Exploration and Development of Unconventional Oil and Gas Resources: Latest Advances and Prospects

1. Introduction

As the global energy structure continues to evolve toward low-carbon, cleaner, and more diversified systems, unconventional oil and gas resources—such as shale oil and gas, tight gas, and coalbed methane—are playing an increasingly vital role in ensuring energy security and promoting economic development [1,2,3,4,5]. Compared with conventional oil and gas, these unconventional resources are more widely distributed and possess substantial reserves. However, their special seepage mechanisms and distinct development models pose considerable technical and economic challenges [6,7,8,9,10]. In this context, achieving the efficient, low-carbon, and intelligent exploration and development of unconventional oil and gas has become a key focus of current research.

The success of the shale revolution in the United States has provided valuable technical pathways for the global development of unconventional oil and gas resources [11,12,13]. Countries such as China and Canada have also made significant progress, demonstrating considerable resource potential [14,15,16,17]. However, due to the typical geological characteristics of unconventional reservoirs—such as low porosity, low permeability, and strong heterogeneity—their commercial development continues to face substantial challenges [18,19,20,21]. In particular, limited permeability and complex reservoir structures restrict the efficient migration and accumulation of oil and gas [22,23,24].

Therefore, technological innovation is urgently required to advance the development of unconventional oil and gas resources [25,26]. On the one hand, the development of high-resolution geophysical exploration techniques and microscopic pore structure characterization methods is essential for enhancing resource identification and reservoir evaluation [27,28,29,30]. On the other hand, fracturing and recovery technologies must be further optimized to enable low-energy, high-efficiency production [31,32,33]. Moreover, the integration of artificial intelligence into reservoir modeling is significantly enhancing the level of development processes [34,35,36,37].

2. Review of the Research Presented in This Special Issue

The papers featured in this Special Issue highlight recent advancements in the exploration and development of unconventional oil and gas resources. These innovations primarily focus on three key areas: reservoir characterization and evaluation technologies, the mechanisms of hydrocarbon enrichment and geological controls, development technologies, and enhanced recovery.

2.1. Advances in Reservoir Characterization and Evaluation Technology

In recent years, with the continuous advancement of unconventional oil and gas exploration and development, substantial progress has been achieved in reservoir characterization and evaluation technologies [38,39,40]. In practical exploration, core samples are often difficult to obtain, and only cuttings may be available, highlighting the need to improve alternative methods for reservoir characterization. Wang et al. [41] demonstrated the feasibility of using cuttings as substitutes for whole cores in carbonate rocks by employing low-field nuclear magnetic resonance techniques, and further investigated the relationship between sample sizes and key reservoir property parameters. The results indicate that cuttings larger than 1 mm can be effectively used for porosity determination, while cuttings smaller than 6.7 mm are unsuitable for analyzing pore size distribution and permeability.

On the other hand, fracture development characteristics are also a critical component of reservoir evaluation. Zhao et al. [42] established a system for identifying favorable fracture development zones in deep coals by integrating tectonic evolution analysis with mechanical simulations. Their study revealed the control mechanism of multi-phase tectonic stress on fracture formation and free gas accumulation, providing theoretical support for fracture prediction in unconventional reservoirs.

It is worth noting that traditional reservoir evaluation methods still face limitations in addressing the structural complexity of reservoirs. To address this problem, Liu et al. [43] proposed a hybrid intelligent model that integrates a convolutional neural network with a visual transformer to efficiently identify diagenetic facies in tight oil reservoirs. This approach significantly improves the accuracy and efficiency of identification based on logging image datasets and provides a novel methodology for diagenetic facies recognition in mature oilfields.

2.2. Advances in Hydrocarbon Enrichment and Geological Control Mechanisms

The study of hydrocarbon enrichment and its geological control mechanisms is essential for evaluating the exploration and development potential of unconventional oil and gas resources [44,45,46]. Zhao et al. [47] systematically analyzed the formation characteristics of the Shuguang reservoir using geochemical methods and identified the primary controlling factors influencing reservoir formation. The findings indicate that oil and gas can migrate efficiently along the faults and fractures, and that a high-quality source–reservoir–cap assemblage, coupled with the coordinated configuration of traps and fractures, provides favorable conditions for hydrocarbon accumulation. In addition, Chen et al. [48] investigated the high-rank coals of the Permian Longtan Formation in the Songzao Coalfield, southwestern China, and examined the impacts of the depositional environment, tectonic–thermal evolution, and regional geological structure on coalbed methane accumulation. The results highlight that favorable geological structures, such as closed folds, play a critical role in controlling CBM enrichment and preservation.

For the geological control of hydrocarbon enrichment, Zhang et al. [49] assessed the shale gas exploration potential of the Taiyuan and Shanxi Formations in the North China Basin through analyses of rock mineralogy, organic geochemistry, and elemental geochemistry. The results indicate that the Taiyuan Formation developed under warm, humid, strongly reducing, and highly water-restricted conditions, whereas the Shanxi Formation formed in a reducing to moderately–strongly closed environment under complex and variable climatic conditions. These palaeoenvironmental conditions were conducive to the enrichment and preservation of organic matter, promoting the development of organic-rich shales in the marine–continental transitional facies.

2.3. Advances in the Development of Technology and Enhanced Recovery

Due to the low porosity and low permeability characteristics of unconventional oil and gas reservoirs, improving recovery efficiency has become a critical factor for successful development [50,51,52]. Through experimental simulations and other technical approaches, researchers have investigated the mechanisms of multi-media driving and enhancing recovery in shale oil and tight oil reservoirs. Tao et al. [53] examined the sweep efficiency of surfactants, CH₄, and CO₂ in shale oil reservoirs. The results indicate that CO₂ maintains excellent oil displacement performance in micro- to nanopores across multiple rounds of displacement experiments, achieving a final recovery of 38.22%, which significantly outperforms surfactants (29.82%) and CH₄ (19.36%), and demonstrates superior repeatability. Regarding the seepage mechanisms in tight oil reservoirs, Li et al. [54] conducted pressure-driven displacement experiments using nuclear magnetic resonance technology and systematically analyzed the distribution and migration behavior of fluids in different pore sizes, providing both theoretical support and practical guidance for improving recovery efficiency in tight oil reservoirs.

3. Conclusions

In recent years, scholars from diverse disciplines—including geology, petroleum engineering, and artificial intelligence—have actively contributed to advancing the exploration and development of unconventional oil and gas resources. This Special Issue presents a collection of innovative research findings that integrate theoretical analysis with practical application, with a primary focus on reservoir characterization, hydrocarbon enrichment mechanisms, and enhanced recovery technologies. These studies offer valuable insights for addressing the key challenges associated with complex unconventional reservoirs. Overall, this Special Issue helps readers to deepen their understanding of the current research progress.