Quantitative Characterization Method for ECD Uncertainty Based on Uncertainty Theory

Equivalent circulation density (ECD) at bottom hole is an important parameter affecting the safety of drilling operations. Accurate prediction of ECD is the prerequisite for safe drilling operations. Presently in China the prediction of ECD is often to calculate with traditional hydraulic models. Calculation of ECD with traditional hydraulic models gives results that roughly reflect the change pattern of ECD, but the precision of the model used and the fuzziness of input parameters for the model make it difficult to get accurate ECD; the calculated ECD is quite different with the actual ECD, and there exist uncertainties in the prediction of ECD. It is therefore necessary to perform uncertainty analysis on the predicted ECD on the bottom of the hole. Based on the comprehensive analyses of models for quantitative calculation of ECD, the sources from which the uncertainty of ECD is produced are discussed first in this paper, then a formula for ECD uncertainty calculation is derived on the basis of the Uncertainty Theory, and a case history of ECD uncertainty calculation is presented. The discussions made in this paper have presented a new clue for scientifically describing ECD, and provided a technical support of safe drilling operations.