沁水煤田煤层气井压裂裂缝内固液两相流动特性

There are coal powder output in all stages of coalbed methane (CBM) drainage in Qinshui coal field, China. Some produced coal powder will remain in the porous media of the proppant in the hydraulic fractures, resulting in a decrease in the permeability of the coal reservoir and premature decay or scrap of the CBM productivity. In order to study the characteristics of solid-liquid two-phase flow of coal powder in the porous media of the proppant in the closed fracture, the mutual verification method of field test, physical experiment with mathematical modeling, program development and numerical calculations is used in this project. Field test and physical experiment are used to study the migration and deposition characteristics of proppants and coal powder in the rough fractures. A coupled mathematical model of solid-liquid two-phase coupling of proppant particle transport in the open fractures and a mathematical model of solid-liquid two-phase flow of coal powder migration in porous media of the proppant in the closed fractures are established, and the corresponding calculation program is developed. Based on the determination of the natural deposition form of proppant in the open fractures, the structural evolution characteristics of the porous media of the proppant in the fractures in different degree of closure are studied. Furthermore, the migration characteristics of coal powder in the porous media of the proppant in the tight deposition form is studied, and the spatial distribution of the dominant channel in the porous media of proppant, from which coal powder can be effectively discharged, can be revealed. Then the critical conditions for the discharge of coal powder can be determined. This study provides a theoretical basis for the scientific development of CBM drainage system to reduce the damage of coal powder to the reservoir.

我国沁水煤田煤层气井排采各阶段均存在煤粉产出，而产生的煤粉在压裂裂缝中支撑剂多孔介质内的滞留会降低煤储层渗透率，使煤层气井产能过早衰减或报废。本项目拟采用现场测试、物理实验与数学建模、程序开发、数值计算相互验证的方法，研究闭合裂缝内支撑剂多孔介质中煤粉的固液两相流动特性。采用物理实验和现场测试，研究粗糙裂缝内支撑剂和煤粉的运移及沉积特征。通过建立张开裂缝内支撑剂颗粒输运的固液两相耦合数学模型和闭合裂缝内支撑剂多孔介质中煤粉粒子运移的固液两相流动数学模型，开发相应的计算程序，在确定张开裂缝中支撑剂自然沉积形态的基础上，研究不同闭合程度裂缝中支撑剂多孔介质的结构演变特征，并进一步通过研究紧密状态下支撑剂多孔介质中煤粉粒子的运移特性，揭示煤粉能顺利排出支撑剂多孔介质时的优势通道的空间分布特征，进而确定煤粉排出的临界条件，为科学制定煤层气井排采制度以减少煤储层煤粉伤害程度提供理论依据。

我国沁水煤田煤层气井排采各阶段均存在煤粉产出，而煤粉滞留对水力压裂支撑裂缝渗透率的伤害是制约煤层气井连续稳定排采和产能提升的关键因素之一，甚至会导致煤层气井产能过早衰减或报废。为探究闭合裂缝内支撑剂多孔介质中煤粉的固液两相流动特性，本项目通过开发支撑剂颗粒受力、运动及其多孔介质内流体流动数值计算程序，开展不同条件下煤粉侵入支撑裂缝物理实验，并建立考虑煤粉运移与沉积的支撑裂缝渗透率演化数学模型和基于煤粉滞留的支撑裂缝渗透率数学模型，揭示了不同闭合程度裂缝中支撑剂多孔介质的结构演变及其流体流动特征，阐明了支撑裂缝内煤粉运移、沉积与滞留特性及其对支撑裂缝渗透率的动态影响规律。主要创新成果如下：（1）研究了不同闭合程度下水力压裂裂缝内支撑剂多孔介质的空隙率、支撑剂运动轨迹、力链及配位数分布特征，揭示了闭合裂缝内支撑剂多孔介质结构的演变特征。（2）基于毛细管束模型，结合Carman-Kozeny公式建立了考虑煤粉运移与沉积的支撑裂缝渗透率演化模型，定量化表征了煤粉在支撑裂缝内的时空分布特征，探讨了煤粉运移与沉积对支撑裂缝渗透率时空演化的影响。（3）引入煤粉滞留系数，建立了基于煤粉滞留的支撑裂缝渗透率模型，揭示了单相流排水阶段恒速与间断流动对煤粉滞留量的影响以及煤粉滞留系数对支撑裂缝渗透率的影响。（4）研究了不同支撑剂多孔介质结构内流体速度场、压力场及流线分布特征，揭示了支撑裂缝内流体流动特征以及优势通道空间分布特征。研究成果为实际生产中采用合理的煤层气排采制度和解决煤粉沉积及滞留问题提供了理论依据。在此期间，共发表高水平学术论文13篇（SCI检索11篇，国内EI检索2篇），申请国家发明专利8项，其中授权专利4项，获得省部级科技奖4项，培养博士生2人，硕士生5人。