Safe Drillpipe Connections During Managed-Pressure-Drilling Operations
Authors: Denney Dennis 
Published: February 2015

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 147278, ’Field Demonstration of a New Method for Making Drillpipe Connections During Managed-Pressure-Drilling Operations,’ by Rachel Johnson, Halliburton; Julio Montilva, SPE, Shell; Mohamed Sati, Jeff Grable, and Saad Saeed, SPE, Halliburton; and Richard Billa and William Derise, Shell, prepared for the 2011 SPE Annual Technical Conference and Exhibition, Denver, 30 October- 2 November. The paper has not been peer reviewed.

Managed-pressure drilling (MPD) is effective for controlling equivalent circulating density (ECD). However, making a drillpipe connection with MPD is more challenging than with conventional drilling. A method was developed for smoothly diverting rig-pump flow during connections from the standpipe to the MPD pressure-control equipment at the annulus by use of a valve manifold with an onboard choke. This method can improve pressure control and increase the operating range of MPD to provide higher pressures during connections and greater drilling flow rates.

Introduction

The use of MPD enables accurate, precise, and dynamic bottomhole-pressure (BHP) control. Current MPD technology incorporates automated-choke (auto-choke) systems coupled with real-time hydraulics models to provide engineered control within set limits. However, there is a common misperception that current MPD systems can provide the same consistent level of accuracy and precision in all phases of drilling. The most-accurate control usually is attained only in limited technical windows, such as the on-bottom drilling phase in which steady-state conditions enable more-accurate evaluation and prediction.

All MPD systems have struggled with periods in a drilling operation that usually involve a variety of transient (startup/shutdown) behaviors. The most significant is the drillpipe-connection phase. Because of the regular frequency and highly dynamic nature of making connections, effects on the BHP can be significant, and if not managed effectively, they can negate the benefits achieved by MPD. In the worst case, they can lead to unintentional induced kicks. The rig-pump diverter (RPD) addresses this problem directly and provides an improved level of control and efficiency on connections.

Background

The BHP (downhole pressure at a datum) consists primarily of hydrostatic pressure of the annular mud column; frictional pressure loss (or dynamic pressure) that may be affected by flow rates, fluid rheologies, pipe movements, or geometric restrictions; and applied surface pressure (backpressure) at the annulus returns line. Automated MPD technology actively manipulates the applied surface pressure by means of the autochoke to control the BHP within a desired range. This control relies on a continuous stable pressure source. While drilling, this source is the rig pumps and it is throttled by the autochokes to apply the desired surface pressure. The challenge arises when the rig pumps are switched off, as in the case of connections. During this scenario, the loss of rig pumps equates to loss of frictional (or dynamic) pressure, which in turn causes a reduction of BHP (if not managed properly). The aim of MPD technology is to maintain a constant BHP by increasing the surface pressure proportionally, accounting for the lost dynamic pressure. Without a pressure source, increased surface pressure can be achieved only by pressure-trapping techniques. Several alternative schemes have been used to remedy this problem, with the most popular providing an alternative pressure source (on the annulus) that is used to drive the autochoke (in the absence of rig flow rate) and, in turn, apply the required surface pressure.