| The tight sandstone gas reserves in West Sichuan Depression are huge and account for a large part of China's tight gas reservoir resources.Therefore,it has a strong practical significance for its development.However,the reservoir structure of the block is complex,the lithology is dense,the heterogeneity is strong,the water saturation is high,and there is a phenomenon of reverse condensate,which ultimately makes gas reservoir development difficult,water production serious,short stable production period,low rate recovery and poor development effect in general.Therefore,it is more urgent to study the physical characteristics,sensitivity analysis and productivity of different well types of tight sandstone condensate gas reservoirs in Western Sichuan depression.Based on the full investigation of the seepage mechanism of tight condensate gas reservoir and the research status of productivity of different well types,the main work carried out and the knowledge gained in this paper are as follows:(1)Reservoir physical properties,irreducible water saturation under different pressure differences and release water lock pressure tests were carried out.The results show that the reservoir is characterized by strong vertical heterogeneity and poor correlation between core pore penneability,and generally belongs to medium-porosity and ultra-low permeability reservoirs.The irreducible water saturation of core is different under different displacement pressure differences,and increasing displacement pressure difference will make more irreducible water be converted into movable water,which will be driven out and gas phase permeability will be enhanced.Fracturing makes gas release water lock easier to break through,and the pressure required is greatly reduced,which improves the gas-water seepage effect to a certain extent.(2)Reservoir productivity sensitivity factors are studied.Reservoir stress sensitivity,start-up pressure gyradient and gas-water phase permeability curves under dif-ferent overburden pressures are tested experimentally.It is recognized that reservoir stress sensitivity causes core elastic-plastic defonmation,core permeability and pressure are exponential function,and stress sensitivity is strong.Start-up pressure gradient of matrix core will increase with water saturation.With the increase of effective overburden pressure,the iso-seepage point of the phase permeability curve will move to the right,the resistance of two-phase seepage will increase,the recovery rate will decrease,and it is not easy to flow in two-phase.(3)On the basis of previous experimental studies,the oil-gas two-phase productivity model of vertical wells is established.In addition,the gas-water two-phase productivity models for vertical wells and fractured horizontal wells is established,which takes into account stress sensitivity,start-up pressure gradient,high-speed non-Darcy effect and skin effect.The results show that with the decrease of formation pressure,the effect of reverse condensation on gas well productivity is increasing.Because of the existence of start-up pressure gradient in formation,there is no production when the differential pressure of gas wells is very low.The gas production of vertical wells and fractured horizontal wells has a linear negative correlation with start-up pressure gradient and a binomial negative correlation with stress sensitivity coefficient.Start-up pressure gradient has no more than 5%effect on productivity,and stress sensitivity has a greater impact on productivity,more than 20%.Considering the overburden pressure,stress sensitivity and start-up pressure gradient,the productivity of gas wells decreases by about 30%.Through the above research,the characteristics of tight sandstone condensate gas reservoirs in Western Sichuan and the infiuence of various sensitive factors on productivity are clearly defined,which has high application value and provides theoretical support for the development of gas reservoirs in this block. |
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