Evaluation of chemostratigraphy in interpreting stratigraphic architecture of the Bone Spring Formation in the Delaware Basin, Eddy County, New Mexico

Subdivision of sedimentary strata is a fundamental method of understanding and interpreting sedimentary deposits and allows geologists to organize and interpret sediments that record Earth's history. In a relatively new approach to interpreting geologic strata, chemostratigraphy is the practice of using whole-rock inorganic geochemical data to subdivide sedimentary strata based on changes in elemental concentrations. This study serves as a practical experiment in chemostratigraphy to enhance existing lithostratigraphic correlations within the Bone Spring Formation of the Delaware Basin, which is a shale resource play. Though the petroleum industry has had great success in exploiting these shale resource plays, there is still a need to better understand and predict the vertical and lateral changes in the rock to continually improve horizontal wellbore placement, completion procedures, and reduce drilling costs. In this study, 294 cuttings samples were collected in the 1st shale interval of the Bone Spring Formation from 11 wells positioned no greater than 5 miles apart. Samples were analyzed using Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) and Instrumental Neutron Activation Analysis (INAA) for concentration data of 50 major, trace, and rare-earth elements.;Analytical data was organized and plotted against depth to create "elemental logs" which show stratigraphic changes in elemental concentrations. These elemental logs were used to interpret stratigraphically unique geochemical packages in an effort to enhance the resolution of existing lithostratigraphic correlations from conventional wireline logs (such as gamma ray, resistivity, and porosity), and to make inferences about the depositional/geochemical environment(s) represented in the samples. Subsequent to the interpretation of the geochemical packages from the elemental logs, ternary diagrams were used to validate the uniqueness of each package, and to differentiate and interpret the relative similarities or differences of the geochemical signatures between geochemical packages. Cross-sections were then constructed in an attempt to correlate the interpreted geochemical packages between wells. However, in some cases correlations of geochemical packages could be proposed and validated, but correlations between some wells were unsuccessful. Ultimately, stratigraphic architecture and depositional/geochemical environment interpretations were improved between some wells, but not in others.