Application of density reducer to the drilling fluid used in the ultra deep water of South China Sea

A certain well in the Yongle Block of western South China Sea has the water depth of 1 893 m and the mud line temperature of 2.3 ℃. Its safety density window is quite narrow, and the static pressure window of the target layer is only 0.1 g/cm³. In order to resolve the contradiction between the hydrate inhibition and the safe drilling of water-based drilling fluid in the formation with narrow density window, a new kind of density reducer was prepared by modifying the surface of glass bead by virtue of vinyl trimethoxysilane, vinyl triethoxysilane and hardener, without influencing the rheological property of drilling fluid. The laboratory experimental results show that this new kind of density reducer has the compressive strength of 40 MPa, less influences the rheological property of HEM drilling fluid system and can effectively reduce the drilling fluid density by 0.4-0.6 g/cm³. And the laboratory performance test results of the drilling fluid are in line with the field measurement data. The field application results indicate that thanks to the application of this density reducer, the field safety density window is broadened effectively, the field operation is smooth and maintained easily and no complex situations occurs.