Publikationsdatum:
2016-08-02
Beschreibung:
We present an integrated 2D model of thermal and microbial generation of methane, migration into the
gas hydrate stability zone (HSZ), and formation of methane hydrates. The model reconstructs the shallow
(0e20 km) thermal structure of the subduction interface between the Australian plate and the subducting
Pacific plate, and the trench basin (Pegasus Basin). Modelled temperatures of less than 110 °C
within Pegasus Basin constrain the generation of oil and gas. Whilst a cool thermal regime is predicted to
limit thermogenic generation of gas to a burial depth of 〉10 km, it extends the interval where prolific
microbial gas generation occurs. The modelled rate of microbial generation of methane increases beneath
the HSZ and peaks at ~1600 m below seafloor. Diffusive upward migration of microbially generated
methane is interpreted to lead to widespread methane hydrate formation and the presence of a semicontinuous
bottom simulating reflector (BSR). Predicted average hydrate saturation within the HSZ is
0.9% for a modelled sedimentary organic matter content of 0.5% and 1.6% for 1% organic matter in finegrained
Pegasus Basin sediments. Considerably higher concentrations of methane hydrate of up to 20
e70% are predicted to occur where gas migration is focussed within the frontal anticline and proto-thrust
zone southeast of the modern accretionary wedge and in channel and basin floor sandstones related to
the Hikurangi Channel. The Hikurangi Channel sedimentary system transported coarse clastic sediments
eroded from the rising Southern Alps along the eastern margin of the Pegasus Basin since the Miocene. It
provides carrier beds specifically for transport of thermogenic gas generated close to the subduction
interface. A buried Mesozoic accretionary wedge originating from subduction of the Pacific Plate beneath
Gondwana further focusses the migration of gas. Focussed migration of thermogenic gas leads to the
highest predicted hydrate concentrations in potential channel sand reservoirs.
Materialart:
Article
,
PeerReviewed
Format:
text
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