Royal Dutch Shell said Tuesday it planned to develop natural gas reserves in China with the nation's state-run energy giant CNPC, as the Asian giant steps up efforts to develop clean sources of energy.

Shell said the two firms would tap tight gas, a natural gas that is difficult to access because it is contained in rock that must be fractured or broken before it can flow easily to production wells.

The reserves are located in a 4,000-square-kilometre (1,600-square-mile) area in the southwestern province of Sichuan, the British company said.

The agreement between the two energy giants has been handed to the Chinese government for approval, Shell chief executive Peter Voser added at a press conference in Beijing.

Voser declined to comment on the size of the investment in the natural gas field or the expected output.

China National Petroleum Corporation is the parent of PetroChina, which has made a joint bid with Shell for Australian coal seam gas producer Arrow Energy.

Arrow on Monday recommended shareholders accept the 3.15-billion-dollar offer for its Australian assets, which include the country's biggest holding of methane gas from underground coal seams.

The transaction needs the approval of shareholders and Australian regulators.

Shell and PetroChina already have a joint venture operating the Changbei tight gas field in China's northern Shaanxi province.

Late last year, the two companies agreed to develop shale gas, which is also difficult to access, in Sichuan province.