井壁破裂与内部应变状态机理分析

Mechanism Analysis of Wellbore Fracture and Internal Strain State

为研究立井井壁破裂与内部应变之间的相互规律,搭建井壁实物模型以模拟井壁受力破裂过程和状态,利用分布式光纤技术对井壁内部应变进行监测,并分别从应力和应变多角度进行深入分析.结果表明:对于应变状态,当施加应力增大,井壁应变程度也随之增大,应变极大值所对应的井壁位置,其应变程度在范围内达到最大,破裂风险也就最高;对于应力作用,不同应力下井壁应变最大值与最小值之间的偏差度越大,井壁稳定性越差,越容易发生破裂;分析了应力、应变二者相互关联性,拟合各方向角所对应的井壁位置应变变化的线性方程,变化率数值越大,井壁应变增长速度就越快,当应变值超过所能承受极限时,井壁会更容易发生破裂;通过对井壁应变数据监测,分析了应变差值、偏差度和应变变化率,结合Lamé公式,建立了井壁应变破裂关系模型,为井壁破裂预警提供了新方案.

To study the mutual law between the vertical shaft wall fracture and the internal strain,a physical model for the shaft wall was built to simulate the process and state of the shaft wall stress fracture.The distrib-uted optical fiber technology was used to monitor the internal strain of the shaft wall,and the in-depth analysis was conducted from multiple perspectives of stress and strain.The results show that,for the strain state,the wellbore strain degree will increase with the applied stress.In the wellbore position corresponding to the maxi-mum strain value,the strain degree will reach the maximum value within the range,and the risk of fracture will be the highest.For the stress effect,the larger the deviation between the maximum and minimum strain values of the wellbore under different stresses is,the poorer the wellbore stability will be,and the more likely it will rupture.The analysis of the correlation between stress and strain,and the fitting of the linear equation of strain change at the wellbore position corresponding to each direction angle indicate that,the larger the change rate value is,the bigger the growth rate of wellbore strain will be.For the strain value exceeding the allowable lim-it,the wellbore is more prone to fracture.Through monitoring of the wellbore strain data and analysis of the strain difference,deviation and strain change rate,and combined with the Lame formula,a wellbore strain rup-ture relationship model was established.The study provides a new scheme for wellbore rupture warning.