Flow assurance for deepwater projects11 April 2018
As they move into more challenging oil fields, companies need strong flow assurance strategies to ensure production. Johan Kristian Sveen of the Institute for Energy Technology tells us why flow assurance is so important, and runs through some of the difficulties posed by deepwater projects.
Following the downturn of the past few years, the oil and gas market has recovered to some extent. In January, crude oil prices topped $65 a barrel for the first time since 2014, and a growth in demand is beginning to offset the US production surge.
However, faced with seesawing prices and ongoing market volatility, oil companies can’t afford to be complacent. They need to make sure they are operationally and financially resilient, whatever market conditions may arise next.
As a result, flow assurance remains critically important. Referring to any discipline designed to secure or optimise oil production, a smart approach to flow assurance can take some of the uncertainty out of the equation. It can help a company cut costs and improve oil recovery, as well as minimising the risk of setbacks.
“Flow assurance is a very broad discipline; it can cover risk and it can cover financial implications, but historically speaking, it has covered a lot of fluid mechanics and thermodynamics,” says Johan Kristian Sveen, head of the fluid flow and process technology department at the Institute for Energy Technology (IFE). “As a field, it tries to address anything that can go wrong in production ahead of time. It is widely used by all the oil companies as part of their decision-making process.”
IFE is well known in the flow assurance world, having developed the pipeline simulator tool OLGA – now owned by Schlumberger. OLGA enables oil companies to calculate their flow conditions and dimension pipelines for transportation, all the way from the well to the platform. Considered the industry-standard tool, it dominates the market, to the extent that it is used in around 90% of offshore oil developments.
“The conception of OLGA is our proudest moment in time,” explains Sveen. “Since then, we have developed special-purpose simulator tools for the industry, all in parallel with OLGA.”
These tools include simulators for the separation of oil and water; simulators for waxy oils, which develop a gel-like structure at low temperatures; simulators for MEG– regeneration facilities; simulators to predict corrosion; and many more.
“We make these kinds of special-purpose simulator tools for all the cases that are so specialised you can’t do it with standard software,” says Sveen. “We also do laboratory work to verify computer models, and we provide flow assurance analyses and perspectives for oil companies.”
He believes that while flow assurance is now a relatively mature subject, with oil companies well versed in what it entails, there will always be scenarios in which the standard tools will not suffice. As oil companies develop more unconventional oil fields with complex fluid properties, they will probably encounter new flow assurance challenges requiring non-standard approaches.
“Oil companies come to us when they want to run experiments around a particular flow scenario that isn’t covered in the existing literature or software,” he says.
Flow assurance as a discipline began to emerge in the early 1990s, with Portuguese company Petrobas coining the term ‘garantia de escoamento’ – literally, ‘guarantee of flow’. The reason was clear: as conventional oil reserves began to decline, and the industry moved into deeper waters, traditional approaches to securing production no longer seemed appropriate.
Oil companies needed new ways to ensure success, even when dealing with extreme temperatures, large distances and great depths.
Flow assurance, then, was developed as a broad category encompassing many different engineering disciplines. Closely linked with multiphase transport technology, it has a software aspect – as per IFE’s simulation tools – and a more hands-on aspect. Engineers are required to handle and analyse many solid deposits, with a view to ensuring these don’t form blockages in the pipeline.
“Since flow assurance covers several siloes, you have to have people who are open-minded enough to work with fluid mechanics, thermodynamics and chemistry, and sciences that don’t normally talk,” says Sveen.
“The topic we think is most important is multiphase flows – being able to characterise, assimilate and predict the transport of multiple fluids in pipelines.”
While there are many potential flow assurance challenges, the central problem in deepwater production is the combination of high pressures and low temperatures. Both can affect the behaviour of the reservoir fluid.
To go back to basics – the oil in a reservoir flows to the surface through the reservoir pressure. The important factor here is the pressure drop between the reservoir and the receiving facilities.
If this grows too high, production will grind to a halt, so it’s important to reduce the pressure drop as much as possible.
“If the pipelines are too small in diameter, you get too high a pressure drop and you lose production,” comments Sveen. “If the pipeline’s too big, you get lower pressure drop, but you can get accumulation of liquids and potentially quite serious slugging issues, as well as deposition of sand and other solids, which can cause large issues in your processing systems downstream.”
Low temperatures, meanwhile, can ultimately cause solids to build up in in the pipeline. These might include gas hydrates, ashphaltenes, wax, scale and naphthenates.
“There are thousands of chemical components in oil, and at a certain temperature and pressure you get precipitation and the formation of solids,” says Sveen.
“For example, those solids can be hard waxes that sit on the pipe walls – anything that grows on pipe walls will cause restrictions in the pipe and will need to be removed.”
He adds that it’s extremely important to be able to predict this upfront, as it will tell you how often you need to conduct pigging or maintenance operations. This, in turn, will help reduce operational costs, and minimise the risk of production interruption.
“Scaling on pipelines can be tough and difficult to remove,” he says. “To some extent, it’s also relatively difficult to model and predict, although we’ve improved those capabilities for the industry in the past decade or so.”
On top of this, deepwater production can lead to issues with riser-based slugging. In a bid to solve the problem, an oil company might inject gas into the riser, but that cause instability.
This is a particular problem that IFE is working on at the moment, driven by the needs of deepwater projects in Brazil and the Gulf of Mexico.
“These are typically flexible risers, maybe 2,000m long, and with the intermittent gas lift that flows in those, you can get quite unstable flows, which can be an issue in terms of production,” says Sveen.
“You definitely want to avoid accumulation of liquids at the bottom of the riser, which may lead to increased back pressure in the wells, and, in the worst case scenario, kill off the wells, so you need to know your way around in the design process.”
Despite its complexity, he feels the industry in general has a good grounding in flow assurance.
“I commend the oil companies because they’re relatively good at identifying the threats, and are extremely good at focusing on minimising risk,” he says. “The key thing you need is informed people. If a certain topic comes up where they haven’t got the knowledge, they would typically come to a third party to develop the intelligence they require to move on.”
This often takes the form of a joint industry project, where several industry partners come together with research institutions or universities.
“This is the standard way the industry has operated for many years, in order to share costs and risks,” he says. “OLGA was developed in this way over the course of 35 years with several consecutive joint industry projects. They can be anywhere from massive, in the order of millions of pounds, to small one-week assessment programmes.”
While these projects require industry sponsorship, resources of public funding are available, particularly in Norway. In fact, Sveen believes that Norway’s tax regime is a reason why the country is strong in flow assurance.
He expects to see more projects focusing on digitalisation, as well as a trend for coupling simulation tools with real-world measurements.
“The flow assurance tools that we’ve used until now have been used mostly in the design phase of field developments,” he says. ”We can use those tools during production too, if we couple them with measured points. This works similarly to weather forecasting, where variables like wind speed and air pressure are combined with simulator tools to predict the weather tomorrow.”
Whatever new trends arise, he doesn’t anticipate that flow assurance as a discipline will change much over the years ahead, as the need to secure oil production in challenging reservoirs isn’t going away.
“Flow assurance is going to stay with us,” he says. “It’s a difficult discipline, because it covers different siloes, but it’s an important one.”