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. Although the concept of continuous circulation has been known to the industry for a long time, it has gained significance in recent years with real-time downhole pressure monitoring and control. Continuous circulation provides an uninterrupted data stream from downhole sensors and surface equipment even while making a connection, thereby never losing downhole pressure. Weatherford has developed a continuous flow system (CFS), including subs that crown the top of a drillpipe stand and an automated control system that switches mud flow between the top drive and the side flow port. During conventional drilling operations, CFS subs are passive drillstring components. When a new stand needs to be added, a CFS sub connected to a stand already drilled into the well is positioned in the rotary table, and a clamp carrying a side flowline is attached to it. Once the clamp has been securely attached, rig hands can move off the rig floor and conduct the rest of the operation from a remote control panel. At this point, the CFS sub works like a three-way valve. When a sleeve inside the CFS sub is pushed upward, it opens a side flow port on the sub and simultaneously closes an internal valve to cut off flow from the top drive. With concurrent operation of mud valves on a manifold skid, mud flow is redirected from the top drive to the side flow port before breaking the top-drive connection. Mud flow is also directed back to the top drive after adding a stand. The CFS can be used during trip-in and trip-out operations in an almost identical manner. Significant advantages of the CFS are easy implementation into the rig flow loop, automated switching of flow from the standpipe to the side entry port and back from a remote location, high consideration for personnel safety, limited impact on connection time, and a small footprint on the rig floor.

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.

As the industry-wide adoption of managed pressure drilling (MPD) continues, the recent emergence of reliable continuous flow systems (CFS) are right on its heels, offering many parallels in wellbore pressure control and protection. The question then presents itself-does continuous flow outperform conventional MPD? Will the industry's adoption of CFS lead to the ultimate obsolescence of the current offerings, or will both coexist? This paper will examine the pros and cons of each system and their respective abilities to mitigate hazards and optimize drilling efficiency.Conventional MPD systems utilize a rotating control device (RCD) and a choke manifold system to create a closed loop circulation system and achieve precise control of a wellbore's pressure profile during drilling and completion. CFS also works to achieve greater control of wellbore pressure through continuous circulation of drilling fluids. A large percentage of all drilling hazards related to wellbore pressure occur when mud pumps are cycled off and on during connections, which causes fluctuations in equivalent circulation densities (ECD) and downhole pressure spikes. This paper examines and compares two state-of-the-art technologies for enhanced pressure control and drilling efficiency; CFS and choke-based MPD systems. The conclusions will highlight the directions of the two techniques and determine if they will coexist or will forever compete in the industry to be the most widely-adopted choice.