Abstract

After a series of successful tests conducted at a research facility for a vertical well using full scale equipment, the Micro-Flux Control (MFC) equipment was taken to its first field applications to begin exploring the performance of the system under actual drilling conditions. These conditions include the presence of cuttings in the return fluid and effects of pipe movement; neither of which could be tested at the research facility.

The accuracy of the MFC had been demonstrated for both WBM and OBM at the research facility, detecting influxes and losses at very low volumes. The first two field wells drilled confirmed the accurate measurement capabilities and showed additional and unique information in terms of flow and pressure.

This paper describes the first two wells drilled with the system. The first was a shallow exploratory well for Petrobras in Brazil using WBM (1824 ft drilled and 3018 ft TD). The second well, drilled for Chevron in Texas using OBM was a development well in a challenging area with ROP approaching 300 ft/hr (2587 ft drilled and 13,000 ft TD).

The system proved to be capable of being used on a wide variety of rigs; whether conventional, without any automation or sophisticated controls and employing a kelly; or latest generations, with fully automated controls and employing a top drive.

The results to be presented include the summary of the planning, the challenges and problems targeted, preparation of the wells, rig up of the equipment, and the results. Among data disclosed is the influence of pipe movement, accuracy of the flow measurements under various conditions, and identification of drilling related problems using the various parameters collected. Several influxes were detected along the well and positively confirmed when gas reached surface. The influx detection data was analogous to the mud logging data.

Introduction

The Microflux Control (MFC) method is a new managed pressure drilling (MPD) technology that was designed to improve drilling in most conditions, from simple wells all the way to high pressure, narrow margin, offshore and other challenging wells and to significantly increase safety through automated kick detection and control. The system has been described in several publications and only a brief description is herein made 1–5. The system operates using a closed loop drilling process that allows for real-time identification of micro influxes and losses and the control and management of downhole pressures through an automated data acquisition and computerized pressure control system. After the successful tests conducted with water and oil based mud at the Louisiana State University Well Control Facility in 2005 and early 2006, the system was taken to its first wells in the summer and fall of 2006 with Petrobras and Chevron.

MPD wells can be divided in basically two categories (suggestions made by the authors):

  • Standard, where the well is statically overbalanced;

  • Special, where the well is statically underbalanced for at least a portion of it.

The MFC can be used with either options, but the first two wells drilled and herein described used the Standard option. As the well is drilled statically overbalanced, all operational procedures, including safety and well control, remain the same. There is no need to change well design criteria or safety, and the main goal is to provide a way of safely reducing the mud weight towards the pore pressure. Very little training is required, and can be provided at the well site for the rig crew in less than one hour.

The Special mode, on the other hand, requires much more elaboration in terms of well design. There is a need to review the operational procedures, including connections, tripping, casing, logging, cementing, and especially safety and well control. Training is extensive and there is a need for expert personnel at the location during drilling. And additional equipment is also another item that needs to be considered, making it more difficult in some cases due to footprint restrictions of some rigs. Not to mention the higher cost associated to it.

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