Extended Reach Well Completion and Operational Considerations
Authors: Mason David , Hey Owen , Kramer Henk 
Published: October 2008

Extended reach wells can offer significant commercial advantages. Greater drainage coverage of a reservoir is achievable from fewer locations. Existing extended reach technology has been reviewed and summarised. Whilst most papers to date have been focused on drilling design and operations, this paper provides an overview on the drilling issues but also examines the completion issues as relevant for a gas production well. A well design for a l0km well with a TVD of 3500m has been prepared taking account of both drilling and completion operations. The casing and drillstring designs were optimised to minimise torque drag and to ensure that drilling the well was feasible. Key issues in cementing were noted. The completion design included extensive analysis of likely coiled tubing operations to identify the required operating envelope for the coiled tubing. The feasibility of using coiled tubing conveyed perforating guns to perforate the well was the primary focus. A tapered coiled tubing string was selected using existing technology. The design of a suitable tubing string for production from such a well was also examined. Given that extended reach wells will be higher in cost than vertical wells, it was assumed that a large diameter well was necessary to justify the economics. A 7" and 5-½" (or 7" and 5") tapered string was therefore designed to maximise well capacity. Tubing stress analyses were carried out and a number of possible configurations (using existing tubing designs) were identified. In this paper it is shown that such a well is feasible, identifies some of the completion issues and identifies possible areas for further improvements in technology.

Introduction

Many companies have developments where drilling of extended reach wells is required. The reasons vary from situation to situation, such as;environmental reasons restricting drilling access,reservoirs underlying urban areas, ormarginal economics for dedicated surface facilities.

The tremendous progress over recent years in drilling such wells creates new challenges in completion design and operations. This study has been focused on gas well design, as per the particular set of reservoirs being studied. Extended reach wells are typically high in cost relative to vertical wells, so in a gas production context, a larger capacity well consisting of 5" or 7" production tubing near surface was the design basis. Whilst even larger diameter production wells are feasible (7-5/8" and 9-5/8" production tubing sizes), the 7" production tubing was a more "standard" type size. Based on local reservoir depths and likely targets, a reservoir depth at 3500m TVD was selected and an along hole depth of 10,500m to 11,500m (depending upon well path), with an outstep of 8,800m.

The two key players in extended reach technology are BP at Wytch Farm and Statoil in the North Sea. The current record for extended reach drilling, with respect to horizontal displacement, is a BP Wytch Farm well with an along hole depth of just over 8000m with a TVD of 1600m (ref. 1). Statoil drilled the longest along hole depth in 1995, with a horizontal displacement of 7853m and a TVD of 2500m (ref. 1).