Hole Cleaning and ECD Management for Drilling Ultra-Long-Reach Laterals

Abstract

Abstract Insufficient hole cleaning in an ultra-long-reach lateral can increase the friction on the drillstring, which can lead to high torque and insufficient weight on bit (WOB). Cuttings affect the equivalent circulating density (ECD) in two ways: by increasing the average density of the drilling fluid and by reducing the open area left for fluid flow, as the cuttings tend to pack in the well and form cuttings beds. This paper presents the key findings regarding cuttings-bed development and ECD management for drilling an ultra-long-reach lateral. Most of the previous cuttings-transport studies only focus on the cuttings-bed prediction in steady-state conditions. Few studies discuss the relationship between the cuttings bed and torque and drag and the effect of cuttings on the ECD. Furthermore, the flow in the wellbore is unsteady because of the frequent change of drilling parameters and wiper trips. In this study, a transient hole-cleaning simulator is used to simulate the cuttings-transport process in the wellbore. This simulator is also able to accurately calculate the ECD by considering the effects of both suspended cuttings and packed cuttings beds, or dunes. The transient simulator is verified by conducting a series of tests using a 90-ft long, 8×4.5-in. drilling-simulation flow loop. Several commonly used rules of thumb for hole-cleaning practice in deviated wells are examined by running the simulator on a practical well. This paper presents new criteria for hole cleaning in deviated wells with ultra-long-reach laterals by considering the amount of cuttings in the wellbore and the requirements for ECD control. Recommendations for a set of hole-cleaning practices for drilling deviated wells with ultra-long-reach laterals will also be presented. In addition to guiding drilling operations, the results of this work can be used to determine the maximum length for a horizontal lateral from an ECD management perspective. They can also be used to improve the torque-and-drag model for drillstring design in horizontal wells.