气井携液机理与临界参数研究

气井井筒携液工况诊断方法主要包括临界流速法和临界动能因子法。目前对于哪种方法更科学、更合理尚无定论,给应用选择造成了困难。为此,从分析圆管流动的基本特征入手,对两相垂管流的携液机理与形式进行了再探讨。研究结果表明:(1)两相垂管流积液的原因是气相无法保持连续,连续携液时液相存在的主要形式是管壁环膜,管流的基本流型是环雾流;(2)气流携液的实质是能量驱动,携液工况变化的本质是单位体积气流动能的量变引起的两相流型的质变;(3)临界动能因子法体现了流体流动依赖于能量驱动的物理学基本原理,携液机理符合圆管流动基本特征和能量守恒定律;(4)而临界流速法则忽视了横截面上流速存在径向差异的管流基本特征,不符合两相垂管流条件下气流携液的实际情况,存在着局限性;(5)液相物性不同导致连续携液的临界动能因子略有差别的管流基本特征,综合确定环雾流临界动能因子的通用取值为10 Pa~(0.5)。该研究成果揭示了两相垂管流气流携液的机理与本质,明晰了采用不同模型所得结果差异大的根源,确立了通用的诊断方法和参数。

Mechanism and critical parameters of liquid-carrying behaviors in gas wells

Currently, the critical velocity method and the critical kinetic energy factor method are mainly applied for in identifying liquid-carrying behaviors in gas wells. However, it is unclear which one is more scientific and suitable. In this paper, the liquid-carrying mechanism and patterns in two-phase vertical pipes were re-discussed in view of the basic features of a circular pipe flow. The following results were obtained. First, liquid accumulation in two-phase vertical pipes occurs predominantly due to the incapability to maintain gas continuously. In the case of continuous liquid-carrying, liquid exists in the form of an annular film around pipe walls, and pipe flow is mainly an annular mist flow. Second, the fluid-carrying behavior of gas flow is, in fact, induced by an energy drive. Alteration in fluid-carrying capacities indicate qualitative changes in the flow patterns of both phases due to the quantitative changes in the gas flow energy of unit volume. Third, the critical kinetic energy factor technique can effectively reflect the basic physical theories related to energy-driven fluid flows. Generally speaking, its fluid-carrying mechanism coincides well with the basic characteristics and law of energy conservation of an annular flow. Fourth, with radial differences in cross-sectional flow velocities ignored, the critical velocity method may not accurately reflect the actual fluid-carrying behaviors in two-phase vertical pipes. Fifth, differences in physical properties of fluids lead to slight variations in critical kinetic factors with continuous liquid-carrying flows. Generally, the critical kinetic energy factor for annular mist flows shall be 10 Pa0.5. These results highlight the fluid-carrying mechanism and the nature of flows in two-phase vertical pipes, clarify root causes for significant differences in models, and define the universal diagnosis techniques and parameters.