Abstract
The hypothetical leakage of methane gas caused by fracking a 1,000-m deep Cretaceous claystone horizon at Damme, Germany, is simulated in a TOUGHREACT reactive-transport model with 5,728 elements. A hypothetical leakage zone connects the Cretaceous horizon with a Quaternary potable-water aquifer (q1). Methane gas rises up to the q1 horizon in less than 2 days in all calculated scenarios. The simulations include the major constituents of groundwater as well as the seven most hazardous trace components that are natural constituents of groundwater (As, Cd, Cr, Ni, Pb, Se and U). The general trend is characterised by depletion of the natural hazardous components with decreasing acidity and oxygen fugacity in the relevant pH range (7–9). Nevertheless, the concentrations of elements whose dominant aqueous species are negatively charged in this pH range (Cr and Se) rise against the general trend due to desorption reactions. Slight enhancement effects are produced by the dissolution of contaminant-bearing oxides such as Cr-bearing goethite. In summary, the geological risks of a fracking operation are minor. The technical risks are more important. This is especially the case when rising methane gas gets into contact with fracking fluid that accidentally escapes through faulty well seals.
Highlights
Methane is both a natural and a man-made contaminant in groundwater
At the start of the simulation, methane gas is only present in the lowermost cell at -969 m a.s.l
The geological risks involved in a fracking operation in methane-bearing shale are minor in comparison to the technical risks
Summary
Methane is both a natural and a man-made contaminant in groundwater. High aqueous methane concentrations affect the groundwater quality in an indirect manner. High pH together with low oxygen fugacity may cause the release of heavy metals or hazardous semi-metals from the aquifer posing a potential health risk. The more evident effect of high aqueous methane concentrations is the separation of a gas phase with pressure lowering causing explosions, fires or asphyxiations. The main reason is the increasing use of unconventional techniques in the exploitation of natural gas reservoirs. These methods are commonly based on hydraulic fracturing or fracking. The basic principle is the injection of a fracking fluid into the reservoir loosening the formation and releasing gas. The fluid is a mixture of water, quartz and dissolved chemicals, some of them toxic
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
