Single piece centralisers

O&G. It’s been said that the challenge of extracting more value from existing reservoirs will become more acute in the coming years. What’s driving this?

CB. Demand. The demand for oil at $90 plus a barrel means almost any deposit is valuable as previously marginal fields become viable. Companies using new and existing technologies and aided by rising crude prices have turned marginal fields into viable producers. But the value equation is one for the oil companies; we are just a service provider using our engineering and manufacturing skills to apply advanced steel technology.

O&G. New sources of oil are tending to be in less accessible, more hostile environments than before. From the drilling and extraction point of view what are some of the challenges that you think will become more common in the next ten to twenty years?

CB. Without a doubt the main one is deep water drilling: more drill ships are being produced and rigs upgraded to operate in deeper waters. Currently, there is a rig in Australia drilling in 12,500 metres of water – now that’s a serious challenge. The deep water opportunities are predominantly off West Africa, the West coast of Scotland, the Gulf of Mexico, Malaysia and Australia.

O&G. Innovation in drilling techniques and technology is being driven by this need to reach further and deeper – have all components in the well-string kept up with the demands of more advanced drilling?

CB. Yes, I think they have. And the proof is that oil is being raised from ever greater depths, due to the innovation and money of oil field service companies. The technology and R&D required to produce and improve components has to be maintained at the highest level in order to meet new demands on drilling and drilling practices.

O&G. Your own company specialises in centralisers – how has your approach to this technology been driven by the needs for more advanced drilling?

CB. We have developed new products to overcome the step change required in centralisers, not just for deep water well drilling, which predominantly involves close tolerance casings, but also challenges brought about by changes in well design to which we have brought new designs and manufacturing methods.

O&G. You’re a young company, what led you to start up?

CB. The founders have all been working in the oil industry for decades. Over the years we had all encountered problems with centralisers of most types causing operational problems, resulting in serious down time and increased costs. As specialists in our field, we sought to address these problems by improving engineering, design and manufacture. We do not subscribe to the notion that failure of a product downhole should be tolerated; rather products that bring innovation, technology and unprecedented field-proven performance will bring rewards. I don’t need to tell you the delay and costs of pulling a drill string back out to retrieve a broken centraliser. Drilling engineers are a creative lot and back in the 1990s we had often discussed how we could make a better centraliser. If it works with mousetraps then a genuinely improved centraliser could have the oil industry beating on our door. By 2001 we had a production product and Centek Limited was formed.

O&G. Did the oil industry come calling?

CB. No of course not, we had to work very hard to get the message out. But what did play into our hands was the fact that there is a genuine problem with periodic centraliser failure out there and, it is an expensive problem. A conventional bow spring centraliser tends to be used in predominately vertical wells where product cost is also extremely moderate. We’re not in that market. We approached operators with much more problematic wells, drill teams tackling extended reach highly deviated wells, where the demands on a centraliser are of a quite different order. Or deep water wells. It is no exaggeration to say that once the rig teams used our centraliser they ordered more. We now supply every significant oil-producing region in the world.

O&G. How different is the Centek product?

CB. I suppose it is evolutionary in that it is a bow spring centraliser, but in design terms it is a revolutionary advance on what has gone before. Conventional bowsprings are either welded or hinged and both construction methods are susceptible to failure in the high-pressure conditions of modern wells. The Centek S2 centraliser is radically different in design and construction, with the end bands and bows manufactured from a single piece of heat-treated steel, giving unequalled flexibility, strength and performance. In six years of worldwide use we have never had a centraliser fail in the field and to my mind that makes it pretty revolutionary in user benefits too.

O&G. Why are centralisers so important?

CB. The centraliser is a relatively humble component of drill string technology and it is not until one fails or jams that most people start to take notice. The centraliser’s job is to assist the passage of the casing into the well bore to the desired depth, by keeping the tubular and its protruding connections off the borehole wall so as to minimise mechanical interference and differential sticking in the open hole. Once you get to final depth the centraliser then has to be tough enough to counteract the various forces exerted by the tubular, and centralise it within the borehole allowing fluids and displacing cements to move freely through the annulus.

O&G. What happens if a centraliser breaks?

CB. If it breaks on the way down, it can jam the casing. If it breaks once it is in place, particularly in highly deviated and horizontal wells, the casing will slump to one side placing greater strain on the casing, reducing centralisation and hindering cleaning out. This also makes it difficult to flow cement into the annulus. Inadequate cementing can result in unwanted mud trapped between the casing and the open hole causing casing pressure and gas migration. Incomplete mud removal can also result in mud channels, the mixing of subsurface zones and reduced fluid separation. Remedial cementation is expensive, and in the worst cases the liner may have to come out.

O&G. You touched on innovation and the technical demands placed on centralisers in deep water drilling. Can you expand on that?

CB. We introduced the Centek CT (Close Tolerance) centraliser initially to operations in the Gulf of Mexico working with US company Protech. A characteristic of deep water wells is reduced tolerances, as operators must run casing through existing casings and the centraliser has to be flexible enough to compress fully to pass through, and once in the open hole expand fully back to gauge with no risk of permanent set.

Because of the close tolerances involved, the CT Centraliser does not use steel stop collars on the outside of the liner casing, instead the end-bands are notched allowing limiting blocks made of Protech’s low-friction, carbon-fibre/ceramic to be inserted, which brings the additional benefit of allowing the centraliser to be pulled into the well rather than pushed, reducing drag.

O&G. How does this compare with previous methods?

CB. Primarily robustness, reliability and reduced drag. Previously centraliser subs were used, but these still use the old welded blade to end-band technology which can fail. Also threading the pin and box ends of centraliser subs is expensive. By comparison, the CT Centraliser is merely slipped onto the pipe, the limiting-blocks attached, and the product is ready to be run downhole when it arrives. That’s a big advantage for the rig teams.

The CT Centraliser is now being used extensively by Chevron and BHP Billington in fields across the Gulf of Mexico and we have signed distribution agreements in the Asia Pacific region.

About the contributor

Cliff Berry is Sales and Marketing Manager at Centek, a position he has held since 2001, and is responsible for worldwide sales. His oilfield career started in 1977 with Halliburton in Brunei, Malaysia and Sarawak as a cementer and tool operator. He has also worked for Diamond B (UK) Limited, and was European Operations Manager for BJ Tubular Services.