多封隔器密闭环空热膨胀力学计算方法及应用

环空温度压力变化对高温高产气井多封隔器管柱力学行为和安全可靠性的影响较大。为此,基于动量守恒定律、能量守恒定律及各层环空流体瞬态传热机理,建立了单层和多层环空的温度、压力场计算模型,分析全井筒环空温度和热膨胀压力的变化规律;针对多封隔器完井管柱,综合考虑密闭环空温度效应和体积变化效应,建立了多封隔器间密闭环空热膨胀压力计算模型,研究双封隔器间密闭环空的热膨胀压力变化规律;以南海西部某高温高产气井作为实例开展分析。结果表明:(1)环空温度效应和体积效应共同作用使全井筒A环空热膨胀压力最小,C环空热膨胀压力最大;(2)双封隔器间密闭环空热膨胀压力与环空温差基本上呈线性关系,温度效应引起的压力增量占主导作用,体积效应对压力增量的贡献率随环空温差的增大而增大;(3)确定实例井最大产气量为212×10~4 m~3/d,在产量为160×10~4 m~3/d时,双封隔器最大坐封间距为312 m。结论认为:在强度允许的前提下,选择内径较大的生产套管有利于降低密闭环空热膨胀压力。

A calculation method for thermal expansion mechanics of sealed annulus between multiple packers and its application

For high-temperature and high-production gas wells, the mechanical behaviors, safety and reliability of strings with multiple packers are more affected by the change of annulus temperature and pressure. In this paper, therefore, a calculation model for the temperature and pressure fields of single-layer and multi-layer annulus was established on the basis of momentum conservation law, energy conservation law and transient heat transfer mechanism of fluid in each annulus. Annulus temperature and thermal expansion pressure were analyzed through the full hole. For completion strings with multiple packers, the calculation model for thermal expansion pressure of sealed annulus between multiple packers was built after temperature and volume change effects of sealed annulus were analyzed comprehensively. And based on the calculation model, the change rules of thermal expansion pressure in sealed annulus between dual packers were studied. And finally, a case study was conducted on a high-temperature and high-production gas well in the western South China Sea. It is shown that the thermal expansion pressure of annulus A is the minimum in the full wellbore and that of annulus C is the maximum under the joint action of the annulus temperature and volume effects. As for dual packers, there is basically a linear relation between the sealed annulus thermal expansion pressure and the annulus temperature difference, with the pressure increment caused by the temperature effect playing a leading role and the contribution of the volume effect to pressure increment rising with the increase of annulus temperature difference. It is confirmed that the maximum production rate of the case well is 212×10⁴ m³/d. And at the production rate of 160×10⁴ m³/d, the maximum setting spacing of dual packers is 312 m. It is concluded that the production casing with larger internal diameters is favorable for reducing the thermal expansion pressure of sealed annulus so long as the strength is allowable.