NATURE CLIMATE CHANGE | ADVANCE ONLINE PUBLICATION | www.nature.com/natureclimatechange 1 D espite two decades of effort to curb emissions of CO 2 and other greenhouse gases (GHGs), emissions grew faster during the 2000s than in the 1990s 1 , and by 2010 had reached ~50 Gt CO 2 equivalent (CO 2 eq) yr −1 (refs 2,3). The continuing rise in emissions is a growing challenge for meeting the international goal of limiting warming to less than 2 °C relative to the pre-industrial era, particularly without stringent climate policies to decrease emissions in the near future 2-4 . As negative emissions technologies (NETs) seem ever more necessary 3,[5][6][7][8][9][10] To have a >50% chance of limiting warming below 2 °C, most recent scenarios from integrated assessment models (IAMs) require large-scale deployment of negative emissions technologies (NETs). These are technologies that result in the net removal of greenhouse gases from the atmosphere. We quantify potential global impacts of the different NETs on various factors (such as land, greenhouse gas emissions, water, albedo, nutrients and energy) to determine the biophysical limits to, and economic costs of, their widespread application. Resource implications vary between technologies and need to be satisfactorily addressed if NETs are to have a significant role in achieving climate goals.options, to be able to decide which pathways are most desirable for dealing with climate change.There are distinct classes of NETs, such as: (1) bioenergy with carbon capture and storage (BECCS) 11,12 ; (2) direct air capture of CO 2 from ambient air by engineered chemical reactions (DAC) 13,14 ; (3) enhanced weathering of minerals (EW) 15 , where natural weathering to remove CO 2 from the atmosphere is accelerated and the products stored in soils, or buried in land or deep ocean [16][17][18][19] ; (4) afforestation and reforestation (AR) to fix atmospheric carbon in biomass and soils [20][21][22] ; (5) manipulation of carbon uptake by the ocean, either

The swelling of clay minerals on contact with an aqueous solution can produce strong adverse effects in the exploration and production of gas and oil. Molecular dynamics and Monte Carlo simulations were used to study the mechanism of swelling of sodium-montmorillonite. The simulations showed that the abundant clay mineral has four stable states at basal spacings of 9.7, 12.0, 15.5, and 18.3 angstroms, respectively. The amount of swelling and the locations of the stable states of sodium-montmorillonite are in good quantitative agreement with the experimental data.

SUMMARYWater-absorbing rocks are formed from minerals that can hold water in their crystal structure or between grain boundaries. Such water absorption is often accompanied by a change in the crystar dimension that manifests itself as a swelling of the rock. Swelling is particularly pronounced in rocks containing phyllosilicates because of the ease with which these minerals hydrate; it is thus of geological and geotechnical relevance in shales, clay-rich soils and zeolitized tuffs. The model of hydration swelling that we present here is based on extended versions of the equations of poroelasticity and Darcy's transport law, which we derive using a non-equilibrium thermodynamics approach. Our equations account for the hydration reaction under the assumption that the reaction rate is fast in comparison with the rate at which hydraulic state changes are communicated through the rock, i.e. that local physico-chemical equilibrium persists. Using a finite-element scheme for solving numerically the governing equations of our model, we simulate the creep of shales during a routine swelling test and calculate the stress and strain distributions around wellbores drilled in shale formations that undergo swelling. We show that swelling effects promote tensile failure of the wellbore wall.

The CO 2 SINK pilot project at Ketzin is aimed at a better understanding of geological CO 2 storage operation in a saline aquifer. The reservoir consists of fluvial deposits with average permeability ranging between 50 and 100 mDarcy. The main focus of CO 2 SINK is developing and testing of monitoring and verification technologies. All wells, one for injection and two for observation, are equipped with smart casings (sensors behind casing, facing the rocks) containing a Distributed Temperature Sensing (DTS) and electrodes for Electrical Resistivity Tomography (ERT). The in-hole Gas Membrane Sensors (GMS) observed the arrival of tracers and CO 2 with high temporal resolution. Geophysical monitoring includes Moving Source Profiling (MSP), Vertical Seismic Profiling (VSP), crosshole, star and 4-D seismic experiments. Numerical models are benchmarked via the monitoring results indicating a sufficient match between observation and prediction, at least for the arrival of CO 2 at the first observation well. Downhole samples of brine showed changes in the fluid composition and biocenosis. First monitoring results indicate anisotropic flow of CO 2 coinciding with the -on-time‖ arrival of CO 2 at observation well one (Ktzi 200) and the later arrival at observation well two (Ktzi 202). A risk assessment was performed prior to the start of injection. After one year of operations about 18,000 t of CO 2 were injected safely.

Existing work on mineral solubility in fluid-infiltrated and stressed rock has remained limited in that it has neglected surface forces. These forces are appreciable only when the fluid exists as a thin film, as in the grain-to-grain contact zone and in microcracks. Indeed, when the film thickness is of the order of 10 -9 m or so, the strength of the forces can be comparable to overburden stress at several kilometers depth. In this contribution we develop the thermodynamics of the phase reaction between nonhydrostatically stressed grains and an intervening water layer by using the concept of the disjoining pressure to account for surface forces acting in the grain-tograin contact zone. Using a thermodynamic extremum principle, we find an extended version of Gibbs's classical condition for the equilibrium of a stressed solid in contact with its solution phase. We then employ nonequilibrium thermodynamics to formulate kinetic equations describing phase boundary migration and intergranular mass transfer.It is demonstrated that surface forces weaken the efficacy with which diffusion removes dissolved material from the grain-to-grain contact zone and enhance the tendency of intergranular pressure solution to flatten initially rough surfaces. IntroductionThis work is concerned with a particular aspect of fluidrock interaction, namely, the contribution of surface forces to the solubility of minerals in a thin, intergranular, aqueous film. Surface forces have their origin in the interactions that the atoms in the solids have with the molecules in the fluid intedayer (see Horn [1990] and Israelachvili [1991] for comprehensive reviews).