煤储层非均质束缚水赋存的地质控制及其排采耦合效应

This project focuses on the distribution of nonhomogeneous irreducible water in middle-high rank coals and its coupling effect on coalbed methane drainage. The coal samples in southern-central Qinshui basin will be collected, and laboratory test, theroretical analysis, mathematical modelling and numerical simulation will be all adopted in this study. The following experiments will be conducted for different purposes: conventional core analysis and field testing for acquiring basic physical characteristics; scanning electron microscope, mercury intrusion porosimetry, liquid nitrogen adsorption and nuclear magnetic resonance for obtaining coal pore structure, micromaceral analysis, scanning electron microscope and energy dispersive spectrometer for achieving material composition, differential scanning calorimetry and nuclear magnetic resonance for analysing the distribution of irreducible water. All the above-mentioned experiments will be analyzed in order to obtain the geological control for irreducible water, combined with some qualitative analyses. Then, irreducible water quantitative models will be thereby established by considering those factors who influence irreducible water strongly. Combined with the experiments of atomic force microscope and CT scan, nonhomogeneous models of irreducible water will be then built. Finally, using permeation test under variable effective stresses, numerical simulation and sensitivity analysis, this project will analyze the impact of irreducible water on permeability variation, investigate the complex variation of nonhomogeneous irreducible water during drainage, study the influence of this complex variation on CBM drainage performance, and reveal coupling effect of irreducible water on CBM drainage.

以限制煤层气产出的束缚水为研究对象，针对束缚水微观赋存及其排采耦合效应问题，采集沁水盆地中南部煤样，以实验、分析、建模及模拟为研究思路，利用常规岩心分析及现场测试得到基础物性特征；采用扫描电镜、压汞、核磁共振及液氮吸附获取孔隙发育及配置；使用显微组分测试、扫描电镜和能谱分析研究显微物质组成及分布；综合分析研究区地质特征并划分区块。基于差示扫描量热法及核磁共振研究束缚水赋存，采用定性分析确定束缚水赋存的影响因素，据此建立束缚水定量模型。之后，利用原子力显微镜和CT扫描技术对孔隙系统及物质组成进行三维重构，将束缚水定量模型拓展为束缚水非均质性定量模型，阐释静态束缚水的地质控制机理。最终，运用变压渗流实验、数值模拟、敏感性分析等手段研究束缚水对渗透率的影响机制，查明束缚水在煤层气排采过程中的动态迁移，及其与煤层气排采表现间的耦合效应，揭示动态束缚水影响下的煤层气排采耦合效应。

煤储层内束缚水赋存特征受非均质煤岩储层的制约。在煤层气开采过程中，其动态迁移及与煤层气排采之间的耦合效应均是复杂的四维空间问题。本项目通过实验测试、数据分析、数值模拟等手段对束缚水赋存评价、排采过程动态迁移及其与煤层气排采耦合效应进行了研究，提出了一套煤岩孔裂隙系统综合划分方案，并细化了研究区煤岩储层类型；查明了三种孔隙系统中束缚水的赋存特征，揭示了煤储层内流体从渗流孔流入裂隙过程的质量/能量转化规律；建立了研究区煤岩孔渗特征及物质组成的三维模型，阐明了研究区煤储层非均质发育特征；计算得到了研究区样品的束缚水饱和度，查明了束缚水的主要影响因素，建立了基于镜质组反射率、孔容影响因子、挥发分产率及镜质组含量等四个参数的束缚水饱和度定量评价模型；提出了基于有效解吸区半径和临储压力差的煤层气产能预测模型，认为煤层气井累计产气量与线性平均临储压力差之间满足三次多项式的关系；基于变压力下的核磁共振实验，查明了实验室条件下煤岩内束缚水的动态迁移过程，认为在煤层气排采过程中，渗流孔内束缚水随储层压力降低逐渐向裂隙中迁移最后产出；模拟并对比了典型煤层气井在束缚水恒定及束缚水动态迁移下的排采表现，阐释了束缚水在煤层气排采过程中的动态迁移机制及其对煤层气排采表现的控制，揭示了非均质储层内束缚水影响下的煤层气排采耦合效应，认为对于渗流孔发育及排采过程储层压力降幅明显的储层，束缚水动态迁移对产能的影响会有较明显的显现，尤其对于区域性的井组/井田而言，束缚水动态迁移对产能的影响亦会随着排采区域的增加而表现显著。上述研究可用于后期细致甄别煤层气排采有利区，为煤层气合理高效的开发提供指导。