Centrica Energy said that, after 30 years years' production, pressure in the North Morecambe field had dropped.
The firm is spending Â£16m on diverting high pressure gas from the Rhyl gas field off Millom to flush out more at the Morecambe site.
The firm said the project would keep the site in production for 15 years.
Graham Sheddy, in charge of Centrica Energy's operations in Morecambe Bay, said: "We've been producing now for some 30 years and the site has made a huge impact on British gas and the UK economy as a whole.
"This project will ensure we can continue to produce in the area for another 25 years."
A new multimillion-pound offshore project to unlock gas reserves off the coast of Cumbria will safeguard 200 jobs, a power firm has said.