Well ECD distribution characteristics during dual-layer coiled tubing dual-gradient drilling

Dual-layer coiled tubing drilling is a novel dual-gradient drilling technique. In order to analyze the ECD distribution characteristics in the well during dual-layer coiled tubing drilling, a computational model for calculating well ECD based on the characteristics of dual-layer coiled tubing drilling technology was developed, taking into account parameters such as well temperature, pressure and cuttings concentration. The impacts of drilling fluid displacement and density on well ECD were analyzed. The case study indicate that the well ECD increases with the increase of drilling fluid displacement and density, while slightly influenced by the increase of penetration rate. And the dimensions of the dual-layer coiled tubing need to be optimized based on the well size and circulating pressure loss. The dual-layer coiled tubing dual-gradient drilling technique can effectively reduce the bottomhole ECD, and achieve dynamic control of well pressure by adjusting drilling fluid displacement and density during drilling, providing an effective solution for addressing challenges such as narrow pressure windows in deepwater drilling and shallow leakage.