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 in T2spectrum on nuclear magnetic resonance(NMR)logging response, which has a longer T2time 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. © 2015, Science Press. All right reserved.