基于液电效应的高强电爆震致裂页岩试验研究

Hydro-electric effect based experimental study on shale cracking caused by high-strength electric detonation

为研究基于液电效应的高强电爆震致裂页岩规律及页岩气储层改造可行性,选取中国四川盆地长宁地区的黑色页岩为试验样品,利用团队自主研制的多地形可移动高强电爆震致裂岩体试验系统,预设放电参数为电压10~14 kV,电容500μF,辅以示波系统、应变测试系统和基恩士VHX-6000数码显微系统,分析了高强电爆震致裂页岩试样的电压电流及应变变化特征,阐明了不同放电参量下电爆震作用前后表面裂隙形貌及断面特征,初步揭示了电爆震致裂页岩机制.结果表明:高强电爆震可明显致裂页岩,峰值电流、压-拉应变最大峰峰值、应变第一高峰值、应变第二高峰值均与放电电压呈正相关;高强电爆震致裂后的试件表面裂隙主要包括贯穿裂隙、放射状裂隙和正交裂隙,在14 kV时出现不同裂隙之间沟通的现象,表面裂隙均呈现良好分形特征;高强电爆震作用试件后,作用面、断面的不平整度较大,表面有较多岩石碎屑;高强电爆震作用下页岩破坏主要形式为鳞片状、波浪状、台阶状等张拉破坏.该试验研究可为基于液电效应的高强电爆震技术应用于页岩气储层改造可行性论证提供支撑.

In order to study the formation of shale due to high-strength electric detonation and the feasibility of reconstructing a shale gas reservoir,the black shale found in the Changning area,Sichuan Basin,China,was selected as the test sample.The test was conducted on a multi-topographic movable high-strength electric detonation test system locally developed for fracturing rock mass.As discharge parameters,voltage of 10 kV to 14 kV and capacitance of 500μF were preset by oscilloscope system,strain testing system and Keynes VHX-6000 digital microscope system.The shale samples were analyzed under different settings of voltage,cur-rent and strain of the high-strength electric detonation.The morphologies of surface cracks and cross sections were expounded before and after the electric detonation under different settings of discharge parameters.And the mechanism of inducing shale by electric detonation was pre-liminarily revealed.The obtained experimental results show that the shale could obviously be cracked by high-strength electric detonation.The peak current,maximum peak of compressive-tensile strain,and the first and second peaks of strain are positively correlated with the dis-charge voltage.The surface cracks after the high-strength electric detonation mainly include penetrating cracks,radial cracks and orthogonal cracks.The communication between different cracks occurred at 14 kV.And the surface cracks showed good fractal characteristics.After the high-strength electric detonation,the roughness of the cross-section was large.There were more rock debris on the surface,and the shale samples were cracked mainly due to flake,wave,step and other tensile failure.This experimental study could demonstrate the applicabili-ty of the high-strength electric detonation technology in reconstructing a shale gas reservoir based on hydro-electric effect.