上扬子地区下寒武统牛蹄塘组页岩气成藏条件

摘要

Based on outcrops,drilling and core data,combining with analysis of thin section,SEM,X-ray diffraction,mer-cury porosimetry and isothermal adsorption ,this paper studied the accumulation conditions and characteristics of shale gas of the Lower Cambrian Niutitang Formation in Upper Yangtze Region ,with focus on the stratigraphic ,petrologic,geoche-mical and geophysical characteristics as well as gas storage capacity .The results show that the distribution of the organic-rich shale of the Lower Cambrian Niutitang Formation in Upper Yangtze Region is controlled by the shallow to deep water shelf sedimentary environment ,where shale thickness generally ranges from 50 to 300 m.The shale has a total organic carbon content over 1 .5%and is highly mature to over mature .The organic-rich shale has abundant brittle minerals and the clay minerals with high evolution are dominated by stable minerals such as illite but without any montmorillonite .The various types of pores and fractures provide effective reservoir space for shale gas ,and the gas content reaches the lowest commercial development value ( 2.0 m3/t ) .Comprehensive analysis of these conditions reveals that the Ziyang-Zigong area,the northern Guizhou ,eastsouthern Chongqing and eastern Hubei and Hunan Province are favorable exploration areas .%基于上扬子地区下寒武统牛蹄塘组黑色页岩的野外露头、钻井、岩心等资料，通过显微薄片、扫描电镜及X-衍射、压汞分析、等温吸附等多项实验测试分析，以牛蹄塘组黑色页岩的地层、岩石学、地球化学、地球物理和页岩含气性等为重点，对上扬子地区下寒武统牛蹄塘组页岩气形成的成藏条件与特征进行了初步探索。研究表明上扬子地区下寒武统牛蹄塘组以浅水-深水陆棚沉积环境控制富有机质页岩的发育，沉积厚度一般在50～300 m；有机碳含量在1.5％以上，有机质成熟度达到高-过成熟阶段；富有机质页岩脆性矿物丰富、粘土矿物演化程度高，以伊利石稳定矿物为主，不含蒙脱石；多种孔隙类型及裂缝发育，可为页岩气的赋存提供良好储集空间；富有机质页岩含气量达到了页岩气商业开发下限2.0 m3/t。综合各种成藏条件，认为资阳-自贡一带、黔北和渝东南-湘鄂西地区为页岩气有利勘探区带。