Subsea Valves for Pre-Salt Drilling

Valve World Americas had the opportunity to speak with an industry expert about the challenges for oil production in the presalt. For example, the types of valves used in offshore and subsea applications, and some of the technologies that make this sector of the industry so unique.

Valves for Offshore and Subsea Applications

The type, size and material of valves vary greatly in offshore applications. The simplest way to discuss valves used in subsea oil production is therefore to first identify which part of the process is being discussed. Just looking at a wet X-mas tree (see Figure 1) on the ocean floor, for example, one can find ball valves, check valves, choke valves, slab gate valves, and emergency shutoff valves.

An FPSO (floating production storage and offloading) is a type of oil platform typically used in to collect, treat, and store the oil from the subsea reservoirs. Depending on the plant complexity, they may use thousands of valves. “An FPSO is essentially a giant ship that receives the oil. This oil is unrefined and typically consists of a mixture of gas, liquefied gas, water, and crude oil. Once the ship has received the mixture, it is treated and stored for future offloading. Each application used in this process, from the riser transporting the oil to the vessel, to the tanks that store it, use a number of valves. However, one can consider the most important valves of the entire operation the subsea and topside shutdown valves,” explained the industry expert. As they are designed to cut off the flow of oil automatically in case of an emergency, shutdown valves are essential to the safety of both the onsite personnel, and the surrounding environment. “Once the oil and gas has been separated and treated, it is offloaded to a tank ship – if the oil platform is an FPSO. If it is an oil platform without storage capability, such as a semi-submersible platform, the separated hydrocarbons are sent through pipelines to the shore, using Brazil’s Rota 1 and Rota 2 systems, for example,” continued the industry expert.

There are substantial differences between the specs of topside and subsea valves. No matter how shallow the water depth, for a subsea valve the standards change considerably. A topside ball valve is commonly designed according to the API 6D, but a subsea ball valve has to comply with standards such as API Spec. 17D (Design and Operation of Subsea Production), API Spec. 6DSS (Specification for Subsea Pipeline Valves), API Spec. 6A (Wellhead and Tree Equipment), and API Spec. 6C (Specification for flanged steel Gate and Plug valves for Drilling and Production Services). An example of a subsea ball valve is shown on Figure 2.

In addition to the design standards, subsea valves also have to comply with more rigorous materials standards, especially in the pre-salt fields. Why? Because the reservoirs contain hydrogen sulfide (H₂S) and carbon dioxide (CO₂). “When you have these chemicals, other issues can occur. For example, CO₂ added to water creates carbonic acid, and H₂S added to water creates sulfuric acid. H₂S is responsible for the ‘hydrogen embrittlement’, which is a problem that affects metallic structures and components causing a decrease in the mechanical properties of the materials, mainly increasing the fragility and decreasing the toughness and strength of the materials. Therefore, in these fields, you need to use specialized materials to prevent problems and failures from happening,” stated the industry expert.

What is the Pre-Salt?

160 million years ago, when the supercontinent Gondwana started breaking apart making way for South America and Africa, a layer of salt was created. This salt layer varies in size and can exceed 2,000m thick in some areas.¹ The reservoir rock located below the salt layer is known as ‘pre-salt,’ and can be found in ultra-deep waters, off the coast of southeastern Brazil (See Figure 3). Until 2006, exploration activities had focused primarily on post-salt objectives – meaning ‘above’ the salt layer; since then, with great technological advances, the pre-salt layer has become an exploration frontier that has shown great results.¹

What Valves Should Be Used in Pre-Salt Applications?

“When working on a pre-salt project, the mindset with which you approach the topic of valves, changes,” expressed the industry expert. While the type of valves used on these projects are the same as those used in shallow subsea system, the specifications are not. As the equipment will be used at the deepest water depth, there will be significantly more pressure, as well as the occurrence of hazardous chemicals such as H₂S and CO₂. They can create a number of difficulties, including, but not limited to, severe corrosion. 

“The material you use for the valves needs to have a very high chemical and mechanical resistance to both corrosion and high pressure. It all comes down to the materials the valves are made of,” the expert explained. Valves to be used in pre-salt applications also require more stringent testing during manufacturing before they can be sent out and used in the field. “The API 6A PSL 3G standard is the ultimate test that every manufacturer needs to pass before sending their valves out into the world for use in pre-salt,” said our industry expert. “When you talk about subsea valves, the name of the game is safety. Everything is related to safety – make sure the materials are right for the job, and there will be no failures.”

Using New Technologies Offshore

To produce oil and gas in the pre-salt means to produce in a location “300 km off the coast, with water depth reaching 2,200 m and reservoirs nestled 5,000 m below the seabed, including a salt layer that is about 2,000 m thick.”² In order to overcome this challenge, pre-salt production required the development of a number of new technologies, such as the first Buoy Supporting Risers (BSR). “Risers are pipelines that take oil or gas from the seabed to the platform. In order to sustain the risers that are connected to the wells’ subsea pipelines, buoys are installed at a point between the seabed and the surface of the sea (about 250 meters in depth). This allows them to be connected to the FPSOs through flexible tube spans. With this setup, the floating platform’s movements are not transferred in full to the rigid risers, reducing the damage caused by fatigue and ensuring their useful life even under severe meteocean conditions.”²

Another new technology is related to environmental concerns. “One of the biggest focuses for offshore oil production is ensuring that CO₂ is not leaked or released into the atmosphere. To combat this, many of the major oil companies have started reinjection the CO₂ into the field,” explained the industry expert. “This process is relatively new and highly beneficial. For a long time, there were not many viable disposal options to avoid thus type of emission. Now companies have started to reinject the CO₂ into the oil reservoirs as the oil is produced.” To that end, Petrobras introduced the first separation of carbon dioxide associated with natural gas in ultra-deep waters (7,283 ft) with CO₂ injection into producing reservoirs. “In a few pre-salt wells, the oil that is produced is associated not only with water and natural gas, but also with CO₂. The CO₂ that is produced is separated from the oil and natural gas using a sophisticated membrane system that separates carbon dioxide molecules from the other fluids through selective permeation. Once separated, the CO₂ is reinjected to increase pressure in the reservoirs and well productivity and to decrease greenhouse gas emissions.”²

The Subsea Market

As our industry expert would say, there are many manufacturers who sell topside valves, and valves that can be used in shallow water (down to approximately 500m). “For real subsea valves, designed for much greater depths, there are only a few high-quality manufacturers across the globe. The exclusivity of these applications, and the necessity to ensure their quality, makes manufacturing and selling them a completely different selling process than for topside valves,” the expert explained. When selling the subsea valves, the manufacturers have to be certain that they will not fail. If there is a failure, there will huge production losses. This is why critical inspection and stringent testing is so important.

“When a major oil player is looking to buy a subsea valve, they know who they are going to turn to, because these companies have proven themselves in the past. Lead times are considerable because the process to get these valves manufactured and tested is tough and takes a long time,” the expert continued. “In terms of pricing, a subsea valve could range from USD $500,000 to USD $1 million. An entire subsea Christmas tree could cost several millions of dollars, because they are very large equipment – almost the height of some buildings. Considering all of these factors, it is easy to see that selling and buying a subsea valve is a completely different process.”

The Future of Offshore and Pre-Salt Drilling

When contemplating the future of drilling projects and subsea exploration, our industry expert foresees a lot of energy being put into pre-salt drilling over the next few years. “There will be a large effort to produce oil from the pre-salt layer. Brazil is adding new FPSOs, as well as offering some of the pre-salt fields to be explored by other international oil & gas players. There will be significant competition to get these pre-salt opportunities,” the expert relayed. “The world may be starting to look to wind and solar energy overall, but subsea oil production is not going anywhere for a long time.”

1. “Brazilian Pre-salt.” Accessed at: https://www2.deloitte.com/br/en/pages/energy-and-resources/upstream-guide/articles/pre-salt-brazil.html 

2. https://presal.hotsitespetrobras.com.br/pioneeringtechnologies/#3