Horizontal wells are more likely than vertical wells to have enlarged wellbore sections due to borehole instability. However, there is scarce research on borehole cleaning of horizontal wells with enlarged wellbore sections. In this paper, we establish a horizontal wellbore model with a breakout enlargement section using field borehole diameter data. We used the three-dimensional computational fluid dynamics (CFD) method and the Realizable k-ε turbulence model with the Euler–Euler approach to simulate the effects of the drilling fluid circulation return speed and the spinning speed of the drill pipe on the cutting movement of conventional horizontal wells and horizontal wells with a breakout enlargement section. The simulation results demonstrate that increasing the drilling fluid circulation return speed and the spinning speed of the drill pipe does not significantly improve the hole cleaning impact for horizontal wells with a breakout enlargement section. We analyzed the effects of the enlargement ratio, ellipticity, and principal axis orientation on the borehole cleaning effect of horizontal wells with a breakout enlargement section. The results show that the cleaning impact is better when the enlargement ratio is lower; moreover, the ellipticity is larger and the principal axis orientation is perpendicular to the gravity direction. This paper fills a gap in the existing theory of hole cleaning in horizontal wells and provides a theoretical basis for improving the hole cleaning effect in actual drilling processes.

Submersible electric pump units are connected by bolts. This paper uses finite element analysis method to simulate how the pump joint bolt behave when it transmit torque.In this paper, temperature method is adopted to simulate the bolt preload and axial deformation.It also used to analyse and calculate the limited value when submersible electric pump units transmit torque under different preload. All of this provide the designing of connecting bolt preload and construction with theoretical basis.

Built up three-dimensional non-linear contact finite element analysis model of the spline shaft and the spline set of the electric pump machine and get the stress distribution of the spline shaft and the spline set when the shaft of electric pump retorts. The maximum stress occurs in the root of linking side of spline and the transition section. According to the calculation and contrast analysis of different material and same material of spline set, the maximum stress of the different material declines by 20.04% than the same material, and the root stress concentration coefficient declines by 13.72%, and this provides theoretical basis and analysis method.