Potential Migration Pathways Research Articles

Machine learning-based analysis of heavy metal contamination in Chinese lake basin sediments: Assessing influencing factors and policy implications

Sediments are important heavy metal sinks in lakes, crucial for ensuring water environment safety. Existing studies mainly focused on well-studied lakes, leaving gaps in understanding pollution patterns in specific basins and influencing factors.We compiled comprehensive sediment contamination data from literature and public datasets, including hydro-geomorphological, climatic, soil, landscape, and anthropogenic factors. Using advanced machine learning, we analyzed typical pollution factors to infer potential sources and migration pathways of pollutants and predicted pollution levels in basins with limited data availability. Our analysis of pollutant distribution data revealed that Cd had the most extensive pollution range, with the most severe pollution occurring in the Huaihe and Yangtze River basins. Furthermore, we identified distinct groups of driving factors influencing various heavy metals. Cd, Cr, and Pb were primarily influenced by human activities, while Cu and Ni were affected by both anthropogenic and natural factors, and Zn tended more towards natural sources. Our predictions indicated that, in addition to the typical highly polluted areas, the potential risk of Cd, Cu and Ni is higher in Xinjiang, and in Tibet and Qinghai, the potential risk of Cd, Cr, Cu and Ni is higher. Pb and Zn presented lower risks, except in the Huaihe and Yangtze River Basins. Temperature, wind, precipitation, precipitation rate, and the cation exchange capacity of soil significantly impacted the predictions of heavy metal pollution in sediments, suggesting that particulate migration, rainfall runoff, and soil erosion are likely the main pathways for pollutant migration into sediments. Considering the migration, pathways, and sources of pollutants, we propose strategies such as low-impact development and promoting sustainable transportation to mitigate pollution. This study provides the latest insights into heavy metal pollution in Chinese lake sediments, offering references for policy-making and water resource management.

Potential migration pathways of broadleaved trees across the receding boreal biome under future climate change.

Climate change has triggered poleward expansions in the distributions of various taxonomic groups, including tree species. Given the ecological significance of trees as keystone species in forests and their socio-economic importance, projecting the potential future distributions of tree species is crucial for devising effective adaptation strategies for both biomass production and biodiversity conservation in future forest ecosystems. Here, we fitted physiographically informed habitat suitability models (HSMs) at 50-m resolution across Sweden (55-68° N) to estimate the potential northward expansion of seven broadleaved tree species within their leading-edge distributions in Europe under different future climate change scenarios and for different time periods. Overall, we observed that minimum temperature was the most crucial variable for comprehending the spatial distribution of broadleaved tree species at their cold limits. Our HSMs projected a complex range expansion pattern for 2100, with individualistic differences among species. However, a frequent and rather surprising pattern was a northward expansion along the east coast followed by narrow migration pathways along larger valleys towards edaphically suitable areas in the north-west, where most of the studied species were predicted to expand. The high-resolution maps generated in this study offer valuable insights for our understanding of range shift dynamics at the leading edge of southern tree species as they expand into the receding boreal biome. These maps suggest areas where broadleaved tree species could already be translocated to anticipate forest and biodiversity conservation adaptation efforts in the face of future climate change.

Reservoir evaluation of dolomitized Devonian strata in the Western Canada Sedimentary Basin: implications for carbon capture, utilization, and storage

Abstract Differentially dolomitized carbonate strata in the Western Canada Sedimentary Basin (WCSB) are increasingly targeted for carbon capture, utilization, and storage (CCUS), yet few studies have evaluated the petrophysical characteristics of these conventional hydrocarbon reservoirs for this purpose. To address this, this study uses drill-core analysis (sedimentology, diagenesis, pore morphology, and distribution), together with core-plug and production data, to evaluate the properties of five depleted oil and gas fields in the Middle to Upper Devonian Swan Hills Formation, Leduc Formation and Wabamun Group. The Swan Hills and Leduc formations are composed of reef, shoal, and lagoon deposits that are predominantly fossil-rich (e.g., stromatoporoid-dominated rudstones and boundstones). In contrast, the carbonate-ramp deposits of the Wabamun Group are fossil-poor, consisting instead of variably bioturbated carbonate mudstones, wackestones, and packstones. Replacement dolomitization is variable throughout each stratigraphic unit, but generally occurs within fossil-rich and/or heavily bioturbated intervals. Fracture densities are broadly comparable in limestone and dolostone. Porosity in the Swan Hills and Leduc formations is predominantly moldic and vuggy, occurring where fossils (e.g., stromatoporoids) are partially or fully dissolved. Pore space in the Wabamun Group is mostly restricted to intercrystalline porosity in burrows. In general, burial cements (e.g., calcite and dolomite) are volumetrically insignificant and only partially fill pores. Exceptions to this include porosity-occluding cements associated with fractures and breccias in the vicinity of faults. Dolomitization and depositional facies are found to exert a strong control on pore morphology, distribution, and interconnectivity. Porosity is principally controlled by the relative abundance of skeletal grains and by the presence of burrows. These highly porous facies acted as fluid pathways during burial diagenesis, resulting in their preferential dolomitization, solution enhancement of pre-existing pores, and creation of volume reduction-related porosity. The high CO2 storage capacity and low unplanned plume migration risk (due to depositional and/or diagenetic baffles) of dolomitized reefal reservoirs (e.g., Swan Hills and Leduc formations) make them more attractive targets for CCUS than those with limited capacity and/or potential migration pathways (e.g., fault-related fractures and breccias in the Wabamun Group). These results demonstrate that drill-core analysis, in combination with legacy data, can provide valuable insights into the factors that control reservoir CO2 injectivity, plume migration, and storage capacity.

Ancient genomes revealed the complex human interactions of the ancient western Tibetans

The western Tibetan Plateau is the crossroad between the Tibetan Plateau, Central Asia, and South Asia, and it is a potential human migration pathway connecting these regions. However, the population history of the western Tibetan Plateau remains largely unexplored due to the lack of ancient genomes covering a long-time interval from this area. Here, we reported genome-wide data of 65 individuals dated to 3,500-300 years before present (BP) in the Ngari prefecture. The ancient western Tibetan Plateau populations share the majority of their genetic components with the southern Tibetan Plateau populations and have maintained genetic continuity since 3,500 BP while maintaining interactions with populations within and outside the Tibetan Plateau. Within the Tibetan Plateau, the ancient western Tibetan Plateau populations were influenced by the additional expansion from the south to the southwest plateau before 1,800 BP. Outside the Tibetan Plateau, the western Tibetan Plateau populations interacted with both South and Central Asian populations at least 2,000 years ago, and the South Asian-related genetic influence, despite being very limited, was from the Indus Valley Civilization (IVC) migrants in Central Asia instead of the IVC populations from the Indus Valley. In light of the new genetic data, our study revealed the complex population interconnections across and within the Tibetan Plateau.

Active gas seepage in western Spitsbergen fjords, Svalbard archipelago: spatial extent and geological controls

This study presents the first systematic observations of active gas seepage from the seafloor in the main fjords of western Spitsbergen in the Svalbard archipelago. High-resolution acoustic water column data were acquired throughout two research cruises in August 2015 and June 2021. 883 gas flares have been identified and characterized in Isfjorden, and 115 gas flares in Van Mijenfjorden. The hydroacoustic data indicate active fluid migration into the water column. Interpretation of 1943 km of regional offshore 2D seismic profiles supplemented the water column and existing gas geochemical data by providing geological control on the distribution of source rocks and potential migration pathways for fluids. In the study area, bedrock architecture controls the fluid migration from deep source rocks. Faults, high permeability layers, heavily fractured units and igneous intrusions channel the gas seepage into the water column. The observations of gas seepage presented in this study are an important step towards the assessment of how near-shore seepage impacts upon the carbon budget of Svalbard fjords, which constitute a globally recognized early climate change warning system for the High Arctic.

Using SWMM for emergency response planning: A case study evaluating biological agent transport under various rainfall scenarios and urban surfaces

To assist in emergency preparedness for a biological agent terrorist attack or accidental pathogen release, potential contaminant levels and migration pathways of spores spread by urban stormwater were evaluated using a Storm Water Management Model (SWMM) of U.S. Coast Guard Base Elizabeth City, North Carolina. The high temporal-spatial resolution SWMM model was built using spore concentrations in stormwater runoff from asphalt, grass, and concrete collected from a point-scale field study. The subsequent modeled contamination scenarios included a notional plume release and point releases mimicking the field study under three rainfall conditions. The rainfall scenarios included a 6-hour natural rainfall event on Dec. 8, 2021 and two design storms (2-year and 100-year events). The observed spore concentrations from asphalt and concrete from the actual field experiment were applied to calibrate the washoff parameters in the SWMM model, using an exponential washoff function. The calibrated washoff coefficient (c1) and exponent (c2) were 0.01 and 1.00 for asphalt, 0.05 and 1.45 for grass, and 2.45 and 1.00 for concrete, respectively. The calibrated SWMM model simulated spore concentrations in runoff at times and magnitudes similar to the field study data. In the point release modeled scenario, the concrete surface generated 55.6% higher average spore concentrations than asphalt. Similarly, in the field experiment, a 175% (p < 0.05) higher average spore concentration in surface runoff was observed from concrete than from asphalt. This study demonstrates how SWMM may be used to evaluate spore washoff from urban surfaces under different precipitation amounts, intensities, and durations, and how visualized spatial migration pathways in stormwater runoff may be used for emergency planning and remediation.

Past climates and plant migration – the significance of the fossil record

This article is a Commentary on Denk et al. (2023), 238: 2668–2684.

Evaluating propensity for fugitive gas migration from integrity compromised oil and gas wells in the Peace Region, British Columbia, Canada, with a petrophysical approach

Oil and gas wells can suffer integrity failure resulting in the release of fugitive gas, formed primarily of methane, into the subsurface and atmosphere. Factors affecting fugitive gas migration in the subsurface, and in particular within and between shallower units intersected by energy wells (i.e. <100 m depth), are usually poorly considered with little focus on specific lithological characteristics that control gas movement, determine environmental impacts and influence how best to detect, monitor and quantify fugitive gases. To better understand and identify properties that can control fugitive gas migration in shallow sedimentary rocks that form the Peace Region of British Columbia, Canada, we developed a workflow by which a series of rock cores from units present in the area were obtained and their flow properties characterised. Insights on propensity for fugitive gas migration within and between these rocks were achieved through laboratory techniques and analytical calculations that are usually applied to the study of deeper hydrocarbon migration and seal integrity. These included Mercury Intrusion Porosimetry, petrographic analysis, X-ray computed tomography, as well as estimations of threshold capillary pressure, gas-column heights, hydrostatic pore pressure and total displacement pressure. Results show a congruent correlation between the examined petrophysical rock characteristics and flow propensity. We find that high capillary pressure will act as an effective mechanism for limiting vertical gas migration in the region, even when potential barrier facies have porosities of more than 10% and permeability of 0.26 mD. Additionally, results suggest that the propensity of studied shallow sediments to transmit fugitive gases will be controlled by heterogeneity, permeability anisotropy and the presence of secondary structural features, such as microfractures. Our approach for evaluating the propensity of fugitive gas migration could be applied elsewhere to enhance understanding of potential migration pathways and aid in development of effective monitoring and detection strategies that can better anticipate gas behaviour in the subsurface and prognosticate reactive transport, impacts and fate.

Localization of potential migration pathways inside a fractured metamorphic hydrocarbon reservoir using well log evaluation (Mezősas field, Pannonian Basin)

The basement of the Pannonian Basin is composed of metamorphic rock complexes that serve as either a pathway for fluid migration or hydrocarbon storage in the fractured rock body. Mezősas field is located in the northern part of the Békés Basin, the deepest sub-basin of the Pannonian Basin. There are three major rock units that exist in the area. An orthogneiss-dominated realm occurs at the lowermost part of the basement, sillimanite biotite gneiss in the middle part, and amphibolite gneiss at the top of the basement. Lithology identification and interpretation of metamorphic rocks from well logs are difficult especially when it involves the basement formation. In addition, core samples from the basement are limited since the process to retrieve the cores is rather difficult and costly. Hence, the aim of this study was to distinguish different metamorphic rock types using well logs and statistical methods using the available data, various cross plots, and a multivariate statistical analysis, namely, discriminant function analysis. The results from this approach showed that the different metamorphic rocks could be grouped statistically, and the boundary of each realm could be determined in each studied well. Thus, one-dimensional lithology columns could be developed, and the spatial arrangement of the lithologies could be defined. From the cross section and the newly developed geological map that integrates all the results revealed the existence of low-angle thrust faults and normal faults inside the metamorphic basement of the study area. From the results too, it was proven statistically that in this Mezősas field, there exists four different lithologies instead of three. Amphibolite and amphibolite gneiss characteristics could be differentiated statistically and using cross plots. In conclusion, the discriminant function analysis is a suitable tool to evaluate complex well logs information and the internal structure of the Mezősas area could be reconstructed.

Random Forest Classification Method for Predicting Intertidal Wetland Migration Under Sea Level Rise

Intertidal wetlands such as mangrove and saltmarsh are increasingly susceptible to areal losses related to sea level rise. This exposure is potentially offset by processes that might enable wetlands to accrete in situ or migrate landward under sea level rise, and planning policies that might open new opportunities for migration. We present and demonstrate a method to predict intertidal wetland distribution in the present-day landscape using random forest classification models, and use these models to predict the intertidal wetland distribution in future landscapes under specified sea level scenarios. The method is demonstrably robust in predicting present-day intertidal wetland distribution, with moderate correlation or better between predicted and mapped wetland distributions occurring in nearly all estuaries and strong correlation or better occurring in more than half of the estuaries. Given the accuracy in predicting present-day wetland distribution the method is assumed to be informative in predicting potential future wetland distribution when combined with best available models of future sea level. The classification method uses a variety of hydro-geomorphological surrogates that are derived from digital elevation models, Quaternary geology or soils mapping and land use mapping, which is then constrained by a representation of the future sea level inside estuaries. It is anticipated that the outputs from applying the method would inform assessments of intertidal wetland vulnerability to sea level rise and guide planning for potential wetland migration pathways.

A review of sources, status, and risks of microplastics in the largest semi-enclosed sea of China, the Bohai Sea

The largest semi-enclosed sea of China, the Bohai Sea, serves as an important sink of microplastics (MPs) originated from terrestrial and marine sources. This study summarized potential sources and migration pathways of MPs in the Bohai Sea and reviewed the abundance and characteristics of MPs in water, sediments, and organisms. Coastal anthropogenic activities (i.e., plastic production, agricultural activities, and industrial and domestic sewage discharge) and marine origins (i.e., aquaculture, marine litters, and transportation) might accelerate the MPs enrichment in the Bohai Sea. The abundance of MPs ranged from 0.07 to 5200 items/m3 in the seawater, mainly influenced by the application of different trawl nets/sieves with different sizes (0.005–0.33 mm). Sediments of coastal rivers contained the MPs ranging from 56.7 to 1795 items/kg, significantly higher than that of the Bohai Sea (6.24–461.6 items/kg). Among organisms, the average abundance of MPs was the lowest in zooplanktons (0.03 items/animal), significantly lower than that in invertebrates (1.39 items/animal) and fish (2.12 items/animal), but no biomagnification of MPs was observed. The preliminary risk assessment indicated that seawater in the Liaodong Bay had medium ecological risk of MPs while other bays of the Bohai Sea had minor risks. To make the ecological risk of MPs quantifiable and comparable, future research priorities are recommended to focus on more frequent field surveys, standardization of sampling methods, and establishment of toxicity database of common polymer types of MPs in the Bohai Sea.

Performance of colloidal silica grout at elevated temperatures and pressures for cement fracture sealing at depth

Hydrocarbon well decommissioning requires the long-term sealing of abandoned wells. Current plug and abandonment (P&A) operations are not always able to address all potential fluid migration pathways, resulting in the possible upwards migration of hydrocarbons from formations penetrated by the wellbore. The development of innovative materials to improve well sealing remains a major challenge. This paper presents a proof of concept for the use of colloidal silica (CS)-based grout to improve the sealing performance of P&A operations. CS is a non-toxic suspension of silica nanoparticles (<100 nm) undergoing gelation upon destabilisation. Due to its excellent penetrability and controllable gel time, CS has the potential for repairing fine-aperture cracks within the cement sheath, at the cement/casing interface, or within a cement plug, where the penetration of cementitious grouts is restricted due to their relatively large particle size. In this study, the suitability of CS grout for deployment up to 1500 m depth was successfully demonstrated. Firstly, a range of CS grout mixes were investigated to test the feasibility of grout emplacement considering a timescale of 2 h for pumping operations from the surface to depth. Secondly, to investigate the sealing performance, the CS grout was injected into fractured cement cores (0.2 and 0.5 mm fracture aperture) and exposed to pressure and temperature conditions simulating downhole scenarios up to 1500 m depth (based on gradients for North Sea, UK). Fracture permeability upon water injection was assessed pre- and post-treatment. This work found that permeability values after treatment were reduced by three orders of magnitude, thus confirming the potential of CS grout for repairing fine-aperture cracks.

Not a bathtub: A consideration of sea-level physics for archaeological models of human migration

Accurately reconstructing past sea level is key to simulating potential migration pathways of ancient hominins, including early Homo sapiens. Models of ancient human migration events commonly construct estimates of paleoenvironments using the “bathtub” model, in which sea level is assumed to rise and fall according to a “eustatic” (global average) value over time. However, large uncertainties exist on past ice sheet sizes and shapes, particularly prior to the Last Glacial Maximum (LGM), ∼26,000 years ago. Moreover, regional sea level varies significantly due to the effects of glacial isostatic adjustment (GIA). That process includes Earth's gravitational, deformational, and rotational response to changing surface (ice plus ocean) loads across the ice age. Here, we offer an updated account of the physics of GIA-induced sea-level change and consider the impacts of these effects, together with a newly published ice sheet history, on sea-level changes across the last glacial cycle. As illustrations, we highlight the significance of these issues for studies of ancient human migration from Sunda to Sahul and for the timing of the final, post-LGM flooding of the Strait of Dover. These examples demonstrate the importance of incorporating updated ice sheet histories and accurate sea-level physics into archaeological research.

Groundwater contamination risk assessment based on advection-dispersion equation

The consequences of contaminated groundwater can seriously affect sustainable development; present and future generations being seriously affected by inadequate drinking water quality, loss of water supply, degraded surface water systems, high remediation costs, more expenses for other water supplies, and likely health issues. Therefore, an effective way to protect groundwater resources is by assessing the risk of groundwater contamination. An assessment of groundwater pollution should be performed to determine the level of risk posed by soil and groundwater contamination and establish if remediation strategies are required to protect controlled waters from site-derived contamination. Furthermore, if remediation is deemed necessary, site-specific remedial targets should be derived. A case study is presented, where a Conceptual Site Model was derived based on a “Source-Pathway-Receptor” exposure mechanism using historical information. Primary sources of contamination at the site are residual contamination within the soil and groundwater, and samples were collected from the site and tested in the laboratory; the concentration of water samples was compared to Romanian Drinking Water Standards. The following potential migration pathways have been identified: Leaching from soil and Migration of contaminated groundwater. The Detailed Quantitative Risk Assessment (DQRA) has modelled the leaching of contaminants from the site via infiltration and vertical migration to the groundwater and subsequent lateral groundwater migration, with dilution and attenuation process active, to the compliance point, using Ogata-Banks equation. The results of this assessment indicate that the concentration of contaminants does not represent a significant risk to controlled waters.

Natal origin and migration pathways of Mekong catfish (Pangasius krempfi) using strontium isotopes and trace element concentrations in environmental water and otoliths.

To improve our knowledge of the migration pathway of a highly threatened fish species along the Mekong River, strontium isotope ratios (87Sr/86Sr) and 18 trace element concentrations were measured in the water and in the otoliths of an anadromous catfish, Pangasius krempfi, to infer its natal origin and potential migration pathways. Water was sampled at 18 locations along the mainstream, tributaries and distributaries of the Mekong River. To check for accuracy and precision, measurements of the 87Sr/86Sr ratios and trace element concentrations were then compared in two laboratories that use different analytical methods. Differences in trace element concentrations between locations were not significant and could not, therefore, be used to discriminate between migration pathways. However, the Mekong mainstream, tributaries and distributaries could all be discriminated using Sr isotopes. The 87Sr/86Sr profiles recorded in P. krempfi otoliths showed that there were three contingents with obligate freshwater hatching and variable spawning sites along the Mekong mainstream, from Phnom Penh (Cambodia) to Nong Khai (Thailand) or further. After hatching, the fish migrated more or less rapidly to the Mekong Delta and then settled for most of their lifetime in brackish water. Spawning habitats and migration routes may be threatened by habitat shifts and the increasing number of hydropower dams along the river, especially the contingents born above Khone Falls (Laos). The conservation of P. krempfi, as well as other migratory fish in the Mekong River, requires agreements, common actions and management by all countries along the Mekong River. This study highlighted the importance of using both Sr/Ca and 87Sr/86Sr ratios to understand life history of anadromous fishes as the 87Sr/86Sr ratio in the water was shown to be less effective than the Sr/Ca ratio in identifying movements between different saline areas.

Field evaluation of 1.75 groundwater profiler and field screening device for on-site contamination profiling of chromium(VI) in groundwater

Groundwater contamination by toxic heavy metals pose serious health hazards to humans and the environment. The remediation of contaminated groundwater requires effective characterization of the concentrations and spatial distribution of heavy metals. Groundwater samples from long screening monitoring wells do not provide an accurate representation of the distribution of heavy metals with depth, as the data obtained from the well are an average along the screen length. This study reports the development and application of two new technologies, a direct push 1.75 groundwater profiler (GWP) that obtains groundwater samples from multiple depths in a single push, and a portable field screening device that uses novel disposable sensors to facilitate rapid, cost-effective, on-site detection of heavy metals in groundwater, surface water, and sediment pore water. Extensive fieldwork was performed at a chromium(VI)-contaminated site to evaluate and validate these two technologies for on-site contamination profiling of Cr(VI) in groundwater. A preliminary investigation was performed with an OIHPT logging tool to determine formation lithology and relative permeability for identifying potential groundwater sampling intervals and contaminant migration pathways in the subsurface. Groundwater samples from selected depth intervals were collected and analyzed by an outside laboratory analysis for total chromium and hexavalent chromium as per EPA standards 6020 (SW) and 7196, respectively. The excellent comparison of the field results with the laboratory test results confirm the potential of these technologies in obtaining high resolution site characterization data to improve the management of heavy metal-contaminated hazardous sites.

Unravelling potential northward migration pathways for tree species under climate change

AbstractAimClimate‐induced range expansion ultimately implies recruitment at sites that were previously unoccupied by a species (i.e. colonization events). Using evidence on abiotic conditions and biotic interactions at these migration sites, we aimed to identify migration pathways from northern temperate to boreal forests for species showing northward range expansion.LocationQuebec, Canada.TaxonTrees of northern temperate/boreal forests.MethodsUsing past (1970–1977) and recently updated (2003–2015) forest inventories across 761,100 km2, we first quantified latitudinal shifts for saplings of eight tree species and investigated colonization events at migration sites. We used field evidence and a consensus modelling approach to determine environmental suitability and identify edaphic, climatic and disturbance conditions, as well as species co‐occurrence patterns, characterizing recent colonization events. The results were interpreted in relation to novel species associations facilitating species migration in unsuitable landscapes.ResultsAll species showed northward latitudinal shifts driven by increased recruitment and colonization northward. Colonization events occurred largely at historically unsuitable sites. Migration sites showed a shift towards humus types characteristic of the boreal forest and not typically found in the core range of most temperate species. Climatic conditions at migration sites were initially colder than at occupied sites, but warming suggests recent climatic suitability. A decrease in conifer basal area at migration sites following disturbances reduced priority effects that possibly constrained deciduous species establishment. Co‐occurrence patterns pointed to deciduous species tolerant of boreal edaphic conditions, leading the way for other temperate species.Main conclusionsTemperate tree species can recruit into sites typical of boreal forests, even under environmentally challenging conditions. Warming and disturbances open up the way for some novel species associations that in turn have the potential to facilitate the recruitment of temperate species into the boreal forest, revealing migration pathways.

Localisation of Ancient Migration Pathways inside a Fractured Metamorphic Hydrocarbon Reservoir in South-East Hungary

Numerous fractured hydrocarbon reservoirs exist in the metamorphic basement of the Pannonian Basin in Hungary. Many decades of experience in production have proven that these reservoirs are highly compartmentalised, resulting in a complex mosaic of permeable and impermeable domains situated next to each other. Consequently, in most fields, only a small amount of the total hydrocarbon reserve can be extracted. This paper aims to locate the potential migration pathways inside the most productive basement reservoir of the Pannonian Basin, using a multiscale approach. To achieve this, evaluation well-log data, DFN modelling and a composition analysis of fluid trapped in a vein-filling zeolite phase are combined. Data on a single well are presented as an example. The results of the three approaches indicate the presence of two highly fractured intervals separated by a barely fractured amphibolite. The two zones are probably part of the communicating fracture system inside the single metamorphic mass. The gas analysis further specifies the migrated fluids and indicates hydrocarbons of a composition similar to that of the recently produced oil. Consequently, we conclude that the two zones do not only form an ancient migration pathway but are also members of a more recent hydrocarbon system.

Carbon Dioxide Storage in Deltaic Saline Aquifers: Invasion Percolation and Compositional Simulation

Summary Storage of large amounts of carbon dioxide (CO2) within deep underground aquifers has great potential for long-term mitigation of climate change. The U.S. Gulf Coast is an attractive target for CO2 storage because of the favorable formation properties for injection and containment of CO2. Deltaic formations are one of the primary targeted depositional environments in the Gulf Coast. In this paper, we investigate CO2 storage in deltaic saline aquifers through a combination of geological modeling and flow simulation. The approach presented in this paper based on a combination of invasion percolation and compositional reservoir simulation focuses on buoyancy-dominant flow of CO2 in the long term and its pressure-driven flow in the short term. The results provide insights into how to screen and identify prospective locations for CO2 storage and determine the underlying geological features controlling CO2 migration for a basin-scale study. The geological model in our study is developed based on a laboratory-scale three-dimensional (3D) flume experiment replicating the formation of a delta structure and populated with geologic properties according to Miocene Gulf of Mexico natural analogues. We used invasion percolation simulations to understand the buoyancy-driven flow and the relationship between architecture, stratigraphy, and fluid migration pathways. The results were used to develop an upscaled model for compositional simulation with the key features of the original geological model and to determine injection schemes that maximize the injection capacity and minimize the amount of mobile CO2 in the formation. To achieve this, we used compositional reservoir simulations to study the pressure-driven flow and phase behavior. The results of invasion percolation simulations were used to identify the key stratigraphic units affecting CO2 migration. The realistic geometries and high resolution of the model facilitate the transfer of results from synthetic to subsurface data. The results allow for the analysis of deltaic depositional environments, important stratigraphic surfaces, and their impact on CO2 storage. The reservoir simulation model and phase behavior were validated against available field and laboratory data. The results of reservoir simulations were used to investigate the effects of main mechanisms, such as gas trapping and solubilization, on storage capacity. We compared our simulation results based on invasion percolation (buoyancy driven) and reservoir simulation (pressure driven). The comparison is helpful to understand the strengths and weaknesses of each approach and determine best practices to evaluate CO2 migration within similar formations. The unique and extremely well-characterized deltaic model allows for unprecedented representation of the depositional aquifer architecture. This research combines geologic modeling, flow simulation, and application for CO2 storage. The integrated conclusions will constrain predictions of actual subsurface flow performance and CO2 storage capacity in deltaic systems while identifying potential risks and primary stratigraphic migration pathways. This research provides insights on prediction of CO2 storage performance and characterization of prospective saline aquifers.

Reducing the risk of finding a working petroleum system using SAR imaging, sea surface slick sampling, and geophysical seafloor characterization: An example from the eastern Black Sea basin, offshore Georgia

As new plays emerge in deepwater settings, sea surface slicks are often overlooked as a source of geochemical information to help define potential petroleum systems. To demonstrate how sea surface hydrocarbon slicks can be used, a case study is presented from the eastern Black Sea in the Rioni Basin, offshore Republic of Georgia. There source rocks of Oligo-Miocene age (Maikop) are suspected of charging upper Miocene deepwater channel-levee sands in fold and thrust system traps. To reduce exploration risk, direct evidence of hydrocarbon generation and migration was sought using sea surface slicks observed there. To provide confirmation of charge, a collection of diverse data was used. First, synthetic aperture radar satellite images were utilized to verify the presence of large recurring sea surface slicks over prospective structures. These slicks were then sampled for later analysis during the acquisition of 3-D seismic data. To verify that the slicks were related to the subsurface expulsion, seafloor bathymetric and amplitude data were extracted from the 3-D seismic volume and used to identify potential seafloor features consistent with hydrocarbon seepage. Some of these seafloor features were found to be coincident with the apparent sea surface origins of the slicks. Seismic imaging was also used to demonstrate potential migration pathways which may link suspected deep subsurface traps and the seafloor. And finally, geochemical analysis showed that the compositional characteristics of the slicks’ hydrocarbons were similar to known Maikop sourced oils in the region. This combination of data provided a high level of confidence that the seismically imaged traps in offshore Republic of Georgia are charged, suggesting a working petroleum system was present. What it cannot tell us is how much petroleum may be in these structures. That question can only be answered by the drill bit.