Analysis Of Weatherford's Microflux Control System

CBHP MPD retains a pressure that is constant between defining limits during both static and dynamic situations. In this context, ‘constant’ refers to maintaining a pressure that is continually within the margins of the drilling window.

Typically within CBHP MPD operations, an automated system such as Weatherford’s Microflux Control system is used to measure and apply the required level of surface backpressure. The following describes the basic mathematics behind this system. [2]

Well-bore pressure during circulation is greater than in static conditions due to friction. ECD at any point within the wellbore is calculated as follows [2];

ECD = EMD + ΔP/(TVDx0.052) Eq.5

Where;

EMW = Equivalent Mud Weight of a static column of fluid open to the atmosphere

ΔP = Frictional Pressure Loss

TVD = True Vertical Depth

During static conditions ΔP = 0 and thus;

ECDstatic = EMW Eq.6

To remain within the drilling window, surface backpressure may be required either during drilling and static conditions or solely when the pumps are off. Fluctuations to ECD occur during trips and
In a conventional system, the pressure decreases as pumps are stopped. The reduction in pressure may result in the well taking a kick, wellbore collapse or differentially stuck pipe. Furthermore, when circulation is stopped, drilling fluid forms a gel, which requires an increase in pressure to be broken down when pumps are resumed. In static conditions, drill cuttings have a chance to collect at the bottomhole assembly (BHA). In a CCS, pumps remain on throughout connections and trips and as a result, ECD fluctuations are avoided. Fluid is continuously circulated, removing variations to the mud viscosity and averting cuttings settlement during static conditions.