中上扬子海相页岩电阻率异常成因分析

Genetic analysis of abnormal resistivity of Middle-Upper Yangtze marine shales

 高和群 丁安徐 蔡潇 何贵松

 （中国石化华东油气分公司勘探开发研究院，江苏 扬州 225007）

 (Research Institute of Exploration and Development, SINOPEC East China Company, Yangzhou 225007, China)

 文中以中上扬子地台下寒武统及上奥陶统—下志留统海相页岩钻井岩心样品为代表，从页岩本身及内部液态流体特征2个方面，对造成同一层位页岩电阻率差异悬殊的原因进行了系统分析。结果表明：受制于导电性矿物质量分数相对较低及页岩较高的成岩变质作用，页岩成分及液态流体因素对电阻率的影响有限；含气性较好、电阻率较高的页岩，在扫描电镜下普遍出现了具有白色光亮环带形状的荷电现象，环带与页岩孔缝密切相关，均位于不同颗粒接触部位或微裂隙上；为此，提出了“荷电缝”的概念。进一步分析认为，荷电缝的普遍存在大大改善了页岩的微观孔隙结构，降低了页岩的导电性能，因而它是决定页岩电阻率的主要因素。页岩电阻率与孔、渗的正相关关系印证了这一现象的存在。

 Taking drilling core samples of Lower Cambrian and Ordovician-Silurian from the Middle-Upper Yangtze craton marine shales as the representatives, the reason of large scalar difference of the same layer marine shale resistivity was analyzed by the shale itself and the internal liquid fluid characteristics. The results show that the influence of shale composition and its internal fluid on the resistivity is limited, because of relatively low content of electrically-conductive minerals and high diagenetic metamorphism of the shales; with a bright girdle, charging phenomenon is found generally in the high gas content resistivity shales under the scanning electron microscope(SEM), and the girdle is closely related to pores and fractures of shale, locating on the contact area of mineral particles or micro fractures; and the concept of "charging fractures" is defined. The further analysis indicates that the general existence of charging fractures has greatly improved the micro pore structure of the shale and reduced the conductivity of the shale, so it is the main controlling factor of the shale resistivity, which is corroborated by the positive correlation between resistivity, porosity and permeability.

10.6056/dkyqt201605007