Abstract
High equivalent circulating density (ECD) may cause serious drilling problems in extended-reach drilling and management of ECD is one of the key issues in designing and drilling extended-reach wells. In addition, ECD fluctuation followed by repeated formation and erosion of cuttings deposit bed in drilling extended-reach wells also causes serious drilling problem such as borehole instability.
In this paper, simulations of ECD and cuttings transport were carried out for two typical extended-reach model wells in which a situation that drilling and mud circulation were alternately repeated was reproduced. Following results were obtained from the simulation study. (1)Under the situation that drilling and mud circulation were repeated, ECD fluctuated so as to be high during drilling and low during circulation. (2)ECD fluctuation could be diminished by lowering the penetration rate and/or reducing the circulation time. (3)Under the situation that drilling and mud circulation were repeated, ECD could be kept lower than that in case of drilling continuously without circulation. (4)Insufficient mud circulation resulted in high ECD, especially in case of high penetration rate, although long circulation time makes ECD fluctuated.
