Research on the Cuttings Transport in Large-Sized Hole Based on CFD-DEM Method

ABSTRACT: During drilling large-sized hole, due to the low return velocity of the drilling fluid and weak cuttings transport effect, it is difficult to clean the borehole, resulting in serious backpressure even pipe sticking, high equivalent circulating density (ECD), low rate of penetration (ROP), etc., which will bring significant time costs and economic losses. In this paper, a CFD-DEM coupling model is built to accurately simulate the dynamic transport process of cuttings. For the liquid phase, the Euler method is used to describe its motion characteristics through the flow field. For the solid phase, the Lagrange method is used to solve the variation of physical quantities of cuttings over time. And the coupling of fluid and solid phase is achieved through mutual forces. The reliability of this CFD-DEM coupling model is validated through experiments. Based on a large number of numerical simulations and the nonlinear regression method, a data-driven mathematical model for predicting the cuttings bed height is developed, which is useful in hole-cleaning design and drilling parameters optimization. The Pearson correlation coefficient R2 is 0.893451, indicating high accuracy of this mathematical model. 1. INTRODUCTION Hole cleaning is one of the major challenges during drilling large-sized hole section, especially in the horizontal sections. Under the effect of gravity, cuttings will accumulate at the bottom of the annulus and be transported upwards in the form of cuttings bed. However, if the cuttings bed is too high, the cuttings in the lower part of the cuttings bed will be stuck and unable to move, resulting in the stationary bed that is difficult to remove and poor hole cleaning. This may cause downhole complications and accidents, such as serious backpressure even pipe sticking, high ECD, low ROP, etc., which bring significant time costs and economic losses. Therefore, conducting research on cutting transport is of great significance for on-site operations. In the past, many researchers have conducted a large number of studies on cuttings transport, including experiments, numerical simulation and theoretical modeling. Experimental studies on cuttings transport began in the 1940s (Zhu 2022), analyzing the influence laws of various parameters through measured results and observation of phenomena. Sorgun (2013) summarized an empirical formula for the height of cuttings bed under water and four non-Newtonian fluids. Kim et al. (2014) studied the transport characteristics of cuttings in inclined annulus with the inclination of 30-75°. Song et al. (2017) proposed a mathematical model for cuttings concentration in a Microhole-Horizontal-Well based on 136 sets of experiments. Through massive experiments, Huque et al. (2022) believed that fluid velocity and cuttings size were the two most key parameters for cuttings transport efficiency in an inclined well.