Search Results (86)

To clarify the oil–gas multiphase flow behavior of natural gas/CO₂ composite flooding in the dual-medium system of the BZ26-6 fractured reservoir, systematic oil–gas relative permeability experiments were conducted under reservoir temperature and pressure conditions. Using the steady-state method, the effects of core type, gas composition, and reservoir pressure on relative permeability behavior were investigated. The results show that the relative permeability curves are characterized by relatively high oil-phase permeability and low gas-phase permeability. Increasing the CO₂ fraction generally enhances oil mobilization and displacement efficiency, whereas the two-phase co-flow zone may reach an optimum at an intermediate CO₂ fraction, depending on the core structure. Specifically, with increasing CO₂ fraction, displacement efficiency increased from 37.05% to 43.70% in fractured metamorphic cores and from 60.74% to 64.63% in fractured carbonate cores. In contrast, decreasing reservoir pressure may induce stress-sensitive fracture compression, narrow the co-flow zone, and reduce flow capacity. Oil–gas two-phase flow behavior is strongly controlled by reservoir structure, with fractured carbonate cores exhibiting higher displacement efficiency and a wider co-flow region than fractured metamorphic cores. Within the scope of this study, a CO₂ fraction of 40% appears to be a comparatively favorable composite-gas composition when both displacement performance and gas-source economics are considered. Full article

The Niger Delta region of Nigeria experiences multiple environmental stresses due to intensive oil exploration and pervasive gas flaring, both of which contribute to local and regional climate changes, extreme weather events, and excessive and erratic rainfall. Consequently, flooding remains a recurrent natural disaster, disproportionately impacting the low-lying states of Delta, Bayelsa, and Rivers. This study employs remotely sensed geospatial data and a GIS-based weighted overlay analysis to delineate flood-prone areas on a regional scale in the central Niger Delta states. Flood susceptibility was determined through a weighted overlay of digital elevation model (DEM), slope, proximity to streams, rainfall, and LULC data, among others. Weights of criteria were derived through an analytical hierarchy process (AHP) with a very good consistency ratio of 2.5%. Land use and land cover (LULC) and rainfall data were further analyzed to detect trends of changes between 2012 and 2022. The results show that relatively 77% of the study region is prone to flooding. Areas prone to very high flooding are about 16%, high is 29%, moderate is 32%, while low and very low flood-prone areas cover 18% and 5% of the study region, respectively. There is also a notable increase in average annual rainfall and land cover changes. Average rainfall increased by 58.1% between 2012 and 2017, and by 11.5% between 2017 and 2022. Land cover change analysis further indicates that approximately 1.3% of the study area was converted predominantly to flooded zones and water bodies from 2017 to 2022. The results of this study could be useful for urban regional planning, flood mitigation, and resettlement policies aimed at reducing flood vulnerability and enhancing resilience in the central Niger Delta, as well as other places where similar challenges exist. Full article

Wetland system design, management and modelling to support ecosystem services during climate change have been evaluated in this structured and critical review. The focus was on non-tidal and agriculture-linked wetlands in oceanic, temperate and boreal regions. After applying 54 search terms using Google Scholar, 229 references have been cited. The review indicates that local wetland improvements rarely have a measurable impact on the overall watershed. Water can be retained mostly successfully in the landscape for relatively low- and medium-level rainfall. For large and less frequent floods, the concept of Retaining Water in the Landscape rarely applies. The success of compensation schemes for European and United States American farmers to control flood retention depends on financial status, farm size, age and the contract term duration. Ecosystem disservices such as greenhouse gas and nutrient release from ditches should be counteracted by rewetting. Combined water level and nutrient management supports carbon sequestration and protects watercourses from eutrophication. Restored wetlands usually reduce diffuse pollution and enhance biodiversity. The conservation of existing natural wetlands compared to restoring former wetlands is normally more effective regarding carbon storage. The value of sustainably managed wetlands is up to 50 times higher than the mean wetland restoration costs. Full article

Natural gas reservoirs characterized by high heterogeneity and containing bottom-bound water often face the problem of water intrusion, making it difficult to recover the recoverable gas. This paper addresses the issue of enhanced gas recovery in water-flooded reservoirs and, through high-temperature, high-pressure long-core displacement experiments, investigates the displacement effects of different reservoir properties and injection media (dry gas, N₂, CO₂) under simulated water-flooding conditions. The experiment utilized two sets of sandstone cores—one with moderate permeability (304.8 mD) and one with high permeability (1004.6 mD). Three cores from each set were spliced together to form a 0.9 m long core, simulating the gas injection and displacement process following water infiltration. The results indicate that while water intrusion occurs more rapidly in high-permeability reservoirs, gas injection yields better recovery results than in medium-permeability reservoirs. Among the three injection media, dry gas demonstrated the best displacement efficiency, followed by N₂, with CO₂ performing the worst. CO₂ tends to react with highly mineralized formation water under high-temperature and high-pressure conditions, forming precipitates and causing energy to be absorbed by the water, which reduces displacement efficiency. It is recommended that dry gas injection be used for enhanced recovery in the moderate-permeability reservoirs of the Y gas field, while N₂ injection may be considered for the high-permeability reservoirs to balance effectiveness and cost. The research results provide experimental support for subsequent gas injection to enhance gas recovery in this gas field. Full article

CO₂-enhanced gas recovery (CO₂-EGR) is a crucial technology for achieving both natural gas production increase and CO₂ geological storage. While pure CO₂ flooding demonstrates favorable recovery performance, the technical challenges and high costs associated with purifying CO₂ remain significant. CO₂ purification from exhaust gas incurs prohibitive costs, while direct injection of an unpurified CO₂–N₂ mixture can greatly cut engineering expenditure. Nitrogen also provides synergistic pressure support, working with CO₂ to drive natural gas displacement. Therefore, from an economic and practical standpoint, employing impure CO₂ mixtures (e.g., CO₂–N₂) for flooding presents a more advantageous approach. To clarify the factors influencing the recovery enhancement in tight sandstone gas reservoirs using CO₂–N₂ mixtures, long-core flooding experiments were conducted at 100 °C. This study systematically investigates the impact patterns of three key factors—injection timing, injection rate, and injection gas composition—on the enhanced recovery of tight sandstone gas reservoirs. The experimental results indicate that: (1) Advancing the injection timing significantly improves the recovery performance for both CO₂ and N₂ flooding. However, the cumulative recovery factor (sum of the depletion recovery and the incremental recovery from gas injection) shows a declining trend. (2) The enhanced recovery effect exhibits a trend of first increasing and then decreasing with the increase in injection rate. When the injection rate exceeds 0.05 mL/min, it tends to cause premature breakthrough of the injected gas, thereby reducing the displacement efficiency. (3) As the proportion of CO₂ in the injected gas increases, the enhanced recovery effect shows a nonlinear rise. The highest incremental recovery (17.02%) was achieved with pure CO₂ flooding, while pure N₂ flooding yielded the lowest result (14.64%). The research findings, from a macroscopic perspective, elucidate the influence patterns of three distinct factors on enhancing gas recovery in tight sandstone reservoirs, thereby providing theoretical foundation and scientific guidance for the development of such reservoirs. In summary, the injection timing, injection rate and CO₂ proportion in injected gas are the key controlling factors for gas flooding enhanced recovery in tight sandstone reservoirs. This study clarifies the macroscopic influence law of each factor, and the optimized development parameters proposed can provide direct theoretical support and technical guidance for the on-site application of gas flooding in tight sandstone reservoirs. Full article

The tight gas reservoirs developed in the central Shenfu block are characterized by ultra-low porosity and permeability (typically < 10% porosity, <1 mD permeability), and high irreducible water saturation (40–60%). The frequent water blocking issue sharply reduces gas relative permeability during the production period, severely limiting well productivity. In this study, core flooding experiments using artificial cores were conducted to systematically evaluate the feasibility of CO₂ injection for enhanced gas recovery (EGR). The results show that the effectiveness of CO₂ EGR is sensitive to many factors, such as injection pressure, injection rate, total injection volume, and core permeability. The higher injection pressure and rate would improve the pressure gradient, CO₂ sweep efficiency, and EGR. An optimal total volume with the value (around 2.0 pore volumes, PV) was recommended as the amount of CO₂ injection are varied in the range of 0.5–2.5 PV. A higher permeable tight reservoir is prone to a higher nature gas recovery. The experimental findings, within the controlled conditions of this study, suggest that a flowback strategy of “slow startup and controlled depressurization” could be considered. Combining CO₂ injection with managed pressure drop of production and optimized fracturing process is proposed as a potential comprehensive strategy focused on “energy supplement, damage mitigation, and water control,” which may provide a useful reference for the efficient development of high-water-saturation tight gas reservoirs. Full article

The efficient extraction of natural gas from water-drive reservoirs is often hindered by premature water breakthrough and the consequent trapping of significant residual gas, which collectively result in suboptimal recovery and economic returns. Traditional production methods have proven inadequate in mitigating water influx and mobilizing this trapped gas, underscoring the need for advanced enhanced gas recovery (EGR) strategies. This research specifically examines the potential of nitrogen injection as a tertiary recovery technique in such reservoirs, with a focus on its mechanistic role and displacement efficiency. Utilizing high-pressure core flooding experiments and complementary numerical simulations, the process of nitrogen injection following water flooding was systematically investigated. Experimental findings at 30 MPa indicate that while water flooding left a substantial residual gas saturation of 28.1%, subsequent nitrogen injection reduced this to 20.8% at breakthrough and ultimately to 7.99%, achieving a final recovery of 88.9%. Simulation results further elucidate that in fractured systems, water preferentially channels through high-permeability fractures, while capillary imbibition leads to gas entrapment within the matrix. Nitrogen injection effectively targets and reduces this trapped gas saturation by 30–50%, demonstrating its efficacy as a viable EGR method. The study thus provides critical theoretical and practical insights for improving recovery in challenging water-drive gas reservoirs. Full article

The growing demand for natural gas and the corresponding expansion of pipeline networks have intensified the need for precise leak detection, particularly due to the increased vulnerability of infrastructure to natural disasters such as earthquakes, floods, torrential rains, and landslides. This research leverages deep learning to develop two hybrid architectures, the Transformer–LSTM Parallel Network (TLPN) and the Transformer–LSTM Cascaded Network (TLCN), which are rigorously benchmarked against Transformer and Long Short-Term Memory (LSTM) baselines. Performance evaluations demonstrate TLPN achieves exceptional metrics, including 91.10% accuracy, an 86.35% F₁ score, and a 95.20% AUC value. Similarly, TLCN delivers robust results, achieving 90.95% accuracy, an 85.76% F₁ score, and 93.90% of the Area Under the ROC Curve (AUC). These outcomes confirm the superiority of attention mechanisms and highlight the enhanced capability realized by integrating LSTM with Transformer for time-series classification. The findings of this research significantly enhance the safety, reliability, sustainability, and risk mitigation capabilities of buried infrastructure. By enabling rapid leak detection and response, as well as preventing resource waste, these deep learning-based models offer substantial potential for building more sustainable and reliable urban energy systems. Full article

The latest climate change predictions indicate that the sea level will accelerate in the coming decades as a direct consequence of global warming. This is expected to seriously threaten low-lying coastal areas worldwide, resulting in severe coastal flooding with significant socio-economic impacts, leading to the loss of coastal settlements, exploitable land, and natural ecosystems. The main objective of this study is to provide a first-order preliminary estimation of potential inundation extents along the northern coastline of the Amvrakikos Gulf, a deltaic complex formed by the Arachthos, Louros, and Vouvos rivers in Western Greece, resulting from long-term sea-level rise induced by climate change, using the integrated Bathtub and Hydraulic Connectivity (HC) inundation method. A 2 m resolution Digital Elevation Model (DEM) was used, along with local long-term sea-level projections, for the years 2050 and 2100. Additionally, subsidence rates due to the compaction of deltaic sediments were taken into account. To assess the area’s proneness to inundation caused or enhanced by sea-level rise, the extent of each land cover type, the Natura 2000 Network protected area, the settlements, the total length of the road network, and the cultural assets located within the inundation zones under each climate change scenario were considered. The analysis revealed that under the optimistic SSP1-1.9 scenario of the Intergovernmental Panel on Climate Change (IPCC), areas of 40.81 km² (min 20.34 km², max 63.55 km²) and 69.10 km² (min 41.75 km², max 88.02 km²) could potentially be inundated by 2050 and 2100, respectively. Under the pessimistic SSP5-8.5 scenario, the inundation zone expands to 42.56 km² (min 37.05 km², max 66.31 km²) by 2050 and 84.55 km² (min 67.54 km², max 116.86 km²) by 2100, affecting a significant portion of ecologically valuable wetlands and water bodies within the Natura 2000 protected area. Specifically, the inundated Natura 2000 area is projected to range from 37.77 km² (min 20.30 km², max 46.82 km²) by 2050 to 50.74 km² (min 38.71 km², max 62.84 km²) by 2100 under the SSP1-1.9 scenario, and from 39.34 km² (min 34.53 km², max 49.09 km²) by 2050 to 60.48 km² (min 49.73 km², max 82.5 km²) by 2100 under the SSP5-8.5 scenario. Four settlements with a total population of approximately 800 people, as well as 32 economic facilities most of which operate in the secondary and tertiary sectors and are small to medium-sized economic units, such as olive mills, farms, gas stations, spare parts stores, construction companies, and food service establishments, are expected to experience significant exposure to coastal flooding and operational disruptions in the near future due to sea-level rise. Full article

Coastal wetlands provide crucial ecosystem services, including habitats for wildlife, carbon storage, greenhouse gas emission reduction, storm surge and flood protection, water purification, recreation, and nature-based tourism. Their protection and restoration are therefore of growing importance to conservationists, scientists, local communities, and policymakers. This paper analyses the European Union’s (EU) policy framework, alongside international and regional agreements relevant to wetland conservation and restoration, focusing on coastal ecosystems. Drawing on policy content analysis, it assesses how 36 EU policies and multilateral agreements support or limit coastal wetland restoration and conservation efforts in Europe. The findings reveal two key gaps: first, an absence of a consistent definition of coastal wetlands within the EU policy framework; and second, the limited number of explicit policy references to these ecosystems. These shortcomings restrict opportunities for their effective inclusion in action plans and undermine coordinated conservation and restoration efforts. Most binding targets and objectives addressing coastal wetlands stem from EU policies and multilateral agreements on nature conservation, including regional sea conventions. This reliance risks overlooking opportunities within other policy sectors. While EU climate policies increasingly recognise the importance of wetland restoration, they often do so through non-binding provisions and voluntary action. To unlock the full potential of coastal wetlands for biodiversity and climate benefits, it is essential to embed coastal wetlands more explicitly within policy targets and to leverage emerging opportunities within the EU policy framework to further upscale coastal wetland restoration. Full article

Floods are among the most destructive natural hazards, with damages expected to intensify under climate change and socio-economic pressures. Effective reservoir operation remains a critical yet challenging strategy for mitigating downstream impacts, as operators must navigate nonlinear system dynamics, uncertain inflow forecasts, and trade-offs between competing objectives. This study proposes a novel end-to-end data-driven framework that integrates process-based hydraulic simulations, a Transformer-based surrogate model for flood damage prediction, and reinforcement learning (RL) for reservoir gate operation optimization. The framework is demonstrated using the Coralville Reservoir (Iowa, USA) and two major historical flood events (2008 and 2013). Hydraulic and impact simulations with HEC-RAS and HEC-FIA were used to generate training data, enabling the development of a Transformer model that accurately predicts time-varying flood damages. This surrogate is coupled with a Transformer-enhanced Deep Q-Network (DQN) to derive adaptive gate operation strategies. Results show that the RL-derived optimal policy reduces both peak and time-integrated damages compared to expert and zero-opening benchmarks, while maintaining smooth and feasible operations. Comparative analysis with a genetic algorithm (GA) highlights the robustness of the RL framework, particularly its ability to generalize across uncertain inflows and varying initial storage conditions. Importantly, the adaptive RL policy trained on perturbed synthetic inflows transferred effectively to the hydrologically distinct 2013 event, and fine-tuning achieved near-identical performance to the event-specific optimal policy. These findings highlight the capability of the proposed framework to provide adaptive, transferable, and computationally efficient tools for flood-resilient reservoir operation. Full article

This study investigates gas injection gravity miscible flooding to enhance oil recovery in fractured-vuggy volatile oil reservoirs of the Fuman area, Tarim Basin. The Fuman 210 reservoir, containing light oil with high maturity, large column heights, and strong fracture control, provides favorable conditions for gravity-driven flooding. Laboratory tests show that natural gas and CO₂ achieve miscibility, while N₂ reaches near-miscibility. Mixed gas injection, especially at a natural gas to nitrogen ratio of 1:4, effectively lowers minimum miscibility pressure and enhances displacement efficiency. Full-diameter core experiments confirm that miscibility improves oil washing and expands the sweep volume. Based on these results, a stepped three-dimensional well network was designed, integrating shallow injection with deep production. Optimal parameters were determined: injection rates of 50,000–100,000 m³/day per well and stage-specific injection–production ratios (1.2–1.5 early, 1.0–1.2 middle, 0.8–1.0 late). Field pilots validated the method, maintaining stable production for seven years and achieving a recovery factor of 30.03%. By contrast, conventional development relies on depletion and limited water flooding, and dry gas injection yields only 12.6%. Thus, the proposed approach improves recovery by 17.4 percentage points. The novelty of this work lies in establishing the feasibility of mixed nitrogen–natural gas miscible flooding for ultra-deep fault-controlled carbonate reservoirs and introducing an innovative stepped well network model. These findings provide new technical guidance for large-scale application in similar reservoirs. Full article

Tight gas reservoirs, as important unconventional natural gas resources, face low recovery rates due to low porosity, low permeability, and strong heterogeneity. CO₂ Storage with Enhanced Gas Recovery (CSEGR) technology combines CO₂ geological storage with natural gas development, providing both economic and environmental benefits. However, the main controlling factors and influence mechanisms remain unclear. This study utilized the PR-EOS to investigate CH₄, CO₂, and natural gas physical properties, established a numerical simulation model considering CO₂ dissolution and geochemical reactions, and explored the influence of injection scheme, injection rate, production rate, and shut-in condition on CO₂ enhanced recovery and storage effectiveness through orthogonal design. Results show that CO₂ exhibits significant differences in compressibility factor, density, and viscosity compared to natural gas, enabling piston-like displacement. Intermittent injection slightly outperforms continuous injection in recovery enhancement, while continuous injection provides greater CO₂ storage capacity. The ranking of the significance of different influencing factors for enhanced oil recovery is as follows: injection rate > production rate > injection scheme > shut-in condition. For the effect of geological storage of CO₂, it is as follows: injection rate > injection scheme > production rate > shut-in condition. During gas injection, supercritical, ionic, and dissolved CO₂ continuously increase while mineral CO₂ decreases, with storage mechanisms dominated by structural and residual trapping. The study provides scientific basis for optimizing CO₂ flooding strategies in tight gas reservoirs. Full article

This study investigated the essential oils (EOs) from leaf, bark, and fruit of Mespilodaphne cymbarum (Kunth) Trofimov (Lauraceae), focusing on their chemical composition and antimicrobial and antibiofilm activities. EOs were extracted from plants collected in the Amazon during dry and flood seasons and analyzed by gas chromatography–mass spectrometry. Although chemical differences were evident among plant organs and chemotypes, the influence of seasonality was not pronounced. Fruit EO was dominated by α- and β-santalene and limonene. Bark EO was rich in phenylpropanoids, including methyl eugenol, myristicin, and elemicin. Leaf EO showed the greatest metabolic diversity, with chemotype-specific variations. Leaf and bark EOs demonstrated superior antibacterial and antibiofilm activities compared to fruit EO, especially against Gram-positive bacteria such as Staphylococcus epidermidis, Staphylococcus aureus, and Micrococcus luteus. Chemotype-1 leaf and bark EOs inhibited S. epidermidis biofilm formation, while chemotype-2 reduced bacterial growth. The leaf EOs from both chemotypes reduced bacterial growth against S. aureus, and bark EO decreased biofilm formation. All leaf and bark EOs showed antibiofilm activity against M. luteus. These findings highlight the potential of M. cymbarum EOs as natural sources of bioactive compounds and emphasize the importance of chemotype and plant organ selection for optimized applications. Full article

The Valencia region exemplifies the intricate interplay of climate, urbanization, and human interventions in managing hydrological systems amidst increasing environmental challenges. This study explores the escalating risks posed by flood events, emphasizing how anthropogenic factors—such as urban expansion, sediment exploitation, and inadequate land use—amplify the vulnerabilities to extreme weather patterns driven by abnormal Greenhouse Gas (GHG) concentration. Nature-based solutions (NBS) like floodplain restoration and dam removal are analyzed for their benefits in enhancing ecosystem resilience and biodiversity but are critiqued for unintended consequences, including accelerated river flow and sedimentation issues. This study further examines the impacts of forest fires, exacerbated by land abandonment and insufficient management practices, on soil erosion and runoff. A critical evaluation of global policies like the Sustainable Development Goals (SDGs) reveals the tension between aspirational targets and practical, locally-driven implementations. By advocating historical insights, ecological restoration practices, and community engagement, the findings highlight the importance of adaptive strategies to harmonize global frameworks with local realities through modeling and scaling simulations, offering a replicable model for sustainable flood mitigation and resilience building in Mediterranean contexts and beyond. Full article