Using Transient Modeling to Define the Effects of Heave on Wellsite Operations

Abstract

Summary The drilling industry is striving to be more efficient, reducing time, costs, and emissions to provide energy solutions for a more climate-conscious world. Reducing nonproductive time (NPT) and invisible lost time (ILT) by utilizing modeling software to optimize tripping operations is one method to combat this. Additional factors such as sea heave have a significant impact on tripping operations on semisubmersible drilling vessels, which do not show a linear response to increased heave. These vessels have compensation systems, but they are often not in use or not completely accurate. Typical heave experienced in the North Sea is between 0.5 and 3-m amplitude and 10–30-second heave period. In this study, transient modeling software is used to create a digital twin of the wellbore to safely predict the tripping speed and define the effect heave has on the tripping operations, from causing additional swab and surge pressures when in or out of slips to reducing tripping speed and improving efficiency by reducing mud gelling at connections. To further understand the effect heave has on tripping operations, experimental simulations of varying heave magnitude were completed in wellbore sections of 0°, 30°, 60°, and 90° inclination. Model validation was completed before running simulations. The results indicate that in horizontal holes, low heave magnitudes result in no bit or pressure response. The same cannot be said for vertical wells, which show smooth bit movement and pressure response throughout the heave magnitude spectrum. However, in a horizontal hole when the wave height is of a larger magnitude, sufficient to break wellbore friction, bit displacement is observed to display jerky axial stick and slip movement, and resultant increased swab and surge pressures are shown even when accounting for the reduced pressure fluctuations due to string eccentricity in an inclined wellbore. It is proposed that much of the related mechanical and pressure response is due to the properties of the drilling mud, string elasticity, and the forced frequency of the waves on the natural frequency of the drilling rig and drillstring. It is clear from definitive and experimental simulations that extra care must be taken when the heave is significant to maintain wellbore stability and reduce wellbore pressure cycling.