Study On Water-locking Law Of Tight Gas Reservoir Considering Pressure Sensitive Effect

Tight gas reservoirs generally have the characteristics of complex pore throat structure,strong stress sensitivity and high water saturation.After foreign fluid invades the formation,water lock damage is likely to occur.At the same time,during the gas well exploitation process,the dynamically changing pore throat structure will further affect the irreducible water saturation,the water phase occurrence state and the gas-water phase permeability characteristics in the reservoir.Therefore,the study of the water lock law of tight gas reservoirs needs to consider the pressure sensitive effect,which has important theoretical and practical significance for the rational and efficient development of tight gas reservoirs.In addition to conventional basic physical testing,combined with mercury intrusion and nuclear magnetic resonance testing,the static microscopic pore throat structure of the reservoir was studied.Through the core stress sensitivity experiment and nuclear magnetic resonance test,the dynamic changes of pore throat structure were studied.The gas flooding method and the nuclear magnetic method were used to measure the irreducible water saturation.Based on the capillary bundle model and the water film theory,combined with the fractal theory,the variation law of the irreducible water saturation under the pressure sensitive effect was studied.Carry out a water lock experiment that considers the pressure sensitive effect and evaluate the degree of water lock damage.Combined with the theory of capillary force and the principle of nuclear magnetic resonance,the water lock law of tight gas reservoirs is comprehensively analyzed.Based on the comprehensive experimental results and theoretical analysis,the following conclusions are obtained: the complex pore throat structure of the tight reservoir and the fine pore throat are determined,and the pore throat size distribution under static and dynamic conditions is quantitatively characterized.With the increase of effective stress,the core permeability and porosity decrease,and the irreducible water saturation increases.A calculation model of the irreducible water saturation considering the pressure sensitivity effect is established.The pressure-sensitive effect will reduce the gas-water flow capacity of the reservoir,and increase the proportion of the impermissible pore throat,resulting in an increase in the degree of water lock damage.