Study On Tight Sandstone Reservoir Evolution And Main Controlling Factors In The Lishu Fault Depression,Songnan

In order to study the reservoir characteristics,the diagenetic sequence and the controls of reservoir evolution of deep buried tight sandstone reservoirs in the Lishu Fault Depression(LFD),Songliao Basin,samples collected from the second member of Shahezi Formation(Sha-2 Member)and the first member of Ying Formation(Ying-1Member)were treated through an integrated process including core observation,thin section identification,XRD,SEM,physical properties testing,high-pressure mercury injection,NMR,cathodoluminescence,fluid inclusions,carbon and oxygen isotope test and numerical simulation.Thought the "macro-micro-macro" + "qualitative and semiquantitative and quantitative" research procedure,the reservoir characteristics,the diagenesis types and characteristics,the quantitatively diagenetic evolution process,the main controlling factors of favorable reservoir evolution,and the corresponding model of reservoir evolution were thoroughly discussed.The results show that the sandstones are dominated by lithic arkose and feldspathic lithic sandstone,with low to medium maturity of mineral composition and structure.The reservoir is characterized by ultra-low porosity and permeability,controlled by abundant primary intergranular pores,secondary dissolution pores and micro-fractures,and their pore throat systems.Compaction,cementation,dissolution and metasomatism can be observed in samples.The diagenetic process through compaction,cementation(metasomatism)and dissolution(two stages),and the model of inorganic weak acidorganic acid in semi-closed environment were established.The Sha-2 Member has stronger interaction and cementation and weaker dissolution than the Ying-1 Member.Rapid compaction,clay carbonate minerals cementation are factors control tight reservoir formation.Five diagenesis stages,including mechanical compaction,early cementation,early dissolution,late cementation and late dissolution,can be confirmed,affecting the four stages pore evolution: original pore reduction(compaction and early cementation superimposed)→ pore increase(early dissolution and tectonic fracture)→ pore reduction(late cementation)→ pore increase(late dissolution and metasomatism).Reservoir evolution in the study area is affected by sedimentation and diagenesis processes,including mineral composition,sedimentary facies,diagenetic intensity and diagenetic sequence.The favorable reservoirs distribution are controlled by coarsegrained sandstone in fan delta facies,rich in feldspar minerals and turbidite;The content and composition of feldspar and clay minerals change with diagenetic environment,which lays a foundation for reservoir evolution.Diagenetic intensity varies with the formation,distribution and sequence of reservoir burial depth and evolution,making diagenetic evolution the main factor of reservoir evolution;Lithofacies of the Fracture facies(MCFF)and mixed dissolution facies(MCMDF)are favorable diagenetic facies with high porosity and low compaction and cementation.The tight sandstone reservoir experienced the non-consolidation sandstone in early burial stage,high porosity and permeability rapid burial stage,pore throat decrease stage,acid and alkali alternating stage,and late burial stage tight reservoir stage.