Prospects for the large-sized tight sandstone gas-bearing regions in China

In China, the conventional reservoirs are limited in number, so the deep tight reservoirs will be more uncountered in the future. Through analyzing and studying the factors of influencing compactification of the sandstones in tight sandstone gas-bearing regions and the characteristics of tight sandstone gas reservoirs, it is considered that only by relying on the local trap, can the gas reservoir be formed in the reservoir bed which petrophysical property is better than the low-porosity and low-permeability sandstone; the `deep basin gas' in the concave part of a depression can be formed in the tight sandstone; and the gas reservoir in supertight sandstone can be formed only under fracture-developed condition. The tight sandstone gas-bearing areas are widely distributed over China, being roughly generalized as four categories: (1) active supertight sandstone gas-bearing areas (as West Sichuan Basin); (2) `deep basin gas' areas (as E'erduosi Basin); (3) rift-depression basin tight sandstone gas-bearing areas (as the J3-K1 rift-depression in Songliao Basin); and (4) superdeep high-abundance tight sandstone gas-bearing areas (as the south part of Zhunge'er Basin). A reservoir formation model of gas-bearing tight sandstones in China is set up by taking the gas-bearing sandstones in West Sichuan Basin as an example. There are four stages: Stage I is the oil and gas accumulation in original conventional reservoir; Stage II `deep basin gas'; Stage III super-compactification; Stage IV fracture-recomposed gas reservoir; and Stage IV prime secondary shallow gas reservoir.