Numerical Investigation on Energy Loss Characteristics in Irregular Annulus Based on Entropy Production Method

Abstract

Abstract The actual downhole annulus is irregular, a variable cross-section geometry, due to the difference between the diameter of tool joints or downhole tools and the inner pipes. With the increasing of well depth, inevitable energy loss caused by contraction or expansion geometry is high in irregular annular flow. However, the energy loss generation mechanism for such irregular annulus flow is still unclear. The entropy production theory is considered as an excellent method for energy loss analysis, which is widely used in fluid machinery flow field. Therefore, the main purpose in this work is to reveal the energy loss generation mechanism caused by contraction and expansion geometry in irregular annulus based on entropy production method. In this paper, the spatial distribution of entropy production rate in irregular annular flow was depicted first. Then the inlet velocity and contraction-expansion ratio influence on different entropy production were discussed. Finally, we identified the high entropy production area and its main energy loss sources by quantitative analysis. The results show that 1) The high entropy production was mainly occurred at the entrance, downstream of the variable cross-section structure and near the wall. The proportion of time-average entropy production rate was relatively small and can be ignored. 2) The main energy loss areas were in narrow annulus and downstream of the variable cross-section structure, which the entropy production portion was about 55.8%~62.0% and 23.4%~26.4% separately. The main energy loss were wall and turbulent entropy production in these two areas. 3) The energy loss generated in downstream of the variable cross-section in annulus was more than that in upstream.