Coiled Tubing Applications In Horizontal Completions
Authors: Dusterhoft Dale M. , Falk Kelly L. , Misselbrook J.G. 
Published: March 2010

The popularity of horizontal drilling has resulted in a number of new completion techniques including the use of coiled tubing in the treatment of horizontal wells.

This paper presents an overview of the characteristics and mechanical properties of coiled tubing in a horizontal environment. A number of workover methods are examined, including horizontal fill cleanout, gas lifting and chemical treatments. The paper also discusses the development of coiled tubing tools and computer simulators.

Introduction

The advent of horizontal drilling has given the petroleum Industry another tool for increasing recoverability of reserves. Horizontal wells have been drilled to:Reduce water and gas coning(1).Effectively drain natural fractures(10).Reduce pressure differential into the wellbore(10).Increase steam flood efficiency(10).Increase heavy oil production(10).Extend reach in surface and space restricted areas(10).Increase production from poor quality thin beds(10).

Horizontal drilling technology has developed rapidly in the last ten years. Horizontal workover technology, however, has not advanced as quickly. Most horizontal completion research performed to date has centered on mechanical completion designs such as slotted liners, etc. Very little work has been done in the area of stimulation.

Numerous completion and stimulation problems are becoming evident as more horizontal wells are put on production. Some difficulties experienced involve:removal of fill from horizontal completionsmechanical problems associated with running in and out of horizontal sections.Production and open hole logging.Placement and setting of routine production tools.

A number of these problems can be solved using coiled tubing.

Coiled Tubing as a Mechanical Transport Tool

Operations routinely performed on vertical wells are often difficult to Execute in horizontal completions. Coiled tubing can be

FIGURE 1: Coiled tubing stress conditions. Illustrations available in full paper.

used to overcome some of these problems, provided the mechanics of the tubing in horizontal wells are understood and computer simulations are performed as part of the job design. Some operations which have been successfully completed are:Setting and pulling plugs for horizontal isolation(1)Opening and closing of sliding sleeves.Openhole logging.Production logging with well flowing.Setting and unsetting inflatable packets.Fishing and retrieval of downhole tools(5).

With proper knowledge, planning and equipment, virtually any procedure run vertically can be performed horizontally.

Force and Stress Conditions

Current coiled tubing materials can endure greater stress condition than previous materials. Improved quality has resulted in consistent strength characteristics which, in turn, have made fracture limits more predictable limits more predictable.

Being cylindrical, or "tube" shaped, coiled tubing has one of the most efficient Configurations for handling compressive, tensile and torsional loading (Figure 1). Primarily intended as a conduct for fluid transport, tube shapes have a high resistance in compressive buckling as well as to internal and external pressure differentials.

In vertical wells, coiled tubing is typically subjected to stress conditions resulting from the han