Industry body Oil and Gas UK has estimated in the past that tax breaks could stimulate investment by up to £2bn.
And the chancellor said the changes would give companies an incentive to "get the most out of" older fields.
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The brown field allowance will shield up to £250m of income in qualifying brown field projects, or £500m for projects in fields paying Petroleum Revenue Tax, from the 32% supplementary charge rate.
The chancellor increased this charge in his 2011 budget to fund a fuel duty cut after a surge in global oil prices.
The level of relief available to an individual project will depend on its size and unit costs.
Speaking about the new allowance, the chancellor said: "This government has signalled its absolute determination to get more investment in the North Sea, a huge national asset."
(NE)
