钻井液宏观传热传质特性影响水合物形成的介观机理研究

During deep water and gas hydrate drilling, the process of gas hydrate phase transformation in the drilling fluid in the annular space of the well would result in a series of complicated situations, which might induce the accidents in the well. More attention is paid currently to the measurement and evaluation of the hydrate inhibition property of the drilling fluid and the balance between the hydrate inhibition property and the low-temperature rheological property, while the hydrate inhibition mechanism is very little analyzed from the view of heat and mass transfer closely related to the phase transformation of gas hydrate with the consideration of the mesostructure of the drilling fluid. Therefore, in this project, considering the synergistic hydrate inhibition effect of the drilling fluid with conventional drilling fluid additives and hydrate inhibitors, the correlations among these macroscopic properties (such as the low-temperature rheological property, acoustic and optical properties, characteristics of heat and mass transfer and the hydrate inhibition property) will be established. With the spatial fractal characteristics of the mesostructure of the drilling fluid, the internal connection between the macroscopic property and the mesostructure will be analyzed. On this basis, with the theories of the phase transformation of gas hydrate and heat and mass transfer, the corresponding models of mesoscopic heat and mass transfer will be built, and the effects of the component type and content of drilling fluids on gas hydrate formation would be further revealed from the view of macroscopic and mesoscopic heat and mass transfer, which is helpful to the relevant research and application of deep water and gas hydrate drilling and oil and gas transportation and is essential to efficient and safe drilling in hydrate reservoirs in South China Sea.

在海洋深水与水合物钻井过程中，井内环空钻井液中存在的水合物相变过程往往会导致一系列井内复杂情况的出现，进而诱发井内安全事故。目前研究人员主要关注于钻井液水合物抑制性的测试评价及其与低温流变性之间的协调平衡，而较少结合钻井液介观结构并从与水合物相变密切相关的传热传质角度来分析水合物抑制机理。为此，本项目考虑典型钻井液处理剂和水合物抑制剂等多组分之间的水合物协同抑制作用，建立钻井液低温流变性、声光学性质、传热传质特性以及水合物抑制性等宏观性质之间的相互关联。基于介观结构空间分形特征，分析宏观性质与介观结构之间的内在联系。在此基础上，结合水合物相变与传热传质等理论，建立相应的介观传热传质模型，从宏观与介观传热传质角度进一步揭示钻井液组分类型及其含量对水合物形成的影响机理，从而为海洋深水与水合物钻井和油气输送等领域的相关研究与应用奠定一定基础，为今后我国南海水合物资源安全高效勘探开发做出相应贡献。

在海洋深水与水合物钻井过程中，井内环空钻井液中存在的水合物相变过程往往会导致一系列井内复杂情况的出现，进而诱发井内安全事故。项目主要考虑钻井液的性能和环保要求、正常钻井与关井停钻工况以及我国南海海水、水合物储层与海底泥线的温度特点，针对含典型处理剂和水合物抑制剂的水基钻井液，进行了相应的传热传质特性、声光学性质、低温流变性、水合物抑制性以及介观结构等研究。在介观尺度下，钻井液中存在着由高分子聚合物水化形成且具有一定强度的网络骨架和由中小水化分子与离子和自由水分子组成的孔隙流体，而且在网络骨架与孔隙流体之间、中小水化分子与离子和自由水分子之间存在着由强弱束缚水形成的边界层。这些网络骨架与孔隙流体的空间形态与相互作用影响其介观传热传质特性，也是其宏观传热传质特性的基础所在，往往受网络骨架组分与结构特征及其力学与热物理性质、孔隙流体压缩与热物理性质、体系中不同状态水及其氢键网络分布特征等因素影响，也与温度变化、声波振动、流动剪切等外部作用所引起不同程度的网络骨架变形或破坏和网络骨架与孔隙流体之间的相对运动密切相关。通常，这些介观结构空间形态会因组分类型不同与外部作用而产生相应变化，而组分浓度增加会增大网络骨架体积并减小孔隙体积，进而使其结构更为规则，从而降低其复杂程度及相应分形维数。总体上，钻井液主要通过组分的水化作用及其对氢键网络的扰动、孔隙结构和聚合物基团吸附的传质阻碍、组分热物性差异和边界层界面热阻的传热影响以及水合物形成中排盐聚集水合盐离子的传质传热影响等方式从降低水合物形成物质数量、延缓水合物晶核形成、阻碍水合物晶核生长三个方面影响体系中水合物的形成。项目研究有助于进一步揭示钻井液中水合物的形成机理，为指导我国海洋水合物与油气钻井液体系优化设计和新型水合物抑制剂设计研制提供参考，从而为海洋水合物试采、油气勘探开发和油气输送等领域的相关研究与应用奠定一定基础。