Study on the prediction model of the open-hole extended-reach limit in horizontal drilling considering the effects of cuttings

Abstract

An open-hole extended-reach limit model was established and published by the authors to determine how far a horizontal extended-reach well (ERW) can extend. The published model shows that the open-hole extended-reach limit (the maximum measured depth of the horizontal ERW) is mainly dependent on the annular pressure drop and the fracture pressure of drilled formation. Moreover, some optimal control methods, such as lowering drilling fluid density, reducing drilling fluid flow rate and optimizing drill pipe eccentricity, were also presented to obtain greater open-hole extended-reach limit. However, the published model was established based on the assumption that the annular fluid is ideal single-phase flow. Failing to consider the effects of cuttings may lead to an inaccurate prediction of the open-hole extended-reach limit and even drilling safety hazards. In this paper, in order to overcome the shortcomings of the published model, a prediction model of the open-hole extended-reach limit in horizontal drilling considering the effects of cuttings is established and analyzed. The study shows that due to an increase of annular pressure drop, the horizontal-section limit (the maximum measured depth of horizontal-section for the horizontal ERW) is relatively smaller when considering the effects of cuttings. Meanwhile, a case study is carried out, and the results show that the horizontal-section limit is 1610 m when the cuttings are considered. In contrast, when the cuttings are ignored, the limit is 1941 m based on the published model. Furthermore, since several main parameters of the established model may greatly affect the annular pressure drop and the horizontal-section limit, parameters sensitivity analysis are also performed and some conclusions are drawn. First, the horizontal-section limit first increases and subsequently decreases with the increase in drilling fluid density. Second, there is an increase in horizontal-section limit when the drilling fluid flow rate increases. Third, the horizontal-section limit gradually increases with the increase in the drill string rotation speed. Finally, there is also a decrease in the horizontal-section limit when the rate of penetration (ROP) and the consistency coefficient increase. In sum, the simulated condition in this paper is more consistent with the situation of field drilling practice than that of the published model. This study will also provide a more accurate result of the open-hole extended-reach limit, which is of great significance to the drilling design and drilling safety.