Modeling of surge and swab pressure of yield power law fluids

Erge, Öner
A mathematical modeling work and computational fluid dynamics (CFD) analysis of surge and swab pressures in concentric annuli is conducted. A commercial CFD package is used to validate the developed model of the flow during surge and swab in concentric annuli. Developed mathematical model incorporates the Yield Power Law (YPL) fluid behavior for closed-end pipes under laminar flow conditions. The results of the mathematical model and CFD analysis is compared with the models from literature. CFD analysis is initially compared with the analytical solution of the surge and swab velocity profiles of a Newtonian fluid to validate the CFD approach. A good agreement is obtained with the analytical solution and the results from the CFD analysis. A similar approach is followed and proposed numerical solution is compared with the results from the CFD analysis to validate the proposed approach. A good agreement is observed with the result from CFD and the proposed finite differencing scheme. Velocity profile comparison among numerical solution, analytical solution and CFD analysis yields less than 5% average absolute percent error. A 3D geometry of concentric annuli is used in the CFD analysis. Also, a mathematical model is developed considering an annular geometry with different inner and outer pipe sizes. The effect of the degree of curvature difference between the inner and outer pipes while surge and swab is captured both with the CFD analysis and the mathematical model. With this approach, more accurate results are obtained than approximating the annuli to a slot. Additionally, dimensionless velocity profiles are presented that better explain the flow during surge and swab conditions in concentric annuli while the inner pipe is reciprocating in steady-state. Most of the drilling fluids can be characterized with Yield Power Law (YPL) model. YPL model includes a yield stress term similar to Bingham Plastic and has the shear thinning ability as the Power Law fluids. YPL model accurately estimates the drilling fluid behavior in low and high shear rates. After drilling, pulling out or running a BHA in the vertical section or running casing with centralizers approximates the position of the tubular to concentric. Therefore, mathematical modeling and CFD analysis of the swab and surge pressures of YPL fluids in concentric annuli has potential to optimize the tripping operations that will help not only avoid hole problems, but also reduce the non-productive time. 
Citation Formats
Ö. Erge, “Modeling of surge and swab pressure of yield power law fluids,” M.S. - Master of Science, Middle East Technical University, 2016.