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Frequently Asked Questions

General Properties and Dimensions (13)

We currently provide 2 3/8”, 2 7/8”, 3 ½’, 4 ½” and shortly in 5” tubing. These tubing sizes have standard API ID’s. Dimensions and tubing weight are as follows:

 
API Size:OD TubingAPI Size:IDWeightThread Type
InchmmID InchID mmLBS/ft
2.375″60.3251.99549~ 3.1any
2.875″73.0252.24457~ 3.1any
3.5″88.92.79571~ 3.1any
4.5″114.33.72494.6~ 3.1any
5″127.04.408111.96~ 3.1any

Tubing weight may vary slightly.

Only ID is provided and not drift.
API-5 allows for 12.5% wall-thickness variation in metal tubing.
Our manufacturing process has much tighter tolerance control, hence ID is between OD and drift.

CFST is composed of a corrosion-resistant liner made of Titanium ASTM Grade-2. The liner is then covered with several layers of Aerospace grade carbon fiber and high-grade epoxy resin. The Ti. liner gives corrosion resistance and prevents permeation of any hydrocarbons into the CF layer. The CF layer provides strength in the axial and radial direction.

CFST is economical from a lifecycle cost perspective. It outlasts any high alloy metallic tubing. Considering the cost of several workovers, new tubing, chemical treatment, and cashflow impact resulting from shut-in periods, the price is very competitive. CFST is more economical than 13Cr tubing and certainly a lot less expensive than Duplex or Inconel tubing. CFST is priced slightly above CR13 tubing but will last many times longer.

CRA-Tubulars plans to manufacture tubing in-country or certainly within the region. In this model we expect to deliver a spool of CFST in under 1 month, combined with HWOU installation, our process can have your well back on production within 2 months. This is much faster than traditional jointed metal CRA completions. Delivery times of Duplex or Inconel are typically over 18 months.

CFST is slightly stronger in axial forces than metallic tubing is. Our prototype testing showed 240,000 lbs. before the tubing broke. Since it weighs only one-third of metal equivalent tubing, it is a much stronger downhole. Example: 10,000 feet of steel tubing weighs 92KLBS, and our tubing weighs only 30KLBS, so we would have ±62KLBS (92-30kLBS) more pulling force than metal tubing.

CFST is provided in two grades: Burst and collapse 10KSI and the high grade >15KSI. Temperature is 180 degrees Celsius; this puts our non-metallic CRA comfortably in the HPHT range of applications. We have a high grade under development aiming to approach 200C.

No, to achieve the highest possible temperature resistance we are using highly crosslinked thus brittle resins. Our combination of resin, fiber, and the liner however is not brittle. Microcracks do occur in the outer layer (none in the inner-liner) as soon as the pipe is spooled on a reel this is normal and does not affect its performance in any way.

Since CFST is as strong as metal, the behavior is expected to be similar. During such conditions steel tubing, drill pipe, and collars have been seen expelled from the well. That will likely happen with CFST too. Will it happen sooner? Not sure, but even if the event fully escalates 50% faster than with metal, the consequences will not be different, only instead of say an hour, it might happen in 30 minutes. Nothing to avert the consequence of such an event can be done in that time frame. Steel pipe, casing, and tubing have been sand-cut in minutes resulting from the extreme velocities of the two mediums together. Similar expectations for CFST.

There is no reason, when looking at other Industries, to believe non-metallic composite is less strong than metallic are. Airplanes are made of carbon fiber (CF), F1 cars are accident impact strengthened with CF. They are all much stronger than metal equivalent material. The unique and extreme forces in an uncontrolled well flow cannot be counteracted by metal or non-metallic composites, they will perform similarly.

Yes, there is sufficient safety on the collapse performance (radial hoop strength) to allow for safe installation and operation. Calculations have shown that with a tubing full of gas, zero pressure at surface, an annulus with packer fluid and max design pressure at surface (ie MDASP) there is no risk of collapse.

In most of the corrosive well-operating environments, the expected life exceeds 20 to 30 years. Titanium is very durable, corrosion-resistant, and in other industries like seawater coolers in nuclear power plants and chemical industries, it is the metal of choice for high corrosion resistance.

Carbon fiber is strong and nearly inert to corrosion bar wet/temperature degradation over time. CRA-tubulars apply a safety factor to the operating envelope. The (initial) operating limits are the limits CF would have after degradation.

We use a propriety cross-over design from carbon-fiber composite to any metal CRA alloy matching any type of premium or non-premium thread required by the client.

As mentioned, we can provide any available thread type. CFST can be connected to any off-the-shelf completion accessory.

Our product is a reeled endless tubing and is delivered in this configuration. The maximum length depends on the number of completion accessories installed. It can be one length from hanger to the packer, or it can be in segments for instance, from hanger to SCSSV and then next to the packer.

Tubing stress analysis indicates that well depths over 6,000 meters are still well within the operating envelope of the tubing.

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