水力压裂切割煤层顶板力学机理及参数优化

煤层开采中,上顶板难以断裂,易形成大面积悬顶结构,进而诱发严重的冲击地压等灾害,不利于矿井的安全高效生产。针对利用水力压裂技术解决煤层上悬顶的工程问题,采用地质-工程一体化模拟技术,考虑岩层纵向分层属性,建立了大尺度水平井段内多簇压裂精细模型,开展了水力压裂切割煤层厚顶板力学机理和施工参数优化研究。研究结果表明：(1)水平井多级压裂能够充分切割上顶板,产生密切割缝网结构,附加诱导应力值增大10%,能够有效解决悬顶卸压问题；(2)高粘滑溜水+交联冻胶压裂液体系形成的裂缝体积高于低粘滑溜水体系约40%；(3)影响裂缝扩展的主控因素从强到弱依次为：压裂液类型、地层物性、液量、排量、段长。本文耦合地质建模-裂缝扩展-应力计算,深入研究了水力压裂裂缝扩展规模及其对厚层顶板弱化改造程度,研究成果将指导含厚层顶板煤层安全高效开发。

Research on Mechanical Mechanism and Parameter Optimization of Hydraulic Fracturing for Cutting Thick Roof of Coal Seam

During coal mine, it is hard to cut the hard roof and a large suspended roof structure can be created, which can induce serious rock burst and other disasters, thus it is not conducive to the safe and efficient production of the coal seam. As for the engineering problem of overhanging roof solved by hydraulic fracturing technology, this paper established a large scale and detailed horizontal well multi-cluster fracturing model based on the geology-engineering integrated simulation technology. Considering the vertical stratification properties of rock strata, this work systematically investigated the mechanical mechanism and construction parameters optimization of hydraulic fracturing when cutting the thick roof of coal seam. The results show that: (1) multi-stage hydraulic fracturing of horizontal well can adequately cut the upper roof and produce a closely fracture network, and increases the induced stress by 10%, which can effectively solve the pressure relief problem of the suspended roof; (2) the fracture volume formed by the combination of high-viscosity slicker water and crosslink fracturing fluid, is about 40% higher than that of the low-viscosity slicker water; (3) factors of influencing fracture volume list as (strong to weak): fracture fluid type, formation properties, fluid volume, fluid displacement, and section length. This work systematically investigated the fracture propagation geometry, the dynamic change characteristic of the induced stress, and the degree of cutting the thick roof. The research results will guide the safe and efficient development of coal seams with thick hard roof.