变压力工况下井口装置的疲劳失效演化规律研究

Fatigue Failure Evolution of Wellhead under Changing Pressure Condition

在页岩气大规模压裂作业过程中,井口装置受到周期性变化的复杂载荷作用,易发生疲劳失效,其疲劳寿命亦成为关注焦点。由于压裂施工工况繁复,现场试验耗费人力物力、数值求解过程繁琐,且均存在一定的难度。为此,利用ANSYS有限元分析软件和FE-SAFE平台开展研究,以寻找变压力工况下压裂井口装置的疲劳失效规律。选取套管头、油管头2个主要部件,通过建立三维模型、设定边界条件、施加工况载荷-压力,揭示不同压力条件下各部件应力、应变状态及疲劳脆弱点位置;求解各部件应力应变及疲劳寿命随压力变化的关系;绘制各部件应力应变、疲劳寿命与压力的关系曲线,以及变压力工况下各部件、井口装置整体的疲劳失效演化图谱。结果表明,压裂井口装置主要部件的最大应力、最大应变随压力近似呈现线性变化趋势,各部件的强度和刚度满足工况要求。

In the process of large-scale shale gas fracturing,wellhead is subjected to complex and cyclical load and appears fatigue failure easily,so its fatigue life becomes the research focus.Fracturing operation condition is very complicated,and the field experiment consumes manpower and material resources.In addition,numerical solving process is also a tedious work.So it is hard to solve such a problem,and in this paper,some researches are carried out by ANSYS software and FE-SAFE platform.These are used to search the fatigue failure evolution of wellhead under the changing pressure condition.Casing head and tubing head,two major parts,are selected.Through establishing the three-dimensional model,setting boundary condition,applying condition loadpressure,this paper reveals two parts＇ stress and strain state and the fatigue weak points under different pressure conditions,clears the regularity and relationship-how stress,strain and fatigue life change with pressure,and then draws the relationship curves and all fatigue failure evolution graphs of wellhead under the changing pressure condition.The results show that there are linear trends between two parts＇ maximum stresses,maximum strains and pressure approximately.In the range of maximum allowance,two parts meet the condition requirement.