Fault Safety Analysis Of X Gas Storage In Gas Injection Process

Depleted gas reservoir storage is currently the world's most widely used underground gas storage,at the end of the gas injection,the characteristic of strong injection and production of gas storage may increases the formation pressure and destroys the fault sealability,and then makes the natural gas leakage accident.In order to avoid this accident,the safety of the fault in the operation of the gas storage is analyzed.This paper has carried out the following research:The fault instability analysis.The upward formation pressure at the end of the injection may overcome the fault plane normal stress and cohesion and causes the fault to open.Or the rock of fault may be fractured under the combined action of the formation pressure and the three main stresses of the rock,both of them can lead to gas leakage.By calculating the formation pressure that causes the fault to open or causes the fault rock to break,compare the pressure,the upper limit value of the formation pressure is chosen as the interruption of the gas reservoir,to ensure the safety of the fault,the formation pressure should not exceed this value.Studies on variation law of formation pressure on the fault.There are many wells in the gas storage operation,it is necessary to obtain the position and pressure value of the maximum formation pressure on the fault.In this paper,the formation pressure has been calculated from the wellhead to the bottom of the well and the fault by the formula of the bottom hole pressure and formation pressure,and explores to improve the accuracy of the bottom hole pressure.The formula of formation pressure distribution in the single well and multi well gas injection mode is obtained by using the principle of pressure drop superposition,on the basis of the analysis,the distribution law of formation pressure in gas reservoir is analyzed.Analysis of influencing factors of formation pressure on the fault.Single factor analysis of 7 factors that influence the formation pressure changes on the fault,the variation law of the maximum fonnation pressure on the fault is obtained under the different influence factors.The influence degree of each influence factor on the maximum formation pressure is obtained by the correlation analysis method in the grey system theory,the degree of influence from large to small is:gas injection rate,reservoir thickness,permeability,porosity,well spacing,the distance of well and fault,operating well number,finds out the key factors from the above sort,these key factors are used as the variables of the drawing plates.Drawing and analysis of plates.In order to ensure the security of interrupt layer,limits the maximum allowable value of the maximum formation pressure on the fault,controls reasonable operation parameters.Drawing on the basis of the actual situation of X gas storage,the relationship between the number of operating wells,the gas injection rate in single well,the vertical distance between the gas well and the fault and the maximum formation pressure on the fault is obtained by drawing the charts.In the case of the number of operating wells,gas injection in single well,and the determination of two parameters in the vertical distance between gas well and fault,the value of another parameter can be selected reasonably,this can avoid the improper operation measures in the operation of the gas storage.When the allowed maximum pressure at the given fault is changed;or if there has a bottom hole pollution or the implementation of stimulation measures to make gas injection capacity changes;or when adde a new well and changes the vertical distance from the well to the fault;or when the number of operating wells changes,it is possible to determine the reasonable operation measures to ensure the safety of the fault by querying the plates.It can also be used to judge whether the current operation measures will reach the upper limit pressure in the operation of the gas storage,so as to make timely adjustments to ensure the safety of the fault.This paper provides a method to select the reasonable operation measures to ensure the safety of the operation of the underground gas storage,and provides a reference for the safe operation of X gas storage.