采油螺杆泵漏失机理的刚柔螺旋曲面与液膜多场耦合研究

Progressive cavity pumps (PCPs) are positive-displacement pumps employed in the petroleum industry for artificial lift. For this kind of PCP, leakage is one of the main factors affecting the lifting capacity. The project proposes that the liquid film might be the main reason to cause the leakage. In the meshing process of metal rotor and rubber stator, single helical rotor is rotating in cavities fluid, and contacting and opening with double helix stator periodically. Cavities fluid is splitting and merging periodically. They make the rubber stator friction heat and hysteresis heat. This is a kind of interactions with rigid helical surface contact and cavities fluid, and accompanied by the multi-physics coupling problem of heat generation and heat transfer. Consider the physical phenomena of thermal expansion and swelling, and apply the wellbore temperature boundary, multi-physics coupling model for cavities fluid and rigid-flexible spiral surface is developed. On the basis of the method of external mesh reconstruction, moving and deformable mesh is structured. Iterative scheme for multi-physics (temperature and heat flux, displacement and pressure) two-way coupling of spiral interface is also presented. The project will reasonable predict the flow characteristics inside the cavities and the mechanical behavior of the PCPs, and analysis the influence factors of the film thickness and several parameters (rotor and stator dimensions, fluid properties, cavities pressure, the rotor speed and the wellbore temperature etc). The project will provide a theoretical basis for explaining the leakage mechanism, and also expand the research category of fluid structure interaction.

采油螺杆泵是一种新兴的人工举升设备，漏失是制约举升能力提高的重要因素之一，本项目认为液膜的存在可能是产生漏失的主要原因。金属单螺旋转子在流域中旋转，与双螺旋定子通过橡胶衬套有周期性的接触密封、开合，使流域有周期性的分割和合并现象，还使定转子摩擦生热及橡胶衬套滞后生热。这是一种刚柔螺旋曲面接触与腔室流域流固耦合作用、并伴随着生热与传热的多场耦合问题。考虑定子温胀和溶胀等物理现象，引入井筒温度边界，采用外部网格重构法，构建腔室流域运动及变形的动网格，提出螺旋界面多物理量(温度、热量、位移、压力)双向耦合的迭代格式，建立腔室流域与刚柔螺旋曲面多场耦合模型。分析腔室内部流动特性以及定转子变形和运动的力学行为，研究液膜厚度与螺旋曲面尺寸、流体特性、腔室压力、转子转速、井筒温度等因素的内在关系。项目预期为解释采油螺杆泵漏失机理提供理论基础，也将扩展流固耦合力学的研究范畴。

采油螺杆泵是一种新兴的人工举升设备，不仅适用于水驱、聚合物驱和三元复合驱的油井，而且适用于稠油、含砂和含气的油井，已广泛应用于世界各油田的机械采油工程中。但是，螺杆泵漏失是影响泵效和举升能力的重要因素之一。本项目针对该问题，开展了定转子刚柔螺旋曲面周期性接触密封与开合的动力学分析，腔室流域周期性分割和合并的腔室流场及转子壁面的受力分析。采用热力耦合方法，研究了摩擦生热对螺杆泵定子衬套温升的影响。采用单向耦合法，进行了定转子多物理场研究。采用温度比拟法，研究了定子溶胀对密封性能的影响。研究发现，腔室流域产生涡流，转子对定子的横向载荷和扭矩呈现周期性变化。滞后生热引起橡胶衬套温升起主要作用，定子溶胀是影响密封性能的主要因素。为实现定转子密封性能和减小漏失，可根据定子的溶胀率，选取合适的初始过盈值或间隙值。在实际应用中，可根据实验测试的定子橡胶溶胀率和实现密封效果的接触压力，指导采油螺杆泵定转子的设计。