高压水作用下构造煤破坏规律及瓦斯渗透特性实验研究

Fracturing coal body through high pressure water is a feasible "pressure relief anti-reflection" measures theoretically, but this measure had not achieved the ideal fracturing effect in many coal seams, especially in tectonic coal seam which is badly damaged by geological structure, the main reason is that implementers was not clear for the fracture characteristics of coal. This project aims at the problem that the technical measures has blindness in practical engineering application, based on a large number of theoretical and practical experience that the effect of hydraulic fracturing measures is closely related the physical characteristics of different types tectonic coal, plans to design and modify the physical simulation experiment device to study the characteristics of expansive plastic deformation of tectonic coal under the high pressure water, investigate the process of tectonic coal broken of formation fractures , the characteristics and scope of tectonic coal crack extension, to discuss changes of fracture properties and timeliness characteristics of tectonic coal in the whole process of hydraulic pressure rise, maintain, uninstall under certain axial ( confining ) pressure, study the dynamic variation characteristics of tectonic coal gas in the process of high pressure water. The expected results will be expected to provide a very definite basis that whether adopting the high pressure water injection technology for different types of tectonic coal seams are suitably, meanwhile, avoid technical and economic losses due to the blindness.

高压水致裂煤体是一种理论上可行的“卸压增透”措施，但该措施之所以在不少煤层（尤其是受地质构造破坏严重的构造煤层）没有取得较理想的效果，主要原因在于实施者对煤体的可压裂特性不明确。本项目针对该技术措施在实际工程应用中的盲目性，基于水力压裂措施的效果与不同类型构造煤自身物理特性密切相关的大量理论、实践经验，拟通过设计、改装物理模拟实验装置研究高压水作用下构造煤的膨胀塑性变形特征；考察构造煤破碎生成裂隙的过程以及构造煤裂隙延展变化特征及其范围；探讨一定轴（围）压作用下水压升高、保持、卸载全过程中构造煤的裂隙性质变化及其时效性特征；研究构造煤高压水加卸载过程中瓦斯渗透性动态变化特征。取得的预期成果可望为不同类型构造煤是否适宜采取高压注水致裂技术提供较明确的依据，避免由于盲目采取该措施而带来技术及经济方面的损失。

高压水挠动致裂煤体理论上是一种可行的“卸压增透”措施，但该措施在松软破碎煤层尤其是受地质构造破坏严重的构造煤层并未取得理想效果。针对这一问题，通过设计改装“高压水载荷下瓦斯渗流”模拟实验装置，在采用“二次成型法”制取松软易破碎煤体原煤样试件的基础上进行了实验研究。高压水载荷下试件破裂过程及压裂前后渗透率实验表明：多组软煤试件的泵注压力曲线随加载时间走势基本一致，大致分为泵压滞留、压力急剧上升、压力瞬间下降、闭合-压裂交替、逐步压实以及停泵6个阶段。开始某一时间内煤样试件在高压水作用下产生裂隙，水侵入至裂隙内部后，由于水的侵泡、湿润作用以及软煤的近水性，很快软煤与水形成“煤泥”，内部裂隙被封堵，煤体逐渐被压实。高压水加载过程中软煤试件经历“压裂-压实-闭合”过程，高压水最终没能使煤体内部的裂隙网络展开。压裂后煤样渗透率较加载前均大幅减小，平均下降79%，最大减小了89%，渗透率的降低证明不适宜对构造软煤采用水力压裂。设计了两个穿层钻孔并在试验矿进行了现场考察，采用相关指标考察了压裂效果。结果表明：水力压裂对松软煤层而言卸压增透效果甚微，甚至高压水抑制了瓦斯的运移，成为了瓦斯解吸的阻力。据此提出了松软煤层顶板压裂以达到对该煤层卸压目的，高压水挠动下顶板岩石内部发生脆性变形，裂隙在持续高水压作用下较好地发育、延展、贯通，为下部煤体瓦斯运移提供了畅通的流动通道。抽放负压作用下“瓦斯解吸→顶板扩散、渗流→钻孔抽放”的煤岩体瓦斯抽采体系形成，松软煤层的渗透率及抽放效果大幅增加。项目取得的成果可为不同类型煤体是否适宜采取高压注水致裂技术提供较明确的依据，避免由于盲目采取该措施而带来技术及经济方面的损失。