Carbon Storage Sites Research Articles

Integrating underground gas storage experience for CCS optimisation

Carbon capture and storage (CCS) sites require diligent assessments to account for potential leakage over time. Leakage pathways include both natural and engineered (e.g. wells) invoking the requirement for a structured technical analysis as part of a risk inventory. This paper focuses on lessons learnt from underground gas storage (UGS) sites to guide CCS technical workflows to handle natural geological risk elements. UGS facilities have been operating for over a 100 years. Their injection and withdrawal histories, by their very nature, test the complex changes that occur to the reservoir and cap-rock over time and provide valuable insight to demonstrate the feasibility of CCS and its potential for long-term storage. Geomechanical assessment of the reservoir and cap-rock requires an inventory of core material, log and seismic data with the aim of selecting the appropriate data to model the ability of that formation to contain a column of CO2. As supercritical CO2 is injected into the formation and pore pressure builds, the geomechanics of the reservoir needs diligent review to assess the potential to trigger failure on the cap-rock and pre-existing faults and fractures. UGS injection/withdrawal histories assist in the reservoir and overburden static and dynamic modelling along with designing a measurement, monitoring and verification process for CCS sites. Technical workflows, from seismic and static modelling to geomechanics and dynamic simulation and back to seismic for containment monitoring, are discussed that have been refined by UGS experience to benefit the selection of potential CCS sites.

Effects of abiotic processes on the correlation between pH and pO2 in the Norwegian Sea: Implications for GCS monitoring

In the absence of abiotic sources of CO2, variation in pCO2 and pO2 is expected to be inversely correlated in the water column due to biogenic processes. It has previously been suggested to use this correlation for leakage monitoring of offshore geological carbon storage (GCS) sites. In this study the aim is to investigate the extent of this correlation in ocean water masses with different origin and history in the Norwegian Sea, as well as in water masses in the vicinity of an active hydrothermal vent field at Mohn's Ridge, where pH is used as a proxy for pCO2. Over a hydrothermal vent site, a strong correlation between pH and pO2 is observed from 0 to 1700 m, whereas at depths >1700 m there is no correlation, likely due to CO2 emissions from the hydrothermal vents. However, at a reference site nearly 200 km from the hydrothermal vents, the intermediate Arctic water masses (700 – 1600 m depth) also show pH-pO2 correlations that are inconsistent with biogenic processes, but less pronounced compared to the hydrothermal vent site. These findings show that the suitability of this monitoring strategy will depend on a thorough site-specific evaluation of pH/CO2 and O2 relationships of relevant water masses.

Stratigraphic change in flow transformation processes recorded in early post‐rift deep‐marine intraslope lobe complexes

AbstractThe Early Jurassic Los Molles Formation in the Neuquén Basin of western Argentina is a rare example of well‐exposed syn‐rift to post‐rift stratigraphy. In the Chachil Graben, the onset of the early post‐rift stage is marked by drowning of a carbonate system and the development of two deep‐marine intraslope lobe complexes. This field‐based study in the Chachil Graben involved field mapping and correlating eleven stratigraphic logs, and petrographic analysis to document how grain size and texture within intraslope lobe sandstones change from the lobe centre to their frontal pinch‐out. Eight different bed‐scale facies are identified and inferred to be formed by turbulent (turbidites; Type A and B beds), transient turbulent–laminar (transitional flow deposits; Type C, D, E and F beds), laminar gravity flows (debrites; Type G) and post‐depositional clastic injections (injectites; Type H beds). Fifteen lobes form two stacked lobe complexes that show stratigraphic evolution from a lower argillaceous sandstone‐dominated lobe complex, built by transitional flow deposits, to an upper coarser‐grained, sandier lobe complex largely constructed by turbidites. Petrographic analysis quantified sandstone mineralogy, matrix content, grain size and sorting, revealing that both lobe complexes are volcanic arc‐sourced. This study proposes that the differences in the character of the two lobe complexes are due to maturation of sediment transport routes through progressive healing of the intraslope relief, with a concomitant decrease in substrate erosion and flow bulking. Also proposed here is a model for intraslope lobe complex development that accounts for the impact of flow‐confinement on flow behaviour and transformation induced by the inherited topography. Bed type distribution suggests that high‐density flows terminate more abruptly against confining slopes and produce greater depositional variability than lower‐density flows. This integrated petrographic, architectural and sedimentary process model provides new insights into how post‐rift intraslope lobe systems may act as hydrocarbon reservoirs, aquifers and carbon storage sites.

Potential Pathway for Reliable Long-Term CO2 Storage as Clathrate Hydrates in Marine Environments

A countermeasure to global warming is removing high CO2 amounts from the atmosphere and locating the emitted CO2 into long-term stable carbon storage sites. The sequestration technologies must be reliable, long-lasting, and environmentally friendly. An alternative and innovative approach that may meet the sequestration requirements is CO2 storage as clathrate hydrates in marine environments. Extensive research has been devoted to CO2-CH4 replacement in natural gas hydrates. Another option is the direct formation of CO2 hydrates into deep ocean water or into marine underfloor sediments. This article deals with the positioning of direct hydrate-based CO2 storage among the other traditional geological options and the discussion of new, by-far, state-of-the-art knowledge required for the development of a hydrate-based CO2 storage pathway that is reliable, stable, durable, efficient, and environmentally benign.

Porosity in mudstones and its effectiveness for sealing carbon capture and storage sites

Abstract Mudstones represent top-seals for many carbon capture sites as they tend to have the correct petrophysical properties, including suitable porosity and pore-size distribution. The pore network of mudstones is thus pivotal for many carbon capture and storage (CCS) projects. The key to understanding the effectiveness of top-seals is an appreciation of the controls on the pore network. For this reason, schemes to classify pore body size, pore type and pore throat size are presented. Pore types include primary and secondary interparticle and intraparticle pores and pores associated with organic matter and fractures. The most relevant mudstone pore body sizes for CCS top seals are likely to be between <62 µm and 1 nm. Pore throat sizes are classified as nano- (<10 nm), transition- (10 nm–0.1 µm), meso- (0.1–0.625 µm), and macro-pore throats (>0.625 µm). Petrophysical, geochemical, and geomechanical properties control porosity and the CO 2 sealing integrity of mudstones; these properties are, in turn, controlled by the rate and extent of compaction, mineral diagenesis and overpressure. The success of a CCS top-seal relies on pore throats in intact top-seal being sufficiently small, and fracture pressure (typically minimum horizontal stress, σ hmin ) not being exceeded by CO 2 pressure. CO 2 sorption, especially by smectite in top-seals, may improve the nanoscale sealing efficiency of clay minerals. The systematic workflow presented here will help facilitate the new drive to understand mudstone properties, as they are essential for establishing safe and durable CO 2 containment.

CAGE13-3 Cruise Report: Sub-seabed CO2 Storage: Impact on Marine Ecosystems (ECO2) (A 7th Framework Programme EU project) PART I.

The ECO2 project sets out to assess the risks associated with the storage of CO2 below the seabed. Carbon Capture and Storage (CCS) is regarded as a key technology for the reduction of CO2 emissions from power plants and other sources at the European and international level. The proposed project will assess the likelihood of leakage and impact of leakage on marine ecosystems. As part of the ECO2 project, cruise CAGE13-3 intend to acquire a 3D seismic volume (which will act as monitor along with the 3D cube collected in 2011) from the Snøhvit carbon capture area. In addition, we will repeat some of the lines twice and in reversed direction in order to study the repeatability of the P-Cable acquisition for monitoring purposes. The primary objective of the hydrological and biogeochemical sampling in the Snøhvit area is to study any possible effects of a Carbon Capture and Storage (CCS) site on the water column and on the bottom sediment.
 The cruise may be known as: HH_2013_ECO2_I

An extended Exp-TODIM method for multiple attribute decision making based on the Z-Wasserstein distance

Z-numbers, as relatively emerging fuzzy numbers, are to a large extent close to human language. For this reason, the Z-number is a powerful tool for representing expert evaluation information. However, the Z-number is more complex than the general structure of fuzzy numbers since it consists of both the fuzzy restriction A and the reliability measure B. As a result, calculating of the Z-number is a very complex process. This paper uses a modified Wasserstein distance to measure the distance between two Z-numbers, which avoids the loss of information better than the existing metric. Then a new decision model is constructed by combining the Z-Wasserstein distance with the exponential TODIM method(exp-TODIM), which is less susceptible to changes in parameters and has good stability. Next, a detailed example of choosing a reasonable carbon storage site is given to illustrate the feasibility of the exp-TODIM method with wasserstein distance. Finally, a sensitivity analysis is given to illustrate the stability of the method, and a comparative analysis is used to state the advantages of the method.

Screening of future carbon storage sites – selecting the best spots

Subsurface carbon storage can occur in depleted oil and gas fields, in water-wet structures, or in open aquifers. All three types of storage sites present advantages and inconveniences, which will be reviewed in this talk. The selection of future sites for carbon storage balances storage capacity (how much CO2 can be stored), injectivity (how efficiently or fast CO2 can be stored), and containment risk (how safely CO2 can be stored). We present a rigorous uncertainty-based approach involving estimates of pore volume, pressure and temperature conditions and resulting fluid properties, and sealing and containment behaviour, to highlight areas with best potential for safe and effective carbon storage.

A Project Lifetime Approach to the Management of Induced Seismicity Risk at Geologic Carbon Storage Sites

AbstractThe geologic storage of carbon dioxide (CO2) is one method that can help reduce atmospheric CO2 by sequestering it into the subsurface. Large-scale deployment of geologic carbon storage, however, may be accompanied by induced seismicity. We present a project lifetime approach to address the induced seismicity risk at these geologic storage sites. This approach encompasses both technical and nontechnical stakeholder issues related to induced seismicity and spans the time period from the initial consideration phase to postclosure. These recommendations are envisioned to serve as general guidelines, setting expectations for operators, regulators, and the public. They contain a set of seven actionable focus areas, the purpose of which are to deal proactively with induced seismicity issues. Although each geologic carbon storage site will be unique and will require a custom approach, these general best practice recommendations can be used as a starting point to any site-specific plan for how to systematically evaluate, communicate about, and mitigate induced seismicity at a particular reservoir.

Development and testing of a rapid, sensitive, high-resolution tool to improve mapping of CO2 leakage at the ground surface

Locating and quantifying anomalous, deep-origin CO2 leakage from the soil to the atmosphere is typically accomplished by interpolating a dataset of point flux measurements, with overall accuracy and uncertainty strongly influenced by sample spacing relative to anomaly size and variability. To reduce this uncertainty we have developed the Ground CO2 Mapper, a low-cost complementary tool that rapidly measures, at high spatial resolution, the distribution of CO2 concentration at the ground-air contact as a proxy of CO2 flux. Laboratory tests show that the Mapper has a low noise level (2σ = 16 ppm) and fast response time (T90 = 1.55 s), while field tests at a small controlled-release site define a high level of reproducibility and sensitivity and illustrate the impact of wind and survey speed on instrument response. Modelling based on these results indicates that the Mapper has a greater than 60% probability of detecting an intersected 2 m wide anomaly having a maximum CO2 flux rate of 75 and 100 g m−2 d−1 at survey speeds of 2.5 and 4.8 km h−1, respectively, under the test conditions. Measurements in a large (4600 m2) grassland field where natural geogenic CO2 is leaking show how the Mapper can produce, in <10% of the time, a more detailed map of CO2 flux distribution than a point flux survey conducted on a ca. 10 m grid spacing. Based on these results we believe the Ground CO2 Mapper can give a useful contribution to diffuse degassing studies in volcanic/geothermal areas and to monitoring of Carbon Capture and Storage (CCS) sites by reducing overall survey time, costs and uncertainty. Future work will test the Mapper's response and capabilities under more diverse site and meteorological conditions than those examined in this study.

Poromechanical analysis of oil well cements in CO2-rich environments

Wells drilled in carbon storage sites could be converted to potential leakage pathways in the presence of CO2-bearing fluids and under the impact of the changes occurring in underground stress. To test this hypothesis, in this study, the behavior of Class G oil well cement in contact with supercritical CO2 has been investigated. The cement cores were cured under lime-saturated water for 28 days at a temperature of 20 ∘C and under atmospheric pressure. Subsequently, they were exposed to supercritical CO2 under a pressure of 20 MPa and at a temperature of 90 ∘C for 30 days. The penetration depth of the carbonation front and the change in the poromechanical properties of the cement core were measured against time. A numerical modeling exercise has also been conducted to simulate the alteration within the cement cores. The results presented in this study show that the precipitation of calcium carbonates reduces the porosity within the outermost layers of the cement cores. This phenomenon shifts the main pore size class towards smaller sizes. In contrast to expectations, the reduction in porosity does not improve the overall strength of the cement specimens. The observed reduction in the strength of the cement specimens might be associated with either the amorphous structure of the precipitated carbonates or the weak bonding between them and the solid walls of the pores and the high degradation of calcium silicate hydrates.

Real-Time Monitoring of Gas-Phase and Dissolved CO2 Using a Mixed-Matrix Composite Integrated Fiber Optic Sensor for Carbon Storage Application.

Novel chemical sensors that improve detection and quantification of CO2 are critical to ensuring safe and cost-effective monitoring of carbon storage sites. Fiber optic (FO)-based chemical sensor systems are promising field-deployable systems for real-time monitoring of CO2 in geological formations for long-range distributed sensing. In this work, a mixed-matrix composite integrated FO sensor system was developed with a purely optical readout that reliably operates as a detector for gas-phase and dissolved CO2. A mixed-matrix composite sensor coating consisting of plasmonic nanocrystals and hydrophobic zeolite embedded in a polymer matrix was integrated on the FO sensor. The mixed-matrix composite FO sensor showed excellent reversibility/stability in a high humidity environment and sensitivity to gas-phase CO2 over a large concentration range. This remarkable sensing performance was enabled by using plasmonic nanocrystals to significantly enhance the sensitivity and a hydrophobic zeolite to effectively mitigate interference from water vapor. The sensor exhibited the ability to sense CO2 in the presence of other geologically relevant gases, which is of importance for applications in geological formations. A prototype FO sensor configuration, which possesses a robust sensing capability for monitoring dissolved CO2 in natural water, was demonstrated. Reproducibility was confirmed over many cycles, both in a laboratory setting and in the field. More importantly, we demonstrated on-line monitoring capabilities with a wireless telemetry system, which transferred the data from the field to a website. The combination of outstanding CO2 sensing properties and facile coating processability makes this mixed-matrix composite FO sensor a good candidate for practical carbon storage applications.

Ranking and Evaluation of CO2 Storage Sites Using an Advanced Workflow

The world is in urgent need of carbon capture and storage (CCS) sites/facilities to achieve ambitious net carbon dioxide (CO2) emission reduction goals. After CO2 capture and transport, storage is the third step of the CO2 journey. Accessing and utilizing regional seismic information is a significant part of any workflow attempting to identify and characterize proposed subsurface CO2 storage sites. In this paper, we have developed and implemented a workflow over a proof-of-concept (PoC) area to assess CCS storage capacity and containment at a candidate saline aquifer site. Injectivity and monitoring/monitorability are assessed as part of an extended workflow. The integrated PoC CCS site assessment workflow allows validation of the various workflow elements and technologies, with the view to creating an efficient and scalable tool for regional site identification and characterization. The current project has been established using a PGS regional multi-client broadband seismic dataset in the North Sea which comprises an extensive cross-border regional dataset in the UK and Norway. The broadband nature of the seismic data allows significant and efficient site assessment, by providing detailed 3D characterization of the subsurface, away from areas with well control, and the parameterization of more accurate/reliable attributes for key storage attributes such as net-to-gross, porosity, and thickness. Finally, the integrated workflow and data integration allowed us to perform an efficient carbon storage site risk assessment as part of an overall site ranking process.

Computational Tools and Workflows for Quantitative Risk Assessment and Decision Support for Geologic Carbon Storage Sites: Progress and Insights from the U.S. DOE’s National Risk Assessment Partnership

Computational Tools and Workflows for Quantitative Risk Assessment and Decision Support for Geologic Carbon Storage Sites: Progress and Insights from the U.S. DOE’s National Risk Assessment Partnership

A Quantitative Comparison of Risk-based Leak Mitigation Strategies at a Geologic Carbon Storage Site

A Quantitative Comparison of Risk-based Leak Mitigation Strategies at a Geologic Carbon Storage Site

Introduction to the STEMM-CCS special issue

• The body of work included in this special issue delivers new insights, guidelines, and tools that will enable effective and efficient monitoring of CO2 storage at putative offshore Carbon dioxide Capture and Storage (CCS) sites.

A Review of Well Integrity Based on Field Experience at Carbon Utilization and Storage Sites

Maintaining well integrity is critical to the success of geologic carbon storage (GCS) and carbon dioxide enhanced oil recovery (CO2-EOR) operations. Wells that experience leakage because of integrity issues can potentially become a risk to the environment or human health if they release previously captured CO2 back into the atmosphere or into freshwater aquifers. There are many GCS and CO2-EOR sites in operation around the world. However, well integrity experiences at these sites are not widely documented in the public domain. This study details findings from a survey of well integrity experiences elicited from operators of GCS and CO2-EOR sites. The goal of the survey was to obtain information about site characteristics and operator experiences with well integrity, monitoring methods, and risk assessment of legacy wells. Literature relevant to the survey questions was also reviewed and summarized to provide context for survey responses and identify areas where field experiences with well integrity do and do not align with the current state of research. We highlight the current state-of-practice, identify research needs, and provide context for future interactions between researchers, operators, and regulators on issues related to well integrity.

Monte Carlo simulations to assess the uncertainty of locating and quantifying CO2 leakage flux from deep geological or anthropogenic sources

Accurately locating and quantifying carbon dioxide (CO2) leakage to the atmosphere is important for diffuse degassing studies in volcanic / geothermal areas and for safety monitoring and/or carbon credit auditing of Carbon Capture and Storage (CCS) sites. This is typically conducted by measuring CO2 flux at numerous points over a large area and applying statistics or geostatistical interpolation. Accuracy of the results will depend on many factors related to survey/data-processing choices and site characteristics, and thus uncertainties can be difficult to quantify. To address this issue, we have developed a Monte Carlo-based program (MC-Flux) that repeatedly subsamples a high-resolution synthetic or real dataset using a choice of different sampling strategies (one random and four grid types) at multiple user-defined sample densities. The program keeps track of the anomalies found and estimates total flux using two statistical and two geostatistical approaches from the literature. This paper describes the use of MC-Flux to assess the potential impact of various sampling and interpretation decisions on the accuracy of the final results. Simulations show that an offset grid sample distribution yields the best results, however relatively dense sampling is required to obtain a high probability of an accurate flux estimate. For the test dataset used, ordinary kriging interpolation produces a range of flux estimates that are centered on the true value while sequential Gaussian simulation tends to slightly overestimate values at intermediate sample spacings and is sensitive to input parameters. These results point to the need for developing new approaches that decrease uncertainty, such as integration with high-resolution co-kriging datasets that complement the more accurate point flux measurements.

Reservoir quality and sedimentology in shallow marine sandstones: Interplay between sand accumulation and carbonate and clay minerals

Sedimentological studies are important in understanding and predicting reservoir quality, especially in shallow buried sandstones that are dominated by eogenetic processes. Understanding the sedimentological controls on siliciclastic depositional environments will enhance the knowledge and prediction of reservoir architecture and reservoir quality, both of which are essential to resource exploitation and future CCS and hydrogen storage projects. Here, we present a study of sedimentology and depositional mineralogy, as well as controls on the deposition of siliciclastic sandstones, from the shallow-buried, Upper Jurassic Corallian marine sandstones of the Weald Basin, UK. These sandstones host small oil accumulations and, being close to large centres of population, are possible gas storage or carbon capture and storage sites. We used wireline log analysis, high resolution core logging, optical petrography, and SEM-EDS imaging to investigate reservoir architecture and the relative importance of depositional versus secondary diagenetic controls on reservoir quality. Shallow marine conditions, adjacent to a continent experiencing a warm humid climate, are interpreted based on ichnofabrics and mineralogy. Tectonic processes influenced water depth which subsequently controlled both the quantity of detrital bioclastic material (and the resulting calcite cement), and the amount of detrital clay matrix. The eustatic influence on deposition led to the development of a relatively thin intra-Corallian mudstone which compartmentalises the reservoir into discrete upper and lower sand bodies. The results of this study underline the importance of integration of detailed sedimentological and wireline log analysis in improving the prediction of reservoir quality in tectonically active environments for shallow buried, eogenetic-dominated sandstones.

Identifying geological structures through microseismic cluster and burst analyses complementing active seismic interpretation

At the Decatur carbon capture and storage site (IL, USA) CO2 has been injected from 2011–2014 and from 2017 to present near the base of the Lower Mt. Simon Sandstone saline reservoir, resulting in microseismicity. Microseismicity is mainly located in the basement and distributed in distinct spatial clusters. The lack of significant impedance contrasts within the basement makes the interpretation of active-source seismic reflection data challenging, however, recent reprocessing allowed to resolve faults above and at the top of the basement. These faults generally do not coincide with the location of microseismic events and their continuation to the general depth of the seismic events cannot be assumed. This paper shows how the interpretation of the microseismicity can complement structural interpretations of active-source seismic reflection data. In particular, we analyze clusters and bursts (abrupt increases) of microseismicity, identify unresolved, smaller-scale weaknesses and extract statistical parameters. These parameters allow comparisons with the interpreted faults, and with fracture sets intercepted by boreholes. During injection at the Decatur site, the injection pressure was kept far below fracture pressure, nevertheless, seismic events were induced and spread far beyond the expected extent of the CO2 plume. We argue that local stress transfers related to the CO2 injection reactivated pre-existing fractures within the critically stressed basement. Finally, we conducted a slip tendency analysis for faults interpreted from active seismic, selected cluster, bursts and nodal planes from focal mechanisms to determine if the interpreted structures are optimally oriented with respect to the stress regime. Our results suggest that the orientation of fractures close to the injection well, generally shows slight deviations from the optimal orientation for slip. This might indicate either slight local deviations of the maximum horizontal stress azimuth from the average direction used in the analysis, or the lack of optimally oriented fractures at this location.