Visualized Experiment on Critical Cutting Transport Behavior of Annular in Horizontal Well Section

The yield of single well is high, and horizontal well technology applications continue to expand. However, the understanding of the mechanism of the complex liquid–solid two-phase flow and cuttings’ migration in the annulus is still unclear, and the mathematical description is still not perfect. Therefore, the research established a mathematical model for the start of cuttings in the annular of the horizontal section on the basis of the force analysis. In this paper, different particle sizes of simulated particles are used as experimental media, and visualization experiments of cuttings’ migration in horizontal wells are carried out. As a result, research and verification of the starting law of the cuttings under different particle sizes and different degrees of drill pipe eccentricity under the two working conditions of sliding drilling and compound drilling, and revised the mathematical model of cuttings’ starting. Results show that the jump-start of cuttings is mainly rolling and saltation in the annular of the horizontal section, and the smaller the particle size and the lower the eccentricity, the smaller capability of critical lifting cuttings is required. Furthermore, the experimental values of the critical return velocity of drilling fluid under the two working conditions of sliding drilling and compound drilling are lower than the theoretical model calculation results, and the relative errors are 10.4 and 13.1%, respectively. Consequently, the revised calculation model can meet the requirement of horizontal well construction accuracy. The results of the study can effectively guide the development of horizontal wellbore purification schemes and the optimization of horizontal well hydraulic parameters, which is of positive significance to ensure safe drilling in horizontal wells and effectively extend the length of horizontal wells.