基于数字岩芯及3D打印的煤岩岩石物理特征研究 ——以华北石炭二叠系主采煤层为例

Recently, many occurred coal-related dynamic disasters, e.g. rock bursts and gas outbursts, have cost a lot of money and lives of coal miners. In order to quantitatively interpret the highly prone zone of those dynamic disasters with seismic, it is necessary to obtain the accurate characteristics of coal rock physics. However, coal rock is so special in lithology that many tectonically deformed coal are very hard to be sampled and to be prepared for lab testing. The observed rock physics characteristics of coal are lack of representative. In this study, we target the main minable coalbeds in the North China, the Carboniferous-Permian coalbeds, to study their rock physics characteristics. First of all, we study the heterogeneity characteristics of a coalbed in vertical direction and research its main controlling factors through the sub-seam core sampling, the ordinary lab testing and the digital core simulating. Then, we test the rock physics characteristics for different tectonically deformed coals through the in-situ glued core sampling, the digital core simulating and the stress-induced anisotropic testing for 3D printed cores. Finally, we study the scale effect on rock physics characteristics for coals and plot templates for those characteristics through the ordinary lab testing and the digital core simulating. The included scales are the core scale, the sub core scale and the coalbed scale. Through the successful implementation of this project, we can provide a basic rock physics parameters for the quantitative seismic interpretation of the highly prone zone of coal-related dynamic disasters and for the high-precision forward modelling of coal bearing strata and.

近年来，矿井煤与瓦斯突出等煤岩相关动力灾害频发，造成了大量的人员和财产损失。为了利用地震数据准确解译煤岩相关动力灾害高危区，必须准确掌握煤岩岩石物理特征。但由于煤岩的特殊性，多数构造煤易碎、煤样制备困难，常规实验测试获得的岩石物理特征代表性不足。本次以华北地区石炭二叠系主采煤层为目标层，首先，结合煤层多细分层煤样采集、常规实验测试和基于数字岩芯的仿真测试，研究煤层岩石物理特征的纵向非均质性及其主控因素。其次，结合构造煤样的原位注胶采集、基于数字岩芯的仿真测试和基于数字岩芯3D打印的构造煤应力各向异性测试，研究多类构造煤的岩石物理特征。最后，结合多尺度煤样制备和数字岩芯构建、常规实验测试和基于数字岩芯的仿真测试，研究煤岩岩石物理特征的尺度效应，并绘制相应的尺度效应模板。通过本次项目的成功实施，可以为煤岩相关动力灾害高危区的地震数据准确解译和含煤地层的高精度正演模拟提供基础的岩石物理参数。

近年来，矿井煤岩相关动力灾害频发，造成了大量的人员和财产损失。为了利用地震数据准确解译煤岩相关动力灾害高危区，必须准确掌握煤岩岩石物理特征。但多数构造煤易碎、煤样制备困难，常规实验测试获得的煤岩岩石物理特征代表性不足。本次以华北石炭二叠系主采煤层为例，系统研究了基于数字岩芯及3D打印的煤岩岩石物理特征，取得的主要成果如下。（1）通过系统测试分析煤岩的岩石物理特征，发现原生煤与低阶构造煤的岩石物理特征相似，明显区别与高阶构造煤。依据煤岩弹性参数，最多可以划分出5类煤体结构。但鳞片煤、糜棱煤的弹性参数相近，碎粒煤、碎斑煤和揉皱煤的弹性参数相近，无法准确划分。（2）通过系统采样和测试，揭示了研究煤层石物理特征的纵向非均质性。相对于纵横波速度、平均孔径、孔隙度等参数来说，模量、密度、总孔容、孔比表面积和工业分析的纵向非均质性规律更好。（3）通过实验测试和数字岩心仿真测试，揭示了型煤的存在明显的尺度效应特征。由尺度效应而引起的纵波速度数值增加约130-140m/s，相对增加约13%-36%。在地震频段到超声频段，频散作用剧烈。超声测试速度不能直接应用到地震频段，否则可能造成误解译。（4）通过实验测试、数字岩心分析和3D打印，系统分析了煤岩岩石物理特征的主控因素。对于煤岩速度来说，煤岩的矿物组成、孔隙度和煤体结构都有显著影响，原生煤和低阶构造煤速度明显高于高阶构造煤。对于煤岩速度和应力各向异性来说，煤岩裂隙及其二次填充矿物是其主要影响因素。（5）通过理论分析和模型正演，改进了现有高频喷射流模型和全频喷射流模型，拓展裂隙-孔隙等效介质模型，提高了相关模型预测饱和流体频散曲线与实验测试频散曲线间的一致性。（6）将项目研究取得的主要参数和方法应用到煤体结构测井识别、地震探测及地应力集中预测中，提高了煤体结果识别和预测精度，改善了地应力集中区预测的可靠性。总之，本次研究不仅具有明显的科学意义，还具有大范围推广的应用价值。