Currently the annulus pressure of gas well becomes more common,so the safe production of several wells has been seriously affected.The annulus pressure mechanism is relatively complex,and it can be approximately classified into annulus pressure induced by temperature effect,by ballooning effect and by leakage or seal failure etc.The article mainly focuses on the annulus pressure mechanism induced by ballooning effect and the corresponding calculation model.For the tubing column with two ends fixed and closed,when tubing internal pressure is larger than the external extrusion force,the external diameter of the tubing column balloons (i.e.ballooning effect).It reduces the annular volume between the tubing and the casing,and consequentially induces annulus pressure.Based on the fundamental theory of elastic-plastic mechanics,the tubing column is simplified into the thin walled cylinder so as to deduce the relation models between the internal pressure and its swell capacity and A annulus pressure value,which provide theoretical support for safety evaluation on annulus pressure and the next treatment program.
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