开采扰动下瓦斯抽采钻井失效机制与防护技术基础

The gas pre-drainage is very bad because of the very low permeability of most coal seams in China. During longwall mining, the permeability of coal seam would be higher because of the depressurization effect, so gob gas venthole(GGV) can extract relieved gas high-efficiently. However, influenced by the shearing, extrusion and some other destructive actions of overlying strata violent movement, the borehole is easy to be broken and failure, which is one of the key issues that restrains the popularization and application of this technique. In the recent five years, the applicant of this program has investigated 37 GGVs which was failure and done much study on the protection technique for borehole fracture by the engineering practice. Based on the priliminary work, the applicant want to take some researches on the deformation mechanism and fracture prevention technology of gob gas venthole during longwall mining: the stratum movement intensity would be described quantitatively, and the effect of stratum impact movement on the movement intensity would be studied; the mechanism of influencing from relative movement of strata with weak intercalation to the borehole force-deformation would be revealed; the mechnical model of dual combined casing would be built and thus stress propagation on the condition of mining would be analyzed; borehole configuration stability under the condition of high-intensive exploitation would be investigated in Yuwu Coal Industry Company of Shanxi Luan Mining Group. Finally, there would be a technology system of protecting borehole fracture. The research results could support a scientific guidance for pushing forward the application of GGVs to extract relieved gas in gassy mining area.

我国煤层渗透率普遍较低，瓦斯预抽效果较差。而开采扰动作用下，煤层渗透率大幅度提高，利用地面钻井则可高效率地抽采卸压瓦斯。但是，煤层开采过程中上覆岩层运动剧烈，对钻井井身产生显著的剪切、挤压和拉伸等破坏作用，甚至造成钻井破断。钻井易破断失效已成为制约该项技术推广应用的关键难题之一。近5年来，申请者系统掌握了37口破断钻井样本，并在井身破断防护技术方面开展了大量工程实践研究。在前期工作基础上，本项目对岩层运动强烈程度进行定量表征，研究岩层冲击性运动对运动强烈程度的影响规律，揭示含软弱夹层岩层的相对运动对钻井受力和变形的影响机制，建立双层组合套管的力学模型并研究开采扰动作用下应力传导特性，同时以潞安集团余吾煤业公司为试验基地研究高强度开采条件下钻井井身稳定特性，形成井身失效防护技术。研究成果可为我国高瓦斯矿区推广应用钻井抽采卸压瓦斯技术提供科学指导。

卸压瓦斯抽采钻井套管破断是制约地面抽采煤矿区瓦斯的关键难题之一。采场上覆岩层的非同步运动，是造成钻井套管发生变形与破断的根本原因。本项目采用实验、理论分析、数值计算和工业性试验相结合的方法，对钻井套管的形变特征与失效机制开展了系统研究。首先，建立了采动作用下套管的剪切力学模型，实验研究了单层套管和双层套管的剪切变形行为和力学特性，揭示了填充材料几何与力学参数对应力传递的影响规律；其次，分析了钻井套管三种典型变形（拉伸变形、挤压变形和剪切变形）的特征参数，研究了气体在典型变形套管内的流场特性，揭示了剪切变形套管局部阻力系数远大于拉伸变形套管和挤压变形套管的机理；并以山西潞安集团余吾煤业公司为基地，考察了套管变形特征及对瓦斯抽采的影响；进而，建立了含软弱夹层岩层区域层间剪应力的力学模型，研究了层间剪应力与岩层弹性模量的关系，并通过数值计算研究了上覆岩层含有软弱夹层对岩层相对运动和钻井套管受力的影响特性，揭示了含软弱夹层岩层对钻井受力与破断的作用机制；最后，提出了采场上覆岩层运动烈度的概念，研究了工作面回采过程中上覆岩层运动烈度沿埋深和采空区的区域分布特征，并分析了煤层开采厚度对岩层运动烈度的影响关系。本项目揭示了钻井套管的破断机制，厘清了套管变形与破断的主要形式和关键区域，为形成井身失效防护技术、提升钻井井身稳定性奠定了基础。项目资助发表论文5篇，申请发明专利4项；项目成果获国家科技进步二等奖1项，省部级科技进步一等奖1项，二等奖2项；培养硕士生4名，其中2名已毕业，2名在读。项目投入经费25万元，支出22.2549万元，各项支出基本与预算相符。剩余经费2.7451万元，计划用于本项目研究后续支出。