Labyrinth Packer Lowers Costs for Steam-Injection Wells
Authors: Bybee Karen 
Published: February 2015

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 110454, "Labyrinth Packer Lowers the Costs for Steam-Injection Wells: Theoretical and Experimental Results," by C. Teodoriu, SPE, and G. Falcone, SPE, Texas A&M U., originally prepared for the 2008 SPE Symposium on Improved Oil Recovery, Tulsa, 19-23 April. The paper has not been peer reviewed.
The full-length paper describes a low-cost completion technique that uses conventional tubing and replaces the expensive thermal packer with a new low-cost design. The new design allows free tubing expansion and protects casing through continuous gas circulation in the annulus. It also makes possible simultaneous injection of combustion gases from steam generators when conventional systems are used, or small amounts of nitrogen (N2) when the generators are not available.

Introduction
Steam injection is an enhanced-oil-recovery technique that is used in heavy-oil exploitation. Steam injection and steamflooding are used widely in heavy-oil production. A typical steam-injection completion contains a special thermal packer designed to withstand the downhole injection temperatures, an expansion joint, and insulated tubing. Temperatures as high as 350°C are common for steam-injection projects. Simplifying the well completion will reduce operating costs and intervention time.
Most of the heat-transport phenomena in steam-injection wells are the result of water in the annulus. Several papers have reported on the importance of water removal from the annulus to reduce heat transfer and keep the casing temperature low. For long-term injection processes it is impossible to prevent the casing from reaching high temperatures. However, when short-term processes are involved, such as in huff ‘n’ puff operations, it is possible to keep the casing cool. Two processes are available to keep the casing cool: passive cooling, in which the tubing is insulated and the casing is kept cool because the heat flux is reduced, and active cooling, in which the heat dissipated by the tubing is transported away from the casing. Active cooling has the advantage that it can keep the casing cool for a much longer time than passive cooling.
The common failures of casing that may occur in wells stimulated through huff ‘n’ puff (cyclic) steam injection are rupture, collapse, connection leaking, and corrosion. Most of these failures are caused by excessive casing temperature. New casing designs and new materials are reducing these failures in new wells. Thus, the new steam-stimulation process is applied to existing wells where casing strings have not been designed to withstand high temperature. The nature of the cyclic steam process keeps the casing exposure time to high temperatures low, and the completion equipment used must keep the heat away from the casing for 4 to 10 days. A classical well completion for cyclic steam injection consists of insulated tubing, expansion joint, and thermal packer. When the steam temperature exceeds 250°C, a gravel-pack completion must be run after the injection phase, because the sand-grain size will shrink or sand will disintegrate in contact with hot steam or water.