Hydraulics play an important function in many oil field operations including drilling, completion, fracturing, acidizing, workover and production. In Managed Pressure Drilling (MPD) applications where pressure losses become critical to accurate estimate and control the well within the operational window, it is necessary to use an appropriate rheological model for mathematical modelling of fluid behavior. The standard API methods for drilling fluid hydraulics assume Herschel-Bulkley (H-B), Power Law (PL) or Bingham plastic rheological model.
This paper summarizes the results of an extensive study on issues and relevant aspects related to the equipment and methods used to characterize the drilling fluids for MPD applications, as well as the operational implications that diverge from conventional practices.
A comparison of Fluid Rheology Characterization will be made by using laboratory high precision rheometers versus conventional FANN35 methods. Subsequently, a comparison of Rheology Model Selection proposed by API 13B opposed to Non Linear Regression (NLR) and the error intrinsically it is also included. Further investigation of shear rates is presented in a MPD "typical" annular geometry will be calculated via Computational Fluid Dynamics (CFD) and the formulas suggested in API RP 13D compared. To conclude it will be presented a discussion of the influences of measurements, data treatment (Curve Fit) and environment (laboratory observations versus field experiences) in the accuracy of fluid rheology characterization.