Slimwell Construction - New Opportunities For Deepwater
Authors: Head Phil , Turner Dan , Cameron Gerald , Bottazzi Franco , Hanson Tim , Holst Tor-Kristian , Al-Rawahi Salim 
Published: October 2008

Deepwater drilling has introduced the oil industry to a whole array of new technical challenges in constructing a well bore to a reservoir deep below the ocean. To build wells with similar dimensions used in shallower water has resulted in a new generation of rig with enormous capacity for riser tension, drilling mud volumes and casing storage. These units are extremely expensive to construct and operate. In addition there are only a limited number available which usually are locked into long term contracts.

Many offshore operators have renewed interest in slimmer well construction1–8, in the search for providing them with the capability to drill in deep water without compromising the hole size across the reservoir. Typically this involves sacrificing one or two contingency strings in the process.

This paper will present one development which has focused on retaining the necessary number of casing strings (including contingency) to TD while reducing the surface casing sizes to fit within the 14" riser envelope. In addition, with the arrival of new commercial materials and processes, this new well construction process offers exciting potential for low cost deepwater exploration and testing from a DSV.

Introduction

With the current trend towards deepwater operations smaller riser and casing configurations offer significant advantage over conventional well architecture. Figures 1 and 2 illustrate two potential casing configurations using this technology. The first illustrates the application of a taut leg moored 3rd /4th generation rig employing a 14" riser (the limit of rigs riser tension, mud and casing storage capability in great water depths). The second and slightly more radical application of this technology illustrates an 8" reeled riser from a DSV deploying the coiled casing option. Both these examples illustrate how this innovative solution will broaden the range of options for well architects/engineers.

The common approach throughout all of the well construction processes described in this paper is a series of liners, with tiebacks to previous liner tops as required. Finally the well is completed with a production tubing tieback to surface.

The main technical advancements are;

A unique liner hanger system which mechanically seals the new liner into the shoe of the previous liner, forming a high pressure metal to metal seal in the process, while still retaining the same tensile load capacity as the virgin pipe.

A novel conveyance system which allows for a high fluid circulation rate while the liner is being deployed and landed in the well, with a conventional mode for circulating and cementing operations.

Technology Development

This project has focused on reducing the clearance between subsequent casing strings to construct a flow path with optimum dimensions to/from the reservoir while significantly reducing the casing dimensions at surface. The casing deployment process includes a circulation method which avoids the casing acting like a huge piston exerting excessive pressure on the open hole.