Ten years ago, Corac engineers set out on an engineering challenge to fit an already small compressor into a tiny package that would appeal to the global oil and gas industry. Today, Corac’s patented compressor technology has demonstrated that in some applications it could double the overall production of gas from a well.
Corac is a UK gas, air and energy technologies group, with a dedicated Technology Centre in Slough. Its brand of centrifugal compressors use a rotating bladed impeller to accelerate gas to very high speed, which then slows down through a diffuser to exit the machine at higher pressure than it entered.
Performance is related to the speed of the impeller blades. Corac Energy Technologies (CET) is thedeveloper. They use highly efficient permanent magnet motors and patented gas film bearings to provide frictionless support to the single rotating part. Tests in industrial settings have logged the shaft spinning for more than 27,000 hours at up to 72,000 rpm. At this speed, the blade tip is travelling at more than 500 metres per second (one and a half times the speed of sound, and at more than 2,000kph, almost as fast as the top speed of a Eurofighter Typhoon).
The engineers at CET first tackled the problem of size by producing an impeller one third smaller, and streamlining it further by removing the external cooling for the motor so that the gas itself became the coolant. The result is a compressor which is just 12cm across and around 70cm long. It fits completely inside a seven inch casing and was demonstrated in Texas last year in a live gas well, with more extensive testing since in CET’s UK facilities.
In these tests, the compressor has consistently produced a pressure ratio greater than 1.2 to 1 at an actual flow rate of approximately 20,000 cubic metres per day.
At these performance levels, CET has been working with energy companies to find the most valuable uses, and suitable configurations for this technology. One such case is to support the production of high performing wells where there are local variations in reservoir pressure. Prolific wells will deplete the local gas quickly, and then stop producing. After a period they can start up again at high productivity. A relatively small reduction in wellhead pressure, for example by 50 or 100 psi on a line pressure of 1000 psi can substantially boost production in the short term and keep the well flowing at high rates for longer.
Current calculations show that use of CET’s patented in-pipe compression technology could double the overall production of this type of well over a period of many months. In high performing wells, this is a really valuable result. Tests and calculations are continuing as CET and its partners define the best uses for this technology. Results are encouraging, as the alternative is to reduce pressure across the whole field using massive and very expensive central compression installations.