Abstract The Stenlille natural gas underground storage is located 70 km SE of Copenhagen and has been in operation since 1989. For safety reasons and to protect the environment it is necessary to monitor the storage carefully. Natural gas is being stored in an anticlinal structure with an expected gas storage capacity of about 3 billion Nm 3 (volume under ‘normal’ conditions) in the upper Triassic Gassum Sandstone Formation 1500–1600 m below the surface; it replaces saline formation water. So far, nineteen deep wells have been drilled on and around the structure. The 300 m thick clay sequence of the Lower Jurassic Fjerritslev Formation above the gas storage reservoir has acted as an efficient seal, since no sign of gas leakage has been observed in the monitoring well located in a sand stringer 15 m above the gas reservoir. Other monitoring wells have been located in order to check for possible lateral escape of natural gas. A baseline study on naturally occurring hydrocarbons performed before the natural gas storage came into operation indicated the presence of only trace amounts hydrocarbon gases in the subsurface of the Stenlille area. Results of analysis by the headspace and sorbed gas methods on drill-cuttings suggest that low-temperature thermal generation of hydrocarbon gases (δ 13 C 1 : −47 to −42‰; δ 13 C 2 : −34 to −30‰) has taken place in organic-rich marine shale below 1300 m. Low concentrations of dissolved methane (<0.5 mg/l) of bacterial origin (δ 13 C 1 : −90 to −62‰) were found in shallow groundwater that is used for water supply in the Stenlille area. After the start of injection of natural gas in 1989 (C 1 :C 2 :C 3 = 91:6:2; δ 13 C 1 : −47‰), no increase in methane concentration and no higher hydrocarbon gases were observed during the regular analysis of groundwater from 10 shallow wells located above the underground natural gas storage. However, a sudden increase in dissolved methane concentration from 0.02 to 27 mg/l was measured in a 130 m deep observation well after a minor gas leakage had been detected at a new deep drilling into the natural gas storage in 1995. Nonetheless, no increase in methane was observed in shallow groundwater at the same locality. Occasional higher concentrations of dissolved methane (up to 15 mg/l) were encountered in shallow observation wells in low permeability layers. Stable isotope analyses (δ 13 C 1 : −69 to −52‰) and radiocarbon dating show that the gas does not originate from the underground gas storage because the methane was less than 300 years old, but it may have formed due to local microbial activity.

Abstract Rising demand and the depletion of its offshore reserves has resulted in the UK becoming a net importer of natural gas. An increased reliance on imports and limited current storage availability mean that the UK faces increasing energy bills and risk of disruption to supply. Because of this the UK government has set about ensuring security of energy supply. Steps taken include the construction of major new pipelines from Norway and Holland and improvements to interconnectors in the southern North Sea. The Government also recognizes that improvements to the gas supply infrastructure are required, including the need for significant increases in gas storage capacity; best met by the construction of underground storage facilities. Focus on energy security has also raised the likelihood of a new generation of coal-fired power-stations. For such a step to be environmentally viable, clean-coal technologies with near-zero greenhouse gas emissions will be required. Underground CO 2 storage will be a key element of this strategy. This volume reviews the technologies and issues involved in the underground storage of natural gas and CO 2 , by means of case-studies and examples from the UK and also from overseas. The potential for underground storage of other gases such as hydrogen, or compressed air linked to renewable sources is also reviewed.

Abstract The UK became a net importer of gas during 2004 and faces an increasing dependency on imports, yet has very little gas storage capacity. The UKs capacity to import, transport and store gas and liquid natural gas (LNG) has to be improved, requiring greater investment in new gas supply infrastructure. Construction of appropriately sited onshore underground gas storage (UGS) facilities is needed. However, local groups oppose most proposed UGS sites on the grounds of safety, citing the dangers of gas migration and rare fatal events, mostly in America. This paper summarizes 228 reported events of widely varying cause, nature and severity at underground fuel storage (UFS) facilities; the majority at USA SPR facilities. Since UGS was first undertaken in 1915, reports of 13 fatalities, around 72 injured and the evacuation of at least 6700 people are found at UFS sites. Some communities have experienced multiple evacuations. In the context of the danger posed to the general public, three of those killed were staff at two UFS facilities. UGS (including LPG) has led to 10 civilian deaths, 25 injured and c. 1250 evacuated. In other areas of the energy supply chain, casualties are orders of magnitude greater, with at least 1525 dead, 6826 injured and the evacuation of over 7000 at incidents involving above ground fuel storage tanks since 1951. When considering UK UGS applications, the risk of UGS and wider UFS experiences should be put into context. Worldwide, over 90 years experience in UGS now exists, with around 630 facilities of different types currently operational. Technologies used are often those of, or derived from, a well-regulated oil and gas exploration industry. In contrast to public perception, industry and academia recognize that UGS has an excellent health, safety and environmental record. Although it should not be claimed that gas will never be found outside the intended well or storage facility area, UFS casualty figures appear to corroborate claims by supporters of the technologies that salt caverns provide one of the safest answers to the problem of storing large amounts of hydrocarbons and that even in urban areas underground gas storage, oil and gas production can be conducted safely if proper procedures are followed. If gas is found outside the intended system, then after recognition of the problem, mitigation and safe operating procedures can and have been developed.

Abstract Basin modelling and compaction studies based on sonic data from the Mesozoic succession in 68 Danish wells were used to estimate the amount of section missing due to late Cenozoic erosion. The missing section increases gradually towards the coasts of Norway and Sweden from zero in the North Sea to c. 500 m in most of the Danish Basin, but over a narrow zone it reaches c. 1000 m on the Skagerrak-Kattegat Platform in northernmost Denmark. The increasing amount of erosion matches the increase in the hiatus at the base of the Quaternary, where Neogene and older strata are truncated, and the Mesozoic succession is thus found to have been more deeply buried by c. 500 Paleocene-Miocene sediments in large parts of the area. These observations suggest that the onset of erosion occurred during the Neogene, and that the Skagerrak-Kattegat Platform was affected by tectonic movements prior to glacial erosion. In southern Sweden just east of the Kattegat, the exposed basement of the South Swedish Dome attains altitudes of almost 400 m. The formation of the Dome started in the Late Palaeozoic, but geomorphological investigations have led to the conclusion that a rise of the Dome occurred during the Cenozoic. We find that the pattern of late Cenozoic erosion in Denmark agrees with a Neogene uplift of the South Swedish Dome and of the Southern Scandes in Norway. This suggestion is consistent with major shifts in sediment transport directions during the late Cenozoic observed in the eastern North Sea, and with formation of a new erosion surface as well as re-exposure of sub-Cambrian and sub-Cretaceous surfaces in southern Sweden. The Neogene uplift and erosion of southern Scandinavia appears to have been initiated in two phases, an early phase of ?Miocene age and a better-constrained later phase that began in the Pliocene. Neogene uplift of the South Swedish Dome with adjoining areas in Denmark fits into a pattern of late Cenozoic vertical movements around the North Atlantic.