Performance of non-Newtonian fluid in vertical annuli with and without rotation of inner cylinder Lina Jassim 1,* , Basima S. Khalaf 2 , Abeer Hashim 3 {dr.linajassim@uomustansiriyah 1 .edu.iq, dr.basima@uomustansiriyah.edu.iq 2 , abeerhashim@uomustansiriyah.edu.iq 3 } Mechanical Department- Engineering college-Mustansiriyah University -Iraq 1,2,3 Abstract. A simulation model of non-Newtonian fluid in vertical, concentric annular flow is used in this work. A prototype of a drilling device is manufactured to compare with the simulation results. Water-based mud rheology is described here with the Bingham plastic model. The simulation results reveal that Bingham plastic fluid has a good attitude during drill pipe rotation in terms of axial velocity, tangential velocity, and molecular viscosity. This influence of rotation on the axial velocity is mirrored in the behavior of the shear stresses inside annular space and hence on the friction factor. However, the rest situation of the drill pipe results in high fluid viscosity. Furthermore, it is found that 0.2 of eccentricity leads to increase the pressure drop inside annuli. Bingham plastic fluid has a great dependence on temperature, and the temperature decreases from top to bottom. This behavior occurs since Bingham fluid flows from up to down during drilling. Keywords: RANs; Annular flow; Inner wall rotation; Wall shear stress; Axial velocity; drilling. 1 Introduction In drilling operation of oil and gas wellbores, non-Newtonian fluid is pumped through the drill string out from drill bit nozzles through annular space between the drill string and casing walls. At the surface, non-Newtonian fluid is separated from the rocks and recirculated. This fluid has certain functions; the most effective duties are cleaning the well and managing the wellbore pressure while drilling operation. To drill at a certain depth, the non-Newtonian fluid must supply the required hydrostatic pressure to prevent formation damage and maintain the wellbore stability. Active interest in the wellbore drilling circumstances has been studied in a large number of works. These circumstances include the drill pipe situations of vertical, horizontal as well as directional position. Moreover, drilling fluid composition plays a vital role in carrying the rock cuttings and clean the hole. Numerous studies have attempted to explain carrying cuttings in horizontal and deviated wellbores experimentally [1,2] and numerically [3-6]. The topic of drilling fluid composition is one of the most crucial areas in drilling technology research today. Werner and his group [7] mentioned the significant relationship between viscoelastic properties of oil-based and water-based drilling fluids with hole cleaning ability. In another study, Gulraiz and Gray, (2020) [8] performed a numerical analysis of plug viscosity effect on pressure drop profile and carrying cuttings. Adding nanoparticles to the drilling fluid has been used to enhance fluids’ ability to clean the hole efficiently [9], and [10]. Drilling fluid is non-Newtonian fluid, which can be aqueous-based fluid or non-aqueous based fluid depending on the continuous phase while the rest are chemical additives. Escudier and research team [11] did an experimental and numerical study of aqueous fluids inside concentric and 80% eccentric annular space with and without inner cylinder rotation. Aqueous based fluids can behave as a Herschel-Bulkley model or Bingham plastic model depending on its consistency. In 2005, Ahmed reported the polymer-based fluid behaved as Hershel-Bulkley model inside concentric and eccentric annular space with center body rotation, and Skjold [12] agreed with Ahmed that pressure drop augmented with rotational speed according to the shear thinning phenomenon. The knowledge of pressure drop inside annuli is significant to drill and circulate fluid efficiently. As a result, a considerable amount of literature has been focused on pressure drop as well as temperature distribution during not only drilling operation but also casing and production operation through annular space. Pressure losses were investigated by Kelessidis et al., [13] and Okon and Udoh [14]. Wang and his team [15] did the most relevant study, their study concentrated on the wellbore temperature and pressure distribution during supercritical CO2 fracturing flow back process. They found that wellbore pressure and temperature were gradually decreasing from the bottom to the top during the CO2 flow back process. The wellbore temperature is the most effective factor that has precise control of managing wellbore pressure during the controlled gradient drilling. Yang [16] predicted the wellbore IMDC-SDSP 2020, June 28-30, Cyberspace Copyright © 2020 EAI DOI 10.4108/eai.28-6-2020.2297928