In Managed Pressure Drilling (MPD), it is possible to drill holes that simultaneously expose formations with narrow safe mud windows and with pore pressures close to the fracture pressures of other exposed formations with minimal formation influx or mud losses, and also minimal future formation damage during production. In Continuous Circulation Systems (CCS), as a sub-class of MPD, the dynamic or circulating pressure is adjusted to control formation pressures. Therefore, the key factor in success of CCS and prevention of unprecedented formation damage is Equivalent Circulating Density (ECD). This is because a small error in calculation of the ECD can cause a kick influx or drilling fluid loss. Therefore, there is a strong need to investigate the effects of various parameters affecting ECD, which is the objective of this work. In this study, a section of a vertical annulus was simulated using Computational Fluid Dynamics (CFD) in 3-D and 2D to determine the effects of different affecting parameters on ECD. The seven investigated parameters in this section consist of DP rotational speed, eccentricity, rate of penetration (ROP), cuttings size, drilling fluid density, rheological parameters, and radius ratio (of drill-pipe OD to wellbore diameter). The CFD simulation results show that the ECD of MPD may be significantly affected by the aforementioned parameters. The ECD shows to change due to unprecedented change of the aforementioned affecting parameters. This can potentially jeopardize the MPD drilling operation success. Among the parameters, in laminar flow, radius ratio Yield Point and ROP showed the greatest effect on ECD whereas in turbulent flow radius ratio, PV and mud density showed to have the greatest effect with the other parameters to have minimal effects.

In 2017, blowouts and then explosions occurred in a Middle Eastern oilfield. A root cause of the incident is lack of study and investigation of the past kicks and blowouts data. Therefore, as a pioneer work in the region, data gathering and analysis of past kicks and blowouts were made in the studied oilfield to learn lessons and find gaps. Out of the 149 drilled wells, a total of 117 kicks and three (3) blowouts occurred. In this work, a list of drilling parameters to be considered in data gathering and analysis were suggested as a guideline for future works elsewhere. The statistical analysis not only showed all the three exploration wells kicked which is not a surprise, but it also showed that 39 out of 146 (26.71%) also experienced kicks during reservoir drilling. The large number of kicks in development wells proved that possibility of kick occurrence in development wells is not low. In exploration wells, the predominant kick causes were gas-cut mud and insufficient mud weight which indicates the necessity of using pressure while drilling in addition to drilling rate control systems in exploration wells. However, in development wells, lost circulation was the predominant kick cause indicating the necessity of using low-weight drilling fluids and managed pressure drilling systems. The direct role of human error exists at least in 60% of kicks occurred in this field, which shows the great importance of improved drilling personnel training. Although only 3.45% kicks in development wells occurred due to improper hole fill-up during tripping, this cause should not only be deemed trivial, but it should also be taken seriously as being the cause of the blowout. The 2.56% possibility of kick conversion to blowouts and 67% risk of blowout conversion to explosion emphasize the necessity of maintaining primary well control and using efficient and early kick detection systems. Bullhead was the more commonly used method than standard well control methods; as this kill method may not always be safe, its application should be revised.