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Integrated Approach to Well-Leak Diagnostics Meets Success Offshore Timor Sea

The identification of low-rate leaks along with low annular-pressure buildup rates in any type of completion presents challenges to well integrity. This paper emphasizes the importance of understanding well-diagnostic problems to determine feasibility, isolate interest zones, enhance stimulation strategies, and optimize the acquisition of high-resolution acoustical data from the wellbore with a new leak-detection tool. This case study discusses the methodology that underlies the successful determination of the depths and the radial locations in the outer casing strings of multiple leaks in an offshore well.

Introduction

The studied well in the Timor Sea offshore Australia was completed as a horizontal gas producer in 2010. The well featured a single packer completion with 7-in./9⅝‑in. tubing and a horizontal lower completion with a swell packer and preperforated 5-in. liner. The well contained a production casing (13⅜ in.) with an A/B annulus (7-in./9⅝-in. tubing×13⅜‑in. casing and 11¾-in./9⅝‑in. liners) and surface casing (20 in.) with a C annulus (13⅜×20 in.).

In late 2016, the pressure of the A/B annulus was observed to have decreased from 10 to 0 barg over a 4-month period, having previously been stable at 10 barg for 1 year. Multiple attempts were made without success to restore pressure by topping up the A/B annulus with inhibited water.

In October 2017, the pressure of the A/B annulus was observed to have a slight vacuum effect of –20 kPa. Diagnostic testing was performed to confirm the issue. The A/B annulus was topped off with 46 m3 of inhibited brine. While filling the last 4 m3, with the A/B annulus confirmed full, the pressure plateaued at 4.25 barg while it continued to pump at 145 L/min, which confirmed a potential leak in the A/B annulus. After the pump was shut down, the A/B annulus pressure stabilized at 3.32 barg, and the fluid levels remained full. The A/B annulus pressure, with the well on line, steadily increased to only 4.2 barg, further confirming the presence of a leak.

In December 2017, a well-integrity logging suite, consisting of an advanced array leak-detection tool and conventional production logging sensors, was conveyed on wireline to determine the A/B annulus leak location. The decision would be made to suspend the well on the basis of the logging results.

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper IPTC 19448, “An Integrated Approach to Well-Leak Diagnostics: Case Study of the Successful Application of the Latest Leak-Detection Technology and Interpretation Offshore Timor Sea, South East Asia,” by Andrew Imrie, SPE, Brendon Negenman, Chung Yee Lee, Mahadevan S. Iyer, Sarvagya Parashar, SPE, and Mohamed Raouf Shata, SPE, Halliburton, and Sean Helton, SPE, ConocoPhillips, prepared for the 2019 International Petroleum Technology Conference, Beijing, 26–28 March. The paper has not been peer reviewed. Copyright 2019 International Petroleum Technology Conference. Reproduced by permission.
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Integrated Approach to Well-Leak Diagnostics Meets Success Offshore Timor Sea

01 January 2020

Volume: 72 | Issue: 1

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