A model for extended-reach limit analysis in offshore horizontal drilling based on formation fracture pressure

In order to solve the problem that how far the offshore extended-reach well (ERW) can extend, the open hole extended-reach limit theory is used to establish the open hole extended-reach limit model for three offshore drilling modes including offshore conventional drilling and two dual gradient-drilling (DGD) modes, and the corresponding case study is analyzed. The results show that, water depth has great influence on the open hole extended-reach limit of ERW due to the particularity of offshore drilling; there is a decrease of the open hole extended-reach limit as the water depth is increased, and in general, the open hole extended-reach limit adopted two kinds of DGD modes are greater than that of offshore conventional drilling mode. Specifically, under the condition given by this article, the horizontal section limit of offshore conventional drilling is 4318 m, while both the two limits of DGD modes are close to 4500 m; as a contrast, the limit of onshore drilling is 7157 m. According to the sensitivity analysis of parameters in above models, the open hole extended-reach limit is decreased with the increase of mud density and mud flow rate, and the mud weight window of DGD mode is wider than that of offshore conventional drilling, which is one of the advantages of DGD; at the same time, there is an optimal eccentricity which can be used to improve the open hole extended-reach limit. (C) 2016 Elsevier B.V. All rights reserved.