| Low permeability tight sandstone gas is the key field of oil and gas exploration and development in recent years.However,the tight sandstone gas reservoir has the characteristics of low porosity,high bound water and abnormal pressure,which caused unclear understanding of the kinetic conditions and process of gas migration in tight sandstone.Nuclear magnetic resonance?NMR?technology with its fast non-destructive,sustainable advantages in the study of oil and gas accumulation is in the application of more and more widely.This thesis firstly analyzes the Xu2 typical tight sandstone reservoirs in Chuanxi depression,then selects suitable samples and artificial core samples to establish a set of simulation method of gas migration in tight sandstone and start with NMR test platform.Through the research of the paper,the main achievements and understanding are as follows:The types of rocks of the Xu2 reservoir are lithic quartz sandstone,feldspar lithic sandstone and lithic sandstone,The average porosity is 4.10%,and the permeability is 0.048×10-3?m2,which is a typical tight sandstone reservoir.The average geothermal gradient is 2.31?/100m.The formation pressure data are between 66.55 and 83.14 MPa,and the pressure coefficient is 1.41 to 1.68.The gas reservoir is a high pressure gas reservoir.The T2 spectrum is used to calculate the saturation at each time.The characteristics of gas threshold and the time variation are summarized.A series of parameters such as threshold pressure,breakthrough pressure and gas migration rate are obtained.Also Based upon T2 spectrum method scaled by mercury data,Pore distribution curve transferred by T2 spectrum is constructed by proposing mercury and T2 spectrum accumulated from right to left,selecting reasonable contrast interval,using longitudinal interpolation and least squares in order to solve the inaccurate problem causing by less than 100%of mercury saturation.The migration path of tight sandstone is mainly affected by reservoir heterogeneity,filling pressure,injection velocity and overburden pressure.The higher the reservoir pressure is,the higher the upper pressure is,the threshold pressure,the breakthrough pressure,the higher the quasi-steady pressure.The lower the final gas saturation is,the lower limit of the physical properties of the tight sandstone gas is porosity 5%and permeability 0.1×10-3?m2.The higher the flow rate,the greater the pressure in the quasi-steady state,but the threshold pressure remains the same.However,with the increase of the pressure difference and the rate of filling,the gas saturation is gradually increased.The sandstone gas migration can be divided into two processes,four stages.The process of intrusion before gas breakthrough includes pressure accumulation and gas invasion.The process of gas migration is divided into two stages:unsteady migration and quasi-stable migration.Abnormal high pressure is the main driving force of filling sandstone gas in Xu2 Formation in Chuanxi depression,Source rock is pressurized and with strong heterogeneity,which lead isolated pressure system formed.For reservoirs with similar porosity,the larger the source pressure difference,the easier it is to fill the core.The XU2 reservoir has strong heterogeneity.During the formation of gas reservoirs,natural gas will first get through high porosity reservoirs of relatively loose lithic quartz sandstone and feldspar lithic sandstone,The gas and water differentiation is obvious and the bottom generally forms water-rich zone;However in the tight body with widely developed lithic sandstone,the gas can not large-scale displace the water in the sand body,so the gas distribution is not obvious,which also forms a number of low gas saturation of the gas layer and beaded locally in the residual formation water.The gas-water relationship is complex and there is no obvious gas-water interface generally in XU2 reservoir.The distribution of gas reservoirs is limited and it is often distributed in the sandstone reservoir. |
PDF Full Text Request