Simulation And Operation Optimization Of Gathering Network Based On Gas Wave Ejector

In the Linxing-Shenfu block on the eastern edge of the Ordos Basin,coalbed methane,tight gas and shale gas reservoirs are vertically stacked upwards.It is not economical to develop a single gas.Therefore,multi-gas combination development can help to increase the overall economic benefits of gas fields.Since the pressure level and attenuation law of the three kinds of natural gas are far apart,if they are simultaneously introduced into a unified gathering network,the high pressure gas will be poured into the low pressure gas wells under the pressure difference.The gas wave ejector is a key device to solve this problem.Therefore,the purpose of this paper is to propose a calculation method to deal with gathering network including gas wave ejector and then develop a corresponding software.Through the software,the practical production is simulated,and the applicability,operating conditions,installation position and optimal operating parameters of the gas wave ejector in the gas field are analyzed.Firstly,this paper establishes a single calculation model of gas wave ejector,which includes characteristic curve fitting module,natural gas physical property calculation module and three-port process parameter calculation module.The entrainment ratio and isentropic efficiency are selected as the characteristic curves of the ejector.Based on the data in the literature,Lagrange interpolation,Shepard interpolation and binary least squares are used to fit the results.After the result,the binary least squares method with the smallest error and favorable for subsequent calculation is selected.In addition,according to the actual production needs,the oxygen component is added to the original BWRS equation.Based on the former two,the relationship between the pressure and flow rate of inlet and outlet ports of the gas wave ejector is established via the entrainment ratio and the isentropic efficiency,and the algorithm is designed for iterative calculation.Subsequently,the ejector model is simplified according to the actual production,and its structure is simplified into a composite model composed of two pipe segments and three nodes,so that the ejector node equations and the pipe network node equations are integrated,and the two virtual pipe segments are characterized.The equations are replaced by an ejector rate equation and an isentropic efficiency equation.The equation set consists of node equations,the pipe equations and the ejector characteristic equations are solved by the improved Newton-Raphson method,and a software is developed to complete the calculation.Taking 18 tight gas wells developed in Linxing block as an example,the calculation results are compared with the results calculated by Pipe Phase and production reports.It is found that the calculation method meets the actual needs of industrial production.Compared with the change of gas field output and wellhead pressure before and after the installation of gas wave ejector,it is found that the gas wave ejector has the effect of increasing production and stabilizing production.Finally,the completed pipe network calculation software is used to simulate different production conditions,and the operation of the gathering network with gas wave ejector is optimized.A series of operation schemes are formed by changing the installation position of the ejector,the entrainment ratio,and the operating parameters such as the pressure and flow rate of each wellhead.The software calculates the pressure and flow rate of each wellhead and the parameters of the gas wave ejector in each scheme,and checks whether it meets the maximum gas production constraint of each well,the wellhead pressure constraint and whether the gas wave ejector is in high efficiency area.In the qualified scheme,the operation plan with the largest total gas production in the gas field is the optimal operation plan.