Supersonic gas separation without chemicals, heavy equipment

Subsea, downhole applications possible

Th 0600ostwister
Th 0600ostwister
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Shell has commercialized a new gas conditioning technology that does not require much of the heavy and expensive equipment commonly used to separate gas offshore. The system, known as "Twister," was invented in 1989 for the air conditioning industry. Shell acquired the technology for the oil and gas industry in the mid-1990s and has been developing it ever since.

The principle grew out of wind tunnel data. According to Kees Tjeenk Willink, CEO and Technical Director of Twister, water vapor separates out of an air stream when forced against a delta wing at supersonic speeds. Using this same principle, the Twister concept harnesses the natural energy of gas stored under pressure in a reservoir. By impacting that gas at supersonic speeds against a delta wing, the liquids and impurities are thrown out of solution. The conditioned gas remains in the middle of the stream, and the contaminants and liquids are thrown to the sides. A collection tube captures the gas and transports it to customers, while the condensates are captured and kept separate for cleaning and disposal.

Twister operates as a closed system, eliminating any problems with hydrocarbon emissions. In addition, the technology accomplishes gas dehydration and hydrocarbon dewpoint in one simple unit, without the need for chemicals such as glycol or methanol. This saves on the cost of chemicals and eliminates the need for glycol regeneration facilities, both a cost and weight savings. There are no moving parts in Twister and the unit is compact compared to conventional dehydration units.

Because it has no moving parts and requires no chemicals, Twister is being marketed as a solution for unmanned facilities. There is some discussion about future versions of the system being applied to downhole separation.

System functions

The official name of the unit is the Twister Supersonic Separator. To perform separation, the gas is delivered at the inlet unit and boosted to supersonic speeds. To achieve the pressure needed to move the gas at that rate, Twister makes use of the natural energy of the formation. Inside, the gas is moving at the rate of mach 1-3, and the temperature of the gas is lowered rapidly.

In an example provided by the Twister staff, gas with an initial temperature at the inlet of 25° C dropped to -45° C inside the Twister. This very low temperature helps the gas achieve cloud point, forming a condensate of water vapor and heavier hydrocarbons. Generally such a condensate is something to avoid. The water vapor can quickly crystallize forming a hydrate plug that can block flow lines.

Often chemical and mechanical remedies are used to avoid such problems. Twister is different. Because the condensate is moving so quickly through the inlet and resides in this pipe for a very short time, there is no opportunity for hydrate crystals to form and impede flow.

Moving at supersonic speeds the gas and condensate impact a specially designed wing section installed in the system. This wing diverts the flow, and sets the condensate into a high-velocity swirl. The centrifugal force of the swirl throws the condensate against the inside diameter of the pipe creating a liquid film on the inner wall of the tube. The tube is designed to transmit this film onto a separation tube.

The dry gas continues to flow through the primary stream swirling at a high rate of speed. To stop the swirl and level off the flow of gas, a weak shock wave is induced. The stabilized flow of gas still maintains 70-80% of the initial gas pressure after the processing is complete. The gas is then recovered from the flow stream using a diffuser.

Shell partners with Beacon to spin off technology

The manner in which Shell's Twister technology was developed is unusual. Shell established a company called Shell Technology Investments (STV), which was spun off of the Shell Technology Ventures group, the element that launched expandable casing technology last year.

The goal of STV is to commercialize new technologies developed internally at Shell. In the case of expandable casing, this was done in the form of two global joint ventures between Shell and Halliburton and Shell and Baker Hughes. The idea was to not only benefit directly from the technology by using it in Shell's own projects, but to offer it to the market in general. This would return some of Shell's research and development investment, but more importantly it would help proliferate the technology among service companies so that it would be more commonly used and advance faster.

This time around, the company took an even more radical approach. The Investment partnership is a 50/50 joint venture between Shell and the venture capital firm Beacon Group. Together, the two put $400 million into Shell Technology Investment Partnership (STIP) with the goal of advancing new technology by forming startup companies based on that technology.

STIP's initial project is the Twister. The officers of Twister, from Shell, are those most closely associated with the technology. The idea, according to Kees Tjeenk Willink, with the Twister Venture Team is to have a company backed by Shell and its partner that acts like a startup. This is an extension of the licensing agreement approach Shell took with expandable casing.

Tjeenk Willink said that arrangement was a good step, but the formation of a separate company eliminates the bureaucracy of large corporations and makes the resulting company more responsive to the developing market. In the future, it is possible Shell and Beacon will sell off a portion of Twister to outside investors or even take the company public. In the meantime the goal is to have a lean well-funded start-up that can develop the Twister concept into a suite of products.

Tjeenk Willink said Twister is the first of what Shell hopes will be many small companies based on unique technologies the company either developed internally or encountered in the market place. The goal to bring forward three or four of these companies per year. In an era when the oil companies are closing ranks technologically this is an unusual approach.

More typical is the policy where an oil company puts the burden or R&D and technology development onto the service company preferring to confine its risk to the produceability of wells. In an era of consolidation and unstable oil prices, Shell did not think it made sense to put all the R&D burden on service companies which are also under tremendous cost pressure from the oil companies.

Shell, Tjeenk Willink said, was concerned about the ability of these companies to develop the needed technology to perform some of the more demanding drilling forecast for the ultra-deepwater. To ensure the technology will be there when needed, Shell has developed this model to bring ideas forward to the market without affecting the company's core business.

Shell chose Beacon as a partner because of the company's experience bringing oil patch companies public and access to the emerging technologies of oilfield-related companies seeking venture capital. Tjeenk Willink said Shell chose to partner in the creation of Twister rather than go it alone for the same reason the company takes concessions on oil fields rather than a 100% stake. Not only does this spread the risk, but it gives Shell access to Beacon's core competencies. In this way Shell commercializes new technology and learns the business of bringing new companies online.

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