# Compressors are heart of natural gas production

By Norm Shade Published: August 6, 2014 2:30PM
With the development of the Utica Shale, more and more natural gas compressors are appearing on the Eastern Ohio landscape. Gas compressors have always been part of Ohio’s oil and gas production, however, the size of the Utica play requires more and larger compressors than ever before.
Raw natural gas is commonly collected from a gr oup of adjacent wells and, after processing at the collection point to remove water and natural gas condensate, it is pipelined to a gas processing plant. After further processing to remove salable liquid hydrocarbons (ethane, propane, butane, etc.), the natural gas is then delivered into the interstate pipeline grid, which takes it to commercial, industrial and residential customers.
Natural gas compressors are literally the heart of natural gas production. Sh ale gas wells tend to produce at very high pressures and flow rates initially, but they decline rapidly to a lower level that is sustained for many years. As the pressure declin es, gas compressors must be deployed to boost the gas pressure high enough to push it through pipelines to market. Just as the heart is vital to collecting and pumping blood throughout the body, a gas compressor collects natural gas from underground wells and “pumps” it to market.

Gas compressors are prevalent throughout the interstate pipeline grid and in gas processing plants, strategically located in a limited number of centralized plants. But upstream of those plants are many more “gathering” compressors, lo cated at or near the actual we lls that produce gas from deep underground. Gathering compressors typically sit out in the open, not housed in buildings. They pull gas from individual or a group of wells and boost the pr essure to push it into a gathering pipeline that leads to various types of processing facilities.
Most natural gas compressors are reciprocat ing (i.e., piston-type) compressors, driven by reciprocating engines that use natural gas fuel. Much larger than the average 110 to 150 horsepower automobile engine or even a 450 horsepower semi-t ruck engine, turbocharged compressor engines are typically more than 1000 to as high as 4500 horsepower or even larger. Engine exhaust is quieted by a large industrial muffler, and to meet environmental regulatory requirements, e xhaust is treated with a catalytic convertor, just as automotive engines are.
Large industrial gas compressors have two to six cylinders with in ternal pistons and check valves. Connected into a pipeline, a compressor draws gas in at a low pressure and delivers it out again at a higher pressure to move it through the pipeline system. Depending on the needs of the particular gathering system, the cylinders on a compressor may be configured to operate in parallel or in series (called staging). Most gas gath ering compressors are configured in two- or three-stages.

10 / 28 / 201 4The compression process naturally causes the gas to heat up, so cooling is required before it enters the next stage for further compression or before conti nuing on into the pipeline. This is accomplished with large air cooled heat exchange rs. Similar in principal to the radi ators in cars and trucks, the heat exchangers also cool the engine and compressor.

The engine, compressor and heat exchanger are mount ed on one or more welded I-beam skids that allow the packaged compressor system to be built ina factory and transported to a field site on one or more large trucks. The skid also provides a platform for mounting accessory items such as gas separators that remove small am ounts of liquid from the gas, pulsation bottles that smooth out the pressure waves from the compressor, controls, and other equipment.

Most compressor packages are built in the S outhwestern states, however, Youngstown, Ohio packager, Dearing Compressor & Pump Co., has enj oyed major growth with the development of the Marcellus and now the Utica Shale. Another Oh io company, Ariel Corporation in Mount Vernon, manufactures the majority of th e large reciprocating gas compre ssors used throughout the world.
Most large compressor packages are mounted on c oncrete slabs. Some are housed inside buildings, but most gathering compressors operate out in the open. Gas gathering compressors operate around the clock, often running more than 8400 hours a year. To put that figure in perspective, driving an automobile 15,000 miles a year at an aver age speed of 50 mph takes only 300 hours.
A typical new Utica Shale gathering compressor ha s the capacity to deliver as much as $50,000 of natural gas each day, make high reliability extremel y important. Computerized controls operate and monitor the engine and compressor, keeping the syst em operating reliably or automatically shutting it off if maintenance is required or a problem occurs . Satellite or cellular links allow operators to remotely monitor the compressors, and mechanics are automatically called out when unscheduled maintenance is needed. With annual maintenance and major overhauls every 4 or 6 years, these large compressor packages typically last for more than 20 years.

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