Research On Sandstone Reservoir Characteristics And Controlling Factors Of Chengzihe Formation In Northern Jixi Basin

Jixi Basin is a typical Mesozoic-Cenozoic sedimentary basin in the eastern part of Heilongjiang Province.The basin contains abundant coal,oil and gas resources.The Chengzihe Formation is the main coal-bearing section within Jixi Basin.It has a large thickness and a wide distribution area and can be used as the primary target of exploration.Based on the results of previous studies,knowledge and approaches of sedimentology,clastic reservoir geology and petroleum geology have been comprehensively applied in this thesis.With the aid of different test methods,such as casting thin sections,drilling cores and logging curves,the characteristics of sandstone reservoirs and reservoir controlling factors of Chengzihe Formation in the northern part of the basin have been studied in depth.The type of sandstones in Chengzihe Formation of the study area is mainly feldspar lithic sandstone,followed by lithic sandstone.The content of feldspar and intermediate-acidic extrusive rock fragments is relatively high,which provides conditions for later dissolution.The grain size of sandstones belongs to the category of fine sandstones and sorting is good to moderate.The overall thickness of the sand body is relatively large,ranging from 200 m to 500 m.Affected by provenance direction,sand bodies are distributed in the east-west direction,shaping like a belt.The overall distribution of the sand body is thicker in the north and thinner in the east.However,the sand body is separated by thin layers of claystone and coal.The thickness of the single-layer sand body is relatively small,located between 2m and 8m.The horizontal distribution of the sand body is limited and the connectivity is poor.The pore types of the sandstone reservoirs in Chengzihe Formation vary widely and can be divided into primary pores,secondary pores,and fractures.Among them,the feldspar or rock debris edge dissolution enlarged pores,the feldspar intragranular dissolved pores,and the rock fragments intragranular dissolved pores are dominant;the common types of fractures are intragranular broken cracks and grain margin dissolution joints.Sedimentary facies are important controlling factors for reservoirs.The reserving capabilities of sand bodies in the river channel–point bar,the deltaic front mouth-bar,the deltaic plain river channels and the lakefront facies are the best.The content of rock debris is positively correlated with the plane porosity;quartz is negatively correlated,and feldspar increased first and then decreased.The larger the sandstone grain size and the better the sorting are,the better the pore development of the reservoir.In addition,in terms of diagenesis,compaction and cementation are major reservoir destruction factors,and alteration and dissolution are the main reservoir favorable factors.Based on the factors,such as porosity,shale content,sedimentary facies,thickness of sand bodies,and exploration and development status quo,a general forecast of the favorable exploration area of the Chengzihe Formation in the study area was conducted.Basically,two favorable areas can be identified: North-Eastern Jidong Depression advantage area and western Jidong Depression favorable area.