INTEGRATED MUDSTONE LITHOFACIES CLASSIFICATION OF THE HUE AND HRZ SHALE, NORTH SLOPE, ALASKA

Abstract:

The purpose of this study is to classify mudstone lithofacies within the Hue and High Radioactive Zone (HRZ) Shale on the North Slope, Alaska based on mineralogy, total organic carbon (TOC), and petrophysical properties to determine their depths, distributions, and depositional and diagenetic environments. Lazar et al. (2008), Wang and Carr (2013) and Bhattacharya and Carr (2019) have classified mudstone lithofacies at prominent producing shale basins across the United States, including the Marcellus and Bakken formations. The goal of this study is to analyze petrophysical logs and core data to better understand the mudstone lithofacies variation at multiple scales of analysis and provide insights into the depositional and diagenetic conditions. Core data from six wells and well logs from eighteen wells are integrated to analyze the variations in rock properties in the shale. Core analytical techniques, including XRD, XRF, , pyrolysis, and scanning electron microscopy (SEM) are integrated with well log data to map vertical and lateral variation in mudstone lithofacies. Results show that the Hue and HRZ Shale both exhibit high degrees of heterogeneity in terms of mineralogy, TOC, and petrophysical properties. These shale formations are composed of eleven mudstone lithofacies. . The TOC content is high across the HRZ Shale, ranging from 1.5–15 wt%. Northern regions of the study area show very high proportions of pyrite compared to the overall study area. In terms of deposition, four different levels of anoxia worked in the system, including dysoxic, anoxic, euxinic, and iron-rich conditions. SEM images show the presence of pyrite framboids, which is indicative of diagenesis. This study provides an understanding of potentially productive lithofacies, in terms of favorable mineralogy, TOC, and petrophysical properties on the North Slope. The quantitative methodology for mudstone lithofacies classification will be directly applicable to other basins worldwide.