天然气水合物降压注热联合作用分解过程传热机制研究

Internal heat transfer mechanism of hydrate sediments, as the basic control method during depressurization combined with thermal stimulation, plays a crucial role in regulating efficiency of hydrate dissociation. However, the complex heat transfer mechanism in hydrate sediments associated with multi-phase morphology and multi-species transport under high pressure and low temperature during the depressurization combined with thermal stimulation dissociation process remains unveiled. To address this issue, the in-situ heat transfer measurement experimental system and the numerical simulation method considering various heat transfer factors as well as time dependent properties will be developed, and the heat transfer mechanism and efficiency of dissociation of natural gas hydrate sediments are thoroughly investigated and analyzed here. First, the dominant time dependent heat transfer factors are experimentally analyzed with coupling effects of gas and water migration and saturations of various components in detail. Then the driving effects of inner heat source, effective thermal conductivity, thermal diffusivity and gas-liquid convection heat transfer on decomposition process are demonstrated. In addition, the inner heat source module, effective thermal conductivity module and gas-liquid module are integrated in the numerical simulation model, and with coupling the experimental data and simulation study, the inner relationship between the heat transfer of hydrate sediment and the efficiency of dissociation of natural gas hydrate sediments by depressurization combined with thermal stimulationis established with coupling the experimental data and simulation study. In the end, this study reveals the heat transfer mechanism in the natural gas hydrate sediments decomposition process by thermal stimulation combined depressurization dissociation method, providing essential theoretical basis for future research on efficient natural gas hydrate sediments dissociation.

水合物沉积物内部传热作为降压注热联合分解水合物的基本控制机理，是控制水合物分解效率的关键问题。联合分解过程涉及高压低温下多物质性态和多相态迁移复杂传热问题，尚未明确。本项目以此为背景，通过构建水合物联合分解过程传热原位测量实验系统和综合考虑各传热因素时变特性的联合分解数值模拟方法，对水合物联合分解过程的传热机制与分解高效性进行全历程分析。首先实验研究联合分解过程气水迁移、组分饱和度的协同作用，解析水合物沉积物储层内部传热主控因素的时变规律；其次探明沉积物储层内热源、沉积物有效导热、热扩散系数以及沉积物中气水对流换热对水合物联合分解进程的驱动作用；然后在联合分解传热模型中添加内热源，有效导热和气水对流三个传热模块，并将实验数据与模拟结合，揭示水合物沉积物内部传热性能与联合分解高效性之间的内在关联，最终阐明水合物联合分解过程的传热机制，为天然气水合物高效分解研究提供基础理论依据。

水合物沉积物内部传热作为降压注热联合分解的基本控制机理，是控制水合物分解效率的关键问题。联合分解过程涉及高压低温下多物质性态和多相态迁移复杂传热问题，尚未明确。本项目以此为背景，通过构建水合物联合分解过程传热原位测量实验系统和综合考虑各传热因素与时变特性的联合分解数值模拟方法，对水合物联合分解过程的传热机制与分解高效性进行全历程分析。研究内容包括：水合物沉积物联合分解过程传热数值模型与实验方法的构建；联合分解过程水合物储层内热源时变特性对水合物分解效率作用机制；水合物沉积物有效导热及汽液对流时变特性对于联合分解进程的驱动机制。在联合开采效率方面：项目研究证明随着饱和度增加，联合分解的产气百分比和平均产气速率显著高于降压和注热法，此外，实验证明联合分解能效较高，能够显著抑制水合物分解过程中结冰问题，在水合物饱和度为57%时，联合开采产气率达到了74%，比单独降压和注热提升了18.63%和31.9%。在联合分解过程气液迁移规律方面：研究发现在联合分解过程中，降压引起的气液固迁移造成了多孔介质层的膨胀率达到176%，并在形态恢复过程中出现了水层消失的现象；同时通过模型建立和图像分析得出气液固迁移是由孔隙演化造成；而孔隙演化则是多孔介质层中有效应力、孔隙压力、背压和补偿压力相互作用的结果；此外气液固迁移造成了气体水合物二次生成过程的异常现象，揭示了联合分解过程气液固迁移对气体水合物二次生成过程的影响机理。本项目研究揭示水合物沉积物内部传热性能与联合分解高效性之间的内在关联，阐明了水合物联合分解过程的传热机制，为天然气水合物高效分解研究提供基础理论依据。