Abstract

The Gorgon LNG Project is one of the world's largest natural gas projects and the biggest single resource development in Australia's history. Once online, gas from 18 subsea producers across the Gorgon and Jansz-Io fields will deliver a combined 15.6 MTPA of liquefied natural gas (LNG) to domestic and international export markets via three LNG trains situated on Western Australia's Barrow Island (Fig. 1).

From May through to November of 2014 the eight Gorgon foundation wells were successfully perforated, intercepting between three and seven commingled zones and gross intervals of up to 500 metres (m) per well. Perforation was conducted on wire-line with a total of 69 perforating runs made during the campaign. Directly following perforation, all eight wells were unloaded and cleaned-up by flowing back each at 80 MMscf/d for 12 – 24 hours to the Ocean America mobile offshore drilling unit (MODU).

This paper will contrast the detailed perforating and flowback plan, developed with numerous likely contingencies, against the actual results of the operation where a number of the planned and also some unplanned contingencies were enacted.

The agreed perforating basis of design called for multiple wireline runs of 4.5" diameter guns with lengths of up to 80 feet, using a specially designed high strength gas blocked cable to accommodate well conditions. A top-down perforating strategy was planned to maximise the dynamic underbalance effect and optimise the clean-out of perforation tunnels. A number of operational events on the first well prompted a switch to a bottom-up perforating methodology that in turn had a number of significant knock-on effects which will be described in full.

The flowback operation represented a once in a field-life opportunity to acquire commingled well samples and provide validation of several critical reservoir, fluid and well properties such as gas contaminant levels, water of condensation, compositional variation, vertical lift performance, sand production and the presence of formation water. As flowback operations progressed a feedback loop was incorporated, ensuring that the program was optimised as data gathered reduced uncertainty levels. Arguably the most commercially significant contribution, was the assurance that the deliverability of the eight Gorgon field producers was sufficient to meet their commitment to the Gorgon project.

Ultimately, though sharing the susccessful case study of the Gorgon Perforating and Flowback campaign, this paper emphasises the value in developing appropriate contingencies in advance of operation commencement as well as retaining program flexibility to enable changes to be made at short notice throughout the operational campaign.

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