页岩气地质力学特征评价方法——中国南方海相强改造区山地页岩地质力学特征

A method for evaluating the geomechanical characteristics of shale gas: the geomechanical characteristics of the mountain shale in the intensively reworked marine area of South China

中国南方海相强改造区山地页岩气储层具有极强的力学各向异性,导致储层水力压裂裂缝扩展模拟和真实工况差异大,显著限制了其对水力压裂工程实施的指导作用。为此,以该区一个山地页岩气区块下志留统龙马溪组为研究对象,在全面分析已有的岩心分析成果的基础上,围绕着深化页岩气各向异性的评价,设计了全新的岩心实验方案并开展了相关实验,分析了龙马溪组储层各小层的各向异性特征及不同力学参数之间的相关关系;基于岩心分析成果,综合测井数据开展单井各向异性地质力学建模,全面评价该区块地质力学特征。研究结果表明:(1)借助于全直径岩心的CT扫描来优选试样柱塞位置,可以提升岩样的代表性及岩样柱塞的质量;(2)超声波的动态测试和多级三轴压缩实验均显示龙马溪组地层具有明显的应力敏感性;(3)通过综合超声波动态测试、三轴压缩实验静态测试及声波测井能够比较可靠地建立动静态转换关系,能够利用电缆及随钻测井声波数据确定静态弹性模量;(4)YS130井区龙一13小层为优质储层中最低刚度及最低应力的小层,是水平井着陆的优选层位。结论认为,该项研究成果可以为水平井着陆位置优选、压裂设计优化及钻井优化提供指导。

The mountain shale gas reservoirs in the intensively reworked marine area of South China have extremely strong mechanical anisotropy,which leads to significant difference between the simulated propagation of hydraulic fractures in reservoirs and the true working conditions,so that its role in guiding the construction of hydraulic fracturing engineering is restricted obviously.To this end,this paper took the Lower Silurian Longmaxi Formation in one mountain shale gas block of this area as the research object to design a brand new core experiment scheme focusing on deepening shale gas anisotropic evaluation,after analyzing available core analysis results comprehensively.In addition,the related experiments were carried out,and the anisotropic characteristics of each sublayer in Longmaxi Formation reservoir and the correlations between different mechanical parameters were analyzed.Then,based on core analysis results,combined with logging data,the geomechanical modeling of single well anisotropy was carried out,and the geomechanical characteristics of this block were analyzed comprehensively.And the following research results were obtained.First,selecting the position of the sample plunger by virtue of the CT scanning of full-diameter core can improve the representativeness of rock sample and the quality of sample plunger.Second,both ultrasonic dynamic testing and multi-stage triaxial compression test show that the Longmaxi Formation has obvious stress sensitivity.Third,by integrating ultrasonic dynamic testing,static testing of multi-stage triaxial compression test and acoustic logging,the dynamic-static conversion relationship can be established more reliably,and the static elastic modulus can be determined by using the data of cable and acoustic logging while drilling.Fourth,the Long 113 sublayer in YS130 Well Block is the sublayer with the least stiffness and stress in the quality reservoir and it is the preferred horizon of horizontal well landing.In conclusion,the research results provide the guidance for the selection of horizontal well landing position and the optimization of fracturing design and drilling.