PRESSURE DRILLING

In most drilling operations, it is evident that a considerable amount of money is spent when faced with drilling related problems such as stuck pipe, lost circulation and excessive mud cost which in turn leads to an increase in non-productive time especially in deep-water environment where the pore pressure and fracture pressure gradient is very close (narrow drilling window). Managed pressure drilling (MPD) has been found to be effective when compared with conventional drilling method to eliminate or reduce these hole problems. The MPD technique is of two types: Reactive MPD (where MPD equipment is rigged up in cases of drilling hazards) and Proactive MPD (MPD equipment is rigged up from the onset). There are four variations of MPD and each variation used must suite the drilling hazard to be mitigated.In this review, three case studies in the deep-water environment (Bolontiku Field in the Gulf of Mexico, Tarim Basin in China and Kristin Field in the Norwegian sea in the haltenbanken area) were taken, to comparatively analyze the challenges, methods used and the drilling hazards encountered when drilling conventionally and with MPD technique, using indices of comparison such as: Cost of drilling, target depth attained, number of drilling days and mud losses seen. In all the three cases considered, the drilling hazards were encountered while drilling conventionally, which were not able to be mitigated. However, with the application of the constant bottom hole managed pressure drilling technique, in the Bolontiku and Tarim Basins, the wells were drilled safely, reduced the number of drilling days by 50% when compared with the conventional drilling technique. Application of the pressurized mud cap drilling was done on the Kristin field and it shows that MPD enabled drilling in highly depleted reservoirs with the application of a static drilling fluid weight below the original pore pressure.