Scheme optimization of deepwater dual gradient drilling based on the fuzzy comprehensive evaluation method

Abstract

Offshore drilling is facing a series of difficulties in deepwater and ultra-deepwater environments, such as harsh operating environments and complex downhole geological conditions. How to achieve full management of the wellbore pressure during deepwater drilling has become one of the main concerns. The dual gradient drilling technology realizes wellbore pressure management by applying multiple pressure gradients in the annulus. It also enables the managed pressure drilling technology, such as constant bottomhole pressure drilling and mud cap drilling, to be applicable for deepwater conditions. However, the decision-making of deepwater dual gradient drilling scheme is always affected by many factors, which brings confusion for scheme optimization of deepwater drilling. In this work, according to the characteristics of four typical dual gradient drilling technologies, the fuzzy comprehensive evaluation method is applied to determine the most effective one from the aspects of drilling capacities and equipment requirements in a particular scenario. The fuzzy comprehensive evaluation results show that the subsea mud lifting pump system has better applicability in this case.