Complex Resistivity Characteristics of High TOC Marine Shale Core Samples and its Applications

Total Organic Content (TOC) is one of the key and important parameters to effectively evaluate the shale gas formation production potential. According to geological deposition theory, the TOC is the basic key element that controls the form of pyrite in the marine sediment under deep water strong reducing deposition environment. There is a close relationship between the TOC and pyrite in such deep water reducing deposition environment. Through the laboratory measurement and analysis of the complex resistivity on marine shale formation core samples from South China, the high TOC shale reservoir core samples contain more pyrite, and they show clearly low resistivity and high polarization anomaly. In comparison with well log data, the laboratory measurements of TOC and pyrite are closely related to the results from the log data analysis. We concluded that high TOC marine shale formation has the characterization of low resistivity and high induced polarization (IP) anomaly. Based on the research results, the application of the induced polarization or complex resistivity method to measure the subsurface resistivity and polarization anomaly is a new approach to effectively evaluate the TOC content within the shale gas formation, and it has high potential value for future shale gas reservoir evaluation and characterization.