Prediction and Analysis of ECD for Deep Water Hydrate Formation Drilling with Riser

Natural gas hydrate reservoirs in the South China Sea are shallow buried and weakly cemented, making it difficult to drill horizontal well. The accurate prediction of equivalent circulation density (ECD) is the key to the safe drilling of horizontal well in hydrate reservoirs. Therefore, in this study, the ECD prediction model of hydrate formation drilling was established considering the influence of annulus hydrate cuttings decomposition. The influence of key hydraulic parameters such as drilling fluid density, displacement and rate of penetration on ECD was calculated and analyzed, and the leakage risk of hydrate layer was also analyzed. The calculation results show that the hydrate cuttings decomposition area is mainly in the upper annulus of the riser section, which is above 620m in the upper annulus of the riser section under the calculated condition. The ECD whether hydrate cuttings decomposition is considered under calculating conditions is 1060 kg/m3 and 1068 kg/m3, respectively. When the initial drilling fluid density is greater than 1064 kg/m3 and the drilling fluid displacement is greater than 23L/s, there is leakage risk in the reservoir. This study can provide reference for prediction of ECD in deepwater hydrate formation drilling.