Genetic Mechanism And Accumulation Model Of Tight Oil In The Es3 Reservoir,dongpu Depression

As one kind of important unconventional resource,tight sandstone oil has gradually become one kind of replacement for conventional oil and gas resources.Burial evolution process of tight sandstone reservoir and hydrocarbon accumulation processes have great significance for the understanding of mechanism of tight sandstone reservoir formation and oil and gas exploration.Tight oil exploration in the Wenliu area of Dongpu Depression is at its infancy,where have a huge potential of tight oil and gas.Based on the collection of 105 core samples from the third member of Shahejie Formation(Es3)in Wenliu area,the petrological characteristics of Es3 is clarified by core observation,conventional and cast thin section observation,inclusion analysis,and so on.Meanwhile,the evolution and hydrocarbon charging process of tight reservoirs in Wenliu area are analyzed in this study.The reservoir in the Wenliu area is mainly composed by feldspathic quartz sandstone and feldspar lithic quartz sandstone,which is fine grained.The reservoir is mostly siltstone,which is highly heterogeneous and generally dense with some high porosity-permeability “dessert” area developed.The analysis of cast thin section observation and scanning electron microscopy shows that the tight reservoirs of the Es3 are mostly in the stage A1 to B of middle diagenesis period,and the deep reservoirs are in the late diagenetic period.The reservoir has experienced pore increasement and pore reduction.The compaction and carbonate cementation are the main diagenesis in the pore reduction process,while the pore increasement stage is mainly dominated by dissolution.The major type of pores is dissolution pores.The differences of pore development characteristics between hydrocarbon-filling and non-hydrocarbon-filling reservoirs indicate that hydrocarbon charging has an inhibitory effect on cementation and compaction,and promotes the development of dissolution.According to the diagenesis process of the tight sandstone reservoir,a pore evolution model is established to restore the reservoir densification process.The analysis of inclusion fluorescence observation and homogenization temperature show that this area experienced two stages of hydrocarbon filling.The dominated charging process occured in the deposition of Dongying Formation.However,the second stage of hydrocarbon charging,happened during the late deposition stage of Minghuazhen Formation,only influenced the adjacent place near the sag.The coupling relationship between the densification and the hydrocarbon accumulation process indicates that there are two kinds of accumulation processes in the tight reservoirs in the Wenliu area,namely,“tightening after first accumulation” and “second accumulation after densification”.This study has clarified the process of formation and development of tight sandstone reservoir,which provides guidance for tight sandstone oil exploration in the similar areas.