Transient cutting transport model for horizontal wells with a slim hole

Compared with conventional drilling methods, the method of drilling horizontal wells with a slim hole (HW-SH) has advantages, such as high productivity, environment-friendliness, and low costs. However, during the drilling process, the narrow annulus may become blocked, which may lead to an increase in the annulus pressure if the wellbore is not clean. This often leads to serious drilling accidents, such as sticking and leaking formations. Many models have been used to study the cutting transport law in an annulus, but the influence of drill-pipe rotation on cutting transport is often ignored and weakened in these models. None of the existing models can effectively simulate the cutting transport law of an entire well section. Therefore, using these models to predict the cutting transport law in the annulus of the HW-SH will cause significant errors. In this study, the authors first establish a pipeline model of the same size as the on-site annulus using computational fluid dynamics (CFD). Subsequently, a one-dimensional (1D) two-layer model that uses three correction factors to express the influence of drill-pipe rotation on cutting transport and annulus pressure loss is developed. Finally, the parameters in the 1D model are calibrated using the CFD simulation results to accurately predict the cutting transport behavior and annular pressure loss. From the calculation results of the annulus cutting quality, annulus section-cutting concentration, and annulus pressure drop, it was observed that the two algorithms proposed in this study have a high degree of coincidence, thereby confirming the reliability of the model. The 1D model provides close to three-dimensional (3D) accuracy at a much shorter central processing unit time than the 3D CFD models. In addition, the accuracy of the developed model was verified using the results of an indoor pipeline two-phase flow experiment conducted at the University of Tulsa, without considering the rotation of the drill pipe.

Automated summary

Compared with conventional drilling methods, the method of drilling horizontal wells with a slim hole (HW-SH) has advantages such as high productivity, environment-friendliness, and low costs. However, the existing models cannot accurately predict the cutting transport law in the annulus of the HW-SH. In this study, a computational fluid dynamics (CFD) pipeline model is established, and a one-dimensional (1D) two-layer model is developed to accurately predict cutting transport and annular pressure loss.