Managed Pressure Drilling, or mpd drilling, is the process of controlling the pressure in a well as it is being drilled. This is done by using specialised equipment, which may include, among other things, a rotating control device, an extra choke manifold, drill string check valves, and fluid/solids control equipment. In order to properly control the annular hydraulic pressure profile, it is important to identify the limitations of the downhole pressure environment.
The goal of mpd drilling is to prevent a constant input of formation fluids to the surface. The right approach will be used to securely contain any influx that is unrelated to the operation. This is one of the very crucial techniques used in well completion services.
Principle of MPD (Managed Pressure Drilling):
The MPD method’s fundamental component is its ability to control the bottom hole pressure profile. The hydrostatic pressure of the drilling fluid and the anticipated annular friction pressure are combined to determine the bottom hole pressure in traditional mpd drilling. In contrast to traditional drilling, MPD uses a closed, pressurized mud system.
The hydrostatic pressure, annular friction pressure, and back pressure applied at the surface are added to create the total bottom hole pressure in the case of the MPD. This back pressure adjustment method makes it easier to respond quickly and precisely to maintain the necessary bottom hole pressure.
The rotating control device and choke manifold make up the MPD system’s basic configuration. The RCD directs flow toward the MPD choke manifold while maintaining system closure. To create back pressure and enable pressure adjustments as needed, the choke is used. The automatic opening and closing of the choke help to maintain the pressure profile inside the pressure window.
Techniques of Managed Pressure Drilling (mpd):
There are three major techniques of mpd drilling and these techniques are as follows:
1) Constant Bottom-Hole Pressure (CBHP):
One of the Managed Pressure Drilling (MPD) techniques, Constant Bottom Hole Pressure (CBHP), uses surface back pressure to keep the bottom hole pressure value consistently above pore pressure and below fracture pressure.
2) Pressurized Mud-Cap Drilling (PMCD):
An mpd drilling method that uses a Light Annular Mud (LAM) cap kept above an open-hole formation that is taking all injected (sacrificial) fluid and drilled cuttings with the help of surface pressure to balancing a full annular fluid column.
3) Dual Gradient (DG):
“Dual-gradient drilling” refers to a number of methods for regulating pressure inside an offshore well while drilling. It is intended to lessen or even eliminate the pressure that drilling fluids in the riser add by using dual systems.. It is desired to have a distinct pressure gradient above and below the mud line.
Safety precautions for drilling operation:
According to the principle of slight overbalance, back pressures in the annular should be adjusted during drilling to maintain a slight overbalance, and the drilling fluid level in the circulation tank should be kept in a slightly dropping state to prevent massive natural gas invasion into the borehole and minimize the fluid of drilling loss.
The following drilling safety procedures have been implemented in order to meet these objectives:
· The drilling fluid density and the fluid level in the circulation tank should be regularly monitored by the on-duty operators and the geologic logging operators.
· The person in charge of controlling pressure should regularly check for minute changes in the flow and density of the fluid that arises while drilling at the outlet, as well as changes in fluid level in the circulation tank.
· To ensure stable properties, the fluid must be kept precisely within the bounds of the design specifications; its density at the inlet must be kept at or below 2.35 g/cm3.
· Before “starting or stopping the pump,” pressure control employees should be informed in advance.
· To prevent a significant bottom-hole pressure surge, the tool pusher should elevate and lower the drilling tools carefully.
· Drilling should stop as soon as fast drilling or blowdown occurs, and drilling tools should be raised before circulating the system for inspection.
· Before the drill collar is tripped out and the well is quickly opened, there should be a sufficient amount of high-density fluid injected to remove back pressure.
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