Biogenic Gas: A New Play in the East Coast Basin of New Zealand

摘要

Exploration wells near Napier (including Kereru-1) and analyses from natural gas seeps indicate that large volumes of methane have been generated by bacteria in Pliocene mudstones. Previously, the only credible source rocks in the area were the Late Cretaceous -Early Tertiary Whangai Shale and Waipawa Black Shale. Exploration has been seen as risky partly because the presence and maturity of these source rocks, along with timing and migration paths to known reservoirs are all problematical. Biogenic gas from Pliocene mudstone, interbedded Pliocene turbidites and coquinas, and contemporaneous compressional tectonism provide the elements of a petroleum system. This new play requires a fresh approach to some traditional exploration technologies. For example the results from Kereru-1 suggest that strong seismic reflectors in the Pliocene section are not necessarily indicative of interbedded reservoirs - the acoustic impedance contrasts may be developed by variations in gas charge in mudstones.