Rotary Steerable Drilling System for the 6-in Hole

Abstract

Abstract The availability of a reliable 3D rotary steerable system in 6-in. hole size opens up considerable opportunities to develop reserves where 3D steering is required, but the risks, difficulties, and delays involve in using bent housing mud motors are excessive. On 10 April 2002, parallel field trials of a 3D, 6-in. rotary steerable system (RSS) started in Oman and the North Sea. The field trials program finished in June with more than 16,000 ft drilled and more than 400 circulating hours experience accumulated in a range of formations without failure. During these trials, the tool displayed steerability and dogleg performance suited to landing and geosteering a well in the reservoir section. The paper outlines the principles of operation and performance capabilities of the system including the technical challenges encountered while developing a rotary steering system of this size. Field trial results from the test program are presented for a range of drilling conditions, formations, bit types, and bottom-hole assembly designs. Introduction The development of rotary steerable drilling systems over the past decade has been rapid and exciting1. The benefits of the ability rotate every part of the drilling assembly from surface to bit whilst controlling the direction of the hole include higher rates of penetration (ROP), improved transfer of weight on bit (WOB), and ease of holding toolface in the presence of drilling parameter and formation changes. Whatever the favored type of rotary steerable drilling system, all such systems cause the centerline of the bit to be offset by a controlled amount in a controlled direction while the drill-string is being rotated. There are many ways in which this may be done. For historical reasons, systems are grouped by principle of operation (that is, either push or point the bit), but in practice systems usually comprise elements of both. The first commercially successful rotary steerable drilling solutions were for the 8.5-in. hole size or larger because the control systems needed to reliably achieve this lateral displacement of the bit were formerly too large for slimhole applications. The lack of a credible solution for smaller hole sizes was therefore a significant shortcoming. However, a small team of engineers set out to develop a 6-in. hole system within 1 year. This paper recounts the work and the key technical issues involved. Development Program The development of a 6-in. rotary steerable system followed this sequence: -Feasibility PhaseDevelopment PhaseField Test PhaseCommercialisation The confidence to proceed with a rapid development evolved from a wide-ranging and detailed concept study into novel steering mechanisms. It was during this work that the key system parameters for a 6-in. RSS were established (Table 1). The concept study implied strongly that these key system parameters could be achieved in a very short time frame by a downscaling of a proprietary steering concept. Furthermore, it was confirmed that the same electronics as used in all the other sizes of the RSS (8 1/2 in. to 18 1/4 in.) could be speedily integrated into this new size of tool.