Wärtsilä’s acquisition of the British-headquartered, global engineering company Hamworthy early in 2012 has added a portfolio of high technology products and systems to the Finnish power solutions company’s offering including vessel internal electrostatic coalescer (VIEC) technology, which improves the efficiency of the separation process, thus enhancing oil recovery. Originally developed by ABB Corporate Research Center in Norway in 1998-2001, VIEC technology is covered by worldwide patents.
Existing fields are maturing and experiencing more water coming out of the reservoirs with less oil, exceeding the design basis for the production equipment in use. Reservoir pressures are dropping, which leads to the installation of pumps and once again causes problems with stable emulsions in the separation process. Future oilfield developments will be more challenging as 50% of the world’s remaining oil reserves can be characterized as either heavy or extra-heavy oil.
Traditionally, heavy oils are separated by using huge separator vessels and allowing extra long periods for the water to settle, as well as adding large quantities of chemicals and heating the crude oil to temperatures of up to 150°C. Significant additional operational costs are inevitable. “Improving the efficiency of the separation process by means of VIEC technology can reduce fluid temperatures below 100°C, allow the optimization of separator vessel size and reduce the use of chemicals,” says Erik Bjørklund, innovation manager and acting director of separation technology at Wärtsilä. “This not only has a positive effect on capex and opex, but also on levels of CO2 emissions.”
Coalescence of dispersed water in an oil-continuous phase can be greatly enhanced by subjecting the emulsion to high-voltage electric fields. This phenomenon is called electrostatic coalescence. When an emulsion consisting of a polar liquid dispersed in a non-conductive liquid is subjected to electric fields, several physical phenomena cause the droplets to merge. In a VIEC system, two primary effects can be identified. Firstly, an electrical dipole attraction causes droplets to coalesce. Secondly, the electric fields distort and weaken the film, i.e. the surfactant components surrounding the water droplets.
Separation efficiency can usually be influenced by increasing gravity forces, density difference and the diameter of the water droplets or by reducing viscosity. Droplet growth caused by the electric fields therefore leads to a substantial growth in the settling velocity of the dispersed droplets and enhances separation efficiency. As the surfactant components prevent coalescence, proper chemical treatment such as a demulsifier is also needed.
“A VIEC system typically consists of 150–200 electrodes – depending on the size of the separator – forming a cross-sectional wall within the separator which allows the fluid to pass the electrodes and be exposed to the electrical field,” Bjørklund says. “Following electrostatic treatment, water quickly settles to the bottom of the separator and is piped to the water treatment system, while the crude oil flows across to the oil section.”
Installing VIEC technology has to be planned carefully. The equipment must be a correct fit at the first attempt and the installation process must be performed quickly to reduce downtime. The whole installation also has to be performed through a manhole just 18-24 inches wide. As well as being designed to pass through the manhole, the component parts have to be bolted together inside the separator unit. “To secure safe and on-time installation, Wärtsilä performs a full-scale test installation prior to equipment delivery,” Bjørklund says. “While installing a VIEC system inside a separator takes just a few days, additional time is required for depressurizing and cleaning prior to installation, and pressurizing and re-commissioning after the installation is complete.”
To deliver the correct VIEC solution for each customer, Wärtsilä analyzes and characterizes the crude oil that it will be handling. “Crude oils are very complicated liquids and are all very different by nature,” Bjørklund says. Customers send a 20–100 liter sample of crude to the Wärtsilä laboratory in Norway. Wärtsilä has analyzed more than 80 different crude oils from all of the world’s primary crude oil producing zones. In addition to a library of real crude oil samples, this allows Wärtsilä to build up a unique database of knowledge.
Characterization of the crude oil includes determining its dielectric properties, viscosity, density, surface/ interface characterization, asphaltene stability and emulsion stability, as well as inorganic/organic solid quantification and residual water quantification.
Following the characterization process, a range of separation tests is performed to verify the effect of a VIEC in combination with different chemicals. Separation testing focuses on retention time in the electrical field, chemical screening, turbulence, shear, recirculation patterns, flow entrainment of small droplets and other dynamic effects.
“As well as verifying the use of electrostatic technology to treat the crude oil, this testing also provides data for oilfield owners and operators, which allows them to optimize and remove bottlenecks from the overall separation process. This can result in smaller separator vessels, reduced processing temperatures and reduced dosing with chemicals.”
Traditional electrostatic coalescer vessels are equipped with uninsulated high voltage electrodes that cannot be exposed to gas, and the more than 10-15% water remaining in the oil. A significant advance has been the development of an electrostatic device with insulated electrodes, making it possible to handle 100% water as well as any gas present. This allows such devices to be installed into upstream production separators.
“We have successfully delivered and installed vessel internal electrostatic coalescers into more than 30 test and production separators treating crude oils ranging from API 12–50°, with an equal split between retrofits and newbuilds, and covering most of the major national and international oil companies,” Bjørklund says.
The newest generation VIEC technology has been delivered to the FPSO OSX-1, the first floating production, storage and offloading unit in OSX’s fleet, which is working for OGX in the Campos basin off Brazil. The system has been installed in both the first stage separator and the test separator in order to improve processing of the heavy crude oil on the Waimea field in the Campos basin. An installation at Qatar Petroleum’s onshore Dukhan field has led to a reduction of the basic sediment and water levels from about 5% to 0.2%, well below the target level of 2%. Salt content in the crude oil was also reduced by up to 90%.
“We are pleased to provide advanced technologies resulting from more than a decade of continuous R&D combined with operational experience from a number of deliveries since 2003 to improve oil and water separation performance for our customers,” Bjørklund says. “We believe this technology will support future developments of heavy oil fields.” OE
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