Over the past decade, there have been remarkable advancements in scientific research and innovations within the oil and gas industry. These transformations have sparked global interest among researchers, particularly in unconventional oil reservoirs and applications of CO2. As we delve into the significant strides made in conventional and unconventional oil reservoir engineering, it is crucial to address the novel challenges and emerging techniques that accompany these developments.

The exploration and production of unconventional oil reservoirs present a set of unique difficulties and obstacles. One of the primary challenges is the complex nature of these reservoirs. Unlike conventional reservoirs, which are relatively easier to extract oil from, unconventional reservoirs require advanced techniques such as hydraulic fracturing or horizontal drilling. The optimization of these techniques and understanding the behavior of these reservoirs pose ongoing challenges for researchers and engineers. Furthermore, the environmental impact of extracting oil from unconventional reservoirs is a pressing concern. The use of hydraulic fracturing, for example, has raised questions about water contamination and induced seismicity. Researchers are actively seeking sustainable solutions to mitigate these risks and ensure responsible extraction practices. In addition to unconventional reservoirs, the application of CO2 in oil reservoirs has gained significant attention. Carbon capture, utilization, and storage (CCUS) technologies offer the potential to reduce greenhouse gas emissions while enhancing oil recovery. However, numerous technical and economic challenges need to be addressed to make these processes more feasible and cost-effective.

Overall, this Special Issue seeks original research and review articles to promote the advancement of oil and gas reservoir engineering by addressing the unique difficulties and emerging techniques associated with unconventional reservoirs and CO2 utilization and storage. It offers a platform for thought leaders in the field to share their findings and ideas, potentially shaping the future of petroleum reservoir engineering. By bringing together experts from various disciplines, we hope to foster an exchange of knowledge that will contribute to the sustainable development of the oil industry while minimizing environmental impacts.

Potential topics include but are not limited to the following:

• Multiphase Flow Mechanisms: A detailed examination of flow dynamics in both conventional and unconventional oil reservoirs, providing insights into the interactions between various phases
• Advanced Chemical Enhanced Oil Recovery (EOR) Methods: A discussion on the latest EOR techniques, their efficacy, and applicability in conventional and unconventional settings
• Reservoir stimulation methods: Mechanisms and field findings in reservoir stimulation techniques in unconventional reservoirs, including hydraulic fracturing, gas fracturing, etc.
• Carbon Capture, Utilization, and Storage (CCUS): An exploration into the practices and prospects of CO2 injection and storage, addressing environmental and operational concerns
• Pore-Scale Modeling: Research focusing on the micro-level modelling of pore structures and its implications for fluid flow and oil recovery
• Phase Behaviors: Investigations into the phase changes occurring in reservoirs and their impact on extraction processes
• Gas Storage: Examination of current techniques and future directions in gas storage within both conventional and unconventional oil reservoirs
• Machine Learning Applications: Articles addressing the incorporation of machine learning techniques in reservoir modelling and prediction
• Geomechanics: Studies on the influence of geological forces on reservoir behavior and the optimization of extraction processes
• Production Decline Analysis: Evaluations of the production lifecycle within oil reservoirs and strategies for managing decline