Power-to-gas technology makes use of surplus electricity by its conversion and storage in the form of a gas. Currently power-to-gas schemes based on biological processes are of great interest. Microbial electrosynthesis (MES) cells are biological systems that produce biogas via microbial action and a supply of electrical energy. The OxyMES scheme proposed is a power-to-gas system that seeks to neutralize the CO2 emissions of a standard industrial process through the hybridization of oxy-fuel combustion and bioelectrochemical processes that produce CH4 (in cathode) and O2 (in anode). This oxygen is used for oxycombustion in an industrial C-fuel boiler. The energy balance analysis yielded a power-to-gas efficiency in the MES cell close to 51%, and the overall performance of the OxyMES integrated system was close to 60% for a cell with a Faradaic efficiency of 80%, CO2-to-CH4 conversion rate of 95%, and ΔVcell = 1.63 V. With the proper sizing of the CO2, O2, and biogas process tank system, it is possible to achieve 100% autonomy, free from external feedstock supplies.

In a reservoir characterization study of the Hontomín deep saline aquifer, the impact of geological heterogeneities on reservoir storage capacity and the migration of the CO2 plume is explored. This work presents, for the first time, very long-term (up to 200 years) simulations of CO2 injection into the naturally fractured Sopeña Formation, of the lower Jurassic age, at Hontomín. CO2 injection was simulated as a dual permeability case with Eclipse compositional software. The matrix permeability of the carbonate reservoir is quite low (0.5 mD) and thus fluid flow through the fractures dominates. The reservoir is dissected by eight normal faults which limited its south-east extension and divided it into several segments. The effect of geological heterogeneities was tested through scenario-based modeling and variation of parameters characterizing heterogeneity within realistic limits based on other similar formations. This modeling approach worked well in Hontomín where the database is completely scarce. The plume migration, the reservoir storage capacity, and pressure, were each influenced in diverse ways by incorporating particular types of heterogeneities. The effect of matrix heterogeneities on reservoir storage capacity was substantial (by factors up to ∼2.8×), compared to the plume migration. As the reservoir matrix permeability heterogeneity increased, the reservoir storage capacity markedly decreased, whilst an increase in porosity heterogeneity significantly increased it. The vertical gas migration in the homogeneous base case was relatively larger compared to the heterogeneous cases, and gas accumulated underneath the caprock via hydrodynamic trapping. It was also observed that, in heterogeneous cases, gas saturation in rock layers from top to bottom was relatively high compared to the base case, for which most of the gas was stored in the topmost layer. In contrast, the impact on storage capacity and plume movement of matrix vertical to horizontal permeability ratio in the fractured carbonate reservoir was small. The impact of the transmissibility of faults on reservoir pressure was only observed when the CO2 plume reached their vicinity.

Monitoring of geological CO2 storage is crucial for large-scale injection to gain public acceptance. Monitoring plans for large-scale operations need to include both the injection and post-injection phases to assure CO2 is safely stored permanently. The SENSE project aims to develop reliable, continuous, and cost-efficient monitoring based on ground movement detection combined with geomechanical modeling and inversion, utilizing new technology developments, data processing optimization, and interpretation algorithms. The proposed research activities include: • demonstration of continuous monitoring of surface deformation and subsurface pressure distribution using satellite data, water pressure sensors and fiber optics; • quantitative characterization of critical geomechanical and hydraulic parameters and automatization routine for data processing and interpretation; • optimization of sampling arrays in order to offer storage site operators a cost-effective monitoring option as part of an effective site assurance program. The SENSE project brings together experts from 14 international institutions of nine different countries to solve challenges in CO2 storage site monitoring and to provide solutions for safe and successful injection and post-closure phases of site operation. The project is organized in five Work Packages (WPs); WP1: Quantification of ground movement, WP2: Geomechanical modeling and rock strain assessment, WP3: History matching inversion and coupled flow-mechanics, WP4: Integration of results for cost-effective monitoring and WP5: Project management. The ultimate goal of SENSE is to offer storage site operators a cost-effective monitoring option that can form part of an effective site assurance/monitoring program and feed into workflows for an early alert system to detect unexpected changes in the subsurface. The SENSE project has four demonstration sites for monitoring technologies and developing concepts and procedures. These sites are both onshore and offshore. The onshore sites include In Salah (Algeria) and Hotfield Moors (UK). For these sites, the project will use satellite data to explore the response of the surface to pressure changes in the subsurface. Algorithms for automatic satellite data processing to facilitate quick access to ground elevation data for site operators are under development at the British Geological Survey (BGS) and Norwegian Geotechnical Institute (NGI). The offshore sites include Bay of Mecklenburg (Germany) and the Gulf of Mexico (USA). In addition, the SENSE partners have requested access to data from the Troll Gas Field, the North Sea, to study its subsidence due to production-related pressure reduction. The Troll Gas Field is located next to the storage site considered for the Norwegian Long Ship project, and its data will provide a good understanding of the geomechanics of the area. In this paper, we present the work on the In Salah and the Bay of Mecklenburg sites. New InSAR data from the In Salah are used to evaluate the ground movement during the post-injection period and thus to assess the behaviour of the storage site after completion of the injection phase. Bay of Mecklenburg is an offshore site for field experiment to inject a gas underground, build-up pressure, uplift the seafloor and measure the resulted uplift. The first field campaign at the Bay of Mecklenburg was completed in late 2019. It provided both gravity cores from the seabed and geophysical data acquisition for characterizing the shallow subsurface layers. The gravity cores were characterized for physical and mechanical properties. The material properties were used for simulating injection and response of the seafloor to induced pressure. Geomechanical 2D and 3D simulations show that the reservoir may sustain very low overpressure before it fails. Hence, this magnitude of overpressure may create a seafloor uplift of about a few millimeters to a couple of centimeters. The monitoring techniques are therefore being designed to capture uplift in this order of magnitude during the injection operation.

Deep saline aquifers are target for carbon sequestration since these geological structures abound in many areas worldwide. Hydraulic characterization tests are focused on site feasibility assessment to inject CO2 in an efficient and safely manner. For this, it is necessary to carry out both laboratory and field tests to determine hydraulic properties and operating parameters such as permeability and injectivity in the reservoir, and the trapping degree of the structural complex. CO2 injection experiences usually come from projects conducted in aquifers composed by sandstones and similar rocks, unlike those carried out in carbonates that are quite limited. Sometimes carbonates are porous mediums, but in other cases, primary permeability is really poor being the fluid transmissivity mainly through the fracture network. Moreover, geochemical reactivity produced by the acidification of the mixture of CO2 and resident brine plays a key role in these cases. This chapter address the innovative on-site hydraulic characterization tests conducted in the deep saline aquifer of Hontomin Technology Development Plant (Spain), which is composed of naturally fractured carbonates with low primary permeability. The impacts of artificial brine and CO2 migration through the fracture network are described, analyzed and discussed, considering that produces hydrodynamic, mechanical and geochemical effects different from those caused by the injection in mediums with a high matrix permeability.

Site characterization for CO2 geological storage needs works at field scale and laboratory to prove the seal-reservoir pair capability to trapping the captured gas in a safely and efficient manner. Laboratory works are used to design field tests and for checking their results in a more controllable monitored environment. Petrophysical characterization through laboratory works intends to quantify operating parameters such as the reservoir injectivity and also the short and long-term trapping ability. For this, both usual routine tests of oil and gas industry, as well as, specific and innovative tests for CO2 geological storage are carried out. This chapter address laboratory tests and results achieved during the characterization of Hontomin Technology Development Plant (TDP). The main singularity is the poor primary permeability of the naturally fractured carbonates that compose the reservoir, which impacts on gas migration that is dominated by fractures. This challenging fact conditions the petrophysical characterization, since hydrodynamic, geomechanical and chemical effects take place induced by the injection and they must be analyzed by innovative works. Innovative tests and results are described, analyzed and discussed, paying special attention to those carried out by the ATAP equipment, a patent of Technical University of Madrid (UPM).

CO2 injection must be safe assuring the integrity of seal-reservoir pair for long-term gas trapping, and it must be also efficient as commercial activity that seeks business profit. Injection in tight reservoirs, as fractured carbonates, usually needs high pressure values to reach proper injectivity ranges, what means the geological complex integrity could be put at risk due to rock fracturing or fault-slip that may generate leakage pathways. The study case of OXYCFB300 Project is addressed in this chapter, analyzing how the CO2 injection in dense state is conducted in the naturally fractured reservoir of Hontomin pilot. Inputs from hydraulic characterization tests developed on site, addressed on Chapter “ On-Site Hydraulic Characterization Tests”, are briefly analyzed, tackling how the injection strategies were designed under mentioned safety and efficiency criteria. Spanish Patent “Industrial process for CO2 injection in dense state from pipeline transport condition to permanent geological trapping” is analyzed in the chapter. Particularly, the innovative process with alternative injection of CO2 and brine, as well as, the necessary mitigation tools to preserve the operation safety. Both measures to control the bottom pressure build up and the effect of impurities existing on CO2 stream are analyzed. Finally, the conditions necessary to become a patent in operation are described, as future works planned in the project.

Drilling is within the core activities of CO2 geological storage since the more wells are drilled the higher amount of data is managed for site characterization and for a successful decision making on project viability. Most of commercial projects worldwide are at the early stage where the costs related to exploration play a key role, as is the case of the traditional drilling techniques from Oil and Gas industry that are usually expensive for on-shore projects whose business model still has to be proven. How to save drilling costs is addressed in the chapter, showing the experiences gained during the construction of the on-shore pilot: Hontomin Technology Development Plant (Burgos, Spain). Hontomin well drilling/completion was a success as the depth of 1600 m was reached using light drilling rigs (mining technique), achieving cost saving close to 60% in comparison to traditional techniques. Some experiences exist in the use of these rigs for mining, shale gas and oil and geothermal recovery, but for CO2 geological storage they are limited to the Hontomin case. The existing technological drilling gaps identified during the plant construction and the future works for improving these rigs to reach the depth of 2500 m with a well geometry adequate to install advanced monitoring, are also addressed in this chapter.

Most European Member States that transposed the EU Directive 2009/31/CE on geological storage of carbon dioxide to each national legislation have not yet developed a regulatory framework to govern the permitting process of this industrial activity. This scenario does not help the deployment of Carbon Capture and Storage (CCS) technologies, as regulators, administrations, operators and general public do not handle a clear compendium of rules and standards to follow. This lack of regulation affects even more to the on-shore sites, which are usually surrounded by communities, industries, farms and other environmental elements that require the compliance of regulations to assure safe and controlled industrial processes. This article describes and analyses the workflow followed for granting the storage permit of Hontomín Technology Development Plant (TDP) in Spain. Hontomín is today the only onshore CO2 injection site in Europe, recognized by the European Parliament as a key test facility for CCS technology development. The authors aim to show the experience gained from this real case as a guideline for regulators, operators and administrations to facilitate the grant of storage permits for supporting the development of industrial scale projects.

The leachability and speciation of inorganic trace contaminants of oxy-coal combustion fly ash from a 20 MWth oxy-pulverized coal combustion (oxy-PCC) demonstration plant have been evaluated. Colle...