Research On Rationality Evaluation Of Production Test For Multi-layer Fractured Vertical Well In Tight Gas Reservoir

In the development of tight reservoirs in the Sulige gas field,vertical wells are often used for fracturing.However,as production progresses,fracturing wells often show signs of diminishing production or even difficult production,which severely restricts the development effect of gas fields.Therefore,it is urgent to establish a percolation model that can reflect the actual condition of single well fracturing and flowback,then evaluate the fracturing wells from multiple aspects based on this,so as to diagnose the problem wells and optimize the potential wells.Finally,provide ideas for new wells to take measures and for problem wells to increase and resume production.This paper first uses the knowledge of percolation mechanics and the principle of volume balance to establish a two.dimensional percolation model of fracturing fluid invasion process,taking into account the filter cake effect and the non.Newtonian nature of fracturing fluid,and the solution method is given by establishing a difference equation in this paper.The model calculation results show that the invasion range of fracturing fluid is greatly affected by the permeability of the reservoir.In tight gas reservoirs,the fracturing fluid invasion rate is slow,and the pressure.enhancing effect is not obvious and the pressure drop is basically lost in the filter cake area and the intrusion area.In addition,when the well is closed,the pressure at the wellhead decreases slowly,so it is not realistic for the fracture to close naturally.Secondly,the flowback process is divided into two stages according to whether the fracture is closed,then the flowback model is established by using the gas.liquid two.phase flow and reservoir numerical simulation theory.The smaller the diameter of the discharge nozzle,the slower the wellhead pressure drops and the longer the fracture closure time.And when the flowback time is long,the smaller the diameter of the nozzle,the lower the ultimate fracturing fluid flowback rate.Finally,based on the model of fracturing fluid invasion and flowback,combined with numerical simulation software,a comprehensive evaluation system has been established for the whole process from fracturing to gas testing,including: evaluation of fracture scale,off.time,backflow process,reservoir water lock,effect of gas testing and rationality of the test horizon.By applying the comprehensive evaluation system,statistical analysis was performed on 124 problem wells in the Su 77 and Zhao 51 blocks of the Sulige gas field,and possible problems in the target block were found out.The reference metrics for evaluation indicators are given by numerical analysis of candidate potential wells.The principle of optimization of potential wells is also determined,and optimization of potential wells is carried out,which has certain practical guiding significance for the stable production and up-production of gas fields in the later stage.The calculation models established in this paper are connected to each other.For tight and strong reservoir reform measures,the calculation results are closer to the actual situation.The research has a certain theoretical innovation significance.On this basis,the comprehensive evaluation system established for each stage of single-well fracturing is somewhat groundbreaking,and has certain practical significance for the diagnosis and optimization of problem wells in tight gas reservoirs.