Fracturing Through Coiled Tubing - Recent Developments and Case Histories
- W.G. Gavin (Nowsco-Fracmaster/B.J. Services Ltd.)
- Document ID
- Society of Petroleum Engineers
- SPE/ICoTA Coiled Tubing Roundtable, 5-6 April, Houston, Texas
- Publication Date
- Document Type
- Conference Paper
- 2000. Society of Petroleum Engineers
- 1.7 Pressure Management, 1.10 Drilling Equipment, 1.6 Drilling Operations, 2.5.1 Fracture design and containment, 4.1.2 Separation and Treating, 2.4.3 Sand/Solids Control, 4.2 Pipelines, Flowlines and Risers, 3.2.5 Produced Sand / Solids Management and Control, 1.14 Casing and Cementing, 3 Production and Well Operations, 2.2.2 Perforating, 2.5.2 Fracturing Materials (Fluids, Proppant)
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Fracturing through coiled tubing has progressed considerably since the first job done in 1993. In southeastern Alberta large numbers of wells are being selectively fractured through coiled tubing with mechanical isolation tools. Conventional fracturing techniques may result in small lenses that have the potential to contribute to production being either bypassed, or ineffectively treated. By utilizing coiled tubing and selective fracturing, all contributing zones can be fractured and the full potential of the well realized. Up to eight zones are being treated per well.
This paper will discuss work currently being undertaken with Carbon Dioxide and Nitrogen energized water based fracturing fluids. A summary of work done to date and case histories will be presented. Current and future developments in isolation tools and fracturing fluids will be discussed and the issues regarding geographical technology transfer examined.
The results of pumping fluids containing abrasive particulates at high pump rates through the coiled tubing are discussed with emphasis on abrasion of the pipe, fatigue and pressure limitations. Specific additional safety considerations are outlined and discussed.
As of year end 1999 approximately 700 wells1 have been fractured industry wide using coiled tubing as a conduit. The number of zones per well varies from 1 to 8 and the total number of fracture treatments performed on these 700 wells is over 5,100. This technology has been predominantly limited to the shallow gas fields of southeastern Alberta.
It is difficult to ascertain when the first coiled tubing fracture treatment took place but a job was carried out in south-eastern Alberta2 in February, 1993 where a 25 tonne treatment was pumped through 73.0 mm (2-7/8 inch) coiled tubing at 3.0 m3/ minute (18.9 bbl/min). The procedure was similar to that performed today with the exception that the coiled tubing was stung into a permanent packer.
While the operational feasibility of fracturing through coiled tubing had been proven the commercial viability of the technique was still questionable and further development shelved. In 1997 the technique was refined for multi-zone fracturing3 which significantly impacted the commercial viability.
The work described in this paper has been performed on gas wells and carried out with the well live. Standard practice is to fracture from the bottom zone up. Initially only one well was fractured per day (up to 8 zones) but this has progressed to two wells per day and the feasibility of three wells per day is being evaluated. Coiled tubing is an excellent medium for the operation as a rig would have to strip out of the hole with the well live. After fracturing the wells are cleaned out periodically with a shallow coiled tubing unit until sand production stops. Indications are that utilizing coiled tubing fracturing over conventional methods may halve the number of cleanouts in certain circumstances.
Other driving forces for fracturing through coiled tubing are the desire to protect old (and/or corroded) casing and completion jewelry from the high pressures and potential erosion associated with the treatment.
For the work evaluated in this study cross-linked water based fracturing fluids are predominantly used in the operation. In general, between five and twenty metric tons of sand is placed at concentrations up to 1800 kg/m3. The fluid is energized with liquid CO2 or gaseous Nitrogen to aid in flowback after the treatment. Liquid CO2 was used in over 95% of the fracture treatments reviewed. Forced closure has been used on some of the treatments, thus, requiring immediate flowback. Pump rates of between 1.2 and 2.5 m3/minute (7.55 to 15.73 bbl/min) are standard.
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