Organic-rich Marcellus Shale lithofacies modeling and distribution pattern analysis in the Appalachian Basin

This study delves into the intricacies of the Marcellus Shale, which is recognized as the most extensive unconventional shale-gas resource in the United States. The article emphasizes two pivotal factors determining the potential of unconventional shale reservoirs: how the unit reacts to hydraulic fracture stimulation and its gas content. These aspects can be traced back to rock mineralogy and the total organic carbon (TOC) content respectively, the latter being indicative of the gas content within the shale. Through the classification of mudstone lithofacies - zones with similar mineral composition, geomechanical properties, and TOC content - a comprehensive three-dimensional (3-D) model was constructed using core, log, and seismic data. To predict lithofacies, the study employed an artificial neural network, identifying eight essential petrophysical parameters from standard logs. Advanced logging techniques further solidified the connection between traditional logs and lithofacies. The spatial distribution of these lithofacies within the Marcellus Shale was influenced by various factors such as organic matter productivity and its dilution by terrestrial debris. Interestingly, the gas production rate trends from horizontal wells corroborated the study's approach to modeling. As such, the 3-D modeling strategy introduced in this article offers valuable insights for enhancing horizontal well design and hydraulic fracturing strategies.