L. Abdulkareem

Investigating the Effect of Pipe Inclination on Two-Phase Gas-Liquid Flows Using Advanced Instrumentation

Pipes that make up oil and gas wells are not vertical but could be inclined at any angle between the vertical and the horizontal which is a significant technology of modern drilling. Hence, this study has been undertaken to look at the effect of inclination on flow characteristics especially at 10 degrees from both horizontal and vertical. Air/silicone oil flows in a 67 mm slightly deviated pipe have been investigated using advanced instrumentation: Wire Mesh Sensor Tomography (WMS) and Electrical Capacitance Tomography (ECT). They provide time and cross-sectionally resolved data on void fraction. Both the ECT probes and WMS were mounted on the inclined pipes upstream just at the point where flows were fully developed. By keeping the liquid flow rate constant at 10 litres/min (or liquid superficial velocity of 0.052m/s), gas flow rate was varied from 10 litres/min to 1000 litres/min (or gas superficial velocity from 0.05m/s to 4.7m/s). Then other values of liquid superficial velocity were considered. Visual observations were considered. Time series and void fraction were then measured for WMS while time series and liquid holdup were measured for ECT. The raw data were processed and then interpreted for proper analysis. From an analysis of the output from the tomography equipment, flow patterns were identified using both the reconstructed images as well as the characteristic signatures of Probability Density Function (PDF) plots of the time series of cross-sectionally averaged void fraction as suggested by some authors. Bubbly, slug and churn flows were observed for 10° from vertical pipe while bubbly, plug as well as slug flow when the pipe was inclined at 10° from horizontal. Examples of the PDFs are well illustrated which compares the use of ECT with WMS. In addition, statistical data such as Power Spectral Density (PSD), dominant frequency, mean void fraction as well as the structure velocities from cross correlation of the two planes of ECT have been identified.Copyright

Characteristics of Air-Oil Slug Flow in Inclined Pipe Using Tomographic Techniques

The structure of gas liquid flow in horizontal and vertical pipes to some extent is well understood. However, the situation in inclined pipes is much more difficult with very little work published in literature. Changes in physical phenomena occur as the pipe inclination angle varies from the vertical through to inclined and then to horizontal. This work describes a study carried out at the University Of Nottingham on the effects of inclination on gas / liquid slug flow. Two advanced tomography techniques were applied simultaneously to the flow of a mixture of air and silicone oil in a 67 mm internal diameter pipe and the pipe was inclined at angles 0, 5, 10, 30, 45, 60, 80, 90 degrees. This paper reports on the use of twin plane electrical capacitance tomography (ECT) system developed by TomoFlow electronics Ltd to measure flow characteristics in gas-liquid flows. We report measurements over a range of liquid superficial velocities from 0.05 m/s to 0.5 m/s and gas superficial velocities from 0.06 m/s to 6 m/s at all the above angles in a pipe 6 m long. A second technique, Capacitance Wire Mesh Sensor (WMS) developed at Forschungszentrum Rossendorf-Dresden/Germany was also present in the tests, The results for the two sensors are shown to be within 1% of each other in some instances when comparing cross-sectional averaged void fraction. The data was recorded at an acquisition frequency of 1000 Hz over an interval of 60 seconds. This enabled an examination of the flow to be carried out at several levels of complexity. Both measuring sensors provide time and cross-sectionally resolved information about the spatial distribution of the phases. In present paper, the effect of inclination on the characteristics of slug flow is presented. Radial gas volume fraction profiles and bubble size distributions were also processed from the wire-mesh sensor output. The results indicate that the pipe inclination has a significant effect on the slug flow characteristics.Copyright

Effect of Inclination on Slug Flow Characteristics

Modern oil/gas well drilling methods in particular in the offshore industry involve deviated drilling in which the production tubing can be inclined at any angle between the vertical and the horizontal. Riser tubes from the seabed to the surface or to floating production vessels (FPSO) will also rarely be exactly vertical. This work describes a study carried out at the University Of Nottingham on the effects of inclination on gas / liquid slug flow. Two advanced tomography techniques were applied simultaneously to the flow of a mixture of air and silicone oil in a 67 mm internal diameter pipe and the pipe was inclined at various angles. A twin plane Electrical Capacitance Tomography (ECT) electrode system driven by Tomoflow electronics was positioned below a Capacitance Wire Mesh Sensor (WMS) developed at Forschungszentrum Rossendorf-Dresden/Germany M. J. Da Silva et al [2]. This enabled an examination of the flow to be carried out at several levels of complexity. Both measuring sensors provide time and cross-sectionally resolved information about the spatial distribution of the phases. Conditions studied were superficial velocities for air ranged from 0.05 to 5.5 m/s and for silicone oil ranged from 0.0 m/s to 0.5 m/s. In present paper, the effect of inclination on the phase distribution in two phase gas liquid slug flow is presented. The liquid hold up within the slug region and in the elongated bubble zone and the averaged liquid hold up were calculated from the output data of the two measurements techniques. Radial gas volume fraction profiles and bubble size distributions were also processed from the wire-mesh sensor data. The shapes of the large bubbles and waves were compared for different inclination angles. The results indicate that the pipe inclination has a significant effect on the slug flow characteristics. Both Taylor bubble and small bubbles in the slug region tend to flow along the upper pipe wall and causing significant variation of Taylor bubble rise velocity with inclination angle.Copyright

Interrogation of Gas/Oil Flow in a Vertical Using Two Tomographic Techniques

Two tomographic techniques have been applied to the flow in a 67 mm internal diameter vertical pipe. One is Electrical Capacitance Tomography (ECT) mounted on the outside of the non-conducting pipe wall. Another technique, known as the Wire Mesh Sensor (WMS) was used. The measuring systems provide time and cross-sectionally resolved information about the spatial distribution of the phases. The information can be used to obtain space and time averaged void fractions, radial profiles of time averaged void fraction and cross-sectional averaged time series of void fraction. Simultaneous measurements were made with the two techniques for gas superficial velocities of 0.05–5.5 m/s and liquid superficial velocities of 0–0.7 m/s with air and silicone oil as the fluids. Bubble, slug and churn flows were identified from the characteristic signatures of the Probability Density Functions of the cross-sectionally averaged void fraction. In addition, the detailed shape of individual large bubbles has been extracted. The output of both instruments shows clearly that the shapes of the large bubbles in slug flow are distinctly different from the smooth bullet-shaped. In this larger diameter pipe, the interface is much more disturbed. In addition, flow can be classified according to the sizes of bubbles present. Distributions of bubble sizes are presented and the fractions of gas flowing in different bubble sizes classes quantified.Copyright