页岩气储层微观孔隙结构连续定量表征与含气量评价

Taking the shale gas reservoir in Sichuan basin as the research target, this project is aim at solving problems in the continuous quantitative characterization of micro-pore structure and evaluation of gas content in shale gas reservoir by combination of laboratory experiments and numerical simulation. Firstly, a series of laboratory experimental study of cores is conducted to more completely understand the characteristics of lithology, wettability and pore structure, and their influences on nuclear magnetic resonance (NMR) T2 spectrum, adsorption of methane and conductivity of rock. Secondly, according to the three-dimensional digital cores of shale gas reservoir, the NMR responses of reservoir is simulated by random walk theory, and the mechanism of NMR response are verified by combining simulation results and experimental results. In addition, based on the mechanism of NMR response, the method of correcting shape of NMR T2 spectrum and model of transforming the NMR T2 spectrum to the pore size distribution curve are established. With the help of the transformation model, the NMR logs are used to characterize the micro-pore structure of shale gas reservoir continuously and quantitatively. Finally，according to the mechanisms of methane adsorption and rock conductivity, models of calculating contents of adsorbed gas and free gas are built or optimized, and then the gas content of shale gas reservoir is calculated by resistivity logs. The results of this project can provide technical supports in evaluating the effectiveness of shale gas reservoirs and assessing the resources potential, which plays an important role in improving the efficiency of exploration and reducing the risk of development.

项目针对页岩气储层微观孔隙结构连续定量表征与含气量评价中存在的问题，选取四川盆地页岩气储层为研究对象，通过配套岩石物理实验与数值模拟相结合的方法，开展研究。首先，基于配套岩石物理实验，明确页岩气储层的岩性、润湿性、孔隙结构等特征，分析这些因素对核磁T2谱、甲烷吸附、导电性的影响。其次，建立三维数字岩心，利用随机游走理论模拟储层核磁响应；将数值模拟结果与实验结果相结合，明确储层的核磁响应机理。然后，基于核磁响应机理，建立核磁T2谱形态校正方法以及孔径分布曲线与核磁T2谱之间的转换模型；根据转换模型，利用核磁测井曲线连续定量表征储层微观孔隙结构。最后，在明确甲烷吸附与岩石导电机理的基础上，建立或优化吸附气与游离气含量计算模型，利用电阻率测井曲线计算储层含气量。项目成果可为页岩气储层有效性评价与资源潜力评估提供技术支撑，对提高勘探效率，降低开发风险起到重要作用。

项目针对页岩气储层微观孔隙结构连续定量表征与含气量评价中存在的问题，以四川盆地龙马溪组页岩气储层为研究对象，开展了配套岩石物理实验、核磁响应机理、孔隙结构连续定量表征、含气量评价等四大方面的研究。研究结果表明:①页岩矿物类型以石英为主，次为粘土矿物与长石。TOC含量变化大。孔隙可分为有机孔、无机孔以及微裂缝；有机孔孔径小于无机孔、无机孔孔径小于微裂缝；页岩表面既亲油又亲水，且页岩表面更倾向于油湿。②页岩的核磁T2谱受有机质及孔隙的双重影响。有机质中沥青使得T2谱产生小于0.3ms的驰豫信号。核磁谱可分为0.01ms-0.3ms、0.3ms-10ms、>10ms三部分；T2在0.01ms-0.3ms之间对应有机质孔，在0.3ms-10ms对应无机孔，大于10ms对应微裂缝。核磁T2谱对比显示有机质孔为油润湿，无机孔为水润湿，微裂缝为中性润湿。利用核磁T2谱可以定量预测页岩的接触角。③页岩储层微观孔隙组分表面弛豫率值大小与润湿性有关；亲油有机孔表面弛豫率最小，混合润湿微裂缝表面弛豫率次之，亲水无机孔表面弛豫率最大。因此，考虑微观孔隙组分润湿性、表面弛豫率的差异，分孔隙类型建立一套核磁共振定量评价页岩气储层微观孔径的方法。④有机质孔隙甲烷以吸附态存在，围压会影响甲烷吸附量，围压到底一定程度时，吸附量明显减小；无机孔、裂缝中甲烷主要以游离态形式存在，甲烷饱和压力越大，游离态甲烷含量越多。因此，对吸附气含量的计算需要考虑地层上覆压力与地层压力；⑤与双水模型相比，W-S模型能更好描述含泥质岩石的导电规律，且胶结指数（m*）只受控于岩石孔隙结构影响。采用W-S模型计算游离气时，国内学者仍采用旧B值图版，计算结果偏低。本项目基于新的B值图版，提出了一种B值计算新方法，计算结果更合理。.整体而言，该项目在核磁响应机理、孔隙结构及含气量表征等方面取得了一些新认识，相关成果已发表论文9篇（6篇SCI），申请与授权专利2项。项目成果可为页岩气储层有效性评价与资源潜力评估提供技术支撑，对提高勘探效率，降低开发风险起到重要作用。