Design, Development, and Testing of a Slimhole Rotary-Steerable System
Authors: Bybee Karen 
Published: February 2015

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 130920, ’Design, Development and Testing of a Slimhole Rotary Steerable System,’ by S. Jones, SPE, J. Sugiura, SPE, and P. Das, PathFinder Energy Services, originally prepared for the 2010 CPS/SPE International Oil and Gas Conference and Exhibition in China, Beijing, 8-10 June. The paper has not been peer reviewed.
The first commercially successful rotary steerable systems (RSSs) were introduced in the mid-1990s for 8½- and 12¼-in. sections on high-end drilling applications. As the systems have matured and day rates have declined, they have been adapted to drill all borehole sizes from surface to the target depth. RSSs are highly complex tools consisting of mechanical, hydraulic, and electrical systems functioning simultaneously. Because of their complexity, systems designed for slimhole applications (5¾- to 6¾-in. sections with 4¾-in. collars) typically have been challenged with poor reliability. As these slimhole systems have matured, reliability and durability have increased through continuous improvements.
Introduction
The development of a slimhole RSS is faced with a unique set of challenges. Component size, mechanical strength, temperature and pressure requirements, onboard sensors, and compact packaging are all complex engineering requirements. A strong team of mechanical and electrical engineers is necessary to execute a project of this scale successfully.
The operational specification of the RSS also is critical to ensure that the system has adequate directional capabilities and reliability to enter an already crowded market where slimhole systems of competitors have had many years to establish themselves. As with any RSS, there are environments where one RSS design will outperform another and vice versa. Using the platform from a larger RSS that already has a track record should enable a faster design and development phase and reduce the learning curve during the customer-trial phase when the tool is subjected to many different drilling environments.
A properly designed and developed slimhole RSS should provide operators with a drilling system that has the following benefits: (1) good reliability, (2) good drilling performance, (3) precise directional control, and (4) better economics than conventional steerable systems. From the repair and maintenance perspectives, the RSS should have an acceptable turnaround time, be easy to reconfigure for various hole sizes (steering pads and stabilization), and have a long shelf life.
Design Specification
The design and operation of the control system for the slimhole RSS were based on a principle similar to that of larger versions of this RSS. Because the larger tools have proved to be reliable and directionally stable, there was little risk involved by using the same operating principle in the slimhole tool.
Some changes were specified to the basic RSS platform layout to allow options for future bottomhole-assembly (BHA) configurations for geosteering and positive-displacement-motor (PDM) -powered RSS (PRSS) applications. Essentially, the first-generation 4¾-in. RSS would act as the benchmark platform for the next-generation larger RSS.