Tight gas in China and its significance in exploration and exploitation

Tight gas reservoirs refer to the tight sandstone fields or traps accumulating natural gas of commercial values. According to reservoir characteristics, reserves, and structural height, they can be divided into two types, continuous-type and trap-type: the former are located at the lower part of the structure and have indistinct trap boundaries, inconsistent gas-water boundaries and reversal of gas and water, and their reservoirs are the same as or near the source; the latter are located at the higher part of the structure, with gas above water in traps, low reserves, and relatively high production. Tight gas in China is all coal-derived, dominantly alkane gases (C1–4), in which the amount of methane is greatest and the alkane gases have positive carbon isotopic series. The content of non-hydrocarbon gases (mainly CO2 and N2) is low. At the end of 2010, the reserves and annual production of tight gas in China accounted for 39.2% and 24.6% of the total natural gas, respectively, and the proportions are expected to increase. Compared to the shale gas and coalbed gas, tight gas should be considered in priority in the exploration and exploitation of unconventional gas in China.