Systematic Exploration of the Knowledge Graph on Rock Porosity Structure

Abstract

The porosity structure of rocks is an important research topic in fields such as civil engineering, geology, and petroleum engineering, with significant implications for groundwater flow, oil and gas reservoir exploitation, and geological hazard prediction. This paper systematically explores the research progress and knowledge graph construction methods for rock porosity structure, aiming to provide scientific foundations for a multidimensional understanding and application of rock porosity structure. It outlines the basic concepts and classifications of rock porosity, including the definitions and characteristics of macropores, micropores, and nanopores. This paper provides a comprehensive overview of the main technical methods employed in recent research on rock porosity structure, including X-ray computed tomography, scanning electron microscopy, nuclear magnetic resonance, and 3D reconstruction technologies. It explores the relationship between porosity structure and the physical and mechanical properties of rocks, focusing on the impact of porosity, permeability, and pore morphology on rock mechanical behavior. A knowledge graph of rock porosity structure is constructed to highlight key research areas, core technologies, and emerging applications in this field. The study utilizes extensive literature review and data mining techniques, analyzing 4807 papers published over the past 20 years, sourced from the Web of Science database. Bibliometric and knowledge graph analyses were performed, examining trends such as annual publication volume, country/region distribution, institutional affiliations, journal sources, subject categories, and research databases, as well as research hotspots and frontier developments. This analysis offers valuable insights into the current state of rock porosity structure research, shedding light on its progress and providing references for further advancing research in this area.

1. Introduction

The porosity structure of rocks refers to the distribution, shape, size, connectivity, and variations in porosity within the rock, which directly determine the rock’s physical properties, mechanical behavior, and fluid flow performance. Macropores, micropores, and nanopores are the three main types of rock porosity structure, classified by pore size. Macropores (pore size greater than 50 μm) typically dominate the rock’s permeability and fluid flow and are commonly found in large-scale geological environments such as oil and gas reservoirs [1]. Micropores (pore size from 1 nanometer to 50 μm) mainly affect the rock’s storage capacity and the movement of small fluids. They are important for oil and gas storage and natural gas storage. Nanopores (pore size less than 1 nanometer) involve molecular-scale processes, greatly impacting gas adsorption, diffusion, and other microscopic behaviors. They also play a key role in the rock’s surface energy and adsorption properties. Different types of pores often exist together and work together to determine the rock’s physical properties and fluid behavior [2].

Porosity is an important measure of a rock’s storage capacity, as it shows how much fluid (like water, oil, or gas) the rock can hold. Permeability describes how easily fluids can move through the rock and is key to understanding fluid flow. The pore structure affects both the storage and flow of fluids and is also linked to the rock’s strength and stability [3]. The pore structure of rocks is of paramount importance in civil and construction engineering, where rocks are widely used as building materials. The porosity and pore connectivity of rock materials directly affect their mechanical strength, durability, thermal conductivity, and resistance to cracking. For instance, high porosity often reduces the compressive strength of construction rocks, making them less suitable for load-bearing applications. Conversely, rocks with low porosity and well-distributed pore structures tend to exhibit greater strength and durability, making them ideal for constructing critical infrastructure. Furthermore, the thermal conductivity of rocks, influenced by their pore structures, plays a role in building energy efficiency, particularly in climates requiring advanced thermal insulation.

The pore structure of oil and gas reservoirs directly affects reserves, fluid flow, and extraction efficiency. Higher porosity typically indicates larger oil and gas reserves; however, reserves are not only related to porosity, but also to the connectivity and permeability of the pores. The uniformity of porosity determines the extractability of oil and gas. A uniform porosity structure helps in the even distribution of oil and gas, improving recovery rates, while uneven porosity may lead to “dead zones” or “barriers”, affecting the extraction process. The shape and connectivity of pores are crucial for fluid flow. Tubular or fracture-type pores facilitate flow, while spherical pores may hinder flow and require enhanced extraction techniques. Reservoirs with low porosity generally have fewer reserves and poorer permeability, making extraction more difficult and usually requiring enhanced recovery technologies. Reservoirs with higher porosity typically have better permeability, allowing for higher recovery rates, but complex or irregular pore structures may still lead to inefficient extraction.

The porosity structure also affects groundwater flow, rock stability, and the occurrence of geological hazards such as seismic activities. Rocks with larger porosity have stronger water storage and flow capabilities, which may lead to groundwater leakage and water level fluctuations, triggering geological disasters. The greater the porosity, the lower the strength of the rock, making it more prone to collapse or landslides. High-porosity rocks absorb seismic waves more effectively, which could influence the propagation of seismic waves, thus impacting earthquake occurrence and disaster assessment. Additionally, the porosity structure affects the accumulation of pore pressure, which may trigger earthquakes or fault slip.

X-ray CT, SEM, NMR, and 3D reconstruction technologies have important applications in the study of rock pore structures and are often used in combination to compensate for each other’s limitations. X-ray CT technology provides three-dimensional images of rocks, accurately displaying features such as pore size, shape, and distribution. It is widely used in fields such as rock mechanics, oil and gas exploration, and groundwater flow analysis. SEM, with its high-resolution imaging, is suitable for studying the micro-pore structure on the rock surface, including pore shape, connectivity, and mineral composition. Combined with electron probe and X-ray energy dispersive spectroscopy (EDS), SEM can reveal the mineral composition and trace element distribution within rocks. NMR technology has unique advantages in studying the distribution of fluids within rock pores, porosity, and pore connectivity, especially in oil and gas reservoir development, where it can reveal fluid retention and migration processes within rock pores, optimizing reservoir development strategies. Three-dimensional reconstruction technology converts the two-dimensional data obtained from X-ray CT and SEM into three-dimensional pore structure models, offering a more intuitive perspective and precise pore characteristic data, which supports predictions of fluid flow paths and reservoir permeability. With advancements in technology and data processing capabilities, the combined application of these techniques has expanded from traditional oil and gas exploration and rock mechanics research to fields such as environmental science, groundwater resource management, and civil engineering. In particular, under the context of interdisciplinary and cross-technological integration, these techniques provide more comprehensive and accurate pore structure information, facilitating the optimal development and management of various resources [4].

Rock pore structures form and change through a complex geological process, influenced by several factors. The type and origin of the rock are important in determining its pore structure. Sedimentary rocks (like sandstone and shale) usually develop more noticeable pores during deposition. Porosity and permeability are mainly affected by the depositional environment, grain size, and changes during diagenesis. Sandstones tend to have higher porosity, while shale has lower porosity with smaller pores. Igneous rocks (like granite and basalt) usually have lower porosity. However, if pores or fractures exist, the pore structure can be unique, as their formation depends on the cooling rate and crystallization of magma. Metamorphic rocks (like marble and schist) often have low porosity and tightly packed pores due to recrystallization during metamorphism, unless fractures or faults are present. The size, shape, and distribution of rock particles also influence pore structure. Coarser grains (like in conglomerates and coarse sandstones) tend to create larger pores, while finer grains (like claystones and fine sandstones) form smaller pores [5]. Irregular particles (like broken rock fragments) usually form more small pores, while regular particles (like round sand grains) create larger pores. The way particles are distributed and the voids between them also affect the connectivity and porosity of the pore structure.

Diagenesis refers to the physical and chemical changes that happen in rocks due to burial and pressure. This process affects the pore structure. Compaction reduces the space between particles as pressure increases, which lowers porosity. Cementation happens when minerals like quartz or carbonates fill the pores, further reducing porosity [6]. In some rocks, like carbonate rocks, dissolution can enlarge the pores, especially when certain chemicals are involved, increasing the rock’s porosity. Tectonic movements, such as faults, folds, and shearing, can also change the pore structure. These movements may create fractures that increase porosity and improve permeability. In hard rocks like granite or quartzite, fractures can become pathways for fluid flow (e.g., water, oil, or gas), which changes the rock’s pore structure and permeability. Folding and other deformations can compress or rearrange the pore structure, affecting both porosity and pore connectivity [7].

Hydrodynamics and fluid interactions are important in the development of rock pore structures. Water flow, especially groundwater movement, can cause minerals to dissolve or precipitate, changing the size, shape, and distribution of pores. Dissolution can make some pores bigger, while precipitation can clog them [8]. This is common in carbonate rocks and evaporites, where dissolved substances in water may form cements and reduce porosity. Changes in temperature and pressure also affect the pore structure. High temperatures can change the mineral structure and crystal shape of rocks, which can change pore size and distribution. This is especially true for igneous and metamorphic rocks, which tend to have lower porosity after high-temperature processes. Rocks buried deep under high pressure can have their pores compressed, reducing porosity or even closing the pores completely [9]. Environmental factors, such as weathering, temperature changes, and humidity, can also affect rock pores. Weathering can increase porosity, especially in surface rocks, by dissolving, oxidizing, or expanding minerals. Temperature and humidity changes can make rocks expand and contract, slightly changing the pores. Biological activity can also affect rock pore structures. Plant roots can grow into rock pores, increasing porosity, especially in weathered or softer rocks [10]. Animal burrowing can also make rock pores bigger, further changing the pore structure.

The formation and evolution of rock pore structures is a complex process affected by many factors. These factors vary in different geological settings and together they decide characteristics like porosity, pore shape, and pore connectivity, which then influence the physical and chemical properties of the rock. This is especially important in areas like groundwater and oil and gas exploration [11].

Research on rock pore structure will continue to grow in the future, primarily driven by the demand from fields such as energy exploration, carbon capture and storage technologies, groundwater management, and pollution control. With the extraction of unconventional energy, the implementation of climate change mitigation measures, and increasing attention to environmental protection, the influence of pore structure on fluid flow, reservoir stability, and pollutant migration is becoming more crucial. The development of advanced imaging technologies and characterization methods, such as X-ray tomography, nuclear magnetic resonance, and scanning electron microscopy, has greatly enhanced the ability to observe microscopic pore structures. The application of big data analysis and artificial intelligence has made the quantitative analysis and prediction of pore structures more precise. As interdisciplinary collaboration deepens, research on rock pore structure will provide more efficient solutions for industries such as energy and environmental management. The growing interdisciplinary cooperation and the increasing demand from materials science have also facilitated the development of this research direction. Overall, research on rock pore structure will continue to grow with the support of multiple fields.

2. Source of Data and Statistical Methods

2.1. Source of Data

Web of Science is a well-known academic database that provides a wide range of literature search and citation analysis tools. It includes journal articles, conference papers, patents, and theses from many fields. The database, maintained by Clarivate Analytics, was created in 1960 and has become one of the most important research resources in the world. This article analyzes data retrieved from the WOS platform on 1 October 2024. First, on the WOS literature data platform, the data source was set to “Search in: Web of Science Core Collection”. Next, the citation index was selected as “Editions: All”, and the document field was set to “Topic”. The search time was set to “Publication Date: All years”, and the keywords “Pore structure of rocks” and “Porosity structure of rocks” were entered for retrieval. A total of 4807 records were retrieved from WOS. To ensure the accuracy and relevance of the literature and facilitate bibliometric and knowledge map analysis, the original data need to be downloaded in different formats, followed by data preparation tasks such as formatting, organization, deduplication, and item-by-item screening.

Unified Format: The data are downloaded in text file format (*.txt), which is required by the VOSviewer software (1.6.18) for tab-separated files as the data source. This format also facilitates bibliometric analysis and visualization in VOSviewer. The *.txt file is named download_1.txt (from WOS). Synonyms are merged, and incorrect words are corrected. Citespace requires plain text files as the data source for knowledge mapping analysis during import.

Item-by-Item Screening: The literature was manually screened based on the type of publication, retaining only those that underwent peer review and editorial supervision. The document types included articles, reviews, letters, and conference papers. Editorial materials, book chapters, and other documents with weaker relevance to this study were removed. After identification and iteration, erroneous records were deleted, resulting in a final count of 4807 valid documents.

2.2. Statistical Methods

This study mainly utilized two approaches: bibliometric analysis and knowledge mapping. The analysis was conducted using VOSviewer and CiteSpace (6.2.2), both Java-based software tools developed by the van Eck and Waltman research team at Leiden University in the Netherlands. These tools, widely recognized by experts in scientometrics, are adept at converting intricate scientific data into clear and insightful knowledge maps. Given that VOSviewer and CiteSpace are capable of creating large, visually appealing maps, they provide different perspectives on research through various aspects. The decision to employ CiteSpace in this study stems from its ability to streamline the identification of key papers within the research domain. It allows for the visualization of prominent patterns within a citation network and helps highlight changes between adjacent nodes, providing valuable visual insights. The data used for keyword clustering analysis were sourced from the Web of Science (WOS) platform and were subsequently organized into a self-constructed text format for further analysis. These data were then imported into VOSviewer, which supports custom text data, to extract keywords and perform co-occurrence clustering based on these keywords. Using these two tools, this paper has created multidimensional knowledge maps covering countries, institutions, authors, journals, and co-citation networks, revealing research hotspots, collaboration trends, and knowledge flow patterns. The analysis of research findings from 2008 to 2025 assesses both the depth and scope of the field, identifies the primary factors influencing research trends, and offers predictions regarding the future directions of development in this area.

2.3. Full-Text Screening

The Preferred Reporting Items of Systematic Reviews and Meta-Analysis guidelines (PRISMA) were used to prepare and facilitate transparent reporting of the systematic review [12]. This guideline enables readers to assess the quality and validity of the reporting. By searching in the Web of Science database, a preliminary total of 5790 potential research reports were obtained. During the preliminary screening process, 921 articles unrelated to the research question were excluded by checking the titles and abstracts. A detailed evaluation was conducted on the remaining 4922 full-text articles, and ultimately 62 studies were excluded due to the lack of full-text conference abstracts. According to the predetermined inclusion criteria, 4807 studies met the requirements and were included in the systematic review. The specific flowchart is shown in Figure 1.

3. Result and Analysis

3.1. Trend of Publication Volume

An analysis was conducted on 4807 core articles selected from the Web of Science database, revealing the trend in annual publication volumes, which reflects the level of activity in research on rock pore structures both domestically and internationally. Figure 2 primarily shows the distribution of annual publication volumes in the field of rock pore structures from 2008 to 2024. By analyzing the publication volumes, it can be observed that in recent years, research on rock pore structures has undergone three stages of development: the rising phase, the apparent growth phase, and the rapid development phase.

According to the publication data presented in Figure 2, research in this domain over the past two decades can be categorized into three distinct phases. The first stage is the rising phase (2008–2013). During these six years, only 392 papers were published, with fewer than 100 papers each year, resulting in an average of 65.3 papers per year. However, the overall trend was steadily increasing. During this time, rock pore structure became an important topic in fields like geology, geotechnical engineering, and oil and gas exploration. Studies showed that rock pore structures affect permeability, mechanical properties, and reservoir characteristics [13]. These structures have applications in oil and gas extraction, hydrogeology, and environmental protection. High-resolution techniques like X-ray CT, scanning electron microscopy, and nuclear magnetic resonance helped researchers explore the relationship between pore structure, permeability, and mechanical properties [14]. This research supported the development of oil and gas reservoirs, carbon sequestration, and water resource management. In shale gas and unconventional resource extraction, even small changes in pore structure are important for predicting fluid flow and reservoir distribution. Factors like porosity, pore connectivity, and pore shape are also key to rock strength and fracture behavior, leading to the creation of models linking pore structure and mechanical properties. Research during this period helped improve the understanding of rock pore structures and provided important support for various applications [15].

The second stage is the growth stage (2014–2017). During these four years, 757 papers were published, nearly double the number from the previous six years, with an average of 189.3 papers per year, three times the rate of the earlier phase. From 2014 to 2017, there was significant progress in rock pore structure research, especially in oil and gas exploration, unconventional energy extraction, geotechnical engineering, and environmental geology [16]. With the development of technologies like X-ray micro-CT, scanning electron microscopy, and nuclear magnetic resonance, the study of rock pore structures became more detailed. Research focused on the pore structure of unconventional oil and gas resources, such as shale gas and tight oil, looking at the relationship between porosity and permeability, as well as how pore connectivity affects hydraulic fracturing. The rock pore structure is closely linked to rock strength and toughness, making it important in geotechnical engineering [17]. Carbon capture and storage technology became a key research area, with porosity and connectivity affecting the injection and stability of carbon dioxide. In environmental geology, the study of how pore structure influences groundwater flow and contamination, especially in groundwater management and pollution control, became more important. Multi-scale simulation and modeling techniques helped researchers gain a better understanding of how pore structure affects rock properties [18].

The third phase, spanning from 2018 to 2024, marks a period of rapid growth and significant development. From 2018 to 2024, there was major progress in rock pore structure research in fields like energy, environment, and engineering. With new technological improvements, high-resolution imaging and multi-scale modeling methods made pore structure studies more detailed and diverse [19]. These studies helped improve the efficiency of extracting unconventional oil and gas resources and optimize hydraulic fracturing. They also impacted rock mechanics, carbon capture and storage, pollution control, and groundwater management. Research on how pore structure affects rock properties, engineering stability, CO₂ storage, and pollutant movement was also expanded [20]. These studies provided strong support for technological advances and applications in related fields. Over 7 years, 3717 papers were published, making up 77.78% of the total [21]. This is an average of 531 papers per year, which is double the number during the growth stage. The large increase in papers is linked to the progress made in this area. In 2023, the number of papers reached 700 [22]. Only eight papers were counted for 2025 due to limited data, but it is expected that the number of publications in 2025 will remain high, suggesting a bright future for research in this area [23].

3.2. Analysis of Output and Cooperation Among Countries

The images in the following text (Figure 3, Figure 4, Figure 5, Figure 6, Figure 7, Figure 8, Figure 9 and Figure 10) are all drawn using the same software, and the colors corresponding to the nodes in the images have the same meaning. In the charts generated by VOSviewer, nodes with the same color usually indicate strong similarity or correlation between these nodes. The color of nodes is determined based on their relative position or clustering during the analysis process. VOSviewer will classify nodes with high similarity into the same category based on their co-occurrence relationships and label them with the same color. This color coding helps to visually display the structure of data, helping us identify which nodes are closely related or belong to the same topic area, thereby simplifying the process of understanding and analyzing data.

Figure 3 illustrates the global distribution of countries and regions that are leading in this field. Among the various nations participating in the research, China stands out with the highest number of publications, totaling 3185 papers, which represents 66.45% of the total. The United States follows with 744 papers, accounting for 15.57%, while Australia and the United Kingdom have contributed 251 (5.26%) and 191 (3.99%) papers, respectively.

Figure 3. Co creation of national distribution knowledge graph.

Figure 3. Co creation of national distribution knowledge graph.

Each node in the graph represents a country that participates in the research, with the node size corresponding to the number of publications from that country, providing a visual representation of each nation’s contribution to the field. The lines connecting the nodes signify the collaborative relationships between countries, with the thickness of the lines offering an intuitive measure of the strength of these partnerships—thicker lines indicate more frequent and stronger cooperation. As depicted in Figure 3, China demonstrates particularly strong collaborative ties with the United States and the United Kingdom. Similarly, the United States has formed partnerships with countries such as the United Kingdom and Germany, highlighting the wide-ranging and varied nature of international cooperation in this area. Moreover, the total link strength (TLS) is an important metric for assessing the extent of international collaboration, reflecting a country’s influence and standing within the global research network.

Table 1. Information statistics of the top 10 countries in terms of number of publications.

Rank	Countries	Publications	Citations	Total Link Strength
1	China	3185	55,094	854
2	USA	744	37,463	600
3	Australia	251	8667	267
4	England	191	5872	251
5	Canada	174	5822	183
6	France	174	5197	174
7	Germany	174	4626	217
8	Italy	118	3009	127
9	Russia	98	1015	45
10	Saudi Arabia	97	1250	88

shows that China, the United States, and Australia rank highest in TLS, with values of 854, 600, and 267, respectively, underscoring their significant roles in global research cooperation.

3.3. Institutional Output and Cooperation

In terms of collaboration between institutions, the co-occurrence feature in CiteSpace software (6.2.2) enables the creation of a network map illustrating institutional partnerships, as shown in Figure 4. The prominence of an institution’s name, indicated by a larger font, corresponds to its publication output, while the number of curves surrounding the name reflects the frequency of its collaborative efforts with other institutions. The analysis reveals that, although the network contains several prominent institutional groups, there is a notable frequency and strength of collaboration among them. Further examination indicates that research on rock pore structures has largely facilitated the development of high-productivity research institutions, such as the China University of Petroleum, China National Petroleum Corporation, and China University of Geosciences. Universities; colleges; and research institutes, which are the primary contributors in this field. As shown in

Table 2. Information statistics of top 10 institutions in terms of number of publications.

Rank	Institution	Publications	Proportion
1	China University of Petroleum (China)	806	16.87%
2	China National Petroleum Corporation (China)	589	12.34%
3	China University of Geosciences (China)	391	8.18%
4	China University of Mining Technology (China)	347	7.26%
5	Sinopec (China)	327	6.84%
6	Chinese Academy of Sciences (China)	310	6.49%
7	Southwest Petroleum University (China)	191	3.99%
8	University of Chinese Academy of Sciences Cas (China)	159	3.33%
9	University of Texas System (USA)	126	2.64%
10	Center National De La Recherche Scientifique CNRS (France)	112	2.34%

, eight of the leading institutions are based in China, with two others located in the United States and France, demonstrating the extensive and varied nature of international collaboration. These institutions are predominantly focused on geology, with China University of Petroleum leading with 806 publications, followed by China National Petroleum Corporation (589) and China University of Geosciences (391).

Figure 4. Knowledge graph of research institution distribution.

Figure 4. Knowledge graph of research institution distribution.

3.4. Main Journal Sources and Co-Citation Analysis of Literature

After thoroughly analyzing the data obtained from WOS, a total of 557 journals were identified, with 20 of them publishing more than 50 articles. This reflects the growing interest in research related to rock pore structures.

Table 3. Main source journals information statistical table.

Rank	Disciplines	Publications	JCI	Citation Index
1	Journal of Petroleum Science and Engineering	237	1.08	SCI
2	Marine and Petroleum Geology	190	1.08	SCI
3	Energy Fuels	177	0.68	SCI
4	Journal of Natural Gas Science and Engineering	153	0.74	SCI
5	Fuel	136	1.11	SCI
6	Geofluids	106	0.53	SCI
7	Energies	102	0.46	SCI
8	Frontiers in Earth Science	82	0.58	SCI
9	Journal of Geophysical Research Solid Earth	81	1.11	SCI
10	Geoenergy Science and Engineering	78	0.51	SCI

presents the top 10 journals based on publication volume. Among these, the three leading journals with the highest number of publications are the Journal of Petroleum Science and Engineering (237), Marine and Petroleum Geology (190), and Energy Fuels (177) with JCI indices of 1.08, 1.08, and 0.68, respectively. As leading journals in the industry, they exert significant influence in the fields of engineering geology and energy, playing a crucial role in advancing the development of the field. In particular, the Journal of Petroleum Science and Engineering has consistently focused on this area over the years and published the most papers.

Figure 5 illustrates the co-citation network, which displays the citation relationships between journals in the area of rock pore structure research. In this network, the size of each node is proportional to the frequency with which the journals are cited. Notably, Marine and Petroleum Geology is represented by the largest node, signifying its position as the most frequently cited journal in this field, with a total of 8467 citations and a link strength of 267,249. The journals Aapg Bulletin and Fuel follow closely, with citation counts of 7728 and 7694, respectively. These three journals, marked by yellow nodes, form the central cluster of research in this domain. The figure also shows different colored clusters representing groups of journals, such as the red cluster centered around Geophysics, with 3913 citations, and the green cluster surrounding the Journal of Petroleum Science and Engineering. The formation of these clusters reveals the division and cross-fusion of research subfields. The thickest lines connect Marine and Petroleum Geology with Aapg Bulletin and Fuel, indicating the closest relationship between these journals. It can be seen that the main research directions of these journals lie in the fields of energy, geology, and fuel.

Figure 5. Knowledge graph of major journal distribution.

Figure 5. Knowledge graph of major journal distribution.

3.5. The Co-Citation Analysis of Key Literature

The WOS data platform shows that the most frequently cited paper is “Characterization of gas shale pore systems by porosimetry, pycnometry, surface area, and field emission scanning electron microscopy/transmission electron microscopy image analyses: Examples from the Barnett, Woodford, Haynesville, Marcellus, and Doig units”, authored by Chalmers, Gareth R., et al., and published in 2012 in Aapg Bulletin [24]. It has been cited 1545 times across all data platforms. This paper uses a variety of characterization techniques, including porosimetry, gas pycnometry, surface area measurements, and electron microscopy analyses, to study gas shale pore systems in detail. This study investigates the pore characteristics of various shale units, including Barnett, Woodford, Haynesville, Marcellus, and Doig. The findings highlight the variations in porosity, pore types, and pore networks across different geological environments. Additionally, the research examines how diagenesis and thermal maturation processes influence the development of pore structures. The findings offer valuable theoretical insights that can aid in the exploration and development of shale gas resources. They contribute to optimizing development strategies and enhancing production efficiency.

To evaluate the distribution of scientific literature on the rock mechanical behavior under thermal conditions, a study was conducted to identify and list the ten most-cited papers in this area. This selection includes three papers published prior to 2010 and seven more recent contributions, as summarized in

Table 4. The top ten most cited core literature.

Rank	Title	Journal	Author	Year	Citation
1	Characterization of gas shale pore systems by porosimetry, pycnometry, surface area, and field emission scanning electron microscopy/transmission electron microscopy image analyses: Examples from the Barnett, Woodford, Haynesville, Marcellus, and Doig units	Aapg Bulletin	Chalmers, G.R. et al. [24].	2012	1237
2	Pore-throat sizes in sandstones, tight sandstones, and shales	Aapg Bulletin	Nelson, P.H. et al. [25].	2009	935
3	Development of organic porosity in the Woodford Shale with increasing thermal maturity	International Journal of Coal Geology	Curtis, M.E. et al. [26].	2012	868
4	Specific surface area and pore-size distribution in clays and shales	Geophysical Prospecting	Kuila, U. et al. [27].	2013	845
5	Petrophysical characterization of coals by low-field nuclear magnetic resonance (NMR)	Fuel	Yao, Y.B. et al. [28].	2010	714
6	Pore types in the Barnett and Woodford gas shales: Contribution to understanding gas storage and migration pathways in fine-grained rocks	Aapg Bulletin	Slatt, R.M. et al. [29].	2011	708
7	Experimental investigation of main controls to methane adsorption in clay-rich rocks	Applied Geochemistry	Ji, L.M. et al. [30].	2012	530
8	Measurements of gas permeability and diffusivity of tight reservoir rocks: different approaches and their applications	Geofluids	Cui, X. et al. [31].	2009	503
9	Nano-scale pore structure and fractal dimension of organic-rich Wufeng-Longmaxi shale from Jiaoshiba area, Sichuan Basin: Investigations using FE-SEM, gas adsorption and helium pycnometry	Marine and Petroleum Geology	Yang, R. et al. [32].	2016	450
10	Natural fracture characterization in tight gas sandstones: Integrating mechanics and diagenesis	Aapg Bulletin	Olson, J.E. et al. [33].	2009	332

. The papers, co-authored by various researchers, focus on the pore systems and reservoir characteristics of different rock and shale types, such as gas shales, tight sandstones, and coal beds, with a particular emphasis on their role in unconventional energy extraction. The studies primarily investigate parameters like porosity, pore size, and pore type, examining their impact on fluid storage and migration within reservoirs, including gas, oil, and methane. Advanced techniques such as SEM, TEM, gas adsorption, helium pycnometry, and low-field NMR are used to analyze pore shape, distribution, and structural changes.

The goal of these studies is to provide better suggestions for oil and gas exploration, extraction, and storage. This helps improve extraction methods and fracture designs, which can increase production efficiency. Although all of these studies examine the characteristics of reservoir pore structures, they vary in terms of their study subjects, methodologies, geographical focus, and specific research areas. For example, the paper “Characterization of gas shale pore systems” primarily investigates gas shales, whereas “Pore-throat sizes in sandstones, tight sandstones, and shales” focuses on the pore-throat characteristics across sandstones, tight sandstones, and shales. The research approaches also differ: for instance, the paper “Petrophysical characterization of coals by NMR” uses low-field NMR techniques to analyze coalbed properties, while “Experimental investigation of main controls to methane adsorption in clay-rich rocks” explores methane adsorption behaviors in clay-rich formations. Additionally, certain studies emphasize the evolution of pore structures with thermal maturation, such as “Development of organic porosity in the Woodford Shale with increasing thermal maturity”, which examines the growth of organic pores as shale undergoes thermal maturation. The study “Pore types in the Barnett and Woodford gas shales” investigates specific pore types in these gas shales and their influence on gas storage and migration. Other papers in this field focus on porosity measurements or provide a comprehensive characterization of pore features across various rock types.

3.6. Authors’ Output and Collaboration Analysis

In the graph, each node represents an individual author, with its size proportional to the number of articles co-authored by that author in collaboration with others. The connecting lines between nodes illustrate the collaborative relationships between authors, with line thickness serving as an indicator of collaboration intensity—the thicker the line, the more frequent and substantial the collaboration. Different colors are used to differentiate various author clusters, helping to clearly visualize and analyze the structure and scale of each research team.

In terms of author collaboration, the author collaboration network knowledge map generated by VOSviewer, as shown in Figure 6, clearly demonstrates the characteristic of “overall dispersion but local concentration” in the authors’ scientific collaboration. Three primary author clusters form a locally concentrated network in the map. We have listed the top five authors based on their publication volume in this field. As shown in

Table 5. The top five leading authors who have published the most articles in the field of rock pore structure research.

Rank	Author	Publications	Proportion
1	Hu, Qinhong	57	1.193%
2	Ba, Jing	49	1.025%
3	Ostadhassan, mehdi	37	0.774%
4	Jiang, Zhenxue	36	0.753%
5	Yao, Jun	33	0.691%

, Hu Qinhong stands out with 57 papers, making him the most prolific author in this field. The central author group, which exhibits the highest density and the largest number of research teams, is anchored around Hu Qinhong. This group also includes “Hao, Fang” (with 15 publications), both of whom belong to academic teams that have produced a significant volume of work. Within this central cluster, collaboration is notably frequent, and scholarly interactions are more intense. However, this core group appears somewhat isolated from the other two major clusters, as the spatial distance between them on the map is relatively large. In contrast, the second large author group, centered around “Zhang, Lei” and “Yao, Jun”, is positioned closer to a third core group led by “Ju, Yang”, suggesting stronger scientific collaboration between these two clusters.

Figure 6. Knowledge graph of author distribution in the research.

Figure 6. Knowledge graph of author distribution in the research.

3.7. Analysis of Research Hotspots

Keyword analysis is a crucial method in scientific research, serving to identify and extract the central themes and framework of a particular field. It also provides valuable insights into the latest trends and emerging developments within the discipline. By creating a knowledge map of frequently occurring keywords, we can visually capture the relationships and hierarchical structure among different research topics.

To better visualize prominent keywords, we first group together terms with similar meanings and then perform co-occurrence analysis on high-frequency keywords using VOSviewer software. As illustrated in Figure 7, different colors are used to represent distinct research themes. The nodes in the map correspond to keywords, with each node symbolizing a key concept or topic in the literature. The number of nodes reflects the diversity of keywords within the field, providing an indication of the breadth and depth of research activity. The lines between nodes represent the co-occurrence relationship between keywords—when two keywords appear together in the same paper, a link is formed, shown as a solid line on the map. This connection visually demonstrates the intersection, integration, and mutual influence of research themes. The size of each node is proportional to the frequency of the keyword it represents in the literature; larger nodes indicate higher frequencies, signifying that these keywords are central and widely discussed in the field. The map further clusters keywords by color, with each color corresponding to a specific subfield or research theme. Figure 7 summarizes four key research topics on rock pore structure. In the red cluster, the keyword “pore structure” stands out as the central theme, indicated by its larger node and central position. Other related terms, such as “shale” and “Ordos Basin”, are closely grouped around this central term, forming a tightly knit network, which highlights the strong focus on rock pore structure in current research. The blue keyword group, centered around “permeability”, represents research on factors affecting rock pore structure, such as “flow”, “porous-media”, and “water”. The green keyword group is relatively scattered, with no obvious core popular keywords, but the research mainly focuses on the relationship between rock mechanical properties and their microstructures, exploring how factors like porosity, pore structure, and mineral composition affect rock strength, deformation, and fracture behavior. It also looks at how rocks react to different conditions, like temperature and stress, and how these affect rock behaviors [34]. The changes in rock structure, crack growth, and permeability are also important topics. The main focus is on “NMR” technology. Research uses nuclear magnetic resonance to study porosity, pore distribution, shape, and connectivity [35]. NMR can tell apart different pore sizes and show how they affect permeability and fluid flow. NMR also looks at how pore structure links to rock strength and deformation, helping us understand how pore shape impacts rock properties. Using tools like X-ray CT and scanning electron microscopy, NMR provides a detailed, non-destructive way to study rock pores, helping to predict rock behavior, permeability, and fluid movement [36].

Figure 7. Knowledge graph of keyword distribution.

Figure 7. Knowledge graph of keyword distribution.

An analysis of

Table 6. Top 10 high-frequency keywords.

Rank	Keyword	Frequency	Year	Link	Centrality
1	pore structure	1121	2008	3558	0.02
2	permeability	899	2008	2788	0.00
3	porosity	847	2008	2760	0.02
4	rock	751	2008	2194	0.01
5	model	499	2008	1225	0.00
6	porous-media	463	2008	983	0.01
7	Sichuan Basin	381	2013	1361	0.05
8	flow	371	2008	1046	0.03
9	shale	366	2008	1168	0.12
10	adsorption	317	2009	1321	0.00

reveals the five most frequent keywords in the research on rock mechanical behavior under temperature influences. These are identified as “pore structure” (1121), “permeability” (899), “porosity” (847), “rock” (751), and “model” (499). These keywords suggest that the research on rock pore structure is developing in a more refined and multi-dimensional direction. Currently, researchers focus on the microstructural features of pores, the connectivity of pore networks, and the complex nonlinear relationships between porosity and permeability. Multi-scale modeling and numerical simulation methods are widely applied to gain a more comprehensive understanding of the impact of pore structure on fluid flow, while machine learning techniques are being integrated to improve prediction accuracy. At the same time, the research is gradually expanding towards practical applications, particularly in fields such as oil and gas exploration, groundwater management, and carbon capture, promoting the use of pore structure modeling in real-world engineering applications and revealing the evolving trends in the field of study [37]. The bar chart of the top ten keywords with the highest frequency of occurrence is shown in Figure 8.

Figure 8. Column chart of the top ten high-frequency keywords.

Figure 8. Column chart of the top ten high-frequency keywords.

In VOSviewer, the average publication year of a journal refers to the arithmetic mean of the publication years of all literature in the journal, which reflects the academic activity trend of the journal. A lower average publication year indicates that the journal focuses on newer research findings, while a higher average publication year means that the journal primarily concentrates on earlier literature. By analyzing this indicator, one can understand the academic trends in the field, identify research hotspots and development trends, and evaluate the academic novelty of journals. In VOSviewer’s visualization, the color and size of journals are usually related to their average publication year, helping to visually present the temporal dimension of journals.

By looking at Figure 9, we can see that the keywords “flow”, “porous-media”, and “rock” appeared early in the study of rock pore structure. This shows that one key issue in this area is how fluid moves through porous media. This highlights the role of rock pore structure in fluid flow, especially in areas like oil and gas extraction, water management, and underground storage, where fluid movement through rock pores directly affects permeability, porosity, and reservoir performance [38]. The early appearance of these keywords shows the focus on understanding fluid behavior in rocks, which laid the groundwork for later studies on seepage, pore structure, and related topics. In recent years, keywords like “pore structure” and “NMR” have become more common, showing a growing use of nuclear magnetic resonance for detailed pore structure analysis. NMR provides high-resolution data on pore characteristics, especially at the micro-scale, which is important for analyzing rocks with low porosity and complex pore shapes [39]. This trend reflects the need for more precise, non-destructive methods to study pore structures, which helps improve understanding of rock performance, permeability, and fluid movement. This also supports advances in rock physics, seepage mechanics, and fields like oil and gas, as well as groundwater research. This shift notably reflects the growing focus on the pore structure of rocks, which is closely related to the increasing demand in engineering practice for material performance prediction, disaster prevention, and efficient resource extraction. This transition not only broadens the scope of research but also provides richer theoretical support and technical means for solving practical problems in related fields.

Figure 9. Knowledge graph of keyword time distribution.

Figure 9. Knowledge graph of keyword time distribution.

To further present the relationships between research hotspots and understand their content and direction, a keyword clustering map was generated using keyword co-occurrence analysis, as shown in Figure 10. The research on rock pore structure can be categorized into 16 clusters, which are as follows: #0 rock physics, #1 case study, #2 dynamic mechanical behavior, #3 opalinus clay, #4 nanopore structure, #5 upper cretaceous Nenjiang Formation, #6 consolidation settlement, #7 pore–throat structure, #8 molecular carbon structure, #9 water–shale interaction, #10 southern Sichuan Basin, #11 generative adversarial network, #12 electrical conductivity, #13 saturated brine injection, #14 tight gas reservoir, and #15 mineral precipitation. The larger the number of clusters, the more publications are associated with them, and thus the more influential they are in the field of research. Therefore, these sixteen clusters can be grouped into five research themes.

The theme of rock pore structure and mechanical behavior explores how the pore characteristics of rocks affect their physical and mechanical properties, particularly their response under different external conditions. The research mainly includes #0 rock physics, with a focus on analyzing physical properties such as porosity and permeability; #2 dynamic mechanical behavior, focusing on the mechanical response and stress–strain relationship of rocks under dynamic loading due to pore structure; consolidation settlement (#6), studying the deformation of rocks or soils under pressure and the changes in their pore structure; and #7 pore–throat structure, an in-depth exploration of the microstructure of rock pores and throats, especially their influence on fluid flow. These studies focus on revealing the evolution process of rock pore structure under different physical and mechanical conditions and its influence on the overall mechanical properties of rocks, aiming to improve the understanding of rock behavior, especially in engineering and geological processes [40].

The study of rock pore structure and reservoir performance mainly focuses on the pore characteristics of different types of reservoir rocks (such as gas reservoirs, shale) and their influence on fluid behavior, especially in low-permeability or compact gas reservoirs. The research in this field covers multiple aspects, including the pore structure and oil and gas reservoir characteristics of specific strata such as the Nenjiang Formation in the #5 Upper Cretaceous Nenjiang Formation, with a focus on exploring the performance of oil and gas reservoirs; the mechanism of the #9 water–shale interaction, studying how the interaction between water and shale affects changes in pore structure; the influence of pore structure of low-permeability rocks in #14 tight gas reservoir on gas storage and flow; and the changes in rock pore structure and reservoir behavior caused by #13 saturated brine injection. These studies contribute to a deeper understanding of the performance of different formations during fluid injection and extraction processes, optimizing the extraction methods of oil, gas, and water resources, as well as improving the accuracy of reservoir performance evaluation and prediction.

The study of rock pore structure and nanoscale focuses on the microscopic characteristics of nanoscale pores in rocks, as well as how these characteristics affect the physical, chemical, and electrical properties of rocks. The research on this clustering mainly includes the influence of #4 nanopore structure in rocks on physical properties, especially how to change the mechanical and thermal behavior of rocks; exploring the #8 molecular carbon structure characteristics of organic matter (such as carbon molecules) in rocks and their impact on rock properties at the nanoscale; and the influence of pore structure, especially #12 electrical conductivity, to reveal the relationship between electrical properties and nanopores. These studies contribute to a deeper understanding of the structural characteristics of rocks at the microscale, particularly how the properties of carbon-based materials are closely related to the overall performance of rocks, such as electrical conductivity and mechanical properties, providing a more refined theoretical basis for the application of rock materials [41].

The theme of “Research on Shale and Specific Strata” focuses on the pore structure of specific strata (such as the southern Sichuan Basin and the Eupalinus clay) and their impact on rock properties. Specifically, the research covers the pore structure and mechanical behavior of #3 opalinus clay shale, particularly its performance in geological reservoirs, exploring how its mechanical properties affect the reservoir performance and resource development potential of shale. At the same time, the rock pore structure and reservoir characteristics in the #10 Southern Sichuan Basin area have been studied, especially the potential for energy resource development such as shale gas [42]. Through case study #1, a detailed analysis of the pore structure in different geological regions and rock types was conducted to reveal how the pore structure in these specific areas affects the mechanical properties, reservoir quality, and resource extraction efficiency of rocks [43]. These studies not only provide in-depth insights into the microstructural characteristics of different rock types but also provide a scientific basis for the exploration and exploitation of resources such as shale gas and shale oil.

The theme of “Advanced Technology and Data Analysis” focuses on the application of modern technologies (such as generative adversarial networks (GANs)) and data analysis methods in the study of rock pore structure, particularly in simulating, analyzing, and predicting mineral precipitation and pore changes. By using artificial intelligence and machine learning technologies such as the #11 generative adversarial network, researchers can efficiently simulate rock pore structures, generate pore images, or conduct complex pore characteristic analysis, providing new perspectives and accurate simulation tools for the study of pore structures. In addition, the research on #15 mineral precipitation focuses on analyzing the mineral deposition process in pores, exploring how sedimentary substances affect the changes in pores, and thus how they have a significant impact on the mechanical properties and reservoir performance of rocks. These advanced technologies and data analysis methods not only promote the depth and accuracy of pore structure research but also provide strong technical support for optimization in areas such as mineral precipitation, pore evolution, and resource extraction [44].

Figure 10. Knowledge graph of keyword clustering distribution.

Figure 10. Knowledge graph of keyword clustering distribution.

Figure 11 is a knowledge graph of the timeline distribution of keyword clustering. Based on the information in the graph, we can analyze that high-frequency keywords and emerging terms are highly concentrated in five main clusters: #0 rock physics, #2 dynamic mechanical behavior, #3 opalinus clay, #7 pore–throat structure, and #9 water–shale interaction. When studying the pore structure characteristics of rocks, the most important factors include pore development, methane adsorption capacity, effective thermal conductivity, complex lithofacies, and water–rock interactions. Pore development directly affects the storage and permeability performance of rocks, methane adsorption capacity reflects the impact of pore structure on gas storage, effective thermal conductivity is related to pore volume and the state of fluid filling, complex lithofacies help understand the diversity of rock pores, and water–rock interactions determine the evolution and changes in pore structure. These factors collectively determine the pore structure characteristics of rocks, influencing their performance in fields such as energy storage, heat conduction, and hydrogeology. These clusters not only reflect the diverse perspectives in pore structure research but also reveal the rise and fall of various research directions along the timeline [45].

On the time axis of cluster #0 rock physics, the study focuses on exploring the relationship between the physical properties of rocks and their pore structure. The characteristics of porosity, permeability, elastic properties, etc., are directly influenced by the pore structure, which in turn determines the fluid storage and transmission capacity, wave velocity propagation, mechanical behavior, etc., of rocks. The research content includes porosity and elastic properties, the influence of pore structure on permeability and mechanical behavior, and the relationship between porosity and mineral composition. In seismic exploration, the relationship between rock wave velocity and pore structure is helpful for evaluating underground rock formations. The application of simulation and numerical models further promotes a deeper understanding of rock pore structure and its physical properties. These studies provide important theoretical basis and technical support for fields such as oil and gas exploration, groundwater resource assessment, and reservoir management [46].

In cluster #2, dynamic mechanical behavior primarily focuses on the mechanical response of rocks under dynamic loading conditions, especially the evolution of rock pore structures under seismic activity, changes in underground pressure, or other external dynamic influences. Research in this area is centered on analyzing the mechanical performance of rocks over different time scales, particularly how rock pore structures evolve over time under the influence of dynamic events such as earthquakes and tectonic movements. Specifically, dynamic mechanical behavior involves the elasticity, plasticity, fracture, and rheological characteristics of rocks, which are closely related to the porosity, pore shape, and fluid filling state of the rocks. Studies on the time-scale axis focus on how rocks respond to dynamic changes during historical periods and under underground conditions, such as seismic wave propagation, tectonic activities, and sediment accumulation. Research has shown that the size, shape, and distribution of pore structures directly affect the mechanical properties of rocks, such as compressibility, elastic modulus, and permeability. Under dynamic loading, the evolution of pore shape can lead to crack propagation or deformation, thus affecting the strength and toughness of the rocks. Dynamic events, such as seismic wave propagation and tectonic activities, can cause deformation and connectivity changes in rock pore structures, which in turn affect their permeability, wave velocity, and energy storage characteristics. Fluids within the pores, such as water and gases, can also significantly influence the mechanical behavior of rocks under dynamic conditions, causing pore expansion, contraction, or crack propagation. Research along the time-scale axis reveals the stability and failure mechanisms of rocks under different dynamic loads, such as the durability of pore structures, failure modes, and plastic deformation and micro-crack propagation under long-term stress. Through experimental and numerical simulation techniques, researchers are able to model the mechanical response of rocks in dynamic environments and reveal the laws governing the changes in pore structures, providing theoretical support for applications such as energy extraction and underground storage [47].

The research on the time-zone distribution axis of cluster #3 opalinus clay, spanning key years from 2008 to 2024, primarily focuses on the evolution of the pore structure of opalinus clay under dynamic loading conditions (such as earthquakes, tectonic activity, groundwater flow) and its impact on the mechanical properties at different time scales. The study shows that factors such as tectonic activity, sedimentation processes, and fluid flow can lead to changes in the pore shape and distribution, thereby affecting the rock’s strength, permeability, and deformation characteristics. Under dynamic loading conditions, opalinus clay may experience phenomena such as fracture extension and micro-crack formation, further altering its mechanical behavior. Through experiments and numerical simulations, researchers have revealed the evolution patterns of the pore structure, providing a theoretical basis for underground storage and nuclear waste disposal [48].

The time-zone distribution of cluster #7 pore–throat structure is mainly used to describe the distribution, morphology, and interconnection of pores and throats. Through analysis at different scales (time-zone axis), the study reveals the heterogeneity of pores and throats and their impact on rock permeability, fluid flow, and mechanical properties. At different scales, the aggregation and distribution characteristics of pores and throats directly influence the rock’s permeability and transport properties. Aggregated pores and throats may promote fluid flow or create localized “blockages”, which in turn alter the rock’s permeability. In addition, the connectivity and morphology of the pore network also have a significant effect on the rock’s elasticity and mechanical response. Therefore, time-zone axis analysis not only helps in understanding the multi-scale evolution of pore structures but also provides important theoretical and practical guidance for fields such as oil and gas reservoirs, groundwater flow, and geotechnical engineering.

On the time-zone axis of cluster #9 water–shale interaction, the focus is on studying water–rock interactions in rock pore structures. Through chemical and physical processes such as dissolution, precipitation, and weathering, water alters the porosity, pore morphology, and pore connectivity of rocks. Water infiltration can lead to mineral dissolution; increasing porosity; or, through precipitation, reducing porosity and changing pore morphology and distribution. Long-term interaction between water and rock may affect the connectivity of pore networks, thus altering the permeability and mechanical properties of the rock. Water’s chemical weathering changes the mineral composition of rocks and affects pore structures. Studying water–rock interactions at different scales helps us understand how pores evolve. This also provides useful support for oil and gas exploration, groundwater storage, and geological engineering [49].

The appearance of keywords like “3D digital” and “micro-focus CT” in 2024 marks a new trend in research. The use of 3D digitalization and micro-focus CT technology is advancing research on rock pore structures. These technologies offer high-resolution 3D images, allowing researchers to closely examine the shape, connection, and details of rock pores, especially at micrometer or smaller scales. They also support data analysis, making it easier to assess porosity, pore shape, and connectivity, as well as to simulate fluid flow in rocks. Unlike traditional methods, micro-focus CT is non-destructive and can monitor rock changes over time. These technologies are key for studying rock pore structures, evaluating reservoirs, and applying them in geological engineering [50].

4. Development History and Future Research Directions

The study of porosity theory has gone through multiple stages of development. In the late 19th and early 20th centuries, early research focused on the physical properties of rocks and their impact on groundwater flow and soil mechanics [51]. Porosity was typically defined as the ratio of pore volume to the overall volume of the rock or soil. At the beginning of the 20th century, the research focus shifted towards the correlation between porosity and rock permeability, compressibility, and other physical properties. In 1912, Karl Stone proposed the Stone formula, which laid the foundation for the quantitative relationship between porosity and permeability [52]. In the mid-20th century, with the deepening of rock mechanics research, the relationship between porosity and the mechanical properties of rocks became increasingly close, and porosity had a significant impact on properties such as rock strength, stiffness, and elastic modulus [53]. Since the 1980s, advances in computer technology and experimental methods have driven the quantification and 3D visualization of porosity theory. New quantitative calculation methods and porosity permeability models have made research more accurate [54].

In the basic research of porosity, researchers have explored the classification and characterization methods of porosity, as well as its impact on rock permeability and mechanical properties. With the advancement of technology, three-dimensional pore structure reconstruction has gradually become a key research field [55]. Through advanced technologies such as CT scanning and nuclear magnetic resonance (NMR) imaging, researchers can intuitively analyze the distribution characteristics and connectivity of rock pores [56]. Traditional experimental methods, such as the volumetric method, specific gravity method, and gas permeability method, as well as techniques such as X-ray CT and NMR imaging, provide various precise means of measuring porosity [57]. The continuous development of porosity theory, especially in quantitative analysis and multi-scale research, has greatly promoted research in rock mechanics, permeability, and other fields, and significantly improved the accuracy and safety of resource exploration and geological engineering applications [58].

With the deepening of activities such as oil and gas extraction, underground energy storage, and carbon dioxide sequestration, the evolution of rock porosity in dynamic environments has become an increasingly important research hotspot [59]. Porosity is not only influenced by rock genesis and mineral composition, but also regulated by external factors such as pressure, temperature, and fluid injection. Studying the changes in porosity under these dynamic factors can help improve the efficiency and safety of resource extraction [60]. Especially the influence of nanoscale porosity on fluid permeability and rock mechanical properties has become an important research direction. By utilizing advanced technologies such as molecular dynamics simulations, researchers can delve into the interactions between fluids and pore walls, revealing the mechanisms of fluid flow in nanopores. This is of great significance for the development of unconventional oil and gas resources, such as shale gas and tight oil exploration [61].

Future research will focus more on the impact of environmental factors on rock porosity, particularly temperature, pressure, groundwater chemical composition, and the influence of climate change on pore structure. Climate change may indirectly lead to changes in porosity by affecting processes such as groundwater flow and fluid injection. At the same time, research on rock porosity will increasingly emphasize interdisciplinary integration, and collaborative efforts in fields such as geology, physics, chemistry, and computer science will promote more systematic and comprehensive research. By combining geostatistics, machine learning, and numerical simulation methods, researchers can explore the formation mechanism, evolution laws, and impact on underground fluid behavior of pores from multiple dimensions. Another important direction of porosity research is to achieve sustainable development of resource utilization and environmental protection. By studying the changes in porosity during processes such as carbon dioxide sequestration and underground energy storage, we can better predict and understand the potential impact of these activities on the underground environment, thereby improving the safety of storage processes, reducing environmental risks, and ensuring the effective utilization of underground resources.

5. Conclusions

The study of rock pore structure has undergone significant evolution, transitioning from early qualitative descriptions to contemporary high-precision quantitative analysis. Despite notable advancements in research techniques and methods, several challenges remain, such as enhancing research accuracy and expanding the scope of applications. This article conducts a statistical analysis of 4807 studies on rock pore structure from the WOS core database, aiming to provide theoretical support for related research and practical applications by investigating advancements in this field. Currently, research on rock pore structure exhibits the following characteristics:

Over the past 16 years, the number of published articles on rock pore structure has significantly increased, with research entering a period of rapid growth since 2018. A comprehensive global cooperation system has been established, with Chinese researchers playing a prominent role, contributing to 66.45% of the total global publications. China has strong cooperative relationships with the United States and the United Kingdom, while the United States also collaborates extensively with the United Kingdom and Germany. Key journals in this field include the Journal of Petroleum Science and Engineering, Marine and Petroleum Geology, and Energy Fuels.

In terms of core literature, three papers were published before 2010, six between 2010 and 2014, and one in the past decade. Eight of these papers focused on the characterization of rock pore structure and gas adsorption, while two utilized scanning electron microscopy and low-field NMR to study coal rock physical properties.

The study of rock pore structure has established a theoretical framework and extended into various research directions and knowledge fields. Current hotspots include the development and prediction of rock pore structure models, permeability models, porosity–temperature relationships, the influence of rock mineral composition on pore structure, and the enhancement of rock mechanical properties through pore structure improvements.

Research on rock pore structure is crucial for fields such as oil and gas exploration, groundwater storage, and geological disaster prevention. Emerging research frontiers include molecular simulation, gas adsorption, and pore structure characteristics. Most scholars currently focus on the relationship between single rock pore structures and fluid flow. With the development of deep underground resources, the coexistence of complex pore systems and multiple fluids is becoming increasingly common. Future research should consider thermodynamic, dynamic, and other factors, exploring the flow, adsorption, and diffusion mechanisms of multiphase fluids in complex pore systems to better guide underground resource development and geological hazard prediction.