Real-Time Measurements Improve Managed-Pressure Operations in HP/HT North Sea Well
Authors: Feder Judy 
Published: February 2020

This article, written by JPT Technology Editor Judy Feder, contains highlights of paper SPE 195767, “Using Real-Time Downhole and Along-String Measurements During Drilling and Cementing Operations To Improve Managed-Pressure Operations in a Complex High-Pressure/High-Temperature North Sea Well,” by Tom Brian, Total, and Andy Hawthorn and Duncan Groves, Baker Hughes, prepared for the 2019 SPE Offshore Europe Conference and Exhibition held in Aberdeen, 3–6 September. The paper has not been peer reviewed.

This paper describes how new technology was implemented and deployed through a downhole acoustic network through a sequence of runs in complex North Sea wells under managed-pressure conditions. The authors demonstrate how measurements and real-time solutions evolved over the course of the wells to exceed the originally perceived value of top-of-fluid under severe losses. As a result of this deployment and the lessons learned, the acoustic telemetry network will now be used on upcoming, equally challenging wells, and its range of operations will be expanded to include drilling, tripping, and liner-cementing operations.

Introduction

Several mature fields in the North Sea experience significant challenges relating to high pressures and temperatures, accompanied by the infill drilling challenge of very narrow margins between pore and fracture pressures. To navigate these narrow mud-weight windows, understanding the bottomhole pressure (BHP) is critical. However, in instances of fractured formations above the target zones, severe losses can be encountered during drilling and cementing operations, often leading to the inability to maintain a full mud column at all times and even threatening the ability to reach total depth (TD).

To address these issues, the operator investigated an acoustic telemetry system that could provide internal and external pressure measurements, along with other downhole measurements, independently of traditional mud-pulse telemetry in the drilling assembly, to provide real-time distributed pressure data essential to understanding the downhole conditions regardless of circulation, even under severe losses or during tripping and cementing operations.

Network Operation

The downhole measurement and acoustic telemetry network was deployed on several wells through multiple hole sizes for loss management, liner running, and cementing operations. The initial primary purpose was to monitor the top of the mud at all times, even in significant loss situations. The network consisted of inline tools that picked up and handled like drillpipe. A surface sensor was deployed and attached to the quill of the top drive. This surface receiver then transmitted through a wireless network to a decoding laptop in a safe area. Once there, the data were integrated with other downhole data from the traditional measurement-while-drilling string and with surface data from the rig floor and sensor measurements from the managed-pressure-drilling (MPD) equipment. This process is described more fully in the complete paper.

As real-time data were acquired, it became apparent that the data could also be used in real time to help quantify actual downhole pressures. New calculations were designed for simpler visualization of equivalent circulating densities (ECDs) at the shoe, bit, and weak zones in the well at depths beyond the acoustic tools themselves. These data were used to manage the BHP within a 300-psi mud-weight window to enable the well to be delivered ultimately to planned TD.