Microscopic and Fractal Characterization of Organic Matter within Lacustrine Shale Reservoirs in the First Member of Cretaceous Qingshankou Formation, Songliao Basin, Northeast China

Abstract

Understanding the occurrences of different fractions of organic matter in shale reservoirs is very important for the evaluation of shale oil. Lacustrine organic-rich shale samples from the first member of the Cretaceous Qingshankou Formation in the Songliao Basin were analyzed with confocal laser scanning microscopy (CLSM) and fluorescence spectral analysis. The results show that the occurrences of different organic components are related to the fabric of samples and vary with depth. The bulk content of light components is significantly higher than heavy components and exhibits a positive relationship with quartz and feldspar contents. Both light and heavy components are distributed parallel with the lamination in microscopic view in laminated samples, and randomly in massive samples. The maximum radius of light components in most of the samples is larger than 20 µm, while it is smaller for heavy components, indicating the micro fractionation from clay/organic lamina to quartz/feldspar lamina. The depth of enrichment of light components corresponds to the oil maturity of organic matter. Both the distribution of light and heavy components fits the same fractal model, with fractal dimensions ranging between 2.2 and 2.5. The CLSM results confirm that it can be a reliable tool for the “sweet spot” exploration.