Differential Evolution Characteristics Between Buried And Uplift Of Tight Sandstone On The Porodynamics

Hydrocarbon in tight sandstones as an important part of fossil fuels have been discovered in Chinese basins as well as all over the world,which indicates a huge potential in hydrocarbon resources.In terms of the processes and models of hydrocarbon accumulations in tight sandstones,the differential buried processes play an important role.Studies on porodynamics of sandstones have a great significance on the evolution of pores and mechanism of accumulation dynamics.This study on porodynamics of tight sandstones in two burial processes make a further understanding in mechanism of hydrocarbon accumulation,as well as for the further hydrocarbon exploration in economic geology.This study aims to solve three issues as follows: 1.As the specificity of the sandstone is ignored,a further study is needed for deciphering the compacting processes and mechanism of sandstones.2.The extent of compaction in sandstones as well as the evolution of porosities need to be systemically studied.3.As the scarcity of rational method for the reconstruction of the evolution of porodynamics in different burial processes,the accumulation dynamics of tight sandstones need to be further studied.Therefore,the study aims to decipher the process and mechanism of sandstones based on the well logs and petrographic evidences.Under the theoretical analysis and quantitative modelling results,differential evolution models of porosities attempt to reconstruct.Combing multiple methods of paleo-pressure reconstructions,evolution models of formation pressure and charging processes of natural gas in tight sandstones are established.This study proposed the cyclical compaction model in sandstone lens.Comparing with the compacting process of the different formation structures,the inter-hindered phenomenon is identified in sandstone lens coated by mudstone.Further evidences from petrographic works,statistic analysis and experiment prove that the compaction is still exist in deeply buried formations.This also leads the decrease of porosities in tight sandstones.The “disequilibrium compaction” is proved by inversion method in porosities.The cyclic trend of disequilibrium compactions can be identified in both basins with different burial processes.The dynamic mechanism of disequilibrium compaction was deciphered.This study suggest the controls of burial processes on the tight extent of sandstones.Time effects is considered as an important factor in deceasing porosities based on the quantitative models and chemical dynamics.Based on the global statistic database,the time effects is proved to make a great contribution on the decreasing porosity of tight sandstones.The porosity in deeply buried basin in the early stage is smaller relative to the basin deeply buried in the late stage and then uplift.Two types of compacting models have been identified in the deep-buried basin and the uplift basin.The deep-buried basin is characterized by a multi-step bimodal model.The uplift basin is expressed by a high amplitude bimodal model.Based on the reconstructions of burial processes in two basins,the pore is evidenced to rebound during the uplift stage.The differential evolution of porosities is established.The deep-buried basin experience decreasing trend in porosities and deeply buried in the late stage.The porosity in uplift basin show a process with consistent decrease in early times and rebound in late uplift stage.The evolution of paleo-pressures in two typical basins is established,as well as the differential structure in the charging of natural gases.A new model for the calculation of formation pressure was proposed based on the skeleton stress.Combing multiple methods of reconstructions of formation pressure,the evolution pattern of formation pressures was established in the tight sandstone.The deep-buried basin is characterized by a low amplitude pressure in the early stage and high amplitude pressure in the late stage.The uplift basin is expressed by a multi-stage increase in formation pressure and decrease during the uplift stage.The overpressure in the Ordos basin exists from the Middle Jurassic to the Late Cretaceous.After the Cretaceous,the huge-scale denudation lead to a hydrostatic pressure with locally negative pressure.The balance static equation is established to decipher the charging process in tight sandstones.The deep-buried basin shows a consistently strong charging in the early stage.In contrast,the uplift basin appears to a bimodal charging process.