Rotary-Steerable System Concept Aims To Increase Efficiency, Reduce Costs
Authors: Carpenter Chris 
Published: November 2019

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of the open-submission paper “Breakthrough Rotary-Steerable System To Reduce Well-Construction and Exploitation Costs,” by François Millet, SPE, Dynasteer, and Christophe Simon and Stéphane Menand, SPE, DrillScan. The paper was not presented at an SPE conference and has not been peer reviewed.
The advent of the rotary-steerable system (RSS) introduced an efficient way to drill both current and future wells. However, current tools still fail to replace positive displacement motors (PDMs). High build-rate RSSs that maximize reservoir contact are more expensive than PDMs that deliver consistent and reliable build rates, whatever the formation, while RSS tools with a low cost of ownership may not deliver expected performances. This paper presents a concept that combines optimal functionalities and directional performances with cost-effectiveness.
Lessons Learned in the Field
Hundreds of potential RSS configurations exist when considering engineering options such as steering principle, geometry, control mechanisms, rotating/nonrotating sections, and power source. In the past, many such systems have been run in two types of bent housing that equipped PDMs. Field experience has shown that an efficient RSS must incorporate features such as the following:
High build rates to maximize reservoir contact and deliver vertical, curve, and lateral sections in one run, thereby eliminating flat times
A slick, short nonrotating section to enhance reliability through a low-activation-frequency steering unit and consistent build rates without hole-cleaning issues
A steady, continuously active, and monitored step-by-step adjustable steering device associated with near-bit continuous inclination and azimuth measurement to drill vertical, curved, and lateral sections in one run with a smooth trajectory that facilitates operations during the whole life of the well
In addition, drillers seek timely near-rig maintenance to minimize both downtime and logistics, and all-mud-compatible low-drop-up pressure tools to drill with both the optimal mud formulation and maximum pressure. Failsafe downhole systems that ease the process of pulling out of hole in the event of failure are also beneficial.
However, these features are rarely available in a single tool. High-build-rate RSSs are more expensive than PDMs mainly because of maintenance cost and downtime. Most cannot deliver a smooth wellbore because of steering-control issues. Low total-cost-of-ownership rotary-steerable tools have limited functionality and thus in-consistent•performance.
Addressing the Issue
To engineer an improved RSS, two complementary elements were incorporated:
A monobloc flexible drive shaft that maximizes system reliability by carrying both torque and weight on bit (WOB) through the RSS.
The short double-tilt unit bent housing, known currently as the point-and-push hybrid steering principle, that provides high build rates with a limited tilt angle.
Unlike most designs, the usual nonrotating main body is split into two sections (Fig. 1): first, an upper carrier integrating all sensors, actuators, electronics, and the antirotation unit, and, second, a lower steerable housing integrating the fully mechanical pressurization device. These modules are linked by a monobloc flexible drive shaft acting as both a multidirectional one-piece joint and a return spring.