Petroleum and Coal Pet Coal (2019); 61(1): 212-221 ISSN 1337-7027 an open access journal Article Open Access PIPE INCLINATION EFFECTS ON HI GH VISCOSITY OIL-GAS TWO PHASE FLOW CHARACTERISTICS Yahaya D. Baba 1,4 Archibong-Eso Archibong 2,4 , Aliyu M. Aliyu 2,4 , Okereke U. Ndubuisi 1,4 , Akinola S. Oluwole 5 , Wasiu A. Ayoola 6 1 Department of Chemical and Petroleum Engineering, Afe Babalola University, Ekiti State, Nigeria 2 Department of Mechanical Engineering, Cross River University of Technology, Calabar, Nigeria 3 Gas Turbine and Transmission Research Centre, Faculty of Engineering, University of Nottingham, UK 4 Oil and Gas Engineering Centre, Cranfield University, United Kingdom 5 Department of Electrical Electronics and Computer Engineering, Afe Babalola University, Ekiti State, Nigeria 6 Department of Metallurgical & Materials Engineering, Afe Babalola University, Ekiti State, Nigeria Received October 9, 2018; Accepted December 21, 2018 Abstract There is a growing interest in the exploration of high viscous unconventional reserves attributable to its huge reserves amidst an increasing decline in low viscous conventional reserves. In this paper, the effects of upward pipe inclination and liquid viscosity on two phase flow characteristics have been carried out experimentally in a 0.0256m ID pipe inclined at an angle of 15°. Air and mineral oil were used as test fluid with oil viscosities ranging from 0.7-5.0 Pa.s. The superficial velocities of gas and liquid velocities were varied respectively from 0.3 to 10 m/s and 0.06 to 0.3 m/s. Electrical tomographic capacitance sensor readings and visual observations revealed four flow patterns. Two phase characteristics measured include pressure gradient, liquid holdup, and slug flow features, i.e. slug frequency and slug liquid holdup. Analysis of the pressure gradient exhibited a gradual increase with increasing superficial gas velocity at a constant superficial liquid velocity which steeped when the superficial liquid velocity was increased. A similar trend was observed for pressure gradient as the angle of inclination is increased. Keywords: Pressure gradient; liquid holdup; Flow pattern; Liquid viscosity; and ECT. 1. Introduction In the petrochemical, geothermal and nuclear industries, gas-liquid two phase flow in pipes is the most occurring phenomenon. A lot of studies have been carried in the literature on low viscosity two phase flows. However, with the diminishing reserves of “conventional” light crude oil, increased production costs amidst increased world energy demand over the last decade, industrial interest has shifted to the production of the significantly and more abundant “un- conventional” heavy crude oil attributable its increasing importance as a veritable energy source. In addition to the fact that it accounts for over two-thirds of the world total oil reserve. The existing technologies for the extraction, processing, and transportation adopted for heavy oil is costly due to their natural composition (i.e., viscosity) thereby making their pro- duction expensive, difficult to transport and refine. This whole process is quite expensive when c ompared to c onventional c rude oil. However, with improvement in technology, this onc e costly energy source is quickly becoming a more viable alternative. Hence, there is the need to carry out a further investigation so as to enhance its further production at reduced cost. The explo- ration of this vast resource for easy production and transportation requires a good under- standing of multiphase flow system for which the knowledge of the effect of fluid viscosity is of great importance. Two phase flow are expected to exhibit a significant behaviour in high 212