A review of CO2 storage in geological formations emphasizing modeling,monitoring and capacity estimation approaches

The merits of CO2 capture and storage to the environmental stability of our world should not be underestimated as emissions of greenhouse gases cause serious problems.It represents the only technology that might rid our atmosphere of the main anthropogenic gas while allowing for the continuous use of the fossil fuels which still power today’s world.Underground storage of CO2 involves the injection of CO2 into suitable geological formations and the monitoring of the injected plume over time,to ensure containment.Over the last two or three decades,attention has been paid to technology developments of carbon capture and sequestration.Therefore,it is high time to look at the research done so far.In this regard,a high-level review article is required to provide an overview of the status of carbon capture and sequestration research.This article presents a review of CO2 storage technologies which includes a background of essential concepts in storage,the physical processes involved,modeling procedures and simulators used,capacity estimation,measuring monitoring and verification techniques,risks and challenges involved and field-/pilot-scale projects.It is expected that the present review paper will help the researchers to gain a quick knowledge of CO2 sequestration for future research in this field.

Appraisal of CO2 storage potential in compressional hydrocarbon-bearing basins: Global assessment and case study in the Sichuan Basin(China)

Carbon capture and storage(CCS)has been proposed as a potential technology to mitigate climate change.However,there is currently a huge gap between the current global deployment of this technology and that which will be ultimately required.Whilst CO2 can be captured at any geographic location,storage of CO2 will be constrained by the geological storage potential in the area the CO2 is captured.The geological storage potential can be evaluated at a very high level according to the tectonic setting of the target area.To date,CCS deployment has been restricted to more favourable tectonic settings,such as extensional passive margin and post-rift basins and compressional foreland basins.However,to reach the adequate level of deployment,the potential for CCS of regions in different tectonic settings needs to be explored and assessed worldwide.Surprisingly,the potential of compressional basins for carbon storage has not been universally evaluated according to the global and regional carbon emission distribution.Here,we present an integrated source-to-sink analysis tool that combines comprehensive,open-access information on basin distribution,hydrocarbon resources and CO2 emissions based on geographical information systems(GIS).Compressional settings host some of the most significant hydrocarbon-bearing basins and 36% of inland CO2 emissions but,to date,large-scale CCS facilities in compressional basins are concentrated in North America and the Middle East only.Our source-to-sink tool allows identifying five high-priority regions for prospective CCS development in compressional basins:North America,north-western South America,south-eastern Europe,the western Middle East and western China.We present a study of the characteristics of these areas in terms of CO2 emissions and CO2 storage potential.Additionally,we conduct a detailed case-study analysis of the Sichuan Basin(China),one of the compressional basins with the greatest CO2 storage potential.Our results indicate that compressional basins will have to play a critical role in the future of CCS if this technology is to be implemented worldwide.

A Method for Evaluating the Suitability of CO2 Geological Storage in Deep Saline Aquifers

This work established an evaluation index system based on a comprehensive analysis of those factors affecting the suitability of CO2 geological storage.This evaluation index system includes three evaluation index layers of geological safety,storage scale and social economy,nine evaluation index sub-layers,and 28 evaluation index factors,and adopts the analytic hierarchy process（AHP）and index overlay methods.Taking the Xining Basin in northwest China as an example,we conducted comprehensive analysis of geological conditions and performed quantitative evaluation based on this evaluation index system,which indicates that the Shuangshu depression of the Xining Basin is comparatively suitable for CO2 geological storage.It is suggested that this evaluation index system and the evaluation method proposed in this study are suitable for most continental sedimentary basins in China and should be widely applied.

Numerical investigation of CO2 storage in hydrocarbon field using a geomechanical-fluid coupling model

Increasing pore pressure due to CO2 injection can lead to stress and strain changes of the reservoir.One of the safely standards for long term CO2 storage is whether stress and strain changes caused by CO2 injection will lead to irreversible mechanical damages of the reservoir and impact the integrity of caprock which could lead to CO2 leakage through previously sealing structures.Leakage from storage will compromise both the storage capacity and the perceived security of the project,therefore,a successful CO2 storage project requires large volumes of CO2 to be injected into storage site in a reliable and secure manner.Yougou hydrocarbon field located in Orods basin was chosen as storage site based on it's stable geological structure and low leakage risks.In this paper,we present a fluid pressure and stress-strain variations analysis for CO2 geological storage based on a geomechanical-fluid coupling model.Using nonlinear elasticity theory to describe the geomechanical part of the model,while using the Darcy's law to describe the fluid flow.Two parts are coupled together using the poroelasticity theory.The objectives of our work were:1)evaluation of the geomechanical response of the reservoir to different CO2 injection scenarios.2)assessment of the potential leakage risk of the reservoir caused by CO2 injection.

Integrated Techniques of Underground CO_2 Storage and Flooding Put into Commercial Application in the Jilin Oilfield, China

Global warming touches everybody＇s nerve, and direct reason for sharp increasing of CO2 in the atmosphere results mainly from the use of fossil fuel in power generation and other industries. How can humans return this ＂devil＂ to underground, and keep a peaceful environment for human？ Scientists from all over the world have been exploring them.

CO_2 –H_2O–coal interaction of CO_2 storage in coal beds

In order to study the physical and chemical reaction after CO2 injected into coal beds at different condition.The physical and chemistry reaction among CO2,H2O and coal was studied,and the influence on permeability and porosity of coal beds was carried out.The experimental method was used,so did the basic theory of mineralogy,coal petrology,geochemistry,analytical geochemistry and physical chemistry.In this experiment,the changes of mineral and permeability of coal and water quality were observed through CO2 solution reacting with different coal samples.The differences could be found out by comparing the properties and microcrystalline structure before and after the reaction.There are three results were carried out:First,the content of carbonate in coal beds decreases because of the dissolution reaction between carbonate minerals and CO2 solution,and precipitation is formed by reaction of chlorite and orthoclase.Second,the result that permeability and porosity of coal beds are improved after the reaction is proposed.Third,the initial permeability of different coal samples plays a great role on the reaction,and the improvement of permeability is not obvious in the samples which have too low or too high permeability,and the improvement is good in medium permeability(0.2–3 mD).

Gas leakage recognition for CO2 geological sequestration based on the time series neural network

The leakage of stored and transported CO2 is a risk for geological sequestration technology. One of the most challenging problems is to recognize and determine CO2 leakage signal in the complex atmosphere background. In this work, a time series model was proposed to forecast the atmospheric CO2 variation and the approximation error of the model was utilized to recognize the leakage. First, the fitting neural network trained with recently past CO2 data was applied to predict the daily atmospheric CO2. Further, the recurrent nonlinear autoregressive with exogenous input(NARX) model was adopted to get more accurate prediction. Compared with fitting neural network, the approximation errors of NARX have a clearer baseline, and the abnormal leakage signal can be seized more easily even in small release cases. Hence, the fitting approximation of time series prediction model is a potential excellent method to capture atmospheric abnormal signal for CO2 storage and transportation technologies.

Risk assessment of CO_2 injection processes and storage in carboniferous formations:a review

Over the last decades,people from almost all over the world have realized that it is necessary to quickly develop strategies for the control and reduction of greenhouse gases (GHG) emissions.Among various GHGs,carbon dioxide (CO2) is the most abundant GHG.Its underground storage involves less risk and lower levels of dangerousness.The paper briefly describes the most effective technologies available in the market for background processes to storage (capture and transport) CO2,as well as the more secure solutions for its storage,in particular for the geological storage in carboniferous formations.This paper also outlines the methodologies for the risk assessment involved in storage of CO2,with a particular focus on cases where the injection is made into unminable coal seams and in abandoned coalmines.Methodologies used for risk analysis are described in detail with particular emphasis on Bayesian network (BN).Some applications regarding the risk assessment of CO2 injection processes and CO2 storage in carboniferous formations and contamination of aquifers are presented and analyzed.Finally,based on the applications of BN,several conclusions are drawn.

Preface to Special Issue: CO_2 capture storage and utilization

Reducing the anthropogenic COemissions from fossil resource combustion and human activities has become one of the major challenges we are facing today.Beyond those practical applications for the utilization of CO,such as the synthesis of salicylic acid,methanol,urea,NaHCO-NaCOchemicals and recently developed polycarbonate synthesis,scientists are still seeking new materials and technologies for efficient capture,

Effect of reactive surface area of minerals on mineralization trapping of CO_2 in saline aquifers

The reactive surface area, an important parameter controlling mineral reactions, affects the amount of mineralization trapping of CO2 which affects the long-term CO2 storage. The effect of the reactive surface area on the mineralization trapping of CO2 was numerically simulated for CO2 storage in saline aquifers. Three kinds of minerals, including anorthite, calcite and kaolinite, are involved in the mineral reactions. This paper models the relationship between the specific surface area and the grain diameter of anorthite based on experimental data from literature （Brantley and Mellott, 2000）. When the reactive surface areas of anorthite and calcite decrease from 838 to 83.8 m^2/m^3, the percentage of mineralization trapping of CO： after 500 years decreases from 11.8% to 0.65%. The amount of dissolved anorthite and the amounts of precipitated kaolinite and calcite decrease significantly when the reactive surface areas ofanorthite and calcite decrease from 838 to 83.8 m2/m3. Calcite is initially dissolved in the brine and then precipitates during the geochemical reactions between CO2-H20 and the minerals. Different reactive surface areas of anorthite and calcite lead to different times from dissolution to precipitation. The pH of the brine decreases with decreasing reactive surface areas of anorthite and calcite which influences the acidity of the saline aquifer. The gas saturation between the upper and lower parts of the saline aquifer increases with decreasing reactive surface areas of anorthite and calcite. The mass density distribution of brine solution shows that the CO2^＋brine solution region increases with decreasing reactive surface areas ofanorthite and calcite.

Reactive Transport Modeling of Long-Term CO2 Sequestration Mechanisms at the Shenhua CCS Demonstration Project,China

Carbon dioxide injection into deep saline aquifers results in a variety of strongly coupled physical and chemical processes. In this study, reactive transport simulations using a 2-D radial model were performed to investigate the fate of the injected CO2, the effect of CO2-water-rock interactions on mineral alteration, and the long-term CO2 sequestration mechanisms of the Liujiagou Formation sandstone at the Shenhua CCS（carbon capture and storage） pilot site of China. Carbon dioxide was injected at a constant rate of 0.1 Mt/year for 30 years, and the fluid flow and geochemical transport simulation was run for a period of 10 000 years by the TOUGHREACT code according to the underground conditions of the Liujiagou Formation. The results show that different trapping phases of CO2 vary with time. Sensitivity analyses indicate that plagioclase composition and chlorite presence are the most significant determinants of stable carbonate minerals and CO2 mineral trapping capacity. For arkosic arenite in the Liujiagou Formation, CO2 can be immobilized by precipitation of ankerite, magnesite, siderite, dawsonite, and calcite for different mineral compositions, with Ca（2＋）, Mg（2＋）, Fe（2＋） and Na＋ provided by dissolution of calcite, albite（or oligoclase） and chlorite. This study can provide useful insights into the geochemistry of CO2 storage in other arkosic arenite（feldspar rich sandstone） formations at other pilots or target sites.

Cost analysis of air capture driven by wind energy under different scenarios

Reducing the concentration of carbon dioxide(CO2) in the air can effectively alleviate climate change.Air capture,which captures CO2 directly from the air in an industrial process,is an alternative option to address climate change.The results of recent studies on the energy demand in CO2 capture process and the costs of CO2transport and CO2 storage in air capture are analyzed in this paper.Considering renewable energy will not produce additional CO2 in the process of utilization,the electric energy in CO2 capture process of air capture driven by wind energy is different from that of carbon capture and storage.Taking externalities of renewable energy intoaccount,the trading price of CO2 emission is taken to assess the cost of electric energy in CO2 capture of air capture driven by wind energy.Finally,the total cost and the total cost savings of air capture driven by wind energy under different scenarios are analyzed.