To make clarify the geological characteristics and resource potentials of tight gas in northern Songliao Basin

the classification and optimization of favorable exploration areas for tight gas were carried out based on comprehensively using the seismic

coal

geological and geochemical data and analyzing the hydrocarbon accumulation conditions in Shahezi Formation

including tectonic evolution

sediment

ary system

source rock

favorable reservoir and abnormal pressure. The results show as follows. (1)The tight gas is mainly concentrated in Shahezi Formation in the deep fault depressions. Influenced by paleo-geomorphology and fault activity

fan delta and braided river delta sediments were formed on the steeps and the gentle slopes of deep fault depressions

and huge pebbly sandstone was deposited

which is the main gas-bearing horizon of tight gas. (2)The coal rock and dark mudstone have high organic matter abundance and are in the high mature-over-mature stage

which provides sufficient material guarantee for the formation of tight gas. Under the joint control of sedimentation and dissolution

high quality reservoirs with intragranular and intergranular solution pores of feldspar as the main reservoir space are developed in tight sandstone

which is the sweet spots for tight gas exploration. Hydrocarbon generation from organic matter results in the 29 MPa to 45 MPa pressurization

forming a large-scale continuous overpressure storage chamber in the middle of the depression

which is the main driving force for tight gas charging. (3)Homogenization temperature simulation of hydrocarbon-bearing fluid inclusions and burial history of strata show that the accumulation time of Shahezi Formation tight gas lasted from the end of Qingshankou Formation to the sedimentary period of Nenjiang Formation (91-72 Ma)

and there were two accumulation processes in the end of Qingshankou Formation and the Nenjiang Formation. (4)Based on the sedimentary system

reservoir thickness and physical property conditions

the tight gas is divided into two favorable exploration types

i.e.

thick-layer and interlayer. Moreover

four favorable exploration zones have been identified

including Anda

Xuxi

Xudong and Xunan

and the amount of tight gas resources is estimated to be about 4 224.10×10

8

m

3

.