Open Journal of Yangtze Gas and Oil, 2021, 6, 129-145 https://www.scirp.org/journal/ojogas ISSN Online: 2473-1900 ISSN Print: 2473-1889 DOI: 10.4236/ojogas.2021.64012 Oct. 19, 2021 129 Open Journal of Yangtze Gas and Oil The Effects of Fluid Rheology and Drillstring Eccentricity on Drilling Hydraulics Anthony Kerunwa, Julian Ubanozie Obibuike, Ugochukwu Ilozurike Duru, Stanley Toochukwu Ekwueme Federal University of Technology, Owerri, Nigeria Abstract Accurate determination of hydraulic parameters such as pressure losses, equiv- alent circulation density (ECD), etc. plays profound roles in drilling, cement- ing and other well operations. Hydraulics characterization requires that all factors are considered as the neglect of any could become potential sources of errors that would be detrimental to the overall well operation. Drilling Hy- draulics has been extensively treated in the literature. However, these works almost entirely rely on the assumption that the drill string lies perfectly at the center of the annulus—the so-called “concentric annulus”. In reality, concen- tricity is almost never achieved even when centralizers are used. This is be- cause of high well inclination angles and different string geometries. Thus, eccentricity exists in practical oil and gas wells especially horizontal and ex- tended reach wells (ERWs) and must be accounted for. The prevalence of drillstring (DS) eccentricity in the annulus calls for a re-evaluation of existing hydraulic models. This study evaluates the effect of drilling fluid rheology types and DS eccentricity on the entire drilling hydraulics. Three non-Newtonian fluid models were analyzed, viz: Herschel Bulkley, power law and Bingham plastic models. From the results, it was observed that while power law and Bingham plastic models gave the upper and lower hydraulic values, Herschel Bulkley fluid model gave annular pressure loss (APL) and ECD values that fall between the upper and lower values and provide a better fit to the hy- draulic data than power law and Bingham plastic fluids. Furthermore, analy- sis of annular eccentricity reveals that APLs and ECD decrease with an in- crease in DS eccentricity. Pressure loss reduction of more than 50% was pre- dicted for the fully eccentric case for Herschel Bulkley fluids. Thus, DS eccen- tricity must be fully considered during well planning and hydraulics designs. Keywords Wellbore, Drilling Fluid, String Geometries, Pressure Losses, Newtonian Fluid Models How to cite this paper: Kerunwa, A., Obibuike, J.U., Duru, U.I. and Ekwueme, S.T. (2021) The Effects of Fluid Rheology and Drillstring Eccentricity on Drilling Hydraulics. Open Journal of Yangtze Gas and Oil, 6, 129-145. https://doi.org/10.4236/ojogas.2021.64012 Received: May 2, 2021 Accepted: October 16, 2021 Published: October 19, 2021 Copyright © 2021 by author(s) and Scientific Research Publishing Inc. This work is licensed under the Creative Commons Attribution International License (CC BY 4.0). http://creativecommons.org/licenses/by/4.0/ Open Access