses the application of proven technology from outside the drilling industry. Core elements such as strain wave gearing transmissions and electrically operated clutches were developed initially for use in industrial robots. Other significant elements are examined such as the shaft design, rotary seal systems and anti-rotation devices to limit housing roll rate. The "steering system" was integrated with an existing MWD system to allow automated or manual control from surface using a bi-directional communication system. This is also discussed. Introduction Back in the 70's and 80's we started hearing the term "I've been replaced by a computer". Mostly these were comical comments made at social gatherings but in reality it was true for many people involved in the manufacturing industry. Today we couldn't imagine a machine shop operating without computerized or robotic controlled machinery such as the common CNC system. It took a while but the task automation revolution of the manufacturing industry has started to make it's way below the rotary table to the point now that some (not all) functions traditionally handled by Directional Drillers are being handled by a computer, changing the nature of what a Directional Driller does at a drilling rig. It is likened to the revenge of the nerds, oil field style. The oil and gas operators continue to challenge the drilling service companies to reduce drilling time and costs while increasing technical limits of the equipment. For rotary steerable tools in particular, this effect is amplified primarily by the offshore market where costs run substantially higher than land based operations and where small incremental savings in drilling time result in impressive money savings to the drilling operation. The other obvious challenge is to pack as much production volume and life from each slot on a platform as possible. That need has never changed and has no apparent limit. This voracious requirement drives the need for multiple target well paths to maximize the capital investment returns in the asset. Attempts to slide a PDM over such tortuous well path geometries often are difficult or impossible as weight transfer to the bit is quickly lost to high drag on the drillstring. With the introduction of rotary steerable tools we are now seeing some operators pushing the limits of well bore geometries, drilling wells that are impossible to drill with a positive displacement motor (PDM) and requires a complete dependence on rotary steerable technology to drill the well. On the flip side of the equation is tool reliability. The cost of tripping failed tools is now a significant factor for wells depending on rotary steerable tools. The technology is new and prone to higher failure rates than more mature products and the industry has had to weigh this against their drilling objectives. More often than not, the current markets in Norway and the U. K. continue to use rotary steerable technology because the benefits still out weight the drawbacks in reliability. This has been a significant issue as it has allowed for this type of technology to gain a foothold in our industry.