A novel transient hole cleaning algorithm for horizontal wells based on drift-flux model

With the continuous expansion of unconventional and offshore oil and gas fields, horizontal wells have become adopted as an economical and effective mining method. However, the inclined and horizontal sections make them prone to cuttings deposition in the wellbore, leading to the formation of a cuttings bed that adversely affects drilling operations. In this paper, we focus on the features of cuttings transport in the wellbore during drilling and propose a solid-liquid two-phase transient flow model by integrating the flow pattern and drift flux model. The model is discretized using a format based on the finite volume method and solved using a preprocessing method. It enables us to predict the flow parameters, cuttings bed distribution, and cuttings removal time in the wellbore of horizontal wells. To validate the model's effectiveness, we verify it using laboratory experimental data, which demonstrates its prediction accuracy. Furthermore, we use the established model to simulate the damage effect of the cuttings bed on the hole cleaning device during drilling. By comparing the complete return time of cuttings under different working conditions, we quantitatively analyze the hole cleaning device's effect and the backreaming operation's cleaning efficiency. The results indicate that the use of hole cleaning devices during drilling, backreaming, well washing, and other operations in the hole cleaning process can effectively suspend the cuttings deposited in the annulus, allowing them to return to the wellhead more quickly, which enhances the cleaning efficiency of the wellbore and reduces the overall construction time. Furthermore, by comparing and analyzing the effect of drilling flow rate, well cleaning flow rate, cutting particle size, temperature gradient and rate of penetration (ROP) on cuttings return efficiency, it was observed that the drilling flow rate and ROP have minimal impact on the time required for complete cuttings removal during drilling. However, cutting particle size has a significant impact on the effective distance of the hole cleaning tool. Meanwhile, the temperature gradient and the flow rate during the well cleaning has a decisive influence on the time needed for complete cuttings removal.