Modeling Lost Circulation Through Drilling-Induced Fractures

Previous lost-circulation models assume either a stationary fracture or a constant-pressure-or constant-flowrate-driven fracture, but they cannot capture fluid loss into a growing, induced-fracture driven by dynamic circulation pressure during drilling. In this paper, a new numerical model is developed on the basis of the finite-element method for simulating this problem. The model couples dynamic mud circulation in the wellbore and induced-fracture propagation into the formation. It provides estimates of time-dependent wellbore pressure, fluid-loss rate, and fracture profile during drilling. Numerical examples were carried out to investigate the effects of several operational parameters on lost circulation. The results show that the viscous pressure losses in the wellbore annulus caused by dynamic circulation can lead to significant increases in wellbore pressure and fluid loss. The information provided by the model (e.g., dynamic circulation pressure, fracture width, and fluid-loss rate) is valuable for managing wellbore pressure and designing wellbore-strengthening operations.