Applying Precision Drill Pipe Rotation and Oscillation to Slide Drilling Problems

Abstract

Abstract The paper describes how a computer controlled top drive can address slide drilling problems and reduce rigfloor personnel exposure using precision pipe rotation and oscillation. It presents the advantages of such a system in solving the problem of setting a downhole toolface orientation and compares itself with the current practice. The paper explains further improvements in drilling efficiency and toolface control in the slide drilling mode in four case studies using field data and log analysis. A case history discusses how an operator was able to use the system to drill complex 3D wells using mud motors where previously only rotary steerable systems were capable. A section presents how the system reduces personnel exposure on the drill floor. The system is compared to other techniques of improving drilling performance in highly deviated directional wells. In the current drilling environment, operators are constantly seeking to reduce costs, improve drilling efficiency and ensure the safety of all personnel. This application adds efficiency to the drilling process in reducing rig flat time caused while establishing downhole toolface settings for directional control. It also adds efficiency by delivering more effective weight on bit in highly deviated directional wellbores and in providing a digital method of controlling downhole toolface while drilling. The improved toolface setting procedure via a touch-screen computer removes the need for directional personnel to chalk drill pipe and spend time on the rotary table, working instead with the driller from the doghouse or control cabin to achieve the required pipe rotation and toolface. The directional steering control system can also be used to maintain a desired toolface setting across drill pipe connections, dramatically reducing the flat time per connection. In these key elements, this system provides significant time saving advantages over the current practices. Introduction Although rotary steerable drilling systems (RSS) have made significant inroads as drilling tools of choice within the last 10 years, the steerable mud motor with bent housing is still the "work horse" for the vast majority of directional drilling projects in the world. The steerable motor assembly provides directional trajectory control with a special sub, or bent-housing a short distance above the bit. The bent housing is set and locked on surface to an angular value, in the approximate range of from 0.5 to 2.5 degrees. The magnitude of this setting is determined by the amount of dogleg severity (DLS) required to drill the curved sections in the planned wellbore. A major advantage of this type of drilling assembly is that it is capable of operating in two distinct modes, rotary and slide drilling. Rotary drilling needs no explanation as it follows the historical convention of clockwise rotation of the drillstring combined with high pressure mud flow and applied weight on bit. In the rotary mode, horsepower is delivered to the bit by a combination of rotary torque from the drill pipe and hydraulic horsepower from the mud flow. Thus the bit rotation speed is proportional to both these power inputs.