Murat Ozbayoglu

Estimating Flow Patterns and Frictional Pressure Losses of Two-Phase Fluids in Horizontal Wellbores Using Artificial Neural Networks

Abstract Underbalanced drilling achieved by gasified fluids is a very commonly used technique in many petroleum-engineering applications. This study estimates the flow patterns and frictional pressure losses of two-phase fluids flowing through horizontal annular geometries using artificial neural networks rather than using conventional mechanistic models. Experimental data is collected from experiments conducted at METU-PETE Flow Loop as well as data from literature in order to train the artificial neural networks. Flow is characterized using superficial Reynolds numbers for both liquid and gas phase for simplicity. The results showed that artificial neural networks could estimate flow patterns with an accuracy of ±5%, and frictional pressure losses with an error less than ±30%. It is also observed that proper selection of artificial neural networks is important for accurate estimations.

A parametric study on coal gasification for the production of syngas

In this parametric study, the effects of coal and oxidiser type, air-to-fuel ratio, steam-to-fuel ratio, reactor temperature, and pressure on H2 and CO amounts at the gasifier output, H2/CO, and higher heating value of the syngas produced have been calculated using a coal gasification model. Model simulations have been performed to identify the optimum values which are assumed to be 100 % for both cold gas efficiency and carbon conversion efficiency in the gasification process. From this study, it may be observed that the moisture content of the coal type is of crucial importance for the air gasification process; the O2 content of similar coals (taking into consideration the moisture and H2 content) is of significant importance for the air gasification process. When compared with air gasification, air-steam gasification becomes a more effective coal gasification method. The optimum working condition for air-steam gasification is to carry out the process at one atmosphere. High gasifier temperatures are not needed for the air-steam gasification of coal.

A New Model to Determine the Two-phase Drilling Fluid Behavior Through Horizontal Eccentric Annular Geometry, Part A: Flow Pattern Identification and Liquid Hold-up Estimation

Flow patterns, liquid holdup, and frictional pressure gradient are three importance parameters to study the multiphase drilling fluid behavior. Although two-phase fluid flow is studied in detail for pipes, there exists a lack of information about aerated fluid flow behavior inside a wellbore. This study aims to identify the flow patterns of gasified fluids flowing inside a horizontal annulus, and to develop a method for measurement of liquid holdup by using the image processing techniques. Experiments have been conducted at Middle East Technical University (METU) Multiphase Flow Loop using air-water mixtures with various in-situ flow velocities. A digital high-speed camera is used for recording each test dynamically for the identification of flow patterns and the measurement of liquid holdup.

A New Model to Determine the Two-phase Drilling Fluid Behaviors through Horizontal Eccentric Annular Geometry, Part B: Frictional Pressure Losses Estimation

Drilling with aerated muds is becoming more often used in underbalanced drilling operations. One of the major challenges that has to be faced in such operations is the estimation of the physical behavior of aerated fluids inside the annulus. In this study, experiments have been conducted at METU Multiphase Flow Loop using air-water mixtures with various in-situ flow velocities of 0–120 and 0–10 ft/s, respectively. This study aims to develop a model to estimate the frictional pressure losses for two-phase flow through horizontal eccentric annular geometry. In order to estimate the frictional pressure losses, three different methods were developed: (i) definition of new friction factors by using experimental data; (ii) modification of Lockhart-Martinelli pressure loss correction factor; and (iii) modification of Beggs and Brill model by changing the equation constants. The comparison of the developed models with experimental data has shown that frictional pressure losses can be estimated with a reasonable accuracy.

The Determination of Two Phase Liquid-Gas Flow Behavior Through Horizontal Eccentric Annular Geometry by Modification of Beggs & Brill and Lockhart & Martinelli Models

Gas-liquid flow in annular geometries is the one of the most frequently encountered flow conditions in petroleum industry, either during drilling operations if aerated fluids are used, or production stages, if the produced fluid is under bubble point pressure. With the increase in the interest in horizontal / extended reach wells, understanding the flow behavior of gas-liquid mixtures in horizontal wells is essential for better pressure control downhole. Although two-phase fluid flow is studied intensively for circular pipes, there exists a lack of information about aerated fluid flow behavior inside annular geometries, both theoretically and experimentally. Existing two-phase fluid flow models available in the literature developed for circular pipes are performing poorly for annular geometries. Using hydraulic diameter definitions or effective diameter terms simply give inaccurate results for both flow pattern estimations and friction pressure loss determination. This study aims to identify the flow patterns of gasified fluids, and to determine frictional pressure losses for two phase flow through horizontal eccentric annular geometry. In order to develop the liquid holdup, Digital Image Processing Techniques have been used. Friction pressure losses are determined by applying two different methods; i) Modifying Lockhart-Martinelli parameter, and ii) Modifying Beggs and Brill’s method, originally developed for circular pipes. Experiments have been conducted at Middle East Technical University (METU) Multiphase Flow Loop using air-water mixtures with various in-situ flow velocities. A digital camera is used for recording each test dynamically for the identification of flow patterns and the measurement of liquid holdup. Friction pressure losses are recorded during each test. The comparison of modified models with experimental data indicates that liquid holdup and friction pressure losses can be estimated with a reasonable accuracy. The information obtained from this study is critical, since very limited information is available in the literature for modeling two-phase flow behavior.Copyright