Sedimentary Characteristics And Reservoir Development Of The Early Cretaceous Hengtongshan Formation In Tonghua Basin

Tonghua Basin,a fault basin is one of the basin group in the eastern Jilin province,formed during early Cretaceous.The Liuhe Basin and the Ji'an Basin are located in the northwest and southeast of the Tonghua Basin,respectively.On the basis of comprehensive regional geological data and previous research results,we studied new drilling data from the Tonghua Basin and performed a series of indoor analyses,such as microscopic identification for core sample the mercury injection analysis,at the same time,we also studied reservoir petrologic feature and pore structure feature of Hengtongshan Formation.This article is intended to study the sedimentary characteristics of the Hengtongshan Formation in the Tonghua Basin and discuss the reservoir developing law,and obtain the following understanding:1.The types of rocks and sedimentary facies developed in the Hengtongshan Formation of the Tonghua Basin.Four types of rocks were identified in the Hengtongshan Formation: they are clastic rocks,pyroclastic rocks,pyroclastic sedimentary rocks and igneous rocks.It can be further divided into 10 subclasses and 24 fundamental types.Four types of sedimentary facies were identified: they are fan delta front,submarine fan,lacustrine facies and volcanic facies.It can be further divided into 7 subfacies and 23 microfacies.2.Planar distribution characteristics of sedimentary facies of the Hengtongshan Formation.The Hengtongshan Formation mainly developed volcanic facies-lacustrine deposits in Sankeyushu depression,and mainly developed fan delta front and alluvial fan deposits in Sanyuanpu depression.S1 sequence is that fan delta front deposits developed in the Sanyuanpu depression and volcanic facies-lacustrine deposits developed in the Sankeyushu depression.S2 sequence is that alluvial fan deposits developed in the Sanyuanpu depression and volcanic facies-lacustrine deposits developed in the Sankeyushu depression.S3 sequence is that alluvial fan deposits developed in the Sanyuanpu depression and volcanic facies-lacustrine deposits developed in the Sankeyushu depression.3.The reservoir characteristics of the Hengtongshan Formation.The main rock types of reservoir are conglomerates,sandstones,siltstones,tuff sandstones,tuffs and tuff lava.The reservoir pore types of the Hengtongshan Formation can be divided into 4 classes,and it can be further divided 6 subclasses.Secondary pores and tectonic fissure are well developed in the reservoir of the Hengtongshan Formation.Through analysis and test,it is found that the reservoir of Hengtongshan Formation is of ultra-low porosity-low porosity and ultra-low permeability.We performed mercury injection testing of 14 samples from the Hengtongshan Formation,and evaluated the reservoirs based on the reservoir classification standard of Daqing oil field.Among these samples,5 samples are ? reservoir,which means poor reservoir,and the rest samples are ? reservoir,meaning very poor reservoir.4.The types and stages of diagenesis of the reservoir in the Hengtongshan FormationThe types of reservoir diagenesis in the Hengtongshan Formation are mainly compaction-pressure solution,cementation and welding,metasomatism,recrystallization,dissolution and cooling consolidation of volcanic material.As a whole,the stage of reservoir diagenesis in the Hengtongshan Formation is in the mesogenetic A stage,belonging to low maturation-maturation stage.5.The reservoir developing law of the Hengtongshan FormationThe reservoir of Hengtongshan Formation is mainly affected by sedimentation and diagenesis.By studying these reservoirs,we found the favorable sedimentary facies of the Hengtongshan Formation are submarine fan facies and volcanic facies.The hydrodynamic conditions of the former are strong and the sand body is relatively thick.The resistance to compaction of the latter is strong,and the primary porosity fissure is well developed.However,the reservoir diagenesis of the Hengtongshan Formation is complex.Firstly,the great burial depth leads to strong compaction,and the sandstones in the study area are transformed into tight sandstones with poor physical conditions.Then,after being subjected to volcanism and other diagenetic transformation,although some secondary dissolution pores appeared,the primary pores were destroyed,and a large amount of self-generated clay minerals were generated,filling and blocking the throat,resulting in poor reservoir physical properties.