China's natural gas reserves as measured by the country are exaggerated in many cases and only part of the reserves can actually be developed, a senior adviser to Sinopec , Asia's top oil refiner, said on Friday.
Inflated estimates have also caused low utilisation of production and transportation facilities and inefficient investment, said Zhang Kang, a senior geologist and deputy director of a consulting committee to Sinopec.

"Reserves that have no chance to be developed should be peeled off," he told an industry forum.

But he did not provide any estimate of the over-evaluation.

Zhang said the Qianmiqiao gas field, the largest in Bohai Bay, was certified in 1998 to have 30.6 billion cubic metres of proven geological reserves, but the field has been barely developed ever since due to very low recoverable reserves.

Output at Sulige in Erdos basin, China's largest gas field, totalled only 274 million cubic metres in 2006 after five years of development, and production in Erdos basin last year fed only 38.7 percent of pipeline capacity, he said.

A total of 2 billion yuan ($266 million) was invested in 2003 to build 1 billion cubic metres of annual gas capacity around the most productive well in the Sulige, but actual output amounted to only 131 million cubic metres in 2004 and has been declinng ever since.

Zhang told the 2007 China Natural Gas Supply Forum in Beijing that compared with gas reserves in some other countries, Chinese gas is usually buried in deeper reservoirs with lower density and permeability.

He declined to comment on official reserve figures in Sinopec's Puguang gas field that boasts 356 billion cubic metres of proven deposits, China's second-largest.

China's commercially extractable reserves of natural gas were 2.449 trillion cubic metres by the end of 2006, equivalent to around four decades of production at current rate, official media had reported.

China seldom releases its oil and gas reserves figures.