Abstract

A number of coalbed methane (CBM) to liquefied natural gas (LNG) projects are currently advancing in Australia, among which is the Arrow LNG project. To ensure reliable supply to an LNG plant, production availability of the integrated CBM system consisting of a large amount of wells and production facilities needs to be understood, including the behavior of CBM wells after planned and unplanned shutdowns. This paper provides an analysis of post-shutdown recovery behavior of horizontal CBM wells based on a large volume of field data. There is no known published work on shutdown recovery for CBM wells to date, so there are no comparison data.

Arrow Energy has produced CBM for domestic consumption since 2004 and currently supplies about 20 per cent of Queensland's gas from fields in the Bowen and Surat basins. A shutdown recovery analysis is conducted on Arrow's Moranbah Gas Project (MGP) in the Bowen Basin. Field data for 6,436 shutdown periods are used, including: gas rates, water rates and bottomhole pressures (BHP). The following effects on recovery times are analyzed: shutdown duration, pre-shutdown water rate, pre-shutdown gas-water ratio, and pre-shutdown producing days.

The results indicate that approximately 70% of wells, shutdown for one day, return to 90% of their previous gas rates within one day. Approximately 20% wells recover in a week and the remaining 10% wells come back to 90% of original rates within 2 months. Furthermore, shutdown periods longer than five days have significantly higher recovery times. Wells with a lower water rate and higher gas-water ratio before the shutdown return to their pre-shutdown gas rate faster than wells with a higher water rate and lower gas-water ratio. Also, late life wells recover faster than wells in early production life.

These findings are critical for planning well shutdown and ramp-up strategies (well classifications and priority lists) to manage required gas supply during the operational phase of integrated CBM-LNG projects.

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