Potential gas reserves in gas hydrate sweet spots on the Hikurangi Margin, New Zealand

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Pecher, I.A.; Henrys, S.A. 2003 Potential gas reserves in gas hydrate sweet spots on the Hikurangi Margin, New Zealand . Lower Hutt: Institute of Geological & Nuclear Sciences. Institute of Geological & Nuclear Sciences science report 2003/23 32 p.

Abstract: Widespread occurrences of bottom simulating reflections (BSRs) suggest the presence of large volumes of gas hydrate on the Hikurangi margin offshore the East Coast of New Zealand’s North Island. We present here a first estimate of the quantities of gas that may be stored in gas hydrates in this region. The gas hydrate province extends from about 600 m water depth to the Hikurangi trench in the east. Its northern termination appears to be at the latitude of Gisborne. Southward, gas hydrate occurrence is indicated as far south as offshore Marlborough. This covers an area of about 50,000 km2. We estimate the volume of gas hydrate on this margin to be at least 228.5 km3, leading to an estimated volume of potentially recoverable gas of 23,010 km3 (813 trillion cubic feet, tcf). More importantly, we suggest that about 10% of this area may be covered by gas hydrate sweet spots, areas with high gas hydrate concentrations. Using speculative, but nonetheless, conservative assumptions we suggest these sweet spots together may contain about 604 km3 of recoverable gas (over 21 tcf), i.e., more than six times the size of the Maui gas field and more than 16 times the size of New Zealand’s known gas reserves as of June 2002. We have more closely analysed one of these sweet spots and concluded that it may contain about 1.47 km3 (0.052 tcf) of potentially recoverable gas using conservative input parameters. This conservative figure still is larger than the estimated size of the Rimu field. Using more optimistic input parameters, this sweet spot may contain 12.25 km3 (0.43 tcf) of potentially recoverable gas, i.e., over 1/10th the original volume of the Maui field. While the ultimate economic viability for producing gas from these gas hydrate sweet spots will depend mostly on production technology, our study suggests that the Hikurangi margin gas hydrate province contains significant volumes of natural gas. (auth)