Continuous circulation of drilling fluid offers many benefits including increased control of downhole pressure in relation to pore and fracture pressures along with enhanced wellbore cleaning. While the concept of continuous circulation has been known for a long time, it has not been until recently that development of reliable systems have begun turning up. Continuous circulation provides an uninterrupted stream of data from sensors mounted downhole and on surface equipment even while making a connection, thereby never interrupting equivalent circulating density.

Weatherford has developed a sub based continuous flow system (CFS) with an automated control system for switching mud flow between the top drive and side flow port. During conventional drilling operations, CFS subs are passive drill string components. When a new stand needs to be added, a CFS sub connected to the stand already drilled into the well is positioned in the rotary table and a clamp carrying a side flow line is attached to it. Once the clamp has been securely attached, rig hands can move off the rig floor with the rest of the operation taking place from a remote control panel. At this point CFS sub works like a three-way valve. When a sleeve inside CFS sub is pushed upward, it opens a side flow port on the sub simultaneously closing an internal valve to cut off flow from top drive. With concurrent operation of mud valves on a manifold skid, mud flow is redirected from the top drive to side flow port before breaking the top drive connection and back to the top drive after a new stand has been connected. Continuous flow system can be used during trip-in and trip-out operations in an almost identical manner.

Significant strides have been made to introduce a new system with input from customers and exhaustive testing. The process of developing a new product can be long and tedious. It is important to lay out a road map to success not only with a thorough testing program but to make sure that once it has been tested the product is suitable to be utilized for field trials.

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