Preliminary reservoir model of enhanced coalbed methane (ECBM) in a subbituminous coal seam, Huntly Coalfield, New Zealand

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• 作者：Sadiq J. Zarrouk ; Tim A. Moore
• 关键词：Enhanced coalbed methane (ECBM) ; Reservoir simulation ; TOUGH2 ; Waikato ; New Zealand
• 刊名：International Journal of Coal Geology
• 出版年：2009
• 出版时间：7 January 2009
• 年：2009
• 卷：77
• 期：1-2
• 页码：153-161
• 全文大小：1411 K

文摘

The Huntly coalfield has significant coal deposits that contain biogenically-sourced methane. The coals are subbituminous in rank and Eocene in age and have been previously characterised with relatively low to moderate measured gas (CH₄) contents (2–4 m³/ton). The CO₂ holding capacity is relatively high (18.0 m³/ton) compared with that of CH₄ (2.6 m³/ton) and N₂ (0.7 m³/ton) at the same pressure (4 MPa; all as received basis). The geothermal gradient is also quite high at 55 °C/km.

A study has been conducted which simulates enhancement of methane recovery (ECBM) from these deposits using a new version of the TOUGH2 (version 2) reservoir simulator (ECBM-TOUGH2) that can handle non-isothermal, multi-phase flows of mixtures of water, CH₄, CO₂ and N₂. The initial phase of the simulation is CH₄ production for the first 5 years of the field history. The model indicates that methane production can be significantly improved (from less than 80 % recovery to nearly 90 % ) through injection of CO₂. However, although an increase in the rate of CO₂ injection increases the amount of CO₂ sequestered, the methane recovery (because of earlier breakthrough with increasing injection rate) decreases. Modeling of pure N₂ injection produced little enhanced CH₄ production. The injection of a hypothetical flue gas mixture (CO₂ and N₂) also produced little increase in CH₄ production. This is related to the low adsorption capacity of the Huntly coal to N₂ which results in almost instantaneous breakthrough into the production well.