This technique (Dynamic Underbalanced Drilling- DUBD) is based on basic physical and fluid mechanics laws to create an underbalanced zone below and around the bit. This technique utilizes the high velocities of drilling fluid coming out from nozzles of drill bits and the kinetic energy associated with this velocity to create this underbalanced zone. As kinetic energy increases at a fixed point the pressure will drop at this point. So we make some modifications to nozzle size and orientation and bit profile to keep this high velocity and prevent hitting the formation perpendicularly to prevent converting this kinetic energy back to pressure when the velocity becomes zero at the formation below the bit. We modify the nozzles to cause the mud flow parallel to the formation below the bit so create pressure drop in this area. This pressure drop will be restored when velocity drops. So as mud enters the annulus above the bit, mud slows down and pressure rises to its normal values. This technique will increase ROP and reduce formation damage. DUBD enables getting data about reservoir while drilling. These data include reservoir fluids, pressure and permeability. The reduction in drilling cost and time will be great.
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