中扬子地区下寒武统岩相古地理及页岩气成藏条件分析

Lithofacies palaeogeographic characteristics and reservoir-forming conditions of shale gas of lower Cambrian in middle Yangtze region

以中扬子地区下寒武统海相页岩为研究对象,以野外剖面及岩心观察、测井资料解释、岩石学微观分析、有机地球化学分析及等温吸附模拟为手段,对研究区早寒武世水井沱期岩相古地理特征,泥页岩的分布特征、生气能力、储层特征等进行论述。研究结果表明：研究区水井沱期主要发育碳酸盐岩缓坡、浅水陆棚和深水陆棚沉积,其中泥页岩主要分布于深水陆棚沉积环境中,沉积厚度主体为100-250 m;有机碳质量分数平均为2.23%,有机质类型主要为Ⅱ型,有机质成熟度普遍达到高-过成熟阶段;具一定量的微孔隙和微裂缝为游离气提供储集空间,有机质质量分数高可以提高吸附气的含量。根据页岩厚度、埋深、有机碳质量分数、有机质成熟度、含气量及保存条件等信息,预测出五峰—酉阳和崇阳—通山2个有利勘探区域。

Taking the lower Cambrian marine shale of the Middle Yangtze Region as object of study, based on the observation of field outcrops and cores, and integrating with analysis of logging data, petrologic feature, organic geochemistry and isothermal adsorption, the lithofacies palaeogeographic characteristics of lower Cambrian Shuijingtuo Formation, distribution of shale, hydrocarbon potential and reservior feature were studied. The results indicate that carbonate ramp, shallow-water and deep-water continental shelf constitute sedimentary environment of Shuijingtuo Formation. The shale with thickness（100-300 m） and organic carbon content（average of 2.23%） is mainly of deep-water continental shelf, and organic matter（mainly type Ⅱ） is generaly in high-over maturation. The reservoir space of free gas consists of micropore and microfracture, and high organic carbon content can improve adsorption capacity. According to the thickness and depth of shale, organic carbon content, maturity of organic matter, gas content, and preservation conditions, two favorable prospecting areas, the Wufeng—Youyang and Congyang—Tongshan are predicted.