上扬子地区下寒武统牛蹄塘组优质页岩储层测井识别——以贵州岑巩页岩气区块为例

南方地区古生界发育多套海相富有机质页岩，是我国页岩气勘探部署的重要战略地区，目前已在四川盆地及周缘龙马溪组获得突破。与龙马溪组相比，下寒武统牛蹄塘组具有更大的沉积厚度与更广泛的分布面积，是我国页岩气勘探开发亟待突破的另一重点层系。地球物理测井贯穿页岩气的勘探开发，是识别与评价页岩气储层的重要手段。为此，通过对研究区3口井下寒武统牛蹄塘组测井资料的对比分析，总结出牛蹄塘组含气页岩具有“四高四低”的测井响应特征；元素测井上表现为硅质(石英)含量增加，铝、铁、钾元素与黏土矿物含量降低的特征；在核磁共振测井T₂谱上以单峰和连续型双峰为主，弛豫时间与振幅明显大于普通页岩。通过选取对富有机质页岩响应敏感的自然伽马能谱、地层电阻率、密度、声波时差和补偿中子测井资料对研究区内不同保存条件下的页岩储层进行叠合与交会分析，总结出不同保存条件下的富有机质页岩、富有机质硅质泥岩、普通页岩、砂岩和灰岩的测井响应特征，为研究区优质页岩储层的测井识别与评价提供依据。此外，地层电阻率与声波时差测井资料对页岩的含气性、流体性质与保存条件具有一定的指示作用，可作为页岩含气性与保存条件的判识性指标。

Logging Identification of the Lower Cambrian Niutitang Shale Gas Reservoir in Upper Yangtze Region:A Case Study of the Cengong Block,Guizhou Province

Currently,China has achieved a breakthrough of the Lower Silurian Longmaxi shale in Sichuan Basin and its surrounding areas.Compared with the Longmaxi shale,the Lower Cambrian Niutitang shale,which has a greater deposition thickness and wider distribution area,is another significant strata for China′s shale gas.Geophysical well logging is one of the significant methods for identification and evaluation of shale gas reservoir that throughout the process of shale gas exploration and development.In this paper,the logging response of Niutitang shale is summarized as the characteristics of “four high and four low” by comparative analysis of three shale gas wells in the Cengong block.The geochemical logging(GEM)data shows that the content of Si and quartz increases and the content of Al,Fe,K and clay minerals decreases with the increasing of depth.In addition,the Niutitang shale mainly has the feature of the single peak and two continuous peaks inT₂ spectrum on nuclear magnetic resonance(NMR)logging response,which has a longerT₂ time and greater amplitude than normal shales.The logging response of different lithology and preservation conditions is summarized by overlapping and intersection analysis with the spectral gamma-ray,resistivity,density,acoustic time and compensated neutron logging data,which are sensitive to the organic-rich shale.Besides,resistivity,acoustic and density logging data are sensitive to gas content,fluid properties and preservation conditions,which can be used as indicators for shale gas content and preservation.