UK Coal resource for new exploitation technologies. Final report

摘要

This focus of this report are the UK coal resources available for exploitation by the new technologies of Underground Coal Gasification, Coalbed Methane production and Carbon Dioxide Sequestration. It also briefly considers the potential for further underground and opencast mining and the extraction of methane from working and closed mines. The potential for mining was mainly considered because it has a bearing on the scope for the new exploitation technologies rather than to identify resources or potential mine development areas. The report covers the UK landward area and nearshore areas, although information on the extent of underground mining was not available for the nearshore areas.udThis work was carried out by the British Geological Survey, with the assistance of Wardell Armstrong and Imperial College, London. It represents a summary of the results of the Study of the UK Coal Resource for New Exploitation Technologies Project, carried out for the DTI Cleaner Coal Technology Programme (Contract No. C/01/00301/00/00) under the management of Future Energy Solutions (Agreement No. C/01/00301/00/00).udCoalbed methane production can be subdivided into three categories:udMethane drained from working mines, known as Coal Mine Methane (CMM), has been exploited in the UK since at least the 1950s. Currently all working mines except Daw Mill and Ellington drain methane. It is used to generate electricity at Harworth, Tower and Thoresby collieries and in boilers at Welbeck, Kellingley and Ricall/Whitemoor collieries. There is potential to increase the exploitation of CMM in the UK but this is mainly a question of economics. There is also an environmental case for further utilisation, as methane is an important greenhouse gas, 23 times more powerful than carbon dioxide on a mass basis.udMethane drained from abandoned mines, known as Abandoned Mine Methane (AMM), is a methane-rich gas that is obtained from abandoned mines by applying suction to the workings. The fuel gas component consists primarily of methane desorbed from seams surrounding the mined seam(s). These unmined seams have been de-stressed and fractured by the collapse of overlying and underlying strata into the void left by the extracted seam(s). Currently AMM is being exploited at sites in North Staffordshire (Silverdale Colliery), the East Midlands (Bentinck, Shirebrook and Markham collieries) and Yorkshire (Hickleton, Monk Bretton and Wheldale collieries). The methane-rich gas is used for electricity generation or supplied to local industry for use in boilers and kilns. Over the last few years, the fledgling UK AMM industry has started to ascend a learning curve. However, it has suffered a major setback since the wholesale price of electricity fell under the New Electricity Trading Arrangements and AMM does not currently qualify as renewable energy in the UK.udCoalbed methane produced via boreholes from virgin coal seams, known as Virgin Coalbed Methane (VCBM), has been the subject of significant exploration effort in Lancashire, North Wales, South Wales and Scotland. The best production of gas and water from a single well is understood to be from the project at Airth, north of Falkirk in Scotland. However, this is not economic at present. The main reason for the slow development of VCBM in the UK is perceived to be the widespread low permeability of UK coal seams, although little work has been carried out in the UK on coal permeability, or to truly identify the reasons for the lack of success. This must be overcome before the otherwise significant resource bases in the Clackmannan Syncline, Canonbie, Cumbria, South Lancashire, North Wales, North Staffordshire and South Wales coalfields can be exploited. A technological breakthrough is required to overcome the likely widespread low permeability in the UK Carboniferous coal seams. Otherwise, at best, production will probably be limited to niche opportunities in areas where high seam permeability exists. The criteria used to define and map the location of VCBM resources are as follows:ud• Coal seams greater than 0.4 m in thickness at depths >200 mud• Seam gas content >1m3/tonneud• 500 metres or more horizontal separation from underground coal workingsud• Vertical separation of 150m above and 40 m below a previously worked seamudVertical separation of >100 m from major unconformitiesudof these areas is thought to be aboutud,900 x 109 m3 (about 29 years of UK natural gas consumption).udhe main criteriaudsed for the delineation and mapping of resource areas with potential for UCG were:udeparation from underground coal workings and currentudomic and environmental grounds as described later in this report.udhe establishment of these criteria do not rule out UCG projects in shallower or thinner seams, ifud• Vertical separation of >100 m from major aquifers, andud•udAreas with a CMM resource (current underground coal mining licences) were excluded. Note that the presence of a CBM resource does not imply permeability in the coal seams or that the resource can be recovered economically now or at any time in the future. Using these criteria resource areas were defined and represented on the maps. The total VCBM resourceud2udUnderground coal gasification (UCG) is the process whereby the injection of oxygen and steam/water via a borehole results in the partial in-situ combustion of coal to produce a combustible gas mixture consisting of CO2, CH4, H2 and CO, the proportions depending on temperature, pressure conditions and the reactant gases injected. This product gas is then extracted via a producing well for use as an energy source. All previous trials of this technology in the UK took place in the 1950’s or before, e.g. Durham (1912), Newman Spinney (1949-1956) and Bayton (c.1955), although this country is well placed for UCG, with large reserves of indigenous coal both onshore and offshore. Tuduud• Seams of 2 m thickness or greaterud• Seams at depths between 600 and 1200 m from the surfaceud• 500 m or more horizontal and vertical scoal mining licences, andud•udGreater than 100 m from major aquifers While seams outside these depth and thicknesses criteria are known to support UCG, the criteria were chosen for this generic study on econudTudlocal site specific factors support it. Mapping of the potential UCG resource has identified large areas suitable for UCG, particularly in Eastern England, Midland Valley of Scotland, North Wales, Cheshire Basin, South Lancashire, Canonbie, the Midlands and Warwickshire. Potential also exists in other coalfields but on a smaller scale; this is often limited by the extent of former underground coal mining activities. The total area where coals are suitable for gasification is approximately 2.8 x 109m2. Where the criteria for UCG are met, the minimum volume of coal available for gasification, calculated assuming only one 2 m thick seam meets the criteria across each area, is app63 roximately 5,698 x 10 m (~7 Btonnes). Using anudverage of the total thickness of coals that meet the criteria across each area gives a more realisticudsource figure of 12,911 x 106m3 (~17 Btonnes).udpass the expensive step ofudparating the CO2 from flue gases. If the main objective, however, is CO2 sequestration rather thanudethane production then separation of the flue gases may be worthwhile.udO2 on coal seams,udis would render them unminable and ungasifiable (because the CO2 would be released). Any futureudining of such coals would require re-capture and sequestration of the stored CO .udion, providing that other issues, such as low seam permeability, can beudvercome. Large areas where coal is below 1,200 m occur in the UK, particularly in the Cheshireudasin and Eastern England.udIn summaryud• and its potential application in the UKudcannot be assessed. However, there are vast areas of coal at depths below 1,200 m that areudpossibly too deep for mining and in situ gasification.