Inventory of Shale Formations in the US, Including Geologic, Hydrological, and Mechanical Characteristics

Abstract

SUMMARY Inventory of Shale Formations in the USThis section provides a summary of the distribution, thickness, and depth of selected shale formations found within many of the sedimentary basins in the contiguous US. Clay-rich shale formations have a number of properties, such as low permeability, high cation exchange potential, and the ability to self seal, which make them candidates for a geologic repository for high-level radioactive waste. The United States has an abundance of thick shale deposits that span a wide range of geologic ages, mineralogic compositions, and geologic environments, some of which might be suitable for hosting repositories to safeguard radioactive waste. The objective of this report is to build upon previous compilations of shale formations within many of the major sedimentary basins in the US by developing GIS data delineating isopach and structural depth maps for many of these units. These data are being incorporated into the LANL digital GIS database being developed for determining host rock distribution and depth/thickness parameters consistent with repository design. Rock Properties and In-Situ Conditions for Shale Estimated from Sonic Velocity MeasurementsThis section presents the development of methods to assess hydrological and geomechanical properties and conditions for shale formations based on sonic velocity measurements. Publically available data sets have been identified for shales under investigation for nuclear waste disposal in Europe and from shales of interest for oil exploration and production in the North Sea. These data have been used in the development of several correlations which link properties to sonic compressional velocity. The advantage of using correlations based on sonic velocity is that properties can be estimated from geophysical logs. This information is often more readily available than direct property measurements on core that would otherwise be required. Furthermore, geophysical logs typically provide a continuous readout along wells that can be more readily used to characterize spatial variability in properties. The correlations developed are then used to assess properties and conditions in several shale formations of interest within the United States which have publically available data on sonic velocity. Some of the proposed correlations have been previously investigated by others and comparisons between correlations are reasonably consistent. The approach has been extended here to other properties as well as insitu conditions, in particular, a method to estimate pore-fluid pressure. A method is also developed and used to account for anisotropy for properties where sufficient information is available to assess directional dependence. Some of the correlations, in particular estimation of sonic velocity parallel to bedding from normal to bedding sonic velocity measurements, and estimation of clay content from sonic velocity were found to be weak, indicating that additional independent measurements are desirable to supplement such estimates. Several ...

How Stress Barriers and Fracture Toughness Heterogeneities Arrest Buoyant Hydraulic Fractures

“…We have compiled a study of multiple shale formations focusing on those in the United States. The estimation of the mechanical properties of the formation is primarily taken from Dobson and Houseworth (2013) and other authors (Schwartz et al 2019;Kong et al 2023;Zhou et al 2023;Jin et al 2018;Jiang et al 2018). We assume a slickwater injection into horizontal wells.…”

“…The buoyancy length scale is crucial to estimate the dimensionless coefficient D (9), which we need to estimate the fractures's regime when it encounters the change. Our compilation of data with a focus on the work of Dobson and Houseworth (2013) has given us an average maximum height of rock formations of about 300-350 m (1000-1500 ft) and a minimum height that can be as low as 50 m (about 150 ft). Neglecting heterogeneities and bedding planes inside the rock formation, we can estimate that the major changes in properties occur at the boundary of these formations.…”