Thesis (M.Sc.) - Cairo University - Faculty of Engineering - Department of Metallurgical Engineering

Underbalanced drilling has many advantages such as high ROP (may reach up to ten times), early information about reservoir, eliminating or minimizing the risk of differential stuck and loss of circulation and avoiding formation damage. However, UBD is expensive and complicated. It isn{u2019}t applicable in certain cases such as pressurized shale. On the other hand, over balanced drilling is cheaper with good control over formation fluids but with lower ROP, losses, differential stuck possibilities and formation damage. A new technique can combine some advantages of UBD while keeping OB by using the general energy equation. By using modified bernoulli equation, an under balanced zone below the bit by could be created by setting the proper nozzle orientation and size. This is simply done by keeping the drilling fluid velocity as high as calculated and predetermined to create the pressure drop required. This drop in pressure is controlled by nozzles orientation, nozzle size and Mud flow rate. The whole well except the zone at the bit will be OB. The pressure drop made is by Mud velocity and this velocity will drop as the mud enters the wider annular space above the bit. This velocity drop will result in increased pressure to the OB values.

Issued also as CD