海相页岩微观非均质性及其吸附机理

The exploitation potentiality of shale gas depends on the adsorption and the permeability of gas reservoir. The adsorption is the core of gas reservoir formation, under the control of the microscopic geology and the reservoir microscopic heterogeneity. The project focuses on the adsorption microscopic heterogeneity of shale gas reservoir, taking organic-rich shales cores from the Niutitang Formation of Lower Cambrian in the Northen Guizhou for an expample. Following the workflow of experimental measurement - numerical simulation - theoretical analysis, C-S Analyer and X-ray diffraction are conducted to test the mineral composition of the reservoir. The isothermal adsorption experiment is applied to reveal the heterogeneity of the adsorbed gas occurrence state. Mercury immersion, low temperature nitrogen/carbon dioxide adsorption and SEM Sample Preparation System, SEM, FE-SEM, AFM, and FIB-SEM are also applied to reveal the microscopic heterogeneity of adsorbed reservoir and pore structure and the effects on the the heterogeneity of adsorption. Using 3D models reconstruction function of FIB-SEM and 3D reservoir heterogeneity geological modeling technology, the microscopic heterogeneity model of reservoir pore is reconstructed based on the morphology, quantitative index, and composition formation of pores. Based on the Double Langmiur equation modeling, the multivariate calibration is fitted many times on the kinds and quantity of adsorption carrier. From the view of the molecular dynamics of adsorption occurrence, the heterogeneity of marine shale adsorption and its microscopic mechanism is revealed and the model of the carrier adsorption heterogeneity is set up.

页岩气开采潜力主要取决于吸附性和渗透性两个关键要素，吸附性是形成气藏的核心基础，高度受到微观地质因素及其非均质性控制。项目针对吸附非均质性微观机理问题，采集黔北牛蹄塘组富有机质页岩段岩心样品，以实验、模拟与理论分析为思路，用碳硫分析仪与X-射线衍射仪测试物质组成；用等温吸附实验揭示吸附气赋存态非均质性；用压汞仪、低温液氮/二氧化碳吸附、氩离子抛光场发射扫描电镜、原子力显微镜和聚焦离子束扫描电镜等技术对物质与孔隙进行微-纳米级观测，揭示吸附载体组成物质及其孔隙微观非均质性，及对吸附非均质性的影响；借助聚焦离子束扫描电镜三维重构功能和储层非均质性三维地质建模技术，构建基于图像形貌、量化指标和物质成因分析的页岩孔隙非均质性模型；在双朗格缪尔方程建模基础上，依据吸附载体种类与数量，进行多元多次拟合校正；从吸附赋存的分子动力学角度，揭示海相页岩吸附非均质性及其微观机理，建立非均质性载体的吸附模型。

吸附性是页岩气形成气藏的核心基础，也是决定页岩气开采潜力的关键因素。本项目针对我国海相页岩吸附非均质性微观机理问题，采集南方上扬子地区龙马溪组和筇竹寺组两套富有机质海相页岩段岩心样品作为研究对象，以理论分析、实验测试以及模拟技术为手段展开研究。通过野外地质调查、资料收集和实验测试，获取了龙马溪组和筇竹寺组两套富有机质海相页岩的储层基本特征。包括沉积相特征、有机地化特征、矿物岩石学特征。运用扫描电镜、压汞仪、低温液氮/二氧化碳吸附实验测试其孔隙特征，对比分析了两套页岩储层孔裂隙特征。两套页岩从物质组成、孔隙结构上较为相似，但进行综合表征可以发现筇竹寺组页岩更为致密，优势孔径范围更小，以微孔为主体发育，虽可能利于页岩气的吸附赋存，可对于页岩气的渗流极为不利，不易于开采。结合孔隙结构特征、形貌特征与微-纳米尺度量化指标，在已有孔隙模型基础上考虑层理孔隙度，建立了基于图像形貌-量化指标-物质成因分析的页岩孔隙非均质模型。该模型表明当各矿物含量相当时，有机质对储层孔隙的贡献最大。超压条件有利于气体的保存，层理的发育对气体的保存与逸散也起到一定的影响。阐明了海相页岩储层非均质特征及影响因素。沉积环境、成岩作用以及构造演化是控制页岩储层非均质性的直接因素。有机质是控制吸附载体的微观非均质性的关键因素，黏土矿物孔隙吸附机理复杂，也是影响孔隙非均质性的重要因素。从微观角度揭示了页岩气赋存相态及储集机理，并对黏土矿物储集效应进行了深入分析。根据吸附载体中黏土矿物的种类和比重进行多元多次拟合与有效校正，构建了非均质性吸附载体的吸附模型。项目取得的认识不仅有助于揭示页岩气赋存富集规律，而且对我国页岩气勘探开发具有指导意义。