Logging Evaluation of Total Organic Carbon Content in Shale, the Ulalike Formation, Northern Portion of the Western Ordos Basin
摘要
Organic-rich shales developed in the Ordovician Ulalike Formation in the northern portion of the Western Ordos Basin (WOB) provide a valuable material basis for shale gas accumulation. To facilitate the exploration and development of shale gas in the region, a logging evaluation method for total organic carbon (TOC) content was proposed in this paper. At the beginning of this study, the distribution range of the Ulalike Formation and the planar distribution pattern of the shale were characterized. The lithological scan logging data was then compared to the geochemical index test results of the source rock. Finally, a data-driven model for evaluating the TOC content of shale in the study area was developed by combining conventional logging data with lithographic scanning logging data. The marine shale of the Ulalike Formation is distributed to the east of the YR Fault, and its thickness shows a decreasing trend towards the east. The average total organic carbon content of the shale in the study area is 1.02%, and the overall quality of the source rock is acceptable. There is a clear correspondence between the natural gamma spectroscopy logging series and the TOC content. The goodness-of-fit of the data-driven model established using the newly constructed spectral parameter and the TOC content is 0.9757. Applying this model to the entire region, the planar distribution pattern of the TOC content can be characterized. The TOC content is above 1.1% on the east and west sides of the study area, while it is less than 0.8% in the central section. Regarding the Ordovician Ulalike Formation in the northern portion of the WOB, a logging evaluation data-driven model for the total organic carbon content of shale was proposed in this paper, which can enrich the technological means for subsequent exploration and development.