Abstract

Increased production and lower costs in shallow gas wells are closely linked to developing and refining new coiled-tubing drilling, completion, and production techniques. Innovations in coiled tubing have reduced the costs of drilling and completing these wells and increased their productivity and life cycles. Coiled-tubing fracturing is one such innovation. This has been used for some time now, predominantly in North American shallow gas wells. In these wells, the cost advantages associated with working over the well in a live condition while reducing job time are attractive.

Coiled-tubing fracturing operations usually employ straddle-type tool configurations. However, with a typical maximum lubricator length of about 30 ft, straddle interval lengths have been restricted, which increases the amount of resets required to effectively fracture individual zones. This restriction also increases the potential risk of communication above the assembly.

This paper describes the development of an economical and reliable coiled-tubing fracturing system that allows selective fracturing of previously bypassed pay zones. This is now possible because the system can be conveyed in a tandem configuration that works within current lubricator restrictions, but is capable of setting repeatedly as a retrievable bridge plug and treating packer combination. This allows longer zones to be precisely isolated multiple times in a single trip in hole.

This innovative technique can not only reduce intervention costs but also reduce the total time required to complete the operation. This paper will examine several case histories, with emphasis on pre-job planning, equipment selection, well site execution and post-job results.

Introduction

A recently developed coiled-tubing fracturing system gives the operator an alternative to conventional completion techniques.Using coiled-tubing fracturing and a tandem tool configuration, the system allows the cost-effective completion of zones of interest previously regarded as uneconomical.These tools are run as a retrievable bridge plug and treating packer combination on coiled tubing, which allows the system to be set downhole in varying intervals repeatedly.

The benefits of this new system in shallow to intermediate gas wells include:

  • Multiple zones of any interval length can be isolated and stimulated efficiently and economically;

  • Total completion time can be greatly reduced compared to conventional methods;

  • Production results are improved over conventional methods that require kill-weight fluids.

Completion Techniques

The most common completion technique for shallow gas zones involves a rig-assisted plug and packer system conveyed on threaded pipe.Normally, these zones of interest would be completed as either a re-entry or workover procedure.Perforation and stimulation of multiple zones with a standard plug and packer system requires kill-weight fluid to be placed in the wellbore prior to moving up hole and relocating the assembly.This method of completion is time consuming, costly, and can cause formation damage.Stimulation equipment, and in many cases the workover rig itself, must be mobilized for each zone.

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