Spacing and distribution of bed-perpendicular joints throughout layered, shallow-marine carbonates (Granada Basin, southern Spain)

This contribution focuses on the controls exerted by sedimentological, petrographic and mechanical rock properties on the distribution of bed-perpendicular joints throughout layered carbonates. The study was conducted on Tortonian, shallow-marine skeletal grainstones and rudstones cropping out in the Granada Basin, southern Spain. The results of combined field and laboratory analyses are consistent with the rock grain size of the studied carbonates exerting a key control on distribution of the bed-perpendicular joints. A positive correlation between joint spacing and mechanical unit thickness is computed for the grainstones, whereas joints are almost absent in rudstones. The rock grain size affected the diagenetic processes, such as cementation and dissolution, and therefore the resulting porosity and uniaxial compressive strength (UCS) values. Quantitative data show that higher UCS values are commonly associated with greater calcite amounts, lower values of porosity and finer grain sizes and, hence, denser bed-perpendicular joint sets. In conclusion, this study documents that it is possible to infer the density of bed-perpendicular joints in layered carbonates based on the sedimentological, petrographic and mechanical parameters. Considering the impact that this type of joints has on subsurface fluid flow, the acquired knowledge can help the management of geofluids as well as the overall prediction of carbonate reservoir quality.