孔隙尺度砂质沉积物中天然气水合物分解—输运机理研究

The natural gas hydrate of high saturation in the arenaceous sediments has been regarded as the favorable exploitation target. Porescale study on the dissociation and transportation mechanism of natural gas hydrate in porous sediments is one of the key scientific issues to realize its efficient exploitation. Considering the internal relationship between the hydrate dissociation -transportation mechanism and the evolution of pore structure as breach, this project conducts the hydrate formation-dissociation experiments in the lab. Then the core samples are tested for physical parameters and imaged to obtain the micro structure characteristics using micro CT technology before and after the dissociation of hydrates. Three-dimensional mesh models are then reconstructed, which can reproduce the real structure and the spatial distributions of rock matrix, pore and gas hydrate. Considering the phase equilibrium of gas hydrate and the heat and mass transfer mechanism of multiphase flow in porous media, the mathematical models of gas hydrate dissociation and transportation in porous sediments are constructed and complied based on the finite volume methods. Then porescale simulations on gas hydrate dissociation are conducted and validated by comparing with the experimental results. Following that, the hydrate extraction processes under different conditions of pressure, temperature and petrophysical parameters are simulated. In this way, the interaction mechanism of the pore structure evolution, gas hydrate dissociation rate, absolute/relative permeability and thermodynamic properties of the sediments is revealed. The outcomes of this project are of great significance to enrich the microscopic multi-physics coupling mechanism of rock & soil and the theory of heat & mass transfer with phase change in porous media, as well as to promote the exploitation of gas hydrate.

高饱和度砂质沉积物中的天然气水合物是水合物开采的有利靶区。孔隙尺度水合物的分解—输运机理是实现其有效开采的关键科学问题之一。本项目以水合物分解—输运机制与孔隙结构动态演化的内在联系为突破口，结合室内水合物生成—分解实验及微CT技术，获取水合物分解前后岩样的物性参数及微观图像特征，进而重建能够真实表征岩样骨架、孔隙结构及水合物形态分布的三维模型；综合考虑水合物相平衡、多孔介质中多相流体传热传质机理，建立孔隙尺度水合物分解及输运数学模型，并基于有限体积法实现数学模型的编译；开展孔隙尺度水合物分解的数值模拟，并与实验结果对比验证模型可行性；开展不同压力、温度及物性参数条件下水合物开采过程模拟，揭示沉积物孔隙结构的动态演化规律与水合物分解速率、绝对/相对渗透率、热力学性能的相互影响机制。研究成果对丰富岩土体微观多物理场耦合机理及多孔介质相变传热传质理论、指导水合物高效开采具有重要意义。

高饱和度砂质沉积物中的天然气水合物是水合物开采的有利靶区。孔隙尺度水合物的分解—输运机理是实现其有效开采的关键科学问题之一。本项目通过室内实验、理论分析、数值模拟相结合的方法，以水合物分解—输运机制与孔隙结构动态演化的内在联系为突破口，创新了3D打印岩心在室内水合物合成/分解及多相流体输运研究中的应用，实现了岩石复杂孔隙结构定量表征，明确了其与沉积物的力学相似性；结合微观CT技术，开发了天然气水合物孔隙尺度合成/分解—多相流体输运的可视化实验技术，研究了岩石中气液、气液固多相渗流规律及其影响因素。形成了一套集图像分割、识别、统计、计算网格模型生成为一体的软件系统，重建了沉积物中天然气水合物、水、气、矿物多计算域网格的装配模型；建立了综合考虑天然气水合物相变、沉积物固体骨架导热、流体对流换热、多相流体渗流过程的宏观尺度水合物分解及多相流体输运数学模型；耦合VOF模型及Enthalpy—Porosity技术建立了孔隙尺度水合物相变—化学反应与孔隙结构演化的数学表征模型，并基于有限体积法，实现了数学模型的编译及二次开发；通过多参数数值模拟，从孔隙—宏观多尺度揭示了沉积物中水合物分解、多相流体输运机理与孔隙结构的动态演化规律，及其对沉积物绝对渗透率、相对渗透率曲线、水合物开采效果的影响。依托该项目，累计发表学术论文18篇，其中SCI论文17篇，EI论文1篇；研究成果形成了建模程序及数值模拟子程序3套，授权发明专利1项，公开发明专利6项；累计培养硕士研究生4名，作为第二导师培养博士生2名；成果受邀作报告两次，组织学术论坛2次，被相关学术网站报道多次。项目成果形成的基础理论、实验和数值模拟技术为天然气水合物开采方案优化提供了基础实验平台和模拟技术，对丰富岩土体微观多物理场耦合机理及多孔介质相变传热传质理论、指导水合物高效开采具有重要意义。