含气页岩的粘弹性及其声学特征实验研究

The gas-bearing shale is mainly composed of clay minerals,mudstone and small gazin-size siltstone. The mechanical behaviour of the shale gas shows obvious visocelasicity because of the fine grain and the abundant organic matter. Research on viscoelasicity and acoustic properties of the shale gas plays an important role in exploring shale gas reservoir, evaluating anisotropy and claculating rock mechanical parameters correctly with acoustics method. The meachism of the acoustic wave propagation and acoustic attenuation through shale gas reservoir would be investigated by intergration of viscous elastic mechanics, acoustics in porous media and petrophysics in the fractured media in the proposal. We try to setup the theoretical models and the experimental basement for shale gas reservoir evaluation with acoustic methods. Three key technologies should be resolved, including viscoelasicity theoretical model of shale gas, ultrasonic experiment of gas-absorbed shale ,the relationship between the acoustic parameters and the rock characteristic parameters. We plan to search for the breakthrough ways through the combination of the composition and the pore structure of the shale with viscoelasicity mechanics to setup the theoretical relationship with the complex modulous, and the models would be tested by the experiment data and the real acoustic logging data. The potential innovations include viscoelasicity theoretical model, ultrasonic characteristics with gas-absorbing, and the relationship between acoustic parameters and the gas mechanical characteristics. Theoretical and experimental results would be directly applied into the shale gas prospecting.

含气页岩由粘土矿物，泥岩和细粉砂岩等组成，岩石颗粒细，富含有机质，在力学性质上表现出粘弹性特征。研究含气页岩粘弹性及声学特征，对于利用声学方法探测页岩气储层，评价储层各向异性，准确求取岩石力学参数等均具有重要意义。本项申请拟从粘弹性力学，多孔介质声学，裂缝介质岩石物理学等理论出发，探索声波在含气页岩地层的传播机理及能量衰减机制，试图为利用声学方法评价页岩气储层提供理论和实验基础。问题的解决依赖于三项关键技术：含气页岩粘弹性理论模型、页岩气吸附超声实验观测、声学参数与物性参数之间的关系。课题计划从粘弹性力学与页岩组分及孔隙结构分析相结合，应用复模量描述方法来建立页岩物理性质参数与声学参数之间的关系，并通过实验观测和实际测井观测数据相结合等来寻找突破途径，尝试在粘弹性理论模型，页岩吸附天然气超声特征，声学特征与粘弹性力学特征之间的关系等方面的创新。研究成果可直接应用于页岩气勘探。

本项研究以四川盆地重庆焦石坝地区龙马溪组和五峰组的页岩，川中地区侏罗系沙溪庙组和凉高山组的致密砂岩和自流井组大安寨段的致密灰岩为研究对象，结合焦石坝地区的页岩气储层测井资料，开展岩石物理实验及测井解释应用基础研究。主要完成的工作包括：分析了致密岩石孔隙度及其影响因素；不同尺度的孔隙尺寸分布及其相互关系；致密岩石的电传输特征及影响因素；考察了页岩纳米压痕实验的影响因素；基于纳米压痕实验分析页岩粘弹性响应特征及粘弹性参数获取方法；开展了粘土矿物类型及含量的定量测井评价方法研究；基于岩石物理体积模型及测井优化解释方法，分析了页岩气储层的声波测井影响因素；以测井资料及粘弹性模型为基础，对比不同的模型考察了弹性及粘弹性的影响因素及应用效果等。取得主要成果包括：发现了含烃致密岩石中的封闭孔隙度，拓宽了对非常规储层总孔隙度的认识；页岩在明显的电频散现象；电阻率响应规律受到孔隙结构的制约，建立了电阻率、饱和度与孔隙结构之间的关系；以NMR、高压压汞、核磁共振等方法相结合，发展了全孔径分布曲线的构建方法；建立了全孔隙尺寸分布与T2谱的关系；考察了页岩纳米压痕的影响因素，加载方式是影响突进“现象”的原因，改变加载方式可以消除突进现象； TOC是影响岩石弹性参数的主要因素；以Maxwell模型和Kelvin-Voigt为基础，推导了载荷与压深响应曲线之间的理论关系，发展了一种页岩粘弹性系数的获取方法；发展了页岩气储层粘土矿物类型及含量的定量测井评价方法；页岩气储层粘土矿物及干酪根的含量对声波测井有显著影响；以Maxwell模型和Kelvin-Voigt为基础，结合测井数据和岩石物理模型，对页岩气储层的弹性和非弹性响应进行了分析，结果表明Kelvin-Voigt模型更适合描述页岩气储层的粘弹性响应。