Use of expandable pipe technology to improve well completions

Abstract

The underlying concept of expandable technology is cold‐working a pipe downhole to the required size. An expansion cone is typically used to permanently deform the pipe downhole. The cone is pulled or pushed through the pipe hydraulically or by mechanical force. The cone introduces a stress to the pipe material above the yield stress and thereby plastically deforms the pipe while keeping the stresses below the ultimate yield. Expandable technology gives the possibility of having more casing points in a well with little or no reduction in inner diameter. It may also increase the productivity of a well by increasing the sizes downhole, thus reducing the frictional pressure drop of the flowing fluids in the production tubing. In addition, expandable technology may give large environmental and economical benefits, such as development of smaller fields and deeper reservoirs, faster drilling speed, and reduced drilling fluids volume, cement volume, and amount of cuttings for disposal. The pipe properties are affected by the expansion process. The cold‐working process, in which the pipe is expanded, increases the yield strength of the material. The increase in yield strength may increase the burst pressure, depending on the expansion ratio and the wall thickness reduction. However, the collapse pressure may be significantly reduced because the D/t ratio is increased in the expansion process. The reduced collapse pressure may limit the range of application of expandable technology. The expandable liners are not, at present, qualified as barriers or to be exposed to well fluids. When used in the reservoir, an expandable liner can be used as a drilling liner, which means that the liner is covered by another liner that acts as a production liner. The expandable liner does not need to be strong enough to handle production loads, only drilling loads. The expandable liners were in this case strong enough to handle most burst and collapse loads. However, they were not strong enough in collapse to handle the worst case scenario, which in this case was lost circulation with mud drop. If lost circulation zones are encountered the expandable liner may collapse. This represents only one example, for other wells the loads need to be determined for the specific case in which expandable liners are to be used.