深水细粉砂水合物试采温压传递特性与非稳态渗流研究

As a new green energy resource, deepwater natural gas hydrate has a broad prospect. The natural gas hydrates of Chinese ocean mainly exist in fine silt deposition, and have entered the stage of engineering trial development nowadays. However, there are a series of high technical risks and challenge, especially the transient percolation theory in the hydrate dissociation process is not clear yet. The reservoir percolation field heat and pressure transfer before and after dissociation is very complicated due to the special phase equilibria of hydrate. Improper prediction and control may lead to low gas production efficiency, serious sand production and even halfway shutdown. Considering the different reservoir properties of hydrate consolidation zone-decomposition zone-near wellbore zone and the gas-water-sand flow difference under overburden pressure, we will focus on unstable percolation temperature-pressure-permeability field mathematical characterization under hydrate phase transition conditions in deepwater reservoir, study the hydrate formation and dissociation kinetics and flow characteristics in sandstone reservoir, establish the unstable multiphase flow theory and related model to describe temperature and pressure transfer in hydrate dissociation zone-flow zone with hydrate phase transition, reveal the mechanism of interaction between hydrate dissociation flow and reservoir as well as unsteady seepage field temperature and pressure transfer and distribution characteristics in the deepwater hydrate reservoir development, improve theoretical system of unsteady seepage field in deepwater hydrate development, which can provide theoretical basis and technical support the rational design of hydrate development scheme and parameters such as temperature and pressure.

深水天然气水合物作为一种绿色环保新能源，具有广阔的开发前景，我国海域水合物以细粉砂型为主，已进入工程试开采阶段，但存在高技术风险与挑战。水合物特有的相平衡性质决定了储层分解前后渗流场与温度压力传递的复杂性，如果预测和控制不当，会导致产气效率低、严重出砂甚至井眼报废而无法继续开发。本项目拟聚焦于深水储层水合物相变条件下瞬态渗流温压场数学表征这一科学问题，针对细粉砂质水合物试采的分解与流动过程，考虑水合物储层固结区-分解区-流动区物理性质及气水砂流动的差异性，分析储层水合物生成与分解动力学机理与流动特性，建立考虑水合物相变的水合物储层分解区域-流动区域非稳态多相流动理论与温压传递模型，揭示水合物分解流动介质与水合物层相互作用机制、非稳态渗流场的温压传递特性及分布特征，完善深水水合物开采多相流动理论体系，为合理设计水合物试开采方案与参数设计提供理论依据与技术支持。

深水细粉砂水合物藏的粒度特征、储层物性和弱胶结特性导致试采过程中存在储层物性变化特征不明晰、气液固非稳态渗流规律复杂，不同分解阶段及分解区域温压传递特性差异明显等复杂问题，掌握储层物性变化特征、气液固多相渗流机理与温压传递机制是深水细粉砂水合物藏高效试采的关键。.本课题针对上述科学和技术难题，采用实验探究、理论分析和数值模拟等研究方法，设计并搭建了水合物岩心渗透率测量实验系统、水合物相变微流控模拟观测实验系统和天然气水合物储层开采模拟实验系统；开展了水合物岩心渗透率表征实验、水合物降压开采微流控模拟观测实验和天然气水合物储层开采模拟实验；探究了细粉砂储层渗透率与水合物饱和度、围压、孔压及基质粒径等因素的定量关系，细粉砂水合物分解储层固相脱落运移特征，细粉砂水合物试采过程中不同分解区域温压传递特征；构建了考虑孔压与围压综合作用的细粉砂水合物储层渗透率模型，水合物分解固相颗粒脱落运移力学模型，细粉砂水合物储层降压开采温压传递与气液固多相渗流模型；揭示了细粉砂水合物储层试采过程中物性变化特征，水合物相变引起的颗粒脱落运移机理，水合物储层降压开采气液固渗流规律与温压传递特征。.研究结果表明，细粉砂水合物储层渗透率随围压、有效应力和水合物饱和度增大均呈现非线性下降趋势；天然气水合物加速分解期间，多孔介质内渗流能力得以改善，部分水合物逐渐由块状破碎、消融成颗粒状，与气水形成多相渗流；细粉砂水合物储层温度传递表现为“四阶段”特征，其中第二阶段为水合物相变主要控制阶段；细粉砂水合物藏降压开采过程中由于渗透率及传热限制导致分解速率较低，气液渗流速度较小，固相脱落运移现象并不显著，储层渗流仍以气液两相为主。以上研究成果丰富和发展了深水细粉砂水合物藏试采温压传递与非稳态渗流理论，为我国深水细粉砂天然气水合物藏高效开发提供技术支撑。