Surge and Swab Pressure Predictions for Yield-Power-Law Drilling Fluids

Abstract

Abstract Surge and swab pressures have been known to cause formation fracture, lost circulation and well control problems. Accurate prediction of these pressures is of crucial importance in terms of estimating the maximum tripping speeds to keep the wellbore pressure within specified limits of the pore and fracture pressures. It also plays a major role in running casings, particularly with narrow annular clearances. Existing surge/swab models are based on Bingham Plastic (BP) and Power law (PL) fluid rheology models. However, in most cases, these models cannot adequately describe the flow behavior of drilling fluids. This paper presents a new analytical solution, which is casted into a simplified model (dimensionless correlation) to predict pressure surge in a more convenient way. The steady state laminar flow equation is solved for narrow slot geometry to approximate the flow in concentric annulus with inner pipe axial movement considering yield-power-law (YPL) fluid. The YPL rheology model is usually preferred because it provides a better description of the flow behavior of most of drilling fluids. The analytical solution yields accurate predictions, though not in convenient forms. Thus, a numerical scheme has been developed to obtain the solutions. After conducting an extensive parametric study, dimensional analysis techniques were applied primarily to develop a simplified model that does not require a cumbersome numerical procedure. The new model is expressed in terms of dimensionless parameters. The performance of the new model has been rigorously tested. Comparisons of the model predictions with previously published results have shown a satisfactory agreement. In most cases, the model makes better predictions in terms of closeness to relevant field measurements. That is due to the application of a more realistic rheology model. The presented model is very useful for slim hole, deepwater and extended reach drilling applications.