Rescerch On Microscopic Pore Structure And Percolation Ability In Tight Sandstone Reservoir

The micro and nanoscale throat is relatively developed in tight sandstone reservoirs.The flow channel of fluid is so subtle that make the boundary layer effect clear,therefore the fluid percolation no longer keep in line with Darcy's law.There is a significant stat-up pressure gradient and stress sensitivity characteristic,which brought great difficulties for the rational development in the tight oil reservoirs.Take the tight sandstone reservoir of chang 7 in LD district as research objects,and by methods of laboratory experiments and based on the reservoir engineering,reservoir physics and fractal theory to study microscopic pore structure and percolation ability.First,on the basic of the experiments such as mercury injection with highpressure(50MPa),mercury injection with constant rate and low-temperature nitrogen adsorption,using fractal theory analysis to study microscopic pore throat distribution and its contribution to the flow capacity from different scales in tight sandstone reservoir.In this way,the intrinsic link between microreservoir structure and non-linear flow characteristics is established.Secondly,the stress sensitivity experiment of reservoir was carried out,by analyzing the relationship between formation pressure and reservoirs physical property,the damage caused by formation pressure decrease to the reservoir macroscopic properties and its influence factors are studied deeply.Based the reservoir physics and fractal theory,the model between microscopic pore structure and irreducible water saturation is established,analyzing the effect of microscopic pore structure on the irreducible water saturation,theoretically explained the reason that irreducible water saturation is relatively low in high permeability reservoir.By analyzing the formation pressure decrease on the microscopic pore throat distribution,and then deep studying the impact of stress sensitivity of tight reservoir on seepage parameters.Then,based on capillary bundle the microscopic percolation model was established,combined with Darcy equation,the fractal expression of permeability and start-up pressure gradient were given respectively,exploring the relationship between permeability and pressure gradient theoretically.On this basis,using the stress sensitivity of permeability and micro pore throat structure parameters as the bridge,the relationship model between start-up pressure gradient and stress sensitivity is built to analyze the formation pressure decrease on start-up pressure gradient and capacity,deepening microscopic pore structure on flow capacity understanding.Finally,NMR experiment was carried out to quantitative study different pore throat distribution to the degree of control of percentage of the movable fluid,and analyze the influence of the boundary layer to flow capacity.Consider formation pressure decrease and the impact of the existence of the boundary layer on oil-water relative permeability in tight sandstone reservoirs,combined with a high pressure mercury experiments and relative permeability experiments,Li and Horne model is improved to give a simple and efficient computation of oil-water relative permeability,analyzing the effect of stress sensitivity of oil-water two-phase flow capability.In this paper,the microscopic percolation theory is developed and improved for results of research,and it is certain degree of theoretical and practical significant for the rational development of tight sandstone reservoirs.