预抽瓦斯钻孔负压沿孔长动态变化特性及影响效应

Gas drainage from virgin coal seam is a fundamental measure to solve the problem of gas disaster. The corresponding code and standard are provided. In recent years, the new phenomena is appeard, the high-power drilling equipment and gas drainage facility and technology of drilling cased have been used widely, the length of drainage borehole and negative pressure and drilling hole rate increased obviously. But the effect of gas drainage has not reached the expected target. Along axial direction of drainage borehole, the effect appears difference. In order to find out the reason of this phenomena, realize the variation character and the influence of negative pressure along gas draining borehole, the project adopts methods of combining theoretical analysis with numerical simulation and laboratory experiments. Using the equipment of testing dynamic negative pressure, the negative pressure and flow quantity are tested in view of different permeability coalseam and different position along the driling hole. Combining with gas adsorption/desorption dynamics theory and gas seepage theory, the model of negative drainage pressure along the hole is found. The dynamics character and the influence of negative pressure along the gas drainage bore are studied. Through the research of this project, the idea of gas drainage borehole disposition will be changed. It would provide the theoretical support for revision of the gas drainage standard.

瓦斯预抽是解决我国煤矿瓦斯问题的根本措施，国家出台了相应的标准、规范。近年来，瓦斯预抽出现了一些新的情况，大功率钻探设备、抽采设备和跟管钻进技术得到广泛应用，预抽钻孔长度、抽采负压和钻孔成孔率均得到了显著提高。在长钻孔、高负压、全钻孔套管护孔的背景下，瓦斯预抽效果并没有达到人们的预期目标，预抽效果沿钻孔长度方向出现分区、分带现象。为了探寻造成这种现象的原因，掌握瓦斯预抽钻孔负压沿孔长动态变化特性及其影响效应，项目拟采用理论分析、实验室实验和数值模拟相结合的方法进行研究，搭建预抽钻孔孔内负压沿孔长动态变化测试平台，对不同透气性煤层、不同孔口负压、不同孔深位置处负压和流量进行检测，结合瓦斯渗流理论和吸附解吸动力学理论，构建预抽钻孔孔内负压沿孔长动态变化模型，得出负压沿预抽钻孔长度方向的动态变化特性及影响效应。本项目的研究，将改变传统上瓦斯预抽钻孔布置理念，为抽采标准修订提供理论支撑。

瓦斯预抽是解决我国煤矿瓦斯问题的根本措施，近年来，在长钻孔、高负压、全钻孔套管护孔的背景下，瓦斯预抽效果并没有达到人们的预期目标，预抽效果沿钻孔长度方向出现分区、分带现象。开展预抽瓦斯钻孔负压沿孔长变化特性及对瓦斯抽采效果影响的研究工作，对研究抽采条件下瓦斯渗流特性，确定合理的瓦斯抽采参数，提高瓦斯抽采效果，有效消除抽采空白带，保障煤矿安全高效开采具有重要的理论和现实意义。通过采用理论分析、实验室实验和数值模拟相结合的方法，得出了抽采钻孔孔内负压沿孔长的分布规律。抽采钻孔孔内负压不是传统上认为的一个恒定值，抽采负压沿钻孔长度方向逐渐减少，与钻孔长度服从负指数关系，抽采钻孔孔内瓦斯流量沿钻孔长度方向逐渐减小，两者符合负指数关系。同时得出了在孔口抽采负压、钻孔直径、煤层透气性系数、抽采时间一定的条件下，和传统上认为抽采钻孔径向上瓦斯压力等值线呈“U”型分布不同，钻孔径向上的瓦斯压力等值线呈“V”型分布。通过数值模拟和现场测试得出了抽采钻孔孔内负压逐渐减少对瓦斯抽采参数的影响，提出了不同孔深位置的有效抽采影响半径，即：有效抽采影响半径不仅与抽采时间、钻孔直径、煤层透气性系数有关，还与钻孔深度密切相关，各参数之间符合相应的函数关系。