title: Systematic investigation of cuttings transport behavior in horizontal and inclined drilling operation
Creators: name: Huque, Mohammad Mojammel
Publisher: name: Memorial University of Newfoundland
Year: 2022

description: Hole cleaning and cuttings transport play a vital role in the drilling operation. Various drilling problems such as a reduction in penetration rate, an increase in the torque and drag, and an increase in the potential of differential sticking are often related to poor cuttings transport from a wellbore. A variety of parameters, including the fluid rheology, mud velocity, cuttings size, and drill pipe inclination generally influence the cuttings transport performance. Although several experimental and modelling research investigations have been conducted in this area, there are controversial findings about the effect of different parameters on cuttings transport. For instance, the interactions among the parameters during cuttings transport which have not been adequately investigated. In this thesis, we systematically study the effect of drilling parameters on cuttings transport, especially interaction effects of the drilling parameters through experiments and Computational Fluid Dynamics (CFD) method. An extensive experimental study was conducted to investigate the flow behavior of solid cuttings based on Newtonian and non-Newtonian Herschel Bulkley fluid models. Experiments were performed to simulate solid transport behavior in horizontal and near horizontal well trajectories. A high-speed imaging technology was used to visualize the cuttings transport behavior in the annulus section. This visualization tool validates the mechanistic three-layer model of cuttings transport and transition from a stagnant solid bed to a homogeneous single layer model of cuttings transport mechanism. An Electrical Resistance Tomography (ERT) system was used to observe the cutting transport which is capable of providing instantaneous cuttings volume fraction in the annular section of the experimental system. ERT data shows cuttings concentration versus with change in fluid rheology, fluid velocity, eccentricity, drill pipe rotation, rate of penetration, and inclination angle. Experimental studies in the horizontal wells show that cuttings transport capability of non-Newtonian fluid increases upon an increase in fluid velocity, and drill pipe rotation. A higher viscous fluid carries more cuttings in the dispersed phase; however, transport capability reduces significantly through suspension mechanism with increasing fluid velocity and drill pipe rotation. A comparison of four different non-Newtonian fluid cases shows that turbulence plays a key role in cuttings transport in the horizontal well regardless of fluid rheology. This experimental study reveals that a higher ‘Minimum Transport Velocity (MTV)’ is required to move a solid dune in the annulus for a highly viscous fluid. CFD modeling approach is employed to simulate the cuttings transport behaviors in the horizontal and inclined wellbore cases. Cuttings transport in the wellbore annulus represents a solid-liquid multiphase flow phenomenon. The Eulerian-Eulerian multiphase flow model is adopted to describe the flow characteristics in the wellbore annular section. A proper Design of Experiments (DOE) is used to systematically study the interactions among the independent variables. A comprehensive parametric sensitivity analysis is then conducted to obtain a better understanding of the relationship between the input variables and the target parameters (cutting transport performance). It is found that the mud viscosity, mud velocity, and drill pipe rotation have a positive impact on cuttings transport, whereas the cuttings size and annular clearance show a significant adverse effect on cuttings transport performance in the horizontal wells. Although both drilling mud viscosity and velocity exhibit the positive effect, the interaction among them shows a negative influence on cuttings transport. Analysis shows that the cuttings with a size of 1 to 2 mm are difficult to be cleaned, compared to larger cuttings. According to the CFD investigation, the critical inclination angle prone to hole clogging is a function of a wide range of flow rates and fluid rheologies. Also, this study investigated two factor interaction of fluid rheology and velocity for the inclined wellbore orientation. Finally, a generalized expression of cutting transport efficiency is proposed for the inclined well considering two factor and three factor interactions.