超临界CO₂直旋混合射流破岩机理及喷嘴结构影响特性研究

【作者】 李俊；

【导师】 薛永志；

【作者基本信息】 西南石油大学 ， 动力工程及工程热物理， 2024， 硕士

【摘要】 超临界CO2直旋混合射流综合了超临界CO2射流和直旋混合射流的技术优势,具有破岩门限压力低、效率高、射孔直径大的优点,在非常规油气资源勘探开发领域具备广阔的应用前景。然而,目前缺乏对超临界CO2直旋混合射流这种新颖技术的系统研究。因此,本文利用数值模拟的方法,对超临界CO2直旋混合射流破岩的流场特性、流-固共轭传热机制以及岩石应力场分布等关键科学问题进行了研究,旨在揭示超临界CO2直旋混合射流的破岩机理,进一步优化该技术的实际应用效果。主要研究内容及结论如下:(1)基于流-固-热耦合理论,建立了超临界CO2直旋混合射流冲击岩石的数值计算模型。利用改进的PR真实气体模型和拟合公式定义了 CO2流体和固体岩石材料,考虑了其热物性参数随温度变化的性质;利用Workbench平台确立了射流破岩的流-固-热耦合计算步骤与策略;将模拟结果与实验数据进行对比,验证了数值计算方法具有可靠性,为后续的研究工作奠定数值计算基础。(2)研究了超临界CO2直旋混合射流冲击岩石的流场、瞬态共轭传热和固体岩石应力场等多场耦合作用机理。首先分析了射流冲击的内外流场特性,揭示了直旋混合射流的形成过程,得到了射流速度场、压力场和湍动能的分布特征与规律;其次分析了流-固温度场和岩石温度梯度的变化规律,揭示了瞬态流-固共轭传热机制;最后分析了多场耦合作用下岩石Mises应力的时空分布规律,并对岩石的损伤区域进行评估,从而揭示超临界CO2直旋混合射流破岩过程涉及的复杂作用机理。(3)研究了超临界CO2直旋混合射流、超临界CO2直射流和直旋混合水射流对岩石的作用机制。对比分析了这三种射流在冲击流场、流-固共轭传热以及岩石应力分布三个方面的差异,得到了不同的流体介质和喷射方式对射流破岩机制的影响特点,有利于超临界CO2直旋混合射流结合超临界CO2直射流和直旋混合水射流的优势,为优化超临界CO2直旋混合射流的应用提供指导。(4)采用单因素分析方法,研究了直旋混合喷嘴关键结构参数对流场速度的影响规律。在此基础上,以岩石的损伤体积比δ为评价指标,利用正交试验方法对喷嘴结构参数进行优化设计,得到了喷嘴最佳的结构参数组合,即叶轮中心孔直径1.5mm,螺旋槽旋转角度60°,叶轮长度6 mm,混合腔长度4 mm,并对优化前后喷嘴进行模型验证,结果表明优化后的直旋混合喷嘴具有更好的破岩性能,使岩石产生更大体积的破坏。更多还原

【Abstract】 The supercritical CO2 straight-rotating mixed jet combines the technical advantages of the supercritical CO2 jet and the straight-rotating mixed jet.It has a low rock-breaking threshold pressure,high efficiency,and a large drilling diameter.This makes it highly applicable in the exploration and development of unconventional oil and gas resources.However,there has been a lack of systematic research on the novel technology of supercritical CO2 straight-rotating mixed jets.In this paper,key scientific issues such as the flow field characteristics of supercritical CO2 straight-rotating mixed jet rock breaking,the flow-solid conjugate heat transfer mechanism,and the rock stress field distribution are investigated using numerical simulations,aiming to reveal the rock breaking mechanism of supercritical CO2 straightrotating mixed jet and further optimize the practical application effect of this technology.The main research and conclusions are as follows:(1)Based on the coupled theory of fluid-solid-heat,a numerical calculation model of supercritical CO2 straight-rotating mixed jet impinging on rocks was established.The thermophysical parameters of CO2 fluids and solid rock materials were defined using an improved PR real gas model and fitting equations that take into account their nature as a function of temperature.Calculation steps and strategies for jet rock breaking with flow-solidthermal coupling were established using the Workbench platform.The simulation results were compared with the experimental data to verify the reliability of the numerical calculation method and establish the foundation for subsequent research work.(2)The multi-field coupling mechanism of flow field,transient conjugate heat transfer and solid rock stress field of supercritical CO2 straight-rotating mixed jet impinging on rock was investigated.Firstly,the internal and external flow field characteristics of the jet impingement were analyzed,the formation process of the straight-rotating mixed jet was revealed,and the distribution characteristics and laws of the jet velocity field,pressure field and turbulent kinetic energy were obtained.Secondly,the changing rules of the flow-solid temperature field and the rock temperature gradient were analyzed,revealing the transient flow-solid conjugate heat transfer mechanism.Finally,the spatial and temporal distribution of rock Mises stress under multi-field coupling was analyzed,and the damage region of the rock was evaluated,so as to reveal the complex action mechanism involved in the supercritical CO2 straight-rotating mixed jet rock breaking process.(3)The mechanisms of supercritical CO2 straight-rotating mixed jets,supercritical CO2 straight-rotating jets and straight-rotating mixed water jets on rocks were investigated.The differences of these three types of jets in terms of impact flow field,flow-solid conjugate heat transfer and rock stress distribution were comparatively analyzed,and the characteristics of the influence of different fluid media and jetting methods on the rock-breaking mechanism of the jets were obtained.This facilitates supercritical CO2 straight-rotating mixed jets combining the advantages of supercritical CO2 straight jets and straight-rotating mixed water jets,which can provide guidance for optimizing the application of supercritical CO2 straight-rotating mixed jets.(4)The influence law of key structural parameters of the straight-rotating mixed nozzle on the velocity of the flow field was investigated by using a one-factor analysis method.On this basis,the damage volume ratio of the rock was used as the evaluation index,and the orthogonal test method was used to optimize the design of the nozzle structure parameters.The optimal combination of structural parameters of the nozzle,i.e.,impeller center hole diameter of 1.5 mm,helical groove rotation angle of 60°,impeller length of 6 mm,and mixing chamber length of 4 mm,was obtained,and the nozzle before and after the optimization was modeled and verified.The results indicate that the optimized straight-rotating mixed nozzle has superior rock-breaking performance,resulting in a greater volume of rock destruction.更多还原