Managed Pressure Drilling ( MPD) is a drilling technique that provides precise control of the wellbore pressure by using a closed and pressurized circulating system. During MPD, wellbore pressure is controlled dynamically by regulating the backpressure, whereas, in conventional drilling, the wellbore pressure is managed by the weight of the drilling fluids, commonly known as “mud weight”. Rotating control devices (RCDs), Continuous Circulation System (CCS) and Back Pressure Pump are the key ingredients of any MPD system.
The major rationale of using MPD is drilling in reservoirs with narrow drilling windows (when pressure between pore and fracture is small) where standard drilling practices fail. There are several other benefits of using MPD, such as faster drilling, less NPT, preserving formation, deep reservoir, mitigating drilling hazards, removing kicks and differential sticking (and stuck pipe risk). Yet, MPD is considered to be a high-risk operation, as such not widely used. Any application of MPD should be thoroughly risk-assessed. In fact, higher costs and drilling issues may be a side-effect of using MPD improperly. Even though the technology has been evolving and improving, there is still a high degree of skepticism in the industry.
Although globally, offshore applications of MPD are predominant, in the GCC MPD was primarily used onshore, since not all offshore drilling rigs are designed to accommodate MPD equipment, due to its size and footprint. In parallel to that, rig equipment must be modified, which is not always possible or feasible. In some cases, there is a limit on how fast a well can be drilled, as logging data cannot be acquired as fast as drilling can progress.
Overall, a detailed cost-benefit analysis should be conducted to understand when to use MPD. MPD has been successfully used in the GCC, but with limited applications.
There are 3 major MPD techniques.
- Constant Bottom Hole Pressure (CBHP) - maintains constant pressure at the bottom, a little higher than the reservoir pressure. This is achieved by applying backpressure from the surface.
- Pressurized Mud Cap Drilling (PMCD) - as defined by the IADC “drilling with no returns to surface and where an annulus fluid column, assisted by surface pressure is maintained above a formation that is capable of accepting fluid and cuttings”. It is widely used in carbonate-reservoirs, HPHT wells and deepwater.
- Dual Gradient Drilling (DGD) - primarily used in deepwater offshore, DGG is a method whereby mud does not return through a drill pipe (conventional method) but via separate small diameter pipe(s). In addition, a lighter mud is used in the upper section of the well and heavier mud at the lower part of the well.