Rotating Control Heads: The When And Why
Authors: Hannegan D. 
Published: March 2010

Abstract
Rotating control head technology has become a key element in many drilling programs, lowering drilling costs and increasing well productivity. Lower drilling costs are achieved primarily by the faster penetration rates, reduced nondrilling time, and reduced mud volume and/or density requirements associated with underbalanced drilling (UBD).
Greater oil and gas well productivity can often be achieved with the application of underbalanced drilling techniques and technology. Underbalanced drilling has been utilized with increasing frequency to minimize problems associated with invasive formation damage which often greatly reduces the productivity of oil and gas reservoirs. Recent advances in rotating head technology have increased the range of well conditions to which this technology can be applied ... where drilling continues over a range of wellbore pressures ... and where drilling efficiency refinements such as closed loop circulation, produce while drilling (PWD), measure while drilling (MWD), flow/well test while drilling, reverse circulation, nitrogen injection, etc. are utilized. UBD may also provide a rapid indication of productive reservoir zones.
In addition, more so now than in the past, rotating control heads are being used solely for the enhanced safety and environmental protection they may afford a drilling program. These are cases even when the drilling conditions or methods, per se, do not require the use of a rotating control head, the inclusion of it's intended usage serves to effectively reduce environmental and rig crew risk assessment values associated with pre-drill planning and regulatory permitting processes.
Specifically what is a rotating control head? A rotating control head functions as a rotating flow diverter, mounted on top of the BOP stack beneath the drilling floor of a drilling rig (typically on top of the annular preventer) ... while drilling for oil, gas, coal bed methane, or geothermal energy sources. See Figures 1 and 2 for both low and high pressure rotating control heads.
Usually rented rather than purchased by the drilling company, the product is commonly called a rotating control head (RCH) because the stripper rubber(s) or sealing elements rotate with the drill string while a robust housing (steel bowl) and bearing assembly provides control of the flow (either by diverting or containing) when the tool is mounted on the head of the BOP stack. Dr. Adam Bourgoyne, lead author of the book Applied Drilling Engineering, describes the product as a rotating blowout preventer. The Energy and Utilities Board of Canada describes the product as a diverter-preventer. The API mentions the product as a rotating head in Recommended Practice 53.
The critical components of all rotating flow diverters, no matter the name one prefers, is the means by which a seal is accomplished around the drill string ... and the bearing assembly by which the inner race rotates with the drill string while the outer race is stationary with the bowl. Both critical components require robust design, appropriate materials of construction, and periodic servicing by the supplier to function in a trouble free manner.
The bearing assembly, particularly when drilling under high well bore pressures, generates considerable heat due to thrust loads on the internal components.