Downhole equipment designer ALC has developed a new cable clamp to attach power and instrumentation cabling to downhole tubing, the BossClamp, which realises considerable cost savings]
Downhole equipment designer ALC has developed a new cable clamp to attach power and instrumentation cabling to downhole tubing. Called the BossClamp, it features superior protection to the cable whilst realising considerable cost savings. The rugged composite fitting can accommodate variations of cable types and tubing diameters.

Importantly, it is quick to install and remove.

'There are a number of oil well operations that require the use of downhole equipment such as pumps, well sensors, etc, to maximise well production' said Director Marcus Dixon: 'These downhole systems often necessitate external power, instrumentation and control cabling that must be run outside and connected to the tubing.

It is not only essential to tie the cable and tubing together securely, but offer it protection against the axial stress, radial crush and twisting forces produced as the pipe and cable system is fed into the hole.

This is particularly true when the cables have to pass over the coupling where the two pipes are connected.

'Abrasion is also encountered during installation, the severity of which is governed by well casing cleanliness, joint profiles and deviation.

This also requires protection for the cable.' ALC looked at the demands of its own expanding suite of downhole tools and equipment that it is currently designing, and specifically at the available cable clamping systems on the market.

They quickly realised that in by far the majority of applications, the commonly used steel protectors were over-engineered, cumbersome and unnecessary.

They therefore set about designing their own solution.

Current attachment methods.

Metal banding is historically assumed to be the cheapest way of connecting the cable to the pipe.

The principal drawback is that it pulls in on the cable and the clips can get caught as they pass through the BOPs and the liner hanger.

If they become sheared off, the metal band may cut into and sever the cable.

The metal banding can also corrode, especially in high-brine annulus fluids.

To prevent this, some operators specify banding composition in exotic materials such as Inconel; however this has an impact on price.

For greater protection, the operator can opt for a pressed steel clamp.

More expensive, this does provide adequate protection over couplings for the cables.

A tapered collet pin secures the clamp in place, although it has been known for these to break and become potential hazards and result in costly fishing operations in the hole.

The third main type is a cast clamp which provides the best protection to the cable.

However it is large, relatively heavy and particularly expensive, maybe US$60-100 each compared with US$2-4 for the metal banding.

Installed at points 30ft apart along the typical 5000ft length, these become an expensive addition to overall cost.

They are secured by bolting.

It can be easy getting them on but problematical removing them, impacting on rig time.

They are also tubing size and type-dependent, which may cause logistical nightmares for the end user.

Performance Benefits.

The design objectives of the BossClamp were to combine the functionality of the high cost protectors yet offer a competitively priced improvement to banding.

The initial idea of a one piece moulding that met all requirements soon proved to be a less effective solution to the clamping task than an assembly with specialised components.

After prototyping and initial testing, a small, strong protector moulding with a standard metal band retaining it to the tubing proved the best solution.

The BossClamp is manufactured in composite materials that will provide sufficient mechanical strength and temperature resistance to compete with steel products in most applications.

However, the additional benefits of using advanced composites in the design are not available from conventional clamps.

These include.

* Cost effectiveness.

* Lightweight.

* Immediately suitable for any pipe diameter or joint length.

* Corrosion resistance.

* Low Inventory requirement for manufacturer and end user.

* Rapid installation and removal time.

* Extremely low profile.

* Lower friction during installation.

The key element of the BossClamp design is that it achieves a very low profile which minimises contact with the pipe wall and therefore offers low resistance when running in the hole, yet is substantial enough to offer the cable suitable protection as it lies over the coupling joint outer diameter - the widest part of the tubing.

The design also protects the retaining strap from any abrasion or impacts.

The clamps can be attached using either conventional steel banding or a specialised friction welded plastic strap.

Lightweight and easy to manufacture, these can be transported by airfreight for rapid distribution and use.

In the engineering development, ALC examined a range suitable varieties of composite materials looking at chemical resistance to well bore fluids, abrasion and shock resistance, creep resistance, cost of material, cost of tooling and ease of processing etc, and evaluated them against criteria simulating downhole oil well conditions.

'We built a test rig for simulating the abrasion experienced while running the product into oil well casing,' said Marcus Dixon: 'A wheel was run against the moulding for the equivalent of 21,640ft (or 541 joints) with a constant 2.5 ton sideload, of a sort that would never occur in the field use.

If the product could pass this test, it would meet almost any downhole requirement'.

Hot water was continuously flooded into the rubbing zone during this time.

The testing focused on the protector moulding abrasion resistance and the temperature stability during high service temperature conditions.

The BossClamp is part of a downhole equipment package currently being developed to facilitate artificial lift.

Apart from the BossClamp, ALC are developing novel downhole sensors and a truly innovative downhole motor.