Densification Mechanism Of Sandstones With Different Provenances Under The Influence Of Multi-stage Tectonic Movement

This thesis uses reservoir geology,sedimentary petrology,structural geology and petroleum geology as the theoretical guidance,applies multiple experiments including ordinary thin sections and pore casting thin section observation,scanning electron microscopy,cathodoluminescence and X-ray diffraction analysis as well as mercury intrusion experiments.Based on the theoretical guidance and experiment results,this thesis studies the petrological characteristics,diagenesis,physical properties,pore types and pore evolution of the tight sandstone reservoirs of the Xujiahe Formation in the northeastern Sichuan Basin,furthermore densification process and mechanism of four different sandstones are analyzed in detail and reservoir development models are established,including lithic sandstone,calcarenaceous sandstone,feldspar lithic sandstone and quartz sandstone of three types of tight sandstones(Xu-2.Xu-3,Xu-4 tight sandstones)in three areas(western Yuanba area,Bazhong area,Malubei area),respectively.The results show that in the late Indosinian period,the difference in provenance supply and the type of parent rock of source area caused by the strength of the basin-forming orogenic activities in the study area resulted in different types of sandstone,which were described before,including the lithic sandstone of the Xu-2 tight sandstones,the calcarenaceous sandstone of the Xu-3 tight sandstones,the feldspathic lithic sandstone of the Xu-4 tight sandstones,and the quartz sandstone with lithic sandstone of the Xujiahe Formation in three area(western Yuanba area,Bazhong area,Malubei area),respectively.Under the continuous influence of Yanshan Movement and Xishan Movement,Malubei strong deformation zone,Bazhong medium deformation zone and western Yuanba weak deformation zone are developed from near to far from the Daba Mountain foreland compressive zone.Different types of sandstones in different tectonic locations have experienced different diagenetic sequences and pore evolution processes,forming distinct reservoir development patterns: first,in the western Yuanba weak deformation zone,lithic sandstone of the Xu-2 tight sandstones have relatively weak compaction,dissolved pores are grown in cuttings and feldspar,therefore low porosity and permeability reservoir development patterns are formed.Secondly,in the same area,the calcarenaceous sandstone of the Xu-3 tight sandstones have relatively weak compaction,strong cementation,strong recrystallization.Due to intercrystalline pores,intergranular dissolved pores,residual intergranular pores and microfracture,Xu-3 tight sandstones have reservoir development patterns as ultra-low porosity with low permeability fracture-porosity reservoir.Thirdly,in the Bazhong medium deformation zone,feldspar lithic sandstone of Xu-4 tight sandstones have reservoir development pattern as feldspar dissolved fractures connected,extremely low porosity and low permeability fracture-porosity reservoir.Fourth,in the Malubei strong deformation zone,quartz sandstone with lithic sandstone of the Xujiahe Formation experience deep burial compaction and structural strong extrusion,and has reservoir development pattern as fractures connecting micropores,ultra-low porosity and low permeability pore-fracture reservoir.The tight sandstone reservoirs of the Xujiahe Formation in the northeastern Sichuan Basin are controlled both by the provenance and tectonic setting,and the tectonic action is the main controlling factor.The provenance controls the composition of the sandstone and then controls the diagenetic process.The tectonic action controls the structural extrusion strength,and crack and fault development degree and scale,which further determines the preservation of the original pores and the later dissolution pores and the connectivity of the pores.It also controls the source-storage relationship and the degree of oil and gas charging,and ultimately controls natural gas production capacity.