Building on the application's success in larger diameter holes, rotary steerable drilling is becoming an established drilling method in 6" hole sections. Rotary drilling in these smaller hole sizes does, however, bring with it some concerns. These include the requirement for high surface rotary speeds to achieve acceptable penetration rates. As a result, these rotary systems may need to place very high dynamic loads on small diameter drillpipe. A new rotary steerable system has been developed which integrates a high performance drilling motor into the bottom hole assembly. By driving the drill bit with the downhole motor, drillpipe rotary speeds and weight on bit can be reduced while simultaneously increasing rate of penetration. This reduces the stress on the drill string and increases drilling performance. This paper describes this new system illustrated with results from real wells.
The mutual objective of oil companies and "drilling and evaluation" service companies is to deliver the most cost effective well, positioned optimally in the reservoir, and capturing high quality formation evaluation data while drilling.Over the last decade there has been significant service company technology investment driven by this objective. One of the key technologies developed has been rotary steerable systems.
Rotary steerable systems were introduced to the drilling industry in the mid 90s. The drilling industry was quick to recognize the value delivered by this technology as observed by the rapid rise in the use of the technology over the last decade. Today it is estimated that 20% of all directional footage is made using rotary steerable technology.
The initial systems were developed for 8 ½" hole size as these sections possessed the need for accurate well placement and steerability in the oil or gas bearing reservoir. Once the the concept and technology was proven, the industry embraced the idea of using the same technology to drill the well to the reservoir and larger hole size were developed. Within 5 years, rotary steerable systems were available on the market that could drill hole size from 18 1/8" to 8 3/8". The most recent development of rotary steerable systems has been for hole size smaller than 8 1/2" and there are now several systems available to drill +/- 6" hole.
Although, in many applications, the use of rotary steerable systems adds significant value, the need for systems to be 100% rotary driven from surface have added drillstring wear and downhole dynamic dysfunctions that can negate the benefits in certain applications. The remainder of this paper will discuss these issues in detail and demonstrate how these issues have been addressed through improved understanding and associated technology development.