The paper may be of particular
interest to the readers as it presented a unsteady flow phenomenon of annular
flow recognition which would occur during underbalanced drilling. This paper presents a feasibility study on calculation of gas volume fraction and visualisation of flow regimes in gas-liquid upwards annular flow using ERT.
Experiments were conducted at three flow regimes, namely bubble, transition
pseudo-static and slug. Gas volume fraction profiles were reconstructed with
the modified sensitivity coefficient back projection method (MSBP) with a
sensitivity map generated from an annular finite element mesh respectively.
Flow regimes were visualised by axial images stacked from diameter-pixels of 2D
tomograms reconstructed with the conjugate gradient method (SCG). Although tomographic images cannot be as clear as the photographs captured during theme asurements, ERT is still able to provide enough information regarding the
prevailing flow regime within the annulus. The air volume fraction profiles in
the annulus region, produced from the ERT, indicate a good agreement between
the profiles and visual observation (photographs). The stacked images are
reasonably accurate representation of air water in the annulus region for the
conditions used in this study.