Earth-Science Reviews最新文献

The complicated flow behaviors of multiphase fluids in shale reservoirs are significantly influenced by fluid-fluid and fluid-rock interactions due to the non-negligible intermolecular forces at the nanoscale, which is crucial for the effective development and efficient extraction of shale oil. The complexity of multiphase fluid distribution and flow behaviors in shale reservoirs is further increased by low porosity, low permeability, poor connectivity, high inhomogeneity, and multi-component minerals, making the development process more challenging. Molecular dynamics simulation is widely to precisely capture the intermolecular forces and effectively explain the complex distribution and flow behaviors of these fluids under fluid-fluid and fluid-rock interaction forces. In this review, the characteristics of mineral composition, pore structure, porosity, permeability, and fluid types are first elaborated to illustrate the particularity of shale reservoirs and fluids compared to conventional scale reservoirs. The results show that shale minerals are composed of inorganic and organic matter with extremely low porosity and permeability, and nanoscale pore size, in which the complicated oil-water-CO₂ multiphase fluid types are caused by the primary underground water, fracturing water and injected CO₂. The research progress of molecular simulation on the fluid-fluid and fluid-rock interaction mechanisms and on multiphase shale fluids flow behaviors are then reviewed in detail. The strong intermolecular interaction forces can result in the different occurrence states of fluids, the fluid-fluid interfacial slip, the fluid-rock boundary slip and heterogeneous fluid viscosity/density, significantly exacerbating the complexity of fluids flow. Meanwhile, the injected CO₂ in the formation becomes a supercritical state with high diffusivity and strong solubility, and causes oil expansion, density and viscosity reduction, interfacial tension reduction, wettability alteration and molecular diffusion, which effectively replaces adsorbed hydrocarbon components by competitive adsorption behaviors, and promotes oil flow. The challenges and outlook of molecular simulation research and upscaling applications are finally discussed. This review aims to provide a microscopic understanding of the distribution characteristics and flow behaviors of multiphase shale fluids in nanoconfined space for both unconventional oil and gas researchers and industry professionals.

Palaeontological and zooarchaeological deposits have been recovered from underwater caves across the globe, but studies on site formation processes in these environments are scattered and have never been systematically examined. Flooded caves in the phreatic zone of karst systems include sinkholes and fensters (windows) that form a connection between the sub-aerial and sub-terranean landscapes, and conduits and chambers that establish underground networks of tunnels. Burial environments in these spaces are variable, and sedimentary, cave morphologic, and hydrologic variability within a single site can have profound impacts on taphonomic processes. The key determinant on long term preservation in these spaces is, however, the presence of water which dictates the nature of any habitation and by which species, and the process of decay. Water tables can fluctuate with long- and short-term sea level changes, with concomitant shifts in burial environments between flooded ‘wet’ or exposed ‘dry’ settings in near-shore cave systems. Distinguishing wet and dry burial conditions is necessary to reconstruct site formation processes in caves exhibiting evidence of changing or cyclical phreatic and vadose conditions. Signatures of aquatic deposition have been identified in underwater sites under marine, lacustrine and fluvial settings, but similar investigations are lacking for submerged cave landscapes. Water influences the decay process, alters bone surfaces, and modifies internal physical and chemical properties of bones. By exploring the environmental properties of flooded caves alongside known aquatic modifications, this review aims to build a framework for taphonomy of underwater cave palaeontological and archaeological sites. We detail biostratinomic and diagenesis processes that can be explored by actualistic, experimental, and observational studies. Future consideration could be given to the effects of human actions on the spatial distribution and modifications of bones in these spaces and the combined effects of environmental and anthropic agents.

Solute transport in partially-saturated porous media plays a key role in multiple applications across scales, from the migration of nutrients and contaminants in soils to geological energy storage and recovery. Our understanding of transport in unsaturated porous media remains limited compared to the well-studied saturated case. The focus of this review is the non-reactive transport driven by the displacement of immiscible fluids, where the fluid-fluid interface acts as a barrier that limits the solute to a single fluid phase. State-of-the-art pore-scale models are described, with a critical analysis of the gaps and challenges. A numerical example is provided to demonstrate the acute sensitivity of solute transport prediction to minute, inevitable uncertainties in the spatial distribution of the fluids' velocities and interface configuration associated with the multiphase flow modeling.

Groundwater dynamics in the coastal unconfined aquifer is one of the most important physical factors in the coastal zone since it greatly influences the nearshore hydrodynamics and beach morphodynamics, as well as interactions between oceanic and inland water systems. A solid understanding of the groundwater behavior in the coastal area is necessary for maintaining efficient coastal water management and supporting sustainable social-ecological development. Coastal unconfined aquifers are complicated while active systems in response to multiple oceanic forces such as tides and waves in various spatiotemporal scales, which have been evaluated and investigated over the last few decades. The present paper provides a comprehensive review of current understandings and advances in groundwater dynamics in coastal unconfined aquifers with respect to water table fluctuations and groundwater flow patterns, with a particular focus on wave-induced groundwater hydrodynamics. Existing analytical approaches for predicting the groundwater response to oceanic forces are summarized and evaluated to reveal their pros and cons. Although great advances have been achieved, some knowledge gaps still remain. While the influences of tide forces on coastal groundwater dynamics are generally well understood and tide-induced groundwater dynamics could be appropriately reproduced by various existing analytical or numerical models, groundwater dynamics in response to wave forces are relatively poorly understood. Accordingly, research needs with respect to groundwater dynamics are discussed and identified in this review. Many studies evaluate the wave-induced groundwater hydrodynamics based on experimental or field observations, while sophisticated theoretical approaches are still lacking to quantify the influence of various complex physical factors during wave swash events, such as capillary truncations, seepage face dynamics, and wetting front evolutions. Such knowledge gaps need to be filled in order to further advance our understanding of the coastal groundwater dynamics and, furthermore, to conduct effective and sustainable coastal water management and protection.

Major sea-level cycles occurred in the Cenomanian-early Turonian greenhouse world and impacted depositional conditions and ecosystems across the paleo-shelf seas. These sea-level cycles have been interpreted from various paleogeographic settings around the globe, such as the Western Interior Seaway (North America), the Proto-North Atlantic, Western Europe, and eastern Tethys (SE India). However, their drivers remain poorly understood and may include glacio-, aquifer-, thermo-, and/or tectono-eustasy. Uncertainties also persist regarding the timing, synchronicity, and magnitude of Cenomanian-early Turonian eustatic cycles. By combining palynological data from northern Africa (Gindi Basin, Egypt) with data available in the literature, a detailed synthesis of Cenomanian palynostratigraphy and sea-level dynamics is presented. Age-diagnostic spores, pollen, and organic walled dinoflagellate cysts (dinocysts) are correlated to global marine biozonation schemes, which provide a comprehensive biostratigraphic framework for the Cenomanian-early Turonian. Additionally, palynological data enable the identification of an early late Cenomanian Dinopterygium bio-event marked by the highest abundances of dinocysts. This bio-event can be correlated to the Neolobites ammonite bio-event and the Jukes-Browne Carbon Isotope Event. The bio-events stratigraphically constrain with a major transgression, which occurred in the early late Cenomanian, slightly preceding Oceanic Anoxic Event 2 (OAE2). Another major transgression spans the late Cenomanian-early Turonian, referred to the Plenus transgression bio-event, and consistent with the onset of the OAE2. Regional to global correlations indicate that these transgressive events reflect eustatic sea-level rises that can be recognized throughout the Tethys, Proto-North Atlantic, Europe, Western Interior Seaway, and India. These transgressions occurred within <1.0 Myr with modest magnitudes of 10–60 m. Rates of sea-level change has commonly been attributed to glacio-eustasy, which is however difficult to reconcile with a probably ice-free Cenomanian-early Turonian greenhouse world. Both transgressions coincide with phases of rising temperatures, whereby warming was most pronounced during the early late Cenomanian transgression. However, we can only speculate whether rising temperatures indicate the demise of polar glaciations. Eustatic processes, including tectono-eustasy, and to some extent aquifer- and thermo-eustasy, likely played a role in the sea-level rise during the early late Cenomanian and early Turonian. Environmental changes associated with the early late Cenomanian transgression may have triggered the onset of OAE2 possibly exacerbated by sluggish ocean circulation in a warming greenhouse world where sea ice formation was limited.