水泥返高对气井持续环空压力的影响与分析

持续环空压力由气井井筒完整性遭到破坏引起,现有防治措施存在一定的局限性。为探究通过水泥返高调控持续环空压力的可行性,用一维不稳定渗流描述气体在水泥环中的运移过程,建立了基于物质守恒和体积守恒的含液环空持续环空压力计算模型,并给出了迭代求解方法。分析表明:持续环空压力随时间的增加而上升,降低水泥返高能够降低持续环空压力的上升速度和极限值;持续环空压力极限值与水泥返高呈线性关系,并且随着环空液体密度的增加而降低;可以通过降低水泥返高把环空压力极限值控制在环空最大允许压力以下。

Impact and analysis of cement back top to control sustained casing pressure in high pressure gas wells

Sustained casing pressure is caused by failure of well integrity. Available control measures have some limitations. To analyze the feasibility of cement back top to control sustained casing pressure, one-dimensional unsteady seepage is used to describe the gas transport process in cement mantle. And then a model is built based on mass conservation and volume conservation to calculate sustained casing pressure when annulus contains liquid. Furthermore, a iteration method is provided to solve the model. The analysis indicates that: sustained casing pressure increases as time continues; the rising speed and extreme value of sustained casing pressure are reduced by lower cement back top; There is liner relationship between sustained casing pressure and cement back top and the extreme value decreases as annular liquid density increases; It is feasible to control the sustained casing pressure extreme value under maximum allowable casing pressure by decreasing cement back top.