Low-efficiency gas reservoirs refer in particular to those with low abundance of reserves and low well productivity.The reserves of such reservoirs in China account for about 70% of our total gas reserves.In China

reservoir rocks of such gas reservoirs are commonly of fluvial and delta facies with relatively large burial depth

which are characterized by poor continuity

low porosity and permeability

as well as strong heterogeneity.As a result

exploration and development of these reservoirs are quite difficult.For the sake of effectively utilizing these gas resources

the characteristics of low-efficiency gas reservoirs in continental clastic rocks have been analyzed

based on systematic correlating the geological features of low-efficiency gas reservoirs both in China and abroad.It is believed that the types of sedimentary facies and diagenesis are two major geologic factors leading to low efficiency of reservoirs.Sedimentary facies control the poroperm characteristics and continuity of reservoirs

while compaction and cementation are the main factors that destroy primary pores and lead to the formation of tight sandstones.