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Gas hydrates as an energy resource

Funder: Ministry of Business, Innovation, and Employment
Programme: Gas Hydrates Resources (2010-2012 & 2012-2018)

Background

Map of New Zealand's hydrate deposits

Gas hydrates contain highly compressed natural gas that may constitute a significant source of energy [Kvenvolden, 1988]. Several countries such as Japan, India, South Korea, China, and the USA, have embarked on national gas hydrate R&D programmes aimed at commercial production of gas from hydrates.

Gas hydrate production tests in Canada have been highly successful [Kurihara et al., 2008]. Subsequently, gas hydrate resources on the Alaskan North Slope have been classified as technically recoverable, i.e., they can be “discovered, developed, and produced using current technology” (Collett et al., 2009). First production tests offshore Japan suggest production of gas from offshore hydrates is now also technically feasible (JOGMEC, 2013).

The Hikurangi Margin east of New Zealand contains a >50,000 km2 large gas hydrate province. First estimates suggest that the volume of gas in concentrated hydrate deposits is in the order of 20 tcf (Pecher and Henrys, 2003). New Zealand's annual gas consumption between 2005 and 2009 has been roughly 0.16 tcf (MED, 2010). Should even only a fraction of New Zealand’s gas hydrates be economically recoverable, they could provide the main source of natural gas for New Zealand for several decades (Pecher and GHR Working Group, 2011).

Gas Hydrates Resources Programme

GNS Science is leading a research programme into the resource potential of New Zealand’s gas hydrate deposits in collaboration with NIWA, the University of Otago, and the University of Auckland, funded by the Ministry of Business, Innovation, and Employment (Harnessing New Zealand's gas hydrate resources: towards exploration drilling; GHR). This programme builds on a pilot programme funded by the Foundation for Research, Science, and Technology, New Zealand’s first dedicated gas hydrates programme (Gas Hydrates Resources, 2010-2012). Our key objectives are (1) to study the regional distribution of gas hydrate distribution and (2) to characterize individual gas hydrate reservoirs. The former includes searching for gas hydrates outside the Hikurangi Margin, the latter analysis of seismic data to improve our understanding of gas-hydrate reservoir rocks and investigation of gas-hydrate-formation mechanisms. Initial production modelling has recently been completed as well as a first assessment of seafloor communities that may be affected by gas hydrate production.Our overarching goal within the current programme is to identify targets for scientific exploration drilling.

Research

Segmented BSRs – implications for reservoir rocks

The quality of reservoir rocks, in particular permeability, is a key parameter controlling the economic viability of gas production from hydrates. In some regions such as the Gulf of Mexico, the strength of bottom simulating reflections (BSRs), reflections primarily caused by gas at the base of gas hydrate stability, is highly variable. High-amplitude patches along otherwise weak BSRs may mark permeable layers that act as gas pathways surrounded low-permeability sediments (Shedd et al., 2009). BSR reflection strength can therefore be utilized to identify high-quality reservoirs.

Reflection coefficients and amplitude-vs.-offset (AVO) character of BSRs on the Hikurangi Margin have recently been analysed (Navalpakam et al., 2012). Reflection coefficients are generally low, compatible with low saturations of gas and hydrates in low-permeability rocks. Some prominent high-amplitude patches however, may mark high-permeability sand layers.

Image above after Pecher and GHR Working Group, 2011

Gas hydrate quantification and reservoir characterization in submarine channels

Submarine channels may contain sand reservoirs that are attractive for gas production from hydrates e.g., offshore Japan [Fujii et al., 2008]. We have recently investigated deposits in a channel system east of the Wairarapa focussing on high-resolution velocity analysis to constrain gas hydrate saturation and AVO character to delineate the lithology of the reservoir rock. Results suggest gas hydrate saturations around 25% of pore space in a ~120 m thick high-quality reservoir with a net-to-gross of ~0.5 (Fohrmann and Pecher 2012).

Image above after Fohrmann and Pecher 2012

Gas hydrate formation mechanisms

Evidence for free gas within the regional gas hydrate stability field found at several locations on the Hikurangi Margin [Pecher et al., 2010] indicates that gas is currently in the process of being transformed to hydrates. Low-resistivity anomalies observed close to the seafloor beneath the Porangahau Ridge are thought to be caused by expulsion of saline pore waters during gas hydrate formation further below providing further evidence for active gas hydrate formation [Toulmin et al., 2010]. These locations present us with an excellent opportunity to study one of the least understood processes behind the occurrence of natural gas hydrates, gas hydrate emplacement.

Elsewhere on the margin, we observe evidence for gas migration into the hydrate stability zone along permeable layers that cut across the base of hydrate stability (Crutchley et al. 2015). In these areas, we expect concentrated hydrate deposits within relatively permeable layers, similar to example investigated in the Gulf of Mexico (Boswell et al. 2012).

Image above after Pecher et al., 2010

Possible sources of gas for hydrate formation

An exceptionally strong link between structures that enhance fluid flow and a presence of BSRs marking gas hydrate deposits has been observed on the Hikurangi Margin. This observation suggests deep sources of gas for hydrate formation. Pre-stack depth migration of a seismic line across the Pegasus Basin to the south of the Wairarapa has identified possible fluid and gas migration paths from the subducted sediment section on the Hikurangi Plateau through the accretionary prism into the hydrate stability field. These findings suggest that some of the gas for hydrate formation originates in the subducted plate and may be of thermogenic origin (Plaza-Faverola et al., 2012).

Gas hydrate deposition modelling with Petromod™ suggests that widespread BSRs are probably the result of biogenic gas production (Kroeger et al. 2015). More localised input of thermogenic gas to the hydrate system will likely lead to concentrated gas hydrate deposits (Kroeger et al. 2015).

Thermogenic gas diagram

Image above from Plaza-Faverola et al.; 2012.

Possible gas hydrates in the Northland and Taranaki Basins

The first evidence for gas hydrates in the Northland and northern Taranaki basins was presented by Ogebule and Pecher (2010). More recently, Kroeger et al. (2017) presented new evidence for gas trapped beneath gas hydrates in the Taranaki Basin in a study of long-offset seismic data and basin modelling.

Taranaki gas hydrate seismic

Image from Kroeger et al. (2017)

Image above from Ogebule and Pecher, 2010.

Analysis of 3-D seismic data around gas-hydrate-bearing seep sites

A survey by the R/V Sonne was completed in 2011 (New Zealand Methane Seep Systems, NEMESYS, led by IfM-Geomar, Kiel, Germany) (Bialas, 2011). Two 3-D seismic volumes were acquired around seep sites where gas escapes through the gas hydrate zone to the seafloor. Results from Plaza-Faverola et al. (2014) revealed the details of fluid flow conduits through the hydrate zone related to compressional, extensional and shear deformation.

3d seismic data seeps

A cartoon depiction (from Plaza-Faverola et al. 2014) of gas flow through various structural features to seafloor methane seep sites.

References

  • Kroeger, K. F., Crutchley, G. J., Hill, M. G., & Pecher, I. A. (2017). Potential for gas hydrate formation at the northwest New Zealand shelf margin-New insights from seismic reflection data and petroleum systems modelling. Marine and Petroleum Geology, 83, 215-230.
  • Plaza‐Faverola, A., Pecher, I., Crutchley, G., Barnes, P. M., Bünz, S., Golding, T., Klaeschen, D., Papenberg, C., Bialas, J. (2014). Submarine gas seepage in a mixed contractional and shear deformation regime: Cases from the Hikurangi oblique‐subduction margin. Geochemistry, Geophysics, Geosystems, 15(2), 416-433.
  • Crutchley, G.J., D. R. A. Fraser, I. A. Pecher, A. R. Gorman, G. Maslen, S. A. 2015. Henrys. Gas migration into gas hydrate-bearing sediments on the southern Hikurangi margin of New Zealand. Journal of Geophysical Research: Solid Earth 02/2015; 120(2). DOI:10.1002/2014JB011503
  • Kroeger, K.F., A. Plaza-Faverola, P.M. Barnes, I.A. Pecher. 2015. Thermal evolution of the New Zealand Hikurangi subduction margin: impact on natural gas generation and methane hydrate formation – a model study. Marine and Petroleum Geology. 02/2015; DOI: 10.1016/j.marpetgeo.2015.01.020
  • Boswell, R., T. S. Collett, M. Frye, W. Shedd, D. R. McConnell, and D. Shelander. 2012. Subsurface gas hydrates in the northern Gulf of Mexico, Marine and Petroleum Geology, 34, 4–30
  • Bialas, J., 2011, FS Sonne Fahrtbericht / Cruise Report SO 214 NEMESYS, Volume 47: Kiel, IFM-GEOMAR, p. 164.
  • Collett, T., Johnson, A., Knapp, C., and Boswell, R., 2009, Gas hydrates: A review, in Collet, T., Johnson, A., Knapp, C., and Boswell, R., eds., Natural Gas Hydrates: Energy Resource Potential and Associated Geologic Hazards, Volume 89, AAPG Memoir, p. 146-219.
  • Fohrmann, M., and Pecher , I. A., 2012, Analysing sand-dominated channel systems for potential gas-hydrate-reservoirs using an AVO seismic inversion technique on the Southern Hikurangi Margin, New Zealand: Mar. and Petrol. Geol., v. 38, p. 19-34.
  • JOGMEC, 2013, Gas Production from Methane Hydrate Layers Confirmed, Volume 2013.
  • MED, 2010, Table E.5b:Natural Gas Consumption by Sector (Gross PJ), Volume 2010, Ministry of Economic Development.
  • Navalpakam, R. S., Pecher, I. A., and Stern, T., 2012, Weak and segmented bottom simulating reflections on the Hikurangi Margin, New Zealand — Implications for gas hydrate reservoir rocks: J. Pet. Sci. Eng., v. 88-89, p. 29-40.
  • Ogebule, O. Y., and Pecher, I. A., 2010, Possible gas hydrates in the Northland and northern Taranaki Basins – indirect evidence from seismic data: N. Z. J. Geol. Geophys., v. 53, no. 4, p. 369-373.
  • Pecher, I. A., and GHR Working Group, 2011, Gas Hydrates in New Zealand - a large resource for a small country?, Fire in the Ice, US Department of Energy, p. 1-3.
  • Pecher, I. A., and Henrys, S. A., 2003, Potential gas reserves in gas hydrate sweet spots on the Hikurangi Margin, New Zealand: Institute of Geological and Nuclear Sciences, 2003/23.
  • Pecher , I. A., Henrys, S. A., Kukowski, N., Crutchley, G. J., Gorman, A. R., Wood, W. T., Coffin, R., Greinert, J., Faure, K., and CHARMNZ Working Group, 2010, Focussing of fluid expulsion on the Hikurangi margin, New Zealand, based on evidence for free gas in the regional gas hydrate stability zone: Mar. Geol., v. 272, p. 99-113.
  • Plaza-Faverola, A., Klaeschen, D., Barnes, P., Pecher , I., Henrys, S., and Mountjoy, J., 2012, Evolution of fluid expulsion and controls on hydrate formation across the southern Hikurangi subduction Margin, New Zealand: Geochem. Geophys. Geosyst., v. 13, no. 8, p. Q08018.
  • Shedd, W., Frye, M., Godfriaux, P., Boswell, R., and Hutchinson, D. R., 2009, Occurrence and variety in expression of the base of gas hydrate stability in the Gulf of Mexico, USA: Fire in the Ice, v. Winter 2009, p. 11-14.