Abstract The HYACINTH suite of equipment has been developed to investigate the pressure sensitive behaviour of sedimentary formations up to 250 bar (25 MPa). It does this by collecting pressure-preserved samples from boreholes that can be retrieved, subsampled and analysed in controlled conditions in the laboratory. This paper reviews the development of the system, how it originated from the need to better understand the nature and distribution of gas hydrates beneath the sea bed, and its achievements to date. While gas hydrates continue to be the major scientific and commercial impetus for using, and further developing, this pressure-sampling technology, other important scientific driving forces, including the growing interest in the deep biosphere beneath the sea floor, are playing an important role. We review the downhole tools, the transfer system and the suite of different pressure chambers that are required to make a complete working system. Non-destructive logging of cores contained in pressure chambers, using existing gammaand X-ray techniques, is discussed, as are future logging techniques that will have sensors embedded within the pressure chambers. Subsamples can now be taken at full pressure and transferred into specialized chambers where intrusive measurements and experiments can be performed (e.g. inoculation chambers for microbiology). The versatile philosophy behind the integrated systems will enable future developments to be made by third parties who want to obtain subsamples at in situ pressure from the HYACINTH system. We conclude by reviewing some of the highlights of the HYACINTH operations on ODP Leg 204 where the downhole tools retrieved cores containing gas hydrates (up to 40% by volume) that were subsequently logged on board in the laboratory. These data have already contributed to the scientific understanding of the nature and distribution of gas hydrates beneath the seabed in one area on the Oregon Margin off the USA.

Abstract Methane hydrates have been recovered or postulated for virtually all continental margins around the world and a few areas onshore. Volumes of about 2 × 10 14 m 3 have been estimated for this potential resource. However, only a few sites have been suggested offshore northwest Europe, despite extensive hydrocarbon exploration and academic studies of the margin. Reasons for this anomaly are unclear. To aid the search a new hydrate stability zone map for the UK is presented. As well as identifying a resource, hydrate studies are also important in assessing geohazards to deep-water exploration and development. Stability, processes and distribution information contribute to the wider climate change debate as methane hydrates are estimated to hold a significant part of the global organic carbon budget. To quantify reserve potential and to identify suitable methods of methane extraction, a full understanding of how hydrates are held within sediments is required. Although modelling (physical and theoretical) can contribute to an understanding, it is important to evaluate in situ conditions to ‘ground truth’ acoustic data and imagery. How hydrate is held and its control of dynamic geotechnical behaviour within the sedimentary system is still very poorly understood. Parameters such as pore size, fluid saturations, sediment mineralogy and cementation will affect hydrate morphology, distribution, behaviour (during dissociation) and potential recovery from porous media. Assessing physical parameters and processes under in situ conditions provides the next step along the route to exploiting methane hydrates as a resource. The requirement to recover samples under in situ pressures and temperature conditions provides a significant technological challenge that has been attempted over the last few years with some success. Currently, the European HYACINTH project is developing systems to recover, analyse and manipulate hydrate-bearing sediments under in situ pressures and temperatures. On Leg 204 of ODP this equipment was used for the first time to recover hydrate cores at in situ pressure, transfer them without loss of pressure into laboratory chambers and to log them geophysically. As the database of in situ properties grows, integrated laboratory studies of synthetic sediment-hosted hydrates can be developed to provide important benchmarking, which is crucial for the study of rare natural core samples.