SummaryIn most drilling environments, wellbore pressure exceeding the fracture–opening/initiation gradient often results in major fluid losses when drilling ahead and fluid returns when circulation is stopped. The phenomenon is generally referred to as wellbore breathing. Because no flow is expected when circulation is stopped, the mudflow return is more noticeable and could lead to kick misdiagnosis. To rapidly identify whether a possible influx is caused by formation breathing (or otherwise), correct interpretation and modeling of this phenomenon are paramount. The latter can be used to generate a reliable diagnostic tool for breathing discrimination, and it can also be turned into a valuable resource. Potentially, several in–situ properties of the fractured formation can be inferred with static flowback signatures and pressure–while–drilling (PWD) data. This paper shows how to use the proposed geomechanical model to generate diagnostic flowback type curves. A step–by–step procedure is then presented to discriminate the nature of the influx and to infer the fracture–network properties (damaged radius, generalized hydraulic diffusivity, average borehole breathability, and generalized total compressibility) through a type–curve matching protocol. Several field data have been analyzed to show the applicability of the proposed diagnostic tool and to validate its ability to rapidly differentiate borehole breathing from a kick.