Sand erosion

The eroding effect of sand is a serious concern for oil rigs, especially in a low oil price environment. Oil and gas drilling companies are constantly fighting lower and lower margins, so any damage to equipment from the elements is a threat to business.

Sand can clog production equipment, erode down completion components and interfere with infrastructure. This means that companies have to consider new and innovative ways to keep damage to a minimum and thus spend less time and money on repairs.

Erosion is dependent on velocity and, to a certain extent, on the size and sharpness of sand particles. In different areas of the world, the shape and size of sand particles vary considerably, from small, rounded particles that probably have little effect, to large particles that have a larger impact.

According to Permasense business development director Tom Fuggle, it’s not so much the wells that get the most sand that are the problem, but the ones that have unpredictable spikes of it.

"Most people will tell you that sand production is unpredictable, it’s transient, it comes in spikes," he says. "So essentially you’re managing the unknown the whole time."

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"We have a lot more knowledge of sand production now than we did 20 to 30 years ago, but every well is different," he adds.

Sand damage: an opportunity?

Fuggle says that sand management is a complex subject, but what is obvious is the damage it does to oil and gas rigs.

"Sand at its worst can go through half an inch of pipe in a 12-hour shift," he says. "So you can actually penetrate a pipe in a 12- or 24-hour shift if you’ve got sand that is really aggressive."

However, rather than a problem, Permasense sees this as an opportunity to get more out of existing systems by adding ultrasonic sensors to oil pipes to monitor where erosion is occurring.

"Sand at its worst can go through half an inch of pipe in a 12-hour shift."

Permasense is a world leader in constructing continuous integrity monitoring systems for oil and gas production facilities, allowing customers to measure wall thickness loss in real time.

The ET sensors – launched last year – are designed for upstream applications where temperatures are generally lower than in refineries. Around 70% of Permasense’s sales have been through the need to combat sand erosion at downstream assets like oil platforms.

The sensors work by sending a ‘thickness value’ back to the main gateway, using ultrasonic wave pulses. The first is a wave that travels via the surface, followed by a backwall (inner pipe) reflection, and then a second backwall echo. The time difference and ultrasonic wave velocity are then used to calculate the thickness of the pipe wall.

The competitive edge

Fuggle says that one industry edge that the ET has is that it is non-intrusive, meaning holes don’t have to be punched into pipes, and production doesn’t need to cease at all to fit them.

"It’s wireless and it’s battery powered, so we don’t need to run a lot of cables," says Fuggle. "The installation is extremely simple and we can fit them virtually on any existing plant anywhere."

In original sensors, the metal coatings on pipework and equipment had to be broken and sealed with rubber. However, the new system can sense through the protective layer, so installation is quick and easy.

"Traditional manual inspection to gather wall thickness measurements is made even more expensive offshore than onshore," says Fuggle. "When you put one of our systems in, the cost of the product itself, the Permasense element, and the cost of installing it are quickly outweighed by the financial payback."

Previous methods of sand detection such as acoustic sand monitors and probes worked by assessing the sand loading and the likely damage, but Fuggle says this was indirect and somewhat empirical.

Probes tend to be in straight pieces of pipe, and typically the erosion occurs on bends, where it is hard to fit them. In comparison, Permasense sensors can be fitted directly on pipes in critical areas.

"What customers do is they’ll put our sensors on each of the wells, and then they can in real time see which well is actually generating sand and indeed whether that sand is causing erosion," says Fuggle.

Information is constantly being sent over the wireless connection and changes can be made to operations to counteract this. If a lot of sand is detected at one well, then production can be halted there by choking the well back and another one accessed, and so on. Fuggle says that this avoids high levels of erosion and is a significant advantage over other systems.

"By putting our sensors on, they can actually see where they’re getting erosion," he says. "They are very accurate point measurements."

Solutions for companies old and new

Fuggle says that reservoir engineers have to try and predict what will come out of the reservoirs, and struggle to do this for 2 or 3 years in advance, never mind over 20.

"When you think about some of the North Sea wells and rigs; they’re 30 odd years old," Fuggle adds. "At end of life they’re dropping the pressures, they’re pulling the reservoirs much harder, and as a result they’re pulling sand."

An area that Permasense is currently focusing on is erosion in the choke valve, because that is the key controlling device, says Fuggle. If that fails, effectively you’ve lost control.

One particular customer, Fuggle says, looked to start up a well, and when they tried to start it up a couple of years ago, they had such high erosion rates that they felt they couldn’t control it.

"Their main problem was that they didn’t know until they did manual measurements that they’d lost so much material," he says. "They’re now going to use our equipment to start the well up so that they can control the well in real time."

"At end of life oil rugs drop the pressures, pull the reservoirs much harder, and as a result they’re pulling sand."

Generally, there are some difficult areas to access on offshore oil rigs, and safety is an increasing concern for big companies. Manual inspection, according to Fuggle, is the main competitor to sensors, however this places rig workers in danger.

Very low power batteries eliminate the need for battery replacement underwater, and as sensors can carry out the work of inspectors, it eliminates the need to place people in areas of potential harm.

In the end, it’s all down to risk and reward, and whether companies think that fitting an expensive sensor system – some reaching $100,000 – is worth the return.

"If the customer wants to run a pilot, the last thing he wants to do is commit to large sums for integration and installation," says Fuggle. "People have to have time to get used to our systems, appreciate the value they have, and gain first-hand experience of our case histories."

Combined future?

With easy installation, companies are more willing to commit to a system, Fuggle says, but to justify million dollar sales in the current environment is quite a challenge.

As for the future, he notes: "I think you will find that these systems coalesce so we will start to take on other techniques, other devices, and integrate them into our system."

Fuggle adds that it will probably take Permasense incorporating other technologies and perhaps partnering with other organisations for these fully integrated systems to become the norm.

One advantage of such a partnership is that customers rarely want to deal with several different suppliers, who all provide different solutions and protocols, as this usually means higher costs in the long term.

"If we could give the customer 90% of what he wants for a relatively low incremental cost, then it’s clearly a lot more attractive to the customer," Fuggle says. "And I think that’s where the technology is going to go in the future."

Fuggle believes that the biggest future step lies in data, and how to turn the massive amounts of information gathered by the sensors into something useful.

"We have one customer that’s actually looking to integrate our data directly into their process control system and actually trigger alarms from our data," Fuggle says. "We are seeing the online integrity data being correlated with other recorded process variables.
"This is generating significant insights into the causes of corrosion and erosion, which helps hugely in designing a mitigation plan."