不同深度页岩储层力学各向异性的试验研究

An experimental study on mechanical anisotropy of shale reservoirs at different depths

为研究不同深度页岩储层力学参数的各向异性,开展了龙马溪组相关储层页岩的单轴压缩试验,探究了页岩储层力学参数在横向和纵向的变化规律,深入分析了页岩储层力学参数的各向异性指数。不同深度页岩储层矿物含量、天然裂缝的发育、层理缝密度等因素均导致储层表现出一定程度的各向异性;取样深度范围内,弹性模量随储层埋深的增加有减小的趋势;泊松比随储层埋深的增加有两头高、中间低的现象;抗压强度随储层埋深的增加表现出两头低、中间高的现象。抗压强度的横向和纵向异性指数均显著大于相同环境条件下弹性模量和泊松比的异性指数,且抗压强度的异性指数波动范围更广。力学参数的横向及纵向异性指数在一定程度上反映岩体力学性能的空间分布,深部岩体工程施工时,应提前开展不同深度和不同方向异性指数的力学试验调查,在优化工程施工的基础上,选取适用的力学本构关系。

This study is to investigate the mechanical anisotropy of shale reservoirs at different depths.Uniaxial compression experiments were conducted on Longmaxi formation shale to explore horizontal and vertical variation laws of mechanical parameters.Meanwhile,anisotropy indexes of mechanical parameters of shale reservoir were comprehensively analyzed.It is found that mineral content,development of natural fractures,the denseness of bedding slit in shale reservoirs all exhibited mechanical anisotropies at a certain degree.With deepening the sampling depth,the elastic modulus decreased.Meanwhile,the Poisson＇s ratio had a seesaw high-middle low phenomenon,whereas the compressive strength opposite.In addition,horizontal and vertical anisotropy indexes of the compressive strength were much higher than those of the elastic modulus and Poisson＇s ratio under the same environmental condition.Moreover,the anisotropy index of the compressive strength varied in a larger scope.Horizontal and vertical mechanical anisotropy indexes reflect the spatial distribution of mechanical properties to some extent.Therefore,the mechanical anisotropy should be investigated at different depths and in different directions in advance when constructing the deep rock engineering.The constitutive relation of rock mass also should be properly chosen to optimize the construction.,