Abstract The UK faces a major change in the nature of its gas supply as North Sea production declines and the country becomes increasingly reliant upon gas imports. As a result the UK Government recognizes that significant investment in gas supply infrastructure is required to maintain security of supply and manage the gas market. Part of that infrastructure will be additional underground gas storage capacity in specially designed and engineered salt caverns. This paper summarizes the distribution and nature of halite (rock salt) deposits in England and Northern Ireland, and reviews the details of existing and planned storage sites in salt caverns. There is considerable potential for further salt cavern development. However, not all of the UK salt fields are suitable, with the halite beds being too shallow, thin or impure.

Abstract Large-scale underground storage of CO 2 has the potential to play a key role in reducing global greenhouse gas emissions. Typical underground storage reservoirs would lie at depths of 1000 m or more and contain tens or even hundreds of millions of tonnes of CO 2 . A likely regulatory requirement is that storage sites would have to be monitored both to prove their efficacy in emissions reduction and to ensure site safety. A diverse portfolio of potential monitoring tools is available, some tried and tested in the oil industry, others as yet unproven. Shallow-focused techniques are likely to be deployed to demonstrate short-term site performance and, in the longer term, to ensure early warning of potential surface leakage. Deeper focused methods, notably time-lapse seismic, will be used to track CO 2 migration in the subsurface, to assess reservoir performance and to calibrate/validate site performance simulation models. The duration of a monitoring programme is likely to be highly site specific, but conformance between predicted and observed site performance may form an acceptable basis for site closure.

Abstract The predicted shortage of indigenous UK natural gas coincides with the continuing decline of the UK deep coal mining industry. Significant capacity has been lost through mine closures over the last few years as a result of competition from cheaper sources of coal from overseas and changes to the UK energy market. It is unlikely that any new large underground mines will be developed in the UK in the short or medium term. There are, however, still vast untouched coal resources in the UK that represent a significant energy resource. Increased awareness of the potential for clean energy from coal seams, advances in technology and recognition of the environmental benefits has seen a revival of interest in the potential to release some of the energy value of UK coal via alternative, non-mining technologies such as coalbed methane production and underground coal gasification. If successful, these could supplement declining conventional UK natural gas production. The utilization of clean energy from coal seams is supported by the UK Government through its Cleaner Fossil Fuels Programme. There is some activity in this field already. Methane is being drained from most of the remaining deep mines and utilized as fuel for electricity generation or on-site boilers. Drained gas that is not utilized is conventionally vented, but at one mine this gas is now flared to reduce greenhouse gas emissions. Methane is also being produced from abandoned mines, but the present low electricity and gas prices have adversely affected its economics. For the longer-term future, there is potential for virgin coalbed methane production and underground coal gasification. The UK has coalbed methane resources estimated to be in the order of 2.9 × 10 12 m 3 CH 4 . However, the limited exploratory drilling for coalbed methane in unmined areas undertaken to date has not led to commercial production — the major barriers are perceived to be low seam permeability, drilling and completion costs, together with planning and access issues. Initial research suggests there is very large potential for underground coal gasification providing the environmental and perceived safety issues surrounding the application of this technology can be overcome.

Abstract In northern Europe numerous industrial point sources of CO 2 surround the North Sea Basin, which contains a number of viable underground sequestration opportunities. These include injection into depleted oil and gas fields and into major regional aquifers; the latter probably offering the greatest ultimate storage potential. At the Sleipner gas field, CO 2 is being injected into the Utsira Sand, a large saline aquifer. More than 6 Mt of CO 2 have currently been injected, with a projected final target of about 20 Mt. Time-lapse seismic reflection data are being used to monitor the operation and have provided clear images of the CO 2 plume and its development with time. Moreover, CO 2 volumetrics derived from the seismic data are consistent with the well injection figures. In conjunction with reservoir simulation studies, time-lapse seismic monitoring seems, therefore, to offer an effective means of predicting the future growth, migration and dispersion of the CO 2 plume. Another important aquifer, the Bunter Sandstone, stretches from Britain to Poland. In the UK sector alone, the pore volume in structural closures is equivalent to about 350 years’ worth of current CO 2 emissions from UK power generation. Industrial CO 2 sources in northern Europe are well placed to exploit these major subsurface reservoirs and European countries are technically very well equipped to use and develop this emerging technology.