Study on lost circulation methods in mud cap managed pressure drilling

Mud cap managed pressure drilling is an advanced technique that used on severe lost circulation formations, the key parameter in mud cap drilling design is the determination of lost circulation pressure. Because of the complexity of the fracture boundary condition, there is still no reliable method to predict lost circulation pressure so far. The influence rules of lost circulation pressure difference and fracture parameters to loss rate is analyzed through the numerical simulation of different types of multiple fractures and curved fractures. The research shows that different types of fractures can be described by equivalent fracture aperture, the relationship between loss rate and fracture aperture would follow Cubic Law, but the inaccuracy increases as the loss rate of the series fractures increasing and the curvature degree of curved fractures increasing. So the lost circulation pressure can be predicted by Cubic Law and this provides theoretical criterion for the prediction of lost circulation pressure and other parameters in mud cap drilling.