Geochemical evaluation of CO2 injection into storage reservoirs based on case-studies in the Netherlands

AbstractOver the past few years several geochemical evaluations of CO2 storage in Dutch potential reservoirs are carried out, including predictions of the short- and long-term impact of CO2 on the reservoir using geochemical modelling. The initial mineralogy of the reservoir is frequently obtained from core analysis and is then used to compute the formation water composition. In this paper geochemical modelling with TOUGHREACT is used to predict and compare the short- and long-term geochemical impact of CO2 injection into three reservoirs. The mineralogical composition of these reservoirs is an assemblage based on commonly observed minerals from the Buntsandstein and Rotliegend formations. These formations contain potential onshore and offshore CO2 storage locations in the Netherlands. The results predict drying out and salt precipitation in the near-well area, due to water evaporation by the injected dry CO2. Several mineral transformations are predicted, dominated by the transformation of albite into dawsonite, thereby fixing CO2. Due to the relatively low density of dawsonite, the porosity significantly decreases, which can lead to a pore pressure increase. Disabling of dawsonite precipitation in the simulations, thereby taking into account the ongoing debate on dawsonite stability, only shows a small increase of the porosity. Future (experimental) work should be focused on dawsonite occurrence for accurate predictions of the long-term reservoir integrity

Modelling of long-term along-fault flow of CO2 from a natural reservoir

Geological sequestration of CO2 requires the presence of at least one competent seal above the storage reservoir to ensure containment of the stored CO2. Most of the considered storage sites are overlain by low-permeability evaporites or mudrocks that form competent seals in the absence of defects. Potential defects are formed by man-made well penetrations (necessary for exploration and appraisal, and injection) as well as (for mudrocks) natural or injection-induced fracture systems through the caprock. These defects need to be de-risked during site selection and characterisation. A European ACT-sponsored research consortium, DETECT, developed an integrated characterisation and risk assessment toolkit for natural fault/fracture pathways. In this paper we describe the DETECT experimental-modelling workflow, which aims to be predictive for fault-related leakage quantification, and its application to a field case example for validation. The workflow combines laboratory experiments to obtain single-fracture stress-sensitive permeabilities; single-fracture modelling for stress-sensitive relative permeabilities and capillary pressures; fracture network characterisation and modelling for the caprock(s); upscaling of properties and constitutive functions in fracture networks; and full compositional flow modelling at field scale. We focus the paper on the application of the workflow to the Green River Site in Utah. This is a rare case of leakage from a natural CO2 reservoir, where CO2 (dissolved or gaseous) migrates along two fault zones to the surface. This site provides a unique opportunity to understand CO2 leakage mechanisms and volumes along faults, because of its extensive characterisation including a large dataset of present-day CO2 surface flux measurements as well as historical records of CO2 leakage in the form of travertine mounds. When applied to this site, our methodology predicts leakage locations accurately and, within an order of magnitude, leakage rates correctly without extensive history matching. Subsequent history matching achieves accurate leak rate matches within a-priori uncertainty ranges for model input parameters

Geo-scientific characterisation of the Boom Clay in the Netherlands in light of permanent confinement of radio-active waste

Recently, the OPERA research program has been initiated in the Netherlands. Its central objective is to develop initial, conditional safety cases for repositories in the Boom Clay and Zechstein rocksalt formations. TNO Geological Survey of the Netherlands has been granted two projects that deal with the geoscientific characterisation of the Tertiairy Boom Clay in the Netherlands, one of which is in cooperation with Utrecht University. The set-up of these projects is presented..

Water and Methane in Shale Rocks: Flow Pattern Effects on Fluid Transport and Pore Structure

Using molecular dynamics simulations we study the two-phase flow of water and methane through slit-shaped nano-pores carved from muscovite. The simulations are designed to investigate the effect of flow patterns on the fluids transport and on the pore structure. The results indicate that the Darcy’s law, which describes a linear relation between flow rate and pressure drop, can be violated when the flow pattern is altered. This can happen when the driving force, i.e., the pressure drop, increases above a pore-size dependent threshold. Because the system considered here contains two phases, when the fluid structure changes, the movement of methane with respect to that of water changes, leading to the violation of the Darcy’s law. Our results illustrate the importance of the capillary force, due to the formation of water bridges across the model pores, not only on the fluid flow, but also on the pore structure, in particular its width. When the water bridges are broken, perhaps because of fast fluid flow, the capillary force vanishes leading to significant pore expansion. Because muscovite is a model for illite, a clay often found in shale rocks, these results advance our understanding regarding the mechanism of water and gas transport in tight shale gas formations

Policy packaging or policy patching? The development of complex energy efficiency policy mixes

The ambition of energy policy has long been to reduce carbon emissions, secure energy supply and provide affordable energy services. In recent years an increasing number of policy instruments has been introduced to promote energy efficiency across the EU. While previous research has analysed the effectiveness of individual policy instruments and their impact on the diffusion of particular energy efficient technologies or practices, our analysis takes a broader view and examines the mix of existing policies aimed at stimulating reductions in energy use. The empirical focus of the paper is on policy goals and instruments aimed at stimulating energy efficiency in buildings in Finland and the United Kingdom. We trace the development of the policy mixes during 2000- 2014 and analyse their emerging overall characteristics. The analysis is based on a mapping of policy goals and instruments, documentary analysis and semi-structured interviews with stakeholders. We find that both countries have increasingly complex policy mixes, encompassing a variety of goals and instruments and make use of a range of different instrument types to encourage users to reduce energy consumption. Despite the shared EU influence, the way in which the policy mixes have evolved in both countries were found to be quite different