Ballooning
Ballooning, or 'Well Breathing' is a term given to the loss/gain situation. Ballooning occurs when the 'Fracture Closure Stress' is greater than the mud weight but less than the Equivalent Circulation Density (ECD). In this situation, the well stands full in the static condition. However, fracture extends and takes mud when circulation is established since ECD exceeds the fracture closure stress. When the pumps are stopped and ECD removed, the fracture closes, forcing some or all the mud back into the wellbore.