Managed pressure drilling technology for fractured carbonate formation in deep water Block S, West Africa

Block S in West Africa has complex problems such as narrow drilling pressure window in the upper mudstone formation, serious leakage in the lower formation with carbonate fractures, containing hydrogen sulfide, and high geological uncertainty. Managed pressure drilling technology is a relatively mature technology to deal with these problems, however, a single managed pressure drilling technology cannot solve all the above problems once. The annular pressure dynamic control drilling technology can solve the problem of mudstone well instability, and the pressurized mud cap drilling technology can solve the problem of well control in the formation bearing hydrogen sulfide under the conditions of serious drilling fluid leakage. And on this basis, a new technology was proposed by combining and applying the two independent managed pressure drilling technologies above. The research was carried out from three aspects: the sharing of managed pressure equipment, the conversion of technical solutions, and the decision-making of key construction points. The case application shows that the managed pressure drilling combined technology can effectively solve many complex problems such as well stability, leakage, and well control in the same well, with better application effect compared with individual managed pressure drilling technology. This study may provide a guidance for the subsequent exploration and development in this block and in similar formations.