Hydraulic Effect of Tool Joints on Annular-Pressure Loss

Abstract

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 142282, ’The Hydraulic Effect of Tool Joints on Annular-Pressure Loss,’ by Majed Enfis, SPE, and Ramadan Ahmed, SPE, University of Oklahoma, and Arild Saasen, SPE, Det Norske and the University of Stavanger, prepared for the 2011 SPE Production and Operations Symposium, Oklahoma City, Oklahoma, 27-29 March. The paper has not been peer reviewed. For a successful drilling operation, downhole pressure, or equivalent circulating-density (ECD), control is critical. Conventional drilling techniques require maintaining the bottomhole pressure (BHP) at a level between the pore and fracture pressures. In deepwater wells, the margin between these pressures is very narrow; therefore, the BHP and ECD must be predicted accurately and be maintained within that narrow margin to avoid kicks and circulation losses. The presence of a tool joint changes the annulus geometry between the drillpipe and the casing or hole, resulting in strong turbulence and fluid acceleration that generate additional viscous dissipation and pressure losses. Theoretical and experimental studies examined the hydraulic effects of rotating and nonrotating tool joints. Introduction While drilling oil and gas wells, drilling mud is circulated in the wellbore to transport cuttings to the surface and control the BHP. In conventional drilling operations, the mud is injected into the well through the drillstring (drillpipe) with a high-pressure pump. The mud flows through the drillpipe and exits the drill bit where it enters the annulus and flows up the annular space to the surface carrying rock cuttings. Significant pressure losses occur as the mud flows through the drillpipe and the annulus. The BHP, which is a critical parameter in any drilling operation, is a function of the hydrostatic head of the mud and annular-pressure loss. Hence, accurate prediction of the annular-pressure loss leads to a good estimation of the BHP and the ECD to prevent kicks and circulation losses. The ECD is a commonly used drilling term that represents the BHP in terms of equivalent fluid density. This means that it combines the density of the fluid and annular-pressure loss. Previous studies focused on the hydraulic effects of a nonrotating tool joint. The purpose of this study was to examine hydraulic effects of tool joints under both static and dynamic conditions, and to develop models for predicting the change in annular-pressure loss caused by the tool joints.