Ballooning (Formation)
Well ballooning is caused by the loss of drilling fluid into the formation when the equivalent circulating density (ECD) exerted on the wellbore is nearly equal to the formation equivalent fracture pressure. When the pumps are turned off, ECD is lost and the fluid returns to the wellbore from the formation. The rate of return will vary with the formation, and the returning fluid may be contaminated with formation fluids. At the surface, this process appears as losses while drilling and gains while making connections or tripping (also referred to as wellbore breathing, supercharging, or micro- fracturing).