There are several problems which an oil and gas industry is facing. These problems can be solved by riserless drilling method which comes under managed pressure drilling umbrella. The most important problem is increasing number of casing strings to complete a well and to control a well in limited pressure profile. A well model was developed and both conventional and riserless drilling approaches were applied to see how many casings will be needed to complete a same well with these approaches. All in all four different cases were established namely: conventional single mud drilling, dual gradient drilling, riserless zero well head pressure (back pressure application) and riserless zero well head pressure (U-tube effect application). Casing design criteria were established to select best possible and available casing with API standards. Criteria were not only from drilling point of view but also production and cementing scenarios. Successfully P110 casing showed to fulfill all pressure requirements. A well control comparison was made and find out that with riserless drilling approach a lot of time can be save in order to circulate the kick out of the well.

Master's thesis in Petroleum engineering