Effect of Drillstring Deflection and Rotary Speed on Annular Frictional Pressure Losses

Abstract

Keeping the drilling fluid equivalent circulating density in the operating window between the pore and fracture pressure is a challenge, particularly when the gap between these two is narrow, such as in offshore applications. To overcome this challenge, accurate estimation of frictional pressure loss in the annulus is essential, especially for multilateral, extended reach and slim hole drilling applications usually encountered in shale gas and/or oil drilling. A better estimation of frictional pressure losses will provide improved well control, optimized bit hydraulics, a better drilling fluid program and pump selection. Field and experimental measurements showed that pressure loss in the annulus is strongly affected by the pipe rotation and eccentricity. Eccentricity will not be constant throughout a wellbore, especially in highly inclined and horizontal sections. In an actual wellbore, because of rotation speed and the applied weight, some portion of the drillstring will undergo compression. As a result, variable eccentricity will be encountered. At high compression, the drillstring will buckle, resulting in sinusoidal or helical buckling configurations. Most of the drilling fluids used today show highly non-Newtonian flow behavior, which can be characterized using the Yield Power Law (YPL). Nevertheless, in the literature, there is limited information and research on YPL fluids flowing through annular geometries with the inner pipe buckled, rotating, and eccentric. Furthermore, there are discrepancies reported between the estimated and measured frictional pressure losses with or without drillstring rotation of YPL fluids, even when the inner pipe is straight. The major focus of this project is on a horizontal well setup with drillstring under compression, considering the influence of rotation on frictional pressure losses of YPL fluids. The test matrix includes flow through the annulus for various buckling modes with and without rotation of the inner pipe. Sinusoidal, helical and transition from sinusoidal to helical configurations with and without the rotation of the drillstring are investigated. Results show a substantial difference of frictional pressure losses between the non-compressed and compressed drillstring. The drilling industry has recently been involved in incidents that show the need for critical improvements for evaluating and avoiding risks in oil/gas drilling. The information obtained from this study can be used to improve the control of bottomhole pressures during extended reach, horizontal, managed pressure, offshore and slim hole drilling applications. This will lead to safer and enhanced optimization of drilling operations.

Frictional pressure loss of drilling fluids in a fully eccentric annulus

“…Experimental data presented by Erge (2013) used in this study. The data has been collected from the outdoor dynamic testing facility located at the Tulsa University Drilling Research Projects (Fig.…”

“…Escudier and Gouldson, 1995;Hansen and Sterri, 1995;Ahmed and Miska, 2008;Erge et al, 2013;Escudier et al, 2002;Hemphill, 2015). Note that the focus in this paper is restricted to the eccentricity effect, and that the effects of pipe rotation will be the topic of future work.…”

“…Proposed model in this study is compared with the experimental data (Erge, 2013) as well as other widely used theoretical and numerical models, including: Narrow Slot (Appendix B), corrected Narrow Slot (Appendix B), Luo and Peden (1990) (Ahmed et al, 2006) andHashemian Adariani (2005). Since, the Narrow Slot approximation does not consider the effect of pipe eccentricity, the obtained pressure loss from this approach is corrected by Eq.…”

“…After implementing the finite difference approximation and further algebraic simplifications, we obtain (Erge, 2013):…”

Pilot size process visualization: Gravity fluid displacement method to stop annular gas migration

“…The sample volume should be 3e5 fold greater than model capacity and should be hydrated for at least 5 days (Erge, 2013) before usage. 3.…”