Charge-Air Compression Systems, the Calgary, Alberta, Canada, manufacturer of stationary and skid-mounted rotary screw compressors, nitrogen generation units and booster compressors for a variety of industrial applications, has developed a new nitrogen-generating system for use in oil drilling applications. The system is based on existing nitrogen-generating technology and is designed to reduce operating costs in drilling operations using the underbalance drilling method.
Underbalance drilling is used in combination with horizontal and multidirectional drilling. It involves the injection of low-density drilling fluid mixed with nitrogen into the underground field, immediately inducing oil flow to the surface. This method differs from the traditional overbalance drilling method, in which densified fluids are pumped into the downhole until the pressure gradually exceeds that of the formation, thus coaxing the oil to the surface.
"With underbalance drilling, you are in effect creating a free-flow well because you are in production while you are drilling," said Chuck Curtis, general manager of Charge-Air Compression Systems.Benefits of underbalance drilling include increased production from marginal wells and reduced contamination of the hydrocarbon field from drilling tailings and cuttings. Because nitrogen is inert, it does not cause downhole fires and is easily separated from the hydrocarbons.
Six years ago, only about a dozen western Canadian wells were drilled using this method, according to Charge-Air Systems. Last year, it was employed on 500 of the approximately 2000 horizontal or multidirectional wells drilled, the company said.
The primary drawback to this drilling method is the need for nitrogen to be present at the well site. Some sites are in remote locations, requiring nitrogen to be transported to the well site. "On top of the transport costs, you also have the problem that liquid nitrogen vents from delivery trucks at the rate of 5 to 15 percent per day," said Curtis. "At some sites, you will have lost a big part of what you paid to have delivered before it gets there."
To combat this problem, Charge-Air Compression Systems developed its portable nitrogen-generating and compression system, which allows the nitrogen to be produced at the well site. "This isn't new and in fact it has probably been around for about 20 years," said Curtis. "Food plants, gas plants and oil refineries all generate nitrogen at their sites. The trick for us was to improve on existing technology and get to the market with a compact, fully mobile package encompassing on-site generation and delivery to the well head."
Charge-Air solved a big part of the equation by sourcing a portable nitrogen generating unit from Praxair. The nitrogen generator takes air from the primary air compressor package, uses it to create gaseous nitrogen, which is then delivered to the well by an engine-powered booster compressor.
The primary compressor package weighs 20,000 lb., is skid-mounted and fits into a container. The skid is 19 ft. long x 7.6 ft. wide x 7.6 ft. high and can be enclosed for use in cold weather applications.
The air compressor is driven by an eight-cylinder, turbocharged and aftercooled Caterpillar 3408E diesel engine rated 625 hp at 2000 rpm. Use of the electronically controlled 3480E engine offers the added benefits of data acquisition, increased fuel efficiency, and reduced emissions, the company said. The engine package, supplied by Finning Power Systems, Calgary, Alberta, Canada, includes a Donaldson air filter, Silex muffler and L&M Mesabi radiator. A Rockford Powertrain fan clutch, which actuates the belt-driven fan, is also included in the cooling system.
The engine drives an oil-flooded rotary screw air compressor through a Falk trunnion-mounted flexible shaft coupling. Rated flow is 1750 cfm at 200 psi discharge pressure. The compressor has a control system that provides zero to 100 percent stepless modulation. Compressor lubricating oil is circulated via air pressure from the compressor itself, thus eliminating the need for a separate oil pump.
Once the air leaves the compressor it is filtered and cooled by a Thermal Transfer aftercooler/radiator. Air is drawn over this cooler by a hydraulic cooling fan drive system powered by a Sauer-Sundstrand pump, which is driven off a h
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