Development of a mathematical model and experimental validation of borehole instability due to gravity displacement during drilling in a fractured formation

Lost Circulation and overflow often occur concurrently in fracture formation due to gravity displacement, causing a downhole complexity, out of control for blowout, reservoir damage, well control difficulty, drilling cycle prolonging and cost overrun. There is still ongoing investigation and lack of basic theoretical understanding. In this paper, a mathematical model of gas-liquid gravity displacement is established and solved, as well as verified by model experiment. The results are used to develop a theoretical foundation that explains the phenomena, and a solution method is proposed for practical application.