Abstract

Fracturing operations through coiled tubing represent one of the newest and best uses of coiled tubing. Large-diameter coiled tubing is used to convey straddle packers that are used to isolate particular zones to be fractured.

Thousands of coiled-tubing fracturing operations have been performed in North America. Most of these jobs were performed on wells with depths shallower than 3,000 feet. One reason why deeper jobs are not more common is because poor depth control is inherent with coiled tubing.

A new tool has been developed that helps solve the problem of straddle packer placement. Based on a proven wireless telemetry design, the new tool is designed specifically to fit the needs of coiled-tubing fracturing.

The tool gives the precise location of casing collars in real time, and a surface computer package allows the collars to be plotted on a standard log format that can readily be correlated to existing well logs.

Once the collar logs have been correlated, and the coiled-tubing measuring-counter depths have been corrected, the tool can be switched from the logging mode to the fracturing mode by simply increasing the flowrate through the tool. At a predetermined rate, a fullbore flowpath through the tool is opened to allow unobstructed fracturing operations to proceed.

This paper discusses the development of the new tool and presents case histories of its use.

Introduction

Fracturing through coiled tubing is especially well suited to shallow wells with multiple thin zones.1 With coiled tubing, these wells can be fractured in a much shorter time than with conventional methods. Often, the fracturing job can be completed in one day. In fact, in some shallow fields in Canada, it is not uncommon to fracture two wells in the same day using the same equipment and crew. This is possible because the coiled tubing can reposition the packers quickly from one zone to the next and can do this in an underbalanced condition. Conventional fracturing operations with jointed pipe on a rig require that the well be in an overbalanced state before moving the tools to the next job.

Coiled-tubing fracturing (CTF) operations have been carried out in Canada for several years, and in fact, most of the wells stimulated using this process have been in Canada. However, CTF operations have now been performed in several areas of the United States, most notably in Colorado, Texas, Alabama, and Virginia. In the United Kingdom, CTF operations have been performed in England and Ireland. Virtually all of these jobs have been performed on shallow, multizone onshore wells.

The techniques used in CTF are similar regardless of the field. A large-diameter coiled-tubing string is needed to achieve sufficient flow rates to properly fracture the zones. 2The most common coiled-tubing strings are 2 ⅜- or 2 ⅞- in. in diameter. Most of the coiled-tubing units (CTU) have an integral mast or derrick to support the injector head and the lubricator. A lubricator is used so that the tools can be retrieved from the well in an underbalanced condition.

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