储气库含裂纹缺陷井筒寿命可靠性预测方法研究

Research on reliability prediction method of gas storage with crack defect wellbore life

为了探究地下储气库井筒管柱裂纹缺陷对井筒寿命的影响,采用随机裂纹扩展融合概率密度演化法(Probability Density Evolution Method,PDEM)模型对含裂纹缺陷井筒进行寿命可靠性预测。通过修正后的裂纹特征向量,采用总变差减小(Total Variation Diminishing,TVD)差分格式求解出特征值概率密度函数,可得到其疲劳寿命可靠性,研究不同裂纹长度和井筒内压下,井筒管柱裂纹处最大应力和应力强度因子K的变化规律,并对其模型预测进行性能分析。结果表明:概率密度演化法得到的井筒裂纹尺寸曲线与Monte Carlo法的结果吻合性良好,且概率密度演化法计算简单、精度高,模型预测误差率在11%以内;最大应力及应力强度因子K随着井筒压力、裂纹长度的增加而增大,当最大应力超过材料屈服强度350 MPa后,则增长趋势逐渐减缓直至趋于平稳。

To predict the reliability of wellbore tubular columns with crack defects in underground gas storage,a reliability prediction model based on the random crack expansion fusion Probability Density Evolution Method(PDEM)is proposed in this paper.Firstly,the Total Variation Reduction(TVD)probability density evolution model is used to calculate the reliability of the wellbore column based on the modified crack feature vectors.Then,the maximum stress and stress intensity factor K at the crack under different crack lengths and internal pressure of the wellbore were analyzed.Finally,the performance analysis of the model prediction effect was performed.The results show that(1)The PDEM takes into account the randomness of materials and loads and derives the time-varying reliability of the wellbore tubular column,which provides a new idea for the prediction of the remaining life of the wellbore tubular column based on crack expansion.(2)The wellbore cracks size curves obtained by the PDEM match the simulation results of the Monte Carlo method,and the PDEM is simple to calculate and highly accurate,with the model prediction error rate within 11%.(3)The maximum stress and stress intensity factor K increase with increasing wellbore pressure and crack length.After the maximum stress exceeds the material yield strength of 350 MPa,the growth trend slows down to a steady state.The model can effectively predict the reliability of wellbore tubular columns in underground gas storage,and provide reference and technical support for the life prediction and safety analysis of oil and gas wellbore tubular columns.Besides,it can maximize the use of the original well site data to optimize the prediction of wellbore life reliability and improve the management capability of the underground gas storage wellbore tubular column in later operation and maintenance.