Review: Thermal water resources in carbonate rock aquifers

Abstract

The current knowledge on thermal water resources in carbonate rock aquifers is presented in this review, which also discusses geochemical processes that create reservoir porosity and different types of utilisations of these resources such as thermal baths, geothermal energy and carbon dioxide (CO 2 ) sequestration. Carbonate aquifers probably constitute the most important thermal water resources outside of volcanic areas. Several processes contribute to the creation of porosity, summarised under the term hypogenic (or hypogene) speleogenesis, including retrograde calcite solubility, mixing corrosion induced by cross-formational flow, and dissolution by geogenic acids from deep sources. Thermal and mineral waters from karst aquifers supply spas all over the world such as the famous bath in Budapest, Hungary. Geothermal installations use these resources for electricity production, district heating or other purposes, with low CO 2 emissions and land consumption, e.g. Germany's largest geothermal power plant at Unterhaching near Munich. Regional fault and fracture zones are often the most productive zones, but are sometimes difficult to locate, resulting in a relatively high exploration uncertainty. Geothermal installations in deep carbonate rocks could also be used for CO 2 sequestration (carbonate dissolution would partly neutralise this gas and increase reservoir porosity). The use of geothermal installations to this end should be further investigated.

The World Karst Aquifer Mapping project: concept, mapping procedure and map of Europe

“…GLiM and other globally available data sources do not provide explicit information on the percentage of carbonate minerals; however, lithological terms, such as limestone, dolomite or chalk, usually indicate Bpure^carbonate rocks. Although the actual degree of karstification can vary greatly as a function of different geological and climatological factors (Goldscheider and Drew 2007), it is safe to assume that exposed carbonate rocks are karstified at least to some degree, unless proven otherwise. The following four principal mapping units were defined ( Fig.…”

“…Karst aquifers form in soluble rocks by flowing groundwater and are characterized by solutionally enlarged fractures, bedding planes and conduits, which form a hydraulically connected drainage network (Goldscheider and Drew 2007). Carbonate sedimentary formations including more than 75% of carbonate minerals such as limestone and dolomite, are the most important karstifiable rocks (Ford and Williams 2007).…”

“…concealed, confined or artesian aquifers) are better protected against direct contamination from the land surface. However, contaminant releases from deeper sources can also result in widespread contamination of these valuable freshwater or thermal-mineral water resources (Goldscheider et al 2010). Because of their hydrogeologic heterogeneity, karst aquifers are difficult to exploit by means of drilling wells, which are often unproductive if they do not succeed in encountering water-bearing fractures, bedding planes or conduits.…”

Early-stage hypogene karstification in a mountain hydrologic system: A coupled thermohydrochemical model incorporating buoyant convection

“…Ford [2006] and Klimchouk [2009] suggest that the above alternative definitions are unified by noting that the most important common hydrogeological feature shared by hypogene karst systems is that they are formed in confined settings by flow of water into a soluble formation from below. The processes, mechanisms, and timescales associated with the origin and development of hypogene karst systems are of significant hydrogeological and speleological interest [Palmer, 1991;Ford and Williams, 2007;Klimchouk, 2009], and also relevant in the context of renewable geothermal energy development and subsurface carbon sequestration in deep karst systems [Dreybrodt and Gabrovsek, 2003;Klimchouk, 2007;Goldscheider et al, 2010]. One subset of hypogene karst systems is formed in settings where meteoric waters circulate to great depths and rise up along high-permeability vertical or subvertical fracture/ fault zones [Ford and Williams, 2007;Perry et al, 1979;Hobba et al, 1979;Severini and Huntley, 1983;Palmer, 1991;Goldscheider et al, 2010;Davidson et al, 2011].…”

“…One subset of hypogene karst systems is formed in settings where meteoric waters circulate to great depths and rise up along high-permeability vertical or subvertical fracture/ fault zones [Ford and Williams, 2007;Perry et al, 1979;Hobba et al, 1979;Severini and Huntley, 1983;Palmer, 1991;Goldscheider et al, 2010;Davidson et al, 2011]. Examples of karst systems of this category include karst springs in the Warm springs valley anticline in northwestern Virginia and other areas within the Appalachians [Hobba et al, 1979;Serevini and Huntley, 1983]; the Roszadomb thermal springs in Budapest, Hungary [Ford and Williams, 2007;Goldscheider et al, 2010]; the thermal springs of Bath, England [Andrews et al, 1982]; and cave systems of the southern Guadalupe mountains in New Mexico and Texas and Black Hills of South Dakota [Palmer, 1991;Ford and Williams, 2007;Bakalowicz et al, 1987].…”