中国南方海相页岩孔隙连通性表征及成因模式研究

With the development of shale gas, the evaluation and reformation of shale reservoirs have attracted the worldwide interest. Current studies are limited to geometrical aspects of pore structure, but lacks effective approaches to characterizing topological attributes of pore connectivity. The project intends to focus on marine shale of south China, using complementary approaches of small-angle neutron/X-ray scattering, field emission-scanning electron microscopy, gas adsorption and so on, to better quantitative characterizing their pore connectivity and clarify the intertwining relations between wettability and pore connectivity. Based on the shale composition and diagenesis, the different genetic types of pore connectivity were analyzed and quantitative and visual models were established. In order to investigate the matrix permeability and diffusivity of shale, we conducted a series of analyses with overburden pressure matrix permeability test, spontaneous imbibition, as well as saturated diffusion with tracer distribution mapped with laser ablation-inductively coupled plasma-mass spectrometry, and further revealed the inner link between pore connectivity and matrix permeability and diffusivity of shale. The outcomes of this project not only have important significance for the fundamental knowledge of pore connectivity and genetic model, but also provide scientific basis for sustainable shale reservoir development in China.

随着页岩气工业的发展，页岩储层的评价与改造越来越受到重视。目前国内外学者主要关注页岩孔隙结构的几何学研究，缺乏对页岩孔隙连通性拓扑学特征的定量表征。本项目拟选取中国南方海相页岩为研究对象，采用小角中子/X射线散射技术、场发射扫描电镜、气体吸附等多种实验分析手段，定量表征页岩的孔隙连通性，同时厘清孔隙连通性与润湿性的关系。以页岩物质组成为基础，以成岩作用为主线，分析不同孔隙连通性的成因模式，建立定量化和可视化的孔隙连通性成因模式模型。通过覆压基质渗透率测试、自发渗吸实验、示踪剂饱和扩散实验等技术手段测定页岩的基质渗透率和扩散率，进一步揭示页岩储层孔隙连通性与页岩基质渗透率和扩散率之间的内在联系。本项目的研究成果不仅对页岩孔隙连通性及成因模式的基础性研究具有重要的科学意义，同时对页岩储层的可持续性开发也提供了科学的理论依据。

本项目主要选取中国南方海相页岩辅以海陆过渡相页岩为研究对象，采用小角中子/X射线散射技术、场发射扫描电镜、气体吸附等多种实验分析手段，定量表征页岩的孔隙连通性，同时厘清孔隙连通性与润湿性对页岩孔隙可进入性的影响。以页岩物质组成为基础，以成岩作用为主线，分析不同孔隙连通性的成因模式，建立了定量化和可视化的孔隙连通性成因模式模型。通过覆压基质渗透率测试、自发渗吸实验、示踪剂饱和扩散实验等技术手段测定页岩的基质渗透率和扩散率，进一步揭示了页岩储层孔隙连通性与页岩基质渗透率和扩散率之间的内在联系。重要结果如下：.1、通过多种方法建立了过成熟海相页岩孔隙连通性评价方法，并测定了多种实验方法的最优测试条件和样品规格，建立了定量化和可视化的孔隙连通性成因模式模型。过成熟海相页岩亲水性孔隙网络的连通性会随页岩成岩作用加强而降低。基于三维可视化技术，过成熟海相页岩中的有机孔隙网络连通性较好，页岩整体孔隙连通性下降是由于无机矿物（主要是脆性矿物）对有机孔隙体系的封闭导致。.2、通过甲烷、水和甲苯在过成熟海相页岩孔隙中的可进入性研究显示当孔喉远大于流体分子时，孔隙表面的润湿性主要影响流体填充孔隙的速率而非体积。孔隙的连通性会直接影响孔隙的可进入性，因此通过流体注入法研究页岩孔隙结构和润湿性时首先要考虑的是页岩孔隙连通性评价。.3、通过小角中子散射与流体注入法联合表征，在龙马溪组、五峰组和筇竹寺组页岩中均有闭孔发育，随着成岩作用加强，压汞闭孔率逐渐升高主要原因是页岩孔喉的变化，小孔喉不断消失，汞无法进入的孔隙空间变大。页岩闭孔的发育会影响页岩储层的储集性和渗透性，从而很大程度上影响着页岩油气的产量和采收率。.4、基于页岩储层孔隙连通性与页岩基质渗透率和扩散率之间的内在联系提出了通过研究页岩孔隙网络的自封闭性和可进入性来评价页岩油气保存条件及储层可开发性的有效方法。