| Within the petroleum industry, the performance of unconventional mudstone reservoirs is in large part a function of their mechanical properties. Mudstone mechanical properties are controlled by a variety of geologic variables, including mineralogy, grain size, grain contact, organic content, cementation, and the spatial distribution of these characteristics (i.e., heterogeneity).;This study investigates the impact of these lithologic controls at the macroscopic (cm) and microscopic (mm) scales for samples of the Mancos Shale obtained in Utah, USA. This work describes the lithologic characteristics of the mudstone using a variety of techniques. The samples were first subdivided into principal macroscopic lithofacies with basic core description. Samples of the macroscopic lithofacies were further characterized petrographically and microscopic lithofacies (micro-lithofacies) were identified. Micro-lithofacies were further analyzed using an electron microprobe (BSE, element mapping, and quantitative point analysis) to identify fine-scale texture and composition. Basic observations of mineralogy, grain size, grain contact, organic content, and cementation were used to classify the micro-lithofacies into mechanical micro-facies. These mechanical micro-facies correspond to industry mechanical classification by mineralogy.;Mudstone mechanical properties were directly measured in bedding oriented axisymmetric compressive tests and cylinder splitting tests. These tests reveal the relationship of micro-lithofacies heterogeneity and the mechanical anisotropy of mudstones. The mechanical anisotropy ratio increases with increasing mean stress ranging from about 1.0 to 1.4. The relatively fine-grained and coarse-grained micro-lithofacies are dominated by ductile and brittle mechanical behavior, respectively. The bimodal behavior of the micro-lithofacies along with their orientation causes mechanical anisotropy. The results of this study may allow more accurate prediction of reservoir performance by developing a multi-scale understanding of mudstone response to reservoir stimulation efforts. |
