页岩气储层微观结构及岩石物理响应数值模拟研究

Shale gas is mainly stored in the micropore, microfracture space between shale rock particles and the surface of organic matter or clay mineral in adsorbed and (or) free condition. Because shale have special rock petrofabric, special micropore space structure and special rock physical properties, there is a big different in rock physical response mechanism to micropure and fracture between shale reservoir and normal reservoir. Thus, there is a urgent need to study microstructure characteristics of shale gas reservoir and rock physical response, electric logging response numerical simulation based on reconstructed shale gas formation model. This project will deals with the research on shale gas reservoir samples of Sichuan basion Longmaxi Formation and Dongying sag Shahejie Formation. First, we use XRD, microexamination, scanning electron microscope and X-CT scanning technology to study shale gas rock mineral composition, micro rock structure, micropore and microfrature structure characteristics, and use X-CT data or X-CT slices to reconstruct micropore and fracture formation model of shale gas reservoir, that is 3D digital core. Secondly, use mathematical morphology and finite element method to simulate resistivity response, formation factors, the resistivity increases coefficient and dual laterolog response. Then, with summarizing the regularities which obtained numerical simulation and considering the actual measured logging curves, we do the research of time-frequency characteristics of signal logging, and we identify shale gas reservoir by time-frequency characteristics of well logging curves with the application of the short time Fourier transform, wavelet transform, and the principal component analysis method. Finally, establish a set method of simulating rock physical response of shale gas reservoir use digital core and identifying shale gas micropore and fracture reservoir use time-frequency characteristics of logging response, which provide the scientific basis for further exploration and potential evaluation of shale gas.

页岩气主要以吸附和（或）游离态赋存于页岩岩石颗粒间的（微）孔隙、（微）裂缝中或矿物、有机物的表面，页岩由于其特殊的岩石组构、孔隙空间结构及岩石物理性质，微孔、缝介质的岩石物理响应机理与常规储层有较大差异，迫切需要开展页岩气储层微观结构特征及岩石物理、电测井响应数值模拟基础研究。本项目选取四川龙马溪组、东营凹陷沙河街组页岩气发育层段的样品，首先，运用XRD、显微观察、X射线CT扫描研究页岩气层的矿物成分、微观岩石结构及（微）孔隙、裂缝结构特征，利用X射线CT数据构建页岩气微孔、缝地层模型即三维数字岩心；其次，利用数学形态学和有限元方法模拟岩石的电阻率、地层因素、电阻率增大系数及双侧向测井响应；然后，总结数值模拟规律，结合实测测井曲线，应用短时傅立叶变换、小波变换等方法提取页岩气层的时-频特征。最终，形成数字岩心模拟页岩气储层岩石物理响应及测井时频识别方法，为勘探及潜力评价提供科学依据。

本项目以济阳坳陷东营、沾化凹陷沙河街组泥页岩层段为研究对象，泥页岩由于其特殊的岩石组构、孔隙空间结构及岩石物理性质，微孔、缝介质的岩石物理响应机理与常规储层有较大差异，针对泥页岩岩石物理特征及其研究难点问题，主要开展了6个方面的基础与应用基础研究。（1）泥页岩分析测试：进行了泥页岩岩石薄片、扫描电镜、物性、X衍射、微孔联测、微量元素、CT（纳米2块、微米1块）及核磁共振测试，为泥页岩微观岩石组构及孔隙结构研究奠定了基础；（2）泥页岩储集空间类型及影响因素：研究了泥页岩储集空间类型，包括粘土矿物晶间孔、黄铁矿重结晶孔（球粒状、草莓状、粒状八面体等）、微裂缝、溶蚀孔隙、少量有机纳米孔，分析了每一种孔隙类型的控制因素，并探讨了泥页岩剖面孔隙发育规律；（3）孔隙结构及数字岩心重构及参数模型提取：利用核磁共振、压汞、物性、微孔测试及CT、薄片与电镜等资料对泥页岩孔隙结构进行了分类，在此基础上，利用核磁自由流体T2谱与孔喉半径之间的多尺度关系，构建了基于核磁共振测井连续反演泥页岩地层剖面孔隙半径分布的方法，进一步利用纳米CT构建了2块不同类型的泥页岩数字岩心，提取了相应的孔隙连通模型、孔喉中心线拓扑结构模型、有机质和孔隙分布模型、有机质分布模型等，对泥页岩微观结构有了深入的认识；（4）泥页岩岩相及岩石结构类型划分及识别：利用薄片鉴定、岩心描述、电镜及测井（包括电成像）等资料，考虑“结构+岩性”区分泥页岩岩相类型，详细划分为12小类、6大类，从宏观和微观上分析了各自的差异性，鉴于测井曲线分形对岩石结构有较好的指示，将敏感CGR分形维数引入到三维交会图中，有效提高了泥页岩岩相结构识别的精度，为在连续井筒剖面中识别有效泥页岩油气储层提供了依据；（5）泥页岩储层测录井识别、裂缝评价：通过气测、测井及泥页岩特征对比分析，建立了测井信息结合气测资料的解释图版，对识别裂隙含油层、油层、气测异常及非储集层有较好的适应性；（6）泥页岩储层参数优化计算：通过物性、岩矿测试及地化分析数据刻度测井信息，并利用回归分析、ΔLgR及改进方法，建立了储层参数、矿物含量、地化指标及产能预测计算模型，也厘定了可压裂性评价的计算指标，为定量评价泥页岩储层提供了依据。基于Forward平台，开发了相应的处理解释程序，成为独立的处理解释模块，能够满足泥页岩油气储层测井评价的要求。