Model for a Shale Gas Formation with Salt-Sealed Natural Fractures

There are reported cases of hydraulically fractured shale wells that exhibit boundary dominated flow in a very short period. This study suggests that dissolution of salt-sealed natural fractures in the shale offers a novel explanation for the early boundary dominated flow. We first discuss a plausible diagenetic history for generation of a salt-sealed natural fracture system in shale gas and how core, log, and conventional test data may behave. We then note that flowback of water with significantly higher salinity than the injected fracture fluid may suggest that the injected low salinity fracturing fluid dissolved salts that sealed an existing natural fracture system. In this scenario, the effective permeability would represent that of the natural fracture system induced by salt dissolution, and the stimulated rock volume would be directly related to the leakoff volume. A simple material balance model tracks salt dissolution by leaked off fracturing fluid and estimates the resulting stimulated rock volume.