Method for Predicting Dangerous Well Section of Gas-Induced Vibration Pipe String and Method for Preventing Failure

Abstract

The present disclosure provides a method for predicting a dangerous well section of a gas-induced vibration pipe string, including: respectively constructing mechanical models; coupling the mechanical models by adopting a finite element method based on field production parameters to obtain a full-well gas-induced vibration analysis model; selecting several nodes on the target gas extraction pipe string, and performing calculation according to the full-well gas-induced vibration analysis model to obtain dynamic characteristic parameters of the several nodes, the dynamic characteristic parameters including an average internal stress and an average external stress; performing calculation according to the average internal stress and the average external stress to obtain a safety factor n of each well section of the target gas extraction pipe string; and performing verification according to the safety factor n to obtain the dangerous well section of the target gas extraction pipe string.

1 . A method for predicting a dangerous well section of a gas-induced vibration pipe string, comprising:
 respectively constructing a first mechanical model, a second mechanical model and a third mechanical model, the first mechanical model being a mechanical model of a target gas extraction pipe string, the second mechanical model being a mechanical model of a casing that sleeves the target gas extraction pipe string, the third mechanical model being a mechanical model of a fluid flowing in the target gas extraction pipe string;   coupling the first mechanical model, the second mechanical model and the third mechanical model by adopting a finite element method based on field production parameters to obtain a full-well gas-induced vibration analysis model;   selecting several nodes on the target gas extraction pipe string, and performing calculation according to the full-well gas-induced vibration analysis model to obtain dynamic characteristic parameters of the several nodes, the spacing between any two adjacent nodes of the several nodes being equal, the dynamic characteristic parameters comprising an average internal stress and an average external stress, the average internal stress being an average of internal stress values at the several nodes, the average external stress being an average of external stress values at the several nodes;   performing calculation according to the average internal stress and the average external stress to obtain a safety factor n of each well section of the target gas extraction pipe string; and   performing verification according to the safety factor n to obtain the dangerous well section of the target gas extraction pipe string.   
     
     
         2 . The method according to  claim 1 , wherein a method for establishing the full-well gas-induced vibration analysis model comprises:
 S 201 : respectively performing discretization processing on the first mechanical model, the second mechanical model and the third mechanical model by using grid units, and defining a coupling simulation area by using a node set;   S 202 : setting an analysis parameter and selecting a gas flow model;   S 203 : transmitting data through a fluid-solid coupling interface between each of the first mechanical model, the second mechanical model and the third mechanical model, and the gas flow model;   S 204 : respectively solving a fluid control equation and a solid control equation of the gas flow model by using a partitioned method according to the analysis parameter in the coupling simulation area; and   S 205 : repeating S 203 -S 204  to obtain a correlation between fluid parameters and solid structure parameters, and constructing the full-well gas-induced vibration analysis model according to the correlation.   
     
     
         3 . The method according to  claim 2 , wherein a method for determining the grid units comprises: 
       respectively verifying grid independence and solution accuracy on at least one of the first mechanical model and the second mechanical model and on the third mechanical model to determine the optimal number of the grid units. 
     
     
         4 . The method according to  claim 3 , wherein the analysis parameter comprises analysis time. 
     
     
         5 . The method according to  claim 3 , wherein the gas flow model comprises a turbulence model. 
     
     
         6 . The method according to  claim 1 , wherein the performing calculation according to the average internal stress and the average external stress to obtain a safety factor n of each well section of the target gas extraction pipe string comprises:
 performing calculation according to the average internal stress and the average external stress to obtain average stress σ s  of all well sections;   determining maximum stress σ max  of each well section, the maximum stress σ max  being a maximum value of the internal stress values and the external stress values at all nodes of each well section; and   calculating a direct ratio of the average stress σ s  to the maximum stress σ max  to obtain the safety factor n.   
     
     
         7 . The method according to  claim 6 , wherein the performing verification according to the safety factor n to obtain the dangerous well section of the target gas extraction pipe string comprises:
 setting a standard safety coefficient n s  of the target gas extraction pipe string; and   determining a well section with n<n s  as the dangerous well section.   
     
     
         8 . The method according to  claim 7 , wherein the standard safety coefficient n s  is 1.03-1.25. 
     
     
         9 . The method according to  claim 8 , wherein the standard safety coefficient n s  is 1.25. 
     
     
         10 . The method according to  claim 1 , wherein the dynamic characteristic parameters further comprise transverse and longitudinal deformation, transverse and longitudinal vibration speed, and three-dimensional bending moment. 
     
     
         11 . A method for preventing a dangerous well section of a gas-included vibration pipe string from failing, comprising:
 determining the dangerous well section according to the method according to  claim 1 ; and   mounting a plurality of stabilizers in the dangerous well section to reduce pipe string vibration.   
     
     
         12 . The method according to  claim 11 , wherein the number of all stabilizers of the plurality of stabilizers is 3-4.