Design and calculation of a MPD model with constant bottom hole pressure

Bottom hole pressure can be maintained in a reasonable range by using the managed pressure drilling (MPD) technique with special equipment. A calculation model is established for the back pressure and drilling fluid density of constant bottom hole pressure MPD, which are calculated by iterative method. The calculation model is applied to the Well Kela 201. In the comparison of the annulus pressures at 3 314 m in the well, the conventional drilling method cannot provide the appropriate drilling fluid density, but the constant bottom hole pressure MPD technique can make the annulus pressure within the pressure window. The design result of back pressure and mud weight of the narrow pressure window illustrated that the well can drill the target zone at 2 800 m directly by using the MPD technique. It can simplify casing program and save drilling cost. The calculation example demonstrates that this technique not only reduces mud density, but also meets the demand of annulus pressure control. Narrow pressure window can be drilled safely. It provides a technical basis for optimizing well profile.