| As a significant unconventional worldwide resource,tight gas has become the focus of China`s energy industry.Different from the conventional accumulation mechanism,which focuses on trapping and buoyancy,the accumulation mechanism of tight sandstone gas is centered on capillary force in micro-or nano-pores.However,there still exsisting limitations in the understanding of dynamic mechanism and fluid distribution characteristics in micro-or nano-pores.The distribution of gas and water in tight sandstone gas reservoirs in Sulige area is of vital complexity,with the distribution characteristics of "dog-tooth interlacing".The formation of gas and water distribution is essentially the result of dynamic mechanism,this push researchers to to reveal the mehcanism of complex gas and water distribution based on microscopic dynamic mechanism.In this work,the dynamic mechanism of tight sandstone gas accumulation is further revealed based on the basic geological theory of natural gas,combined with the interdisciplinary research of capillary mechanics,percolation mechanics,theoretical mechanics,thermodynamics,interface physics.The effects of pore morphology and the water film at the vinitiy of pore are studied during the gas charging and migration process.Considering the characters of tight gas migration and accumulation,the corresponding core simulation experiments and microscopic visualized simulation experiment are also carried out.The tight gas migration and accumulation numerical simulation technology and method are developed,the influence factors in the process of charing is analized.At last,this paper discusses the percolation mechanism and gas-water distribution mechanism under the action of inconsistent capillary force during the tigh gas accumulation process.he main conclutions are as follows:(1)Considering the diverse geometry of pores in tight sandstone reservoir and the interactions between fluid and surface wall,a dynamic model of tight gas charging is established,and a method for determining dynamic characterization parameters of fluid migration process is established.The Young-Laplace equation currently used underestimates the capillary pressure in angular pores,and the water film will further increase the capillary pressure in pores.When the pore scale is less than 1000 nm,the influence of pore morphology and water film on the dynamics and the gas-water distribution can not be ignored.(2)Considering the tight gas migration charaters,a core experiment and and microvisualization experiment are carried out.The gas-water distribution characteristics and formation mechanism are clarified.The fluid flow path in the process of tight gas accumulation and charging are obviously different from those in the process of production and development.The capillary pores in the process of tight gas charging have the characteristic of step by step movement,so the analysis should be based on the seepage area of some produced pores in the process of dynamic research.(3)The multi-scale numerical simulation technology of tight sandstone gas accumulation,is developed.The lattice Boltzmann method is introduced into the study of petroleum geology,and the variation characteristics of water film on pore wall in micro-and nano-pores were captured.The dynamic pore network simulation technology is introduced into petroleum geology research,and push the application of 3D CT scanning technology from static reservoir characterization to dynamic reservoir formation simulation is extended,revealing the mechanism of gas-bearing growth at the core scale and the cause of free and bound water in connected pores.(4)A mechanical model for the continuous action of porous media in the process of tight gas accumulation was explored and established.The gas-water distribution characteristics and formation mechanism of tight reservoir under the action of differentiated capillary force in the process of accumulation is reveealed.The model shows that driven by hydrocarbon generation expansion force,the gas phase migrates in continuous phase along the low-resistance percolation path,and the gas phase is in the same pressure system during the migration process of charging,and only a few bubbles are stuck in the frontiers.The unique dynamic characteristics of tight sandstone gas accumulation form the macroscopic gas-water distribution characteristics.The physical property difference and charging pressure difference control the complex gas-water relationship of tight gas. |
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