Abstract
Sinusoidal buckling of drill strings will be easily caused during drilling process of extended-reach horizontal wells due to the factors such as excessive well length and larger friction torque, which will cause measurement errors of well depth and vertical depth and furthermore influence the accurate calculation of ECD. We have corrected the traditional ECD calculation model, considered the measurement errors of well depth and vertical depth caused by the sinusoidal buckling of drill strings, and established a set of equivalent circulating density (ECD) calculation model suitable for extended-reach horizontal wells to meet the requirements for fine ECD control during the drilling operation. We have combined the data from an extended-reach horizontal well in the East China Sea and compared the ECD data obtained from the recorded stand pipe pressure with the prediction results from Landmark commercial software、the model in this work and the conventional model. Results show that the prediction results by the model in this work are closest to the recorded values when drill string sinusoidal buckling occurs. Besides, the ECD value predicted by the model considering the measurement errors of well depth and vertical depth caused by the sinusoidal buckling of drill strings is smaller due to the factor that the length of drill strings with sinusoidal buckling is larger than the actual well depth. With the identical case well data, the larger the sinusoidal buckling degree of downhole drill strings, the smaller the predicted ECD value. The model can reduce risks for drilling operations of extended-reach horizontal wells and provide more accurate reference data for their well control operations.