Downhole Well Connections By Use of Rotating-Magnetic- Ranging-Service and Single-Wire-Guidance Tool
Authors: Bybee Karen 
Published: February 2015

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 119420, "Rotating-Magnetic- Ranging Service and Single-Wire- Guidance Tool Facilitates in Efficient Downhole Well Connections," by Ray T. Oskarsen, SPE, and John W. Wright, SPE, John Wright Company, and Donal Fitterer, Dave Winter, Anthony Nekut, and Jed Sheckler, Vector Magnetics, originally prepared for the 2009 SPE/IADC Drilling Conference and Exhibition, Amsterdam, 17-19 March. The paper has not been peer reviewed.
Downhole connections between multiple wellbores have applications in many operations such as extended-reach drilling (ERD), multilateral completions, subsurface pipelines, and downhole fluid separation. A research-and-development project was undertaken to develop and validate an electromagnetic-ranging concept for enabling cost-efficient downhole connections. After extensive testing that found the ranging technology suitable, an existing offshore well jacket was identified as a good candidate for field validation of the concept.

Introduction
Determining the distance and direction to adjacent wellbores is a critical task when drilling relief wells or preventing wellbore collisions. Because of the cumulative and systematic errors inherent in measurement-while-drilling (MWD) or gyroscopic tools, the measured survey coordinates of a wellbore will have increasing uncertainty with depth, which is referred to as the "cone of uncertainty." For example, for a vertical well drilled using a surveying tool with an error cone of 1.5 m/1000 m, the radius of uncertainty at a true vertical depth (TVD) of 10 000 m is 15 m. Hence, for blowout intervention, to steer a relief well accurately to a deep intersection by relying only on the survey data of the target well is practically impossible. Instead, the homing-in process must be accomplished by a downhole ranging technique.
Although some unique ranging technologies currently are being researched, the most common methods are passive-magnetic and active-electromagnetic ranging, which both depend on steel, such as casing or drillstring, in the target well. During the last decade, feasibility studies, field trials, and implementation of downhole ranging technology have been performed for additional applications. The full-length paper contains examples of applications for downhole well connections and describes the single-wire-guidance (SWG) and rotating-magnetic-ranging-service (RMRS) technology developed and tested for these types of applications.

Well-Connection History
Downhole well intersections are common for relief wells and have been per-formed regularly for decades as a last-resort well-intervention method when other surface-kill efforts have failed. The original purpose of a relief well was to relieve pressure on a blowing formation by drilling a vertical well and producing the formation at high rates. In 1933, a directionally drilled relief well intersected the flowing reservoir below the surface location of a cratered blow-out in Conroe, Texas, marking the first milestone in relief-well development.