An innovative diagnosis method for lost circulation with unscented Kalman filter

Abstract Lost circulation, as a widespread and costly drilling problem, not only wastes a lot of drilling fluid, but also produces a large amount of nonproductive time (NPT). Therefore, detecting the symptoms of lost circulation opportunely, pinpointing the loss depth and evaluating the loss rate precisely are extremely crucial. A diagnosis method for detecting the occurrence of lost circulation and identifying the loss depth as well as loss rate at an early stage is proposed, which combines a transient pressure and temperature coupling model with unscented Kalman filter (UKF) estimation. We first establish the transient pressure and temperature coupling model under the conditions of normal drilling operation and lost circulation. Then the detection and identification estimators for estimating pressure-loss factors, flow rate factor, loss depth and loss rate are constituted by embedding the detection and identification models, which are derived from the transient pressure and temperature coupling model, into UKF estimation. In the end, a simulated case study is presented to illustrate the performance of the diagnosis method. In the simulation, the estimated pressure and outlet flow rate trace the measurements well with the evolution of pressure-loss factors and flow rate factor. Moreover, the pressure-loss factor in annulus and flow rate factor, which fluctuate to a little extent in normal drilling condition, deviate from the base value once lost circulation occurs. The simulation indicates the superior performance of the diagnosis method with the introduction of pressure-loss factors and flow rate factor, and the average error of estimated loss depth is less than 5%. In addition, the parametric sensitivity analysis illustrates the universality of the diagnosis method, which has certain ability to improve drilling safety and efficiency with lower NPT.