Table of Content

20 February 2023, Volume 29 Issue 1

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Current Status and Recommendations of Offshore CO₂ Geological Storage Monitoring

LI Qi, LI Yanzun, XU Xiaoyi, LI Xiaochun, LIU Guizhen, YU Hang, TAN Yongsheng

2023, 29(1):  1-12.  DOI: 10.16108/j.issn1006-7493.2023008

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Marine carbon dioxide (CO₂) storage is an important means to cope with greenhouse gas emissions in China’s coastal areas, and is an indispensable key technology to achieve the goal of “emission peak and carbon neutrality”. The coastal areas of China are industrially developed and rich in carbon sources. Owing to the good physical properties and reservoirs and trap characteristics, offshore basins have huge storage potential. At present, the first marine demonstration project of China has been officially launched in the Pearl River Estuary Basin in the South China Sea. As an important part of CCUS technology, CO₂ monitoring runs through the whole life cycle of CO₂ geological storage and is a necessary method to ensure the safety and rationality of storage works. However, China’s CO₂ marine storage technology is in its infancy, and the task of marine storage monitoring is quite challenging. For this reason, this paper reviews the relevant representative research and demonstration project cases of international CO₂ marine storages, summarizes the monitoring indicators, technologies and schemes, and puts forward the screening and optimization methods of monitoring CO₂ marine storage and suggestions for monitoring technology. The outcome of this study provides a reference for the development of CO₂ marine storage demonstration projects in China.

Analysis of Monitoring Technologies of Offshore CO₂ Geological Storage in Japan’s Tomakomai and Its Enlightenment

XU Xiaoyi, LI Qi, TAN Yongsheng, LIU Guizhen, LI Xiaying

2023, 29(1):  13-24.  DOI: 10.16108/j.issn1006-7493.2022096

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Offshore carbon dioxide (CO₂) capture and storage (CCS) is one of key technologies to cope with global climate change and reduce greenhouse gases such as CO₂, and also an important solution to achieve carbon neutrality goal of China. Offshore sedimentary basins of China have huge storage potential, and the first offshore CO₂ geological storage demonstration project has been officially launched in the Pearl River Mouth Basin of the South China Sea in 2022. Japan’s Tomakomai CCS project is the most successful offshore CO₂ geological storage project in Asia so far, and its monitoring work provides important practical references and technical experiences for the development of China offshore CCS projects. Based on this consideration, this paper comprehensively reviews the case of Tomakomai CCS project, analyzes its implementation, site monitoring items and distribution, monitoring facilities and technologies, monitoring results, etc., summarizes the successful experience of the Tomakomai CCS project and the multi-level and all-round monitoring system of land-wellbore-marine integration, aiming to help offshore CCS projects of China run smoothly, and to ensure the security and safety of the marine ecological environment.


Analysis of CO₂ Geological Storage Condition in Jiangsu Province and Offshore Area

ZHU Qianlin, CHEN Dongbao, GONG Yijie, CHEN Fu, SANG Shuxun, LIU Shiqi

2023, 29(1):  25-36.  DOI: 10.16108/j.issn1006-7493.2022080

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The analysis of the geological condition in Jiangsu Province and offshore area shows that the Subei-Southern South Yellow Sea basin developed in the Lower Yangtze block is a potential site for CO₂ geological storage in Jiangsu Province. The suitable formation for CO₂ storage lithology is analyzed according to the stratigraphic and lithological data. On this basis, according to the drilling and seismic survey profile data, the suitability of CO₂ storage space is discussed through the thickness of CO₂ storage suitable stratum in 800-3500 m depth range of each tectonic unit. The results show that the sandstone layers in lower Yancheng formation, Sanduo formation, Dainan formation, the first and third members of Funing formation, and Chishan formation have good CO₂ storage space. The Chishan formation is less distributed in the basin, and the Yancheng formation, Sanduo formation, Dainan formation and Funing formation are widely distributed. Jinhu depression, Gaoyou depression, Qintong depression, Hai’an depression, Baiju depression, Funing depression, Yancheng depression, Naner depression, Nansi depression, Nanwu depression, Nanqi depression and the Naner low uplift have good CO₂ storage potential. The CO₂ storage potential of Hongze Sag, Linze Sag, Liannan Sag, Lianbei Sag, Nansan Sag and Nanliu Sag is relatively poor.


Effects of Physical Parameters of Shale on CO₂ Storage Capacity with Different Mechanisms

YIN Shuguo, YANG Guodong, FENG Tao, MA Xin, CAO Wei, HUANG Mian, GUO Tianqing

2023, 29(1):  37-46.  DOI: 10.16108/j.issn1006-7493.2022071

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CO₂ enhanced shale gas recovery (CO₂-ESGR) can not only increase CH4 production, but also store CO₂. In order to investigate the effects of physical parameters of shale on CO2 sequestration mechanisms, a dual-porosity, dual-permeability homogeneous model was established using CMG-GEM based on the shale of Yanchang Formation in Ordos Basin. This study analyzed the effects of vertical permeability to horizontal permeability ratio (Kv/Kh), water saturation and porosity of shale on CO₂ storage capacity with different mechanisms in CO₂-ESGR. Moreover, 27 sets of orthogonal tests were designed to investigate the extent of influence of these three factors by range analysis. The results showed that Kv/Kh increase in the range of 0.1 to 1 leads to enhanced CO₂ storage capacity with different mechanisms, and the maximum storage capacity can increase by 69.96%, of which the adsorption storage capacity can increase by 97.96%. Water saturation increase in the range of 0-0.9 induces the total CO₂ storage to show an increase first and then a decrease. The maximum storage capacity can reduce by 67.12%, of which the dissolved storage capacity can reduce by 83.35%, with the largest range fluctuation. Shale porosity increase in the range of 0.1- 0.99 leads to the reduction of total CO₂ storage capacity, and the maximum storage capacity can reduce by 95.38%, of which the adsorption storage capacity can reduce by 99.99%. Range analysis showed that water saturation has the largest impact on the amount of structural trapping, residual trapping and solubility trapping, porosity has the largest impact on total CO₂ storage capacity and adsorption storage capacity, and Kv/Kh has the least effect on CO₂ storage capacity with different mechanisms. For CO₂ storage in shale reservoirs, shale with low water saturation, low-porosity and high Ky/Kh ratio is suggested to obtain the maximum storage capacity.

Research on Inter-well Interference Law of Supercritical CO₂ Staged Multi-cluster Fracturing

PENG Shouchang, XU Dongsheng, GAO Yang, ZHANG Fang, SHI Leiting, ZHANG Yulong, LIU Tong, WEI Xiaochen

2023, 29(1):  47-56.  DOI: 10.16108/j.issn1006-7493.2022083

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The staged multi-cluster fracturing of horizontal wells is a key technology for the development of unconventional oil and gas reservoirs. While rationally using fracturing-induced stress to increase the volume of reservoir reconstruction, avoiding sand plugging and fracturing interference caused by inter-well interference is a key scientific issue in fracturing process optimization. In this paper, aiming at the problem of fracture interference and interwell interference of staged multi-cluster fracturing using supercritical CO₂, a fluid-solid coupling extended finite element method is used to establish a fracture-induced stress calculation model for studying single wells and multi-wells. We consider the flow and fluid loss of supercritical CO₂ in fractures, and systematically study the disturbance stress of fracturing operation from the lithological characteristics of unconventional oil and gas reservoirs, the distribution of in-situ stress field and construction technology, etc. The propagation mechanism and stress disturbance characteristics of multi-cluster hydraulic fractures in a single well are revealed, and on this basis, the inter-well fracture interference law of multi-wells is studied. The results show that the fracturing interference limit in reservoirs with high level of stress difference and high elastic modulus is relatively large, and the formation of low level of stress difference and low elastic modulus needs to appropriately increase the cluster spacing to reduce inter-cluster interference. After well 1# is fractured, the asymmetry coefficient of hydraulic fractures in adjacent well 2# first increases and then decreases with the well spacing; when the well spacing is equal to the fracturing interference limit, the asymmetry coefficient λ reaches the maximum, and the well circumference is reformed The range is the largest, but the asymmetry of the two wings of the fracture may lead to insufficient reservoir production. This research provides a theoretical basis for horizontal well subdivision cutting and fracturing and threedimensional well pattern design optimization, which is of great significance for the efficient development of unconventional oil and gas resources in the context of the“carbon peaking and carbon neutrality”strategy.

Effects of CO₂ Purity on Residual Water During Carbon Sequestration in Deep Saline Aquifers

HU Zhikai, LI Yi, SUO Ruiting, DIAO Yujie, LI Qi, MA Xin

2023, 29(1):  57-65.  DOI: 10.16108/j.issn1006-7493.2022061

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During the process of CO₂ being injected into deep saline aquifers, residual water formed in rock pore has negative impacts on CO₂ injectability, storage capacity and safety. Therefore, it is important to investigate the formation and evolution of residual water under various influencing factors. In this study, natural rock core taken from the deep reservoirs of the Ordos Basin were used to conduct core-flooding experiments using 3 sets of CO₂ purity (99.999%CO₂, 75%CO₂+25%N2 and 50%CO₂+25%N2) at 40℃ and 8 MPa to investigate the effect of CO₂ purity on residual water. The experimental results show that the order of time required to reach the breakthrough point and the drainage endpoint are, 99.999%CO₂<75%CO₂+25%N2<50%CO₂+50%N2; the order of the irreducible water saturations is: 99999%CO₂<75%CO₂+25%N2<50%CO₂+25%N2. The analysis revealed that changes in CO₂ purity lead to changes of important properties in two-phase floods, such as interfacial tension, wettability, and viscosity ratio. By analyzing the LogCa-LogM displacement stability diagram, the capillary force was determined to be the dominant factor affecting the results of experiments. This study is of great value for predicting residual water saturation under various conditions and evaluating CO₂ sequestration capacity.

Progress of Methods for Assessing CO₂ Mineralization Storage Potential in Basalt

GAO Zhihao, XIA Changyou, LIAO Songlin, YU Xiaojie, LIU Muxin, LI Pengchun, LIANG Xi, DAI Qing, HUANG Xinwo

2023, 29(1):  66-75.  DOI: 10.16108/j.issn1006-7493.2022099

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CO₂ geological storage is an important technology to reduce CO₂ emissions, which can safely store CO₂ in geological formations for millions of years. Conventional CO₂ storage reservoirs include deep saline aquifers and depleted oil and gas reservoirs. Basalt is a new type of CO₂ storage reservoir that has been attracting attention in recent years. CO₂ storage in basalt would increase the technical method and potential of CO₂ geological storage. Storage potential assessment is one of the fundamental works of CO₂ geological storage study. This paper systematically examines the current methods for assessing the storage potential of CO₂ in basaltic rocks, and analyzes the principles and application scenarios of various methods. Then, the study takes the basalt of Icelandic Active Rift zone as an example to compare each of the methods. The study suggests that the current CO₂ mineralization storage potential assessment methods generally include three categories: ① Unit rock storage potential assessment method, which evaluates carbon sequestration potential based on the reaction volume or area of rocks; ② Mineral replacement storage potential assessment method: based on the volume of minerals that can react with CO₂ in basalts. ③Pore filling storage potential assessment method, which evaluates the proportion of secondary minerals that can fill reservoirs’ pore space after CO₂ mineralization. The authors note that the first method requires special experimental analysis, making it more challenging, the second method is more appropriat for basalts with high porosity and low reactive mineral content, while the third method is more suitable for basqlts with low porosity and high reactive mineral content.


Assessment of Carbon Dioxide Mineralization Sequestration Potential of Volcanic Rocks in Leizhou Peninsula, Guangdong Province, China

LI Pengchun, JIANG Jinglian, CHENG Jinhui, ZHAO Minghui

2023, 29(1):  76-84.  DOI: 10.16108/j.issn1006-7493.2022078

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Mineral carbon sequestration by volcanic rocks, providing a permanent sequestration solution for reducing atmospheric CO₂, is one of an economic and safe way of carbon capture and storage (CCS). Volcanic rocks are widely distributed in China, but research on the carbon sequestration potential of volcanic rocks is still very limited. In this paper, we selected the volcanic rocks of Leizhou Peninsula, Guangdong Province as the study area, and used MapGis software to establish a vector geographic information database of the thickness distribution of volcanic rocks in Leizhou Peninsula, and interpolated to obtain a three- dimensional gridded data body. The results show that the total area of volcanic rocks in Leizhou Peninsula is approximately 3940 km², with a total volume of 257 km³, and calculated results of the theoretical CO₂ mineralization storage capacity ranges from 1.9 to 45.9 billion tons. Among them, the volcanic rocks in the Leinan area have the largest potential, with the theoretical storage capacity ranging from 1.3 to 32.6 billion tons, followed by volcanic rocks in the area east of Suixi County in Leibei and west of Zhanjiang City, with the capacity from 0.2 to 5.6 billion tons. Although the theoretical storage capacity of volcanic rocks in the Donghai Island area is relatively small (0.15 to 3.5 billion tons), they have a good source-to-sink matching condition due to their proximity to the surrounding industrial emission sources, and so they also have good CCS prospects. The results of this study not only provide an important basis for the screening site of CO₂ mineralization volcanic rocks, but also offer support for future development of regional CCS projects or industries.

Status and Advances of Research on Caprock Sealing Properties of CO₂ Geological Storage

CHEN Bowen, WANG Rui, LI Qi, ZHOU Yinbang, TAN Yongsheng, DAI Quanqi, ZHANG Yao

2023, 29(1):  85-99.  DOI: 10.16108/j.issn1006-7493.2023010

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CO₂ Geological storage is one of the key technologies to address global climate changes and reduce greenhouse gas emissions. Large-scale CO₂ injection into the formation is prone to inducing CO₂ leakage problem. In particular, the leakage problem of CO₂ through caprock includes capillary leakage, hydraulic fracture and leakage along pre-existing faults crossing caprock. Therefore, evaluation of caprock seal is crucial for prediction of long-term safety and stability of CO₂ geological storage. This paper provides an overview of the current status of research on sealing mechanisms, influencing factors, and damage modes affecting caprock seal of CO₂ geological storage. It is concluded that caprock seal mechanisms include capillary seal, hydraulic seal, and overpressure seal. The main influencing factors of caprock seal characteristics include caprock lithology, mudrock-sand ratio, caprock mechanical properties, and sequestration pressure. Then, the damage modes of caprock seal during CO₂ injection are illustrated, and some insight into the shortcoming of caprock seal is provided.


Risk Transmission Characteristics of Carbon Dioxide Geological Storage Based on Social Network Analysis

JING Meng, LIU Guizhen, LI Qi, XU Xiaoyi, LI Xiaochun

2023, 29(1):  100-109.  DOI: 10.16108/j.issn1006-7493.2023009

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As an essential and necessary means for emission reduction, carbon dioxide geological storage technology is of great significance for ecological and environmental protection, promotes international cooperation on global medium and long-term climate changes, and advances green, recycling and low-carbon development. This study summarizes 46 risk factors that may emerge throughout a lifecycle of carbon dioxide geological storage projects. A risk network relationship model was created using the social network analysis method to investigate the transmission relationship between risk factors associated with carbon dioxide geological storage projects. By analyzing the of overall local risk network parameters, this study identifies key factors such as key initial node, key risk-causing node, and key transmission node in the risk transmission processes. The following three potential risk transmission chains are identified: (1) Geologic hazard → Unexpected disruptions of CO₂ supply, access or transportation → Unexpected changes in construction or operation costs; (2) Insufficient knowledge of an operator or lack of corresponding qualification → Man-made leakage → Environmental damage of the project → Public participation → Unexpected construction or operation cost changes; (3) Improper departmental coordination → Talent recruitment and management risk → Operator’s lack of knowledge or lack of corresponding qualification → Unexpected construction or operation cost changes. The findings of this study can serve as a theoretical and technical reference for risk research in carbon dioxide geological sequestration projects and promote the healthy development of carbon dioxide capture, utilization and storage (CCUS) projects.

Current Research Status and Tendency of Hydrogen Production Coupled CCUS Technology Based on Bibliometrics

CAO Xiaomin, LI Qi, XU Liang

2023, 29(1):  110-119.  DOI: 10.16108/j.issn1006-7493.2022073

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Hydrogen energy is the “ultimate form” of energy in the future. Currently, industrial production of hydrogen mainly relies on fossil fuels. Carbon capture, utilization and storage (CCUS) is an important way to realize the transformation from “grey hydrogen” to “blue hydrogen” and “dual carbon goals”. In this paper, related literatures were collected from the Web of Science core collection. CiteSpace software was used to analyze the literature source, research strength, research hotspots and research frontiers in the coupling field of hydrogen production and CCUS technology. The results show that China ranks the first in the number of publications and also has extensive cooperation with other countries. The main research forces at home and abroad are research institutes and universities. Sorption enhanced steam methane reforming (SESMR) hydrogen production technology, chemical looping combustion (CLC) hydrogen production technology, catalysts, adsorbents and oxygen carriers are the main research hotspots. Metal oxygen carriers are at the forefront of research. Development of composite catalysts with catalytic and adsorption functions and application of electricity-hydrogen generation technology combining CLC technology and coal gasification in the thermal power industry are the two main research directions in the future. Considering the industry-wide adoption of “dual carbon goals”and the additional cost of carbon tax, the hydrogen production technology accompanying CCUS is still a preferred option.

Research on Tortuosity Fractal Characteristics of Sandstone Pores Based on Nuclear Magnetic Resonance Imaging Technology

XIANG Lei, WANG Huimin, SHENG Jinchang, LUO Yulong, ZHAN Meili, TAO Kai, TIAN Jiali

2023, 29(1):  120-127.  DOI: 10.16108/j.issn1006-7493.2022074

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Under the context of “double carbon” emission reduction, saline aquifer of sandstone is the most potential medium for carbon dioxide storage. The study of pore-structure characteristics determines the fluid migration and storage efficiency, which has great scientific significance. Fractal dimension is usually used to quantitatively characterize the distribution of sandstone pore structures in three-dimensional space. However, when studying the fractal dimension of sandstone pores in the past, the fractal dimension was calculated based on the characteristic values such as porosity, average pore radius, and average tortuosity, which could not well reflect the heterogeneity and arrangement of pore structures. Therefore, in this paper, pore structures of sandstone are generalized into capillaries with tortuosity. First, the image of rock slices is obtained by means of nuclear magnetic resonance imaging (MRI) technology, and the fractal dimension of pore distribution obtained by the box-counting dimension method is used. The fractal dimension of the pore distribution is the target parameter, and the fractal dimension of the tortuosity is calculated iteratively by combining the fractal scalar relationship between the number of capillaries and the pore size under different tortuosities. Compared with the traditional fractal dimension calculation method, the fractal dimension of tortuosity determined in this paper is larger, and the difference between different rock samples is more obvious, which can better reflect the heterogeneous characteristics of pore distribution.

The Effect of Pre-existing Fracture Complexity on Rupture Characteristics of Tight Reservoir

YIN Chen, SHI Xuewen, CAI Bo, WEN Shanshi, LIANG Tiancheng, WANG Xin, FU Haifeng, HAN Fusheng

2023, 29(1):  128-137.  DOI: 10.16108/j.issn1006-7493.2022081

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Pre-existing microscale fractures, cracks and pores in geological layer, which makes the rock or/and stratum heterogeneity, response the difference of rupture characteristics under artificial injection. The exploitation and development of unconventional oil and gas reservoirs represented by tight oil and gas accounts for an increasing proportion of China’s oil and gas production capacity, and artificial fractures are often produced by hydraulic fracturing to enhance oil and gas flow and achieve the scale of economic production, they also are the important target for CO2 injection and geological storage. Based on the true triaxial hydraulic fracturing experiment and the microseismic data in geological setting, this paper studies multiscale rupture process in sandstone through the temporal and spatial characteristics of acoustic event and the microseismic event. The results show that the pre-existing fractures in rock dominate the rupture pattern under the stable triaxial hydraulic fracturing stress and geological settings.


Experimental Verification of Gas-operated Sampling Technology for Subsurface Fluid

LI Xiaying, LIU Xuehao, LI Qi, XIAO Wei, LI Xiaochun

2023, 29(1):  138-146.  DOI: 10.16108/j.issn1006-7493.2022072

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Obtaining underground fluid samples with high quality is important for CO₂ leakage monitoring in CO₂ geological utilization and storage (CCUS). The gas-operated underground fluid sampler has the advantages of high sampling accuracy, low formation disturbance, and in-situ monitoring through integrating downhole monitoring technologies, and has been widely applied in several CCUS applications. However, during practical application processes, sampling volume of the sampler is unstable and greatly affected by groundwater level. In order to solve these problems, a visualized experimental device to simulate subsurface fluid sampling in a wellbore was developed. A set of fluid sampling experiments at different liquid heights were carried out to explore sampling process and sampling mechanism of the gas-operated sampler. The results show that there is no disturbance to the liquid height during the sampling process, indicating the gas-operated sampling technology is characterized by passive sampling and low interference to external environment. The sampling volume depends on the size of the storage container and the liquid height in the wellbore. The sampling volume can be calculated accurately by the liquid height and the pipeline size. The measured sampling volumes under different liquid heights are basically consistent with the theoretical values. The error between the measured volume and calculated one decreases with the increasing liquid heights. The maximum error is less than 6.6%. Both the sampling time and average sampling rate mainly depend on the injection pressure and present a power function relationship with the injection pressure with a correlation coefficient of greater than 99%. The above experimental results can help to understand the sampling mechanism of gas-driven sampler and are of great significance to feedback and guide sampling performance in field by optimizing the structure. In addition, it can improve the ability of warning environmental risks in CCUS and contaminated sites.