Gudni Axelsson

Rapid carbon mineralization for permanent disposal of anthropogenic carbon dioxide emissions

Inject, baby, inject! Atmospheric CO2 can be sequestered by injecting it into basaltic rocks, providing a potentially valuable way to undo some of the damage done by fossil fuel burning. Matter et al. injected CO2 into wells in Iceland that pass through basaltic lavas and hyaloclastites at depths between 400 and 800 m. Most of the injected CO2 was mineralized in less than 2 years. Carbonate minerals are stable, so this approach should avoid the risk of carbon leakage. Science, this issue p. 1312 Basaltic rocks may be effective sinks for storing carbon dioxide removed from the atmosphere. Carbon capture and storage (CCS) provides a solution toward decarbonization of the global economy. The success of this solution depends on the ability to safely and permanently store CO2. This study demonstrates for the first time the permanent disposal of CO2 as environmentally benign carbonate minerals in basaltic rocks. We find that over 95% of the CO2 injected into the CarbFix site in Iceland was mineralized to carbonate minerals in less than 2 years. This result contrasts with the common view that the immobilization of CO2 as carbonate minerals within geologic reservoirs takes several hundreds to thousands of years. Our results, therefore, demonstrate that the safe long-term storage of anthropogenic CO2 emissions through mineralization can be far faster than previously postulated.

Aquifer characterization with tracer test technique; permanent CO2 sequestration into basalt, SW Iceland

Abstract Mineral sequestration is among several promising methods of CO2 reduction. It involves incorporation of CO2 into a solid phase via precipitation of carbonate minerals. A prerequisite to carbonate precipitation is the availability of aqueous metal cations and a network of porous media for fluid flow and water-rock interactions. The Hellisheidi-Threngsli lava field in SW Iceland comprises ideal conditions for studying the feasibility of permanent CO2 storage as minerals in basaltic rocks. In this paper we report on a tracer test conducted between two wells at the Hellisheidi-Threngsli site to characterize the physical properties of the main aquifers. The results suggest that most of the water flow between the wells is through an homogenous thick layer with high tortuosity along flow paths and a high reactive surface area for water-rock interactions.

The Tanggu geothermal reservoir (Tianjin, China)

Abstract The Tanggu geothermal system is an extensive, highly permeable, horizontal sandstone reservoir, situated within the North China Sedimentary Basin. Twenty-three successful production wells, yielding water with an average temperature of about 70°C, have been drilled into this reservoir since 1987, distributed over an area of some 330 km 2 . The hot water is mostly used for space heating. In 1995 the annual production exceeded 5 million tons. Hot water extraction has caused the water level to drop to a depth of 80 m in the production wells, and it continues to decline at a rate of 3–4m per year. This has raised the question as to whether the reservoir may be overexploited. The main objective of a reservoir evaluation carried out in 1996 was to estimate the long-term production potential of the Tanggu reservoir. Two simple models were developed for this purpose. The potential is determined by specifying a maximum allowable pump setting depth of 150m. On this basis the potential of the Tanggu reservoir is estimated to be about 10 million tons per year, for the next ten years. A comprehensive reservoir management program must be implemented in Tanggu. The first priority of such a program should be to improve the energy efficiency of space heating in the district, which should result in about 50% reduction in hot water consumption. Another management option is reinjection, which would counteract the water level draw-down.