Balanced-Pressure Drilling With Continuous Circulation Using Jointed Drillpipe
Authors: Denney Dennis 
Published: February 2015

This article, written by Technology Editor Dennis Denney, contains highlights of paper SPE 102859, "Balanced-Pressure Drilling With Continuous Circulation Using Jointed Drillpipe - Case History, Port Fouad Marine Deep-1, Exploration Well Offshore Egypt," by A. Calderoni, SPE, A. Chiura, SPE, and P. Valente, SPE, Eni-E&P Div.; F. Soliman, SPE, and E. Squintani, Petrobel; R.E. Vogel, SPE, Natl. Oilwell Varco; and J.W. Jenner, SPE, Coupler Developments Ltd., prepared for the 2006 SPE Annual Technical Conference and Exhibition, San Antonio, Texas, 24-27 September.

Previous attempts to drill this section failed, and balanced-pressure drilling (BPD) was identified as the only safe and practical drilling technique to use. The use of this drilling technique, together with the associated changes in drilling and well-control procedures, is presented.

Introduction

In the Port Fouad Marine Deep-1 (PFMD-1) well, a critical-pressure-gradient zone exists below 13,125 ft, with pore pressures exceeding 2.0-specific-gravity (SG) equivalent mud weight (EMW) and the difference between pore- and fracture-pressure gradients as low as 0.10 SG EMW. The dynamic- vs. hydrostatic-pressure difference between the equivalent circulating density (ECD) and the mud weight was equivalent to approximately 0.07 SG during drilling operations. The well was re-entered in June 2005 with a system that provides continuous circulation, and the problem zone was drilled maintaining constant ECD. Drilling difficulties resulting in the earlier suspension were overcome. BPD with uninterrupted circulation and revised drilling and well-control procedures significantly improved drilling performance and operational safety in the critical-gradient zone.

Background

In drilling environments having a narrow pore-pressure vs. fracture-pressure window, the difference between the ECD and mud weight is greater than (or very close to) the difference between pore pressure and fracture pressure. Drilling conventionally through such an environment is extremely difficult. The target depth of the well may not be achieved because the formation fracture pressure often is exceeded by the ECD, and losses occur when circulating normally. When the pumps are stopped to make a connection, removing the dynamic circulating pressure can induce flow and formation collapse. The solution is to avoid extreme transitory downhole-pressure effects during drillpipe connections by maintaining continuous circulation with a constant bottomhole pressure while adding drillpipe to or removing it from the drillstring.

System

The system shown in Figs. 1 and 2 is rig-floor-based and is used with a top-drive drilling system. It allows drillpipe connections to be made up or broken out without interrupting drilling-fluid circulation to the wellbore. The main unit is a pressure container constructed from three blowout-preventer (BOP) bodies, with pipe rams at the top, blind rams in the center, and inverted pipe rams at the bottom. A combination make/break power tong and a snubber are attached to the top and drillpipe slips to the bottom. The bore is 9 in. with a working-pressure rating of 5,000 psi and a maximum circulating rate of 1,000 gal/min. The unit is centered over the rotary table and the drillstring passes through it while drilling. The system also uses a mud-diverter unit, a top-drive interface, a control panel, and a control container with a hydraulic power unit.