Sky News understands that Carlyle, which is one of the world's biggest backers of oil and related businesses, is likely to announce the takeover of EnerMech within days.
The deal will value the company at about ten times last year's earnings - the last period for which figures are available - and underline the rebound in asset prices in the oilfield services sector.
EnerMech is owned by Lime Rock Partners, another buyout firm, which invested in it a decade ago.
The company, which specialises in mechanical and electrical services, recently made it into a Sunday Times ranking of the fastest-growing privately owned mid-market businesses in Britain.
Carlyle's investment is being made through its International Energy Partners team, which focuses on deals in oil and gas exploration and production, refining and marketing, and oilfield services.
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In total, Carlyle's energy, natural resources and infrastructure platform has $25bn in assets under management and 107 active portfolio companies.
A Carlyle spokeswoman declined to comment on Friday.