Oil migration through preferential petroleum migration pathway (PPMP) and polycyclic faults: A case study from the Shijiutuo Uplift,Bohai Bay basin,China

The Shijiutuo uplift is an oil enriched uplift in the offshore Bohai Bay Basin. Petroleum migration is a key factor for oil enrichment in Neogene reservoirs far away from the hydrocarbon kitchen. In this article, an integration of geological, geophysical and geochemical analyses are employed to investigate the petroleum migration and accumulation on the Shijiutuo uplift. Hydrocarbons in the QHD32-6 and QHD33 oilfields are mainly originated from the third (E₂s₃) and first (E₂s₁) member of the Shahejie Formation. The shallow traps have significant contributions of late-stage E₂s₁-derived oil. Lateral petroleum migration is a major mechanism forming large oilfields on the Shijiutuo uplift. The large oilfields have multiple hydrocarbon kitchens, multiple source rocks, and numerous preferential petroleum migration pathways (PPMPs). Once petroleum arrives at the structural highs on the Shijiutuo uplift through the Guantao Formation (N₁g) carrier-beds, neotectonic faults cutting through Guantao (N₁g) and Minghuazhen (N₁m^L) formations could serve as effective conduits for vertical petroleum migration. Neotectonic faults have experienced polycyclic fault activities. Fluid inclusions indicate episodic hydrocarbon charging. Crude oils display duplex properties of biodegradation and non-biodegradation, which is strong evidence for multiple and episodic oil charging on the Shijiutuo uplift. Finally, episodic petroleum charging along polycyclic neotectonic faults causes the late-stage E₂s₁-derived oils to occur in the shallow reservoirs.     

The genetic structure of the exotic ascidian Styela plicata (Tunicata) from Italian ports,with a re‐appraisal of its worldwide genetic pattern

The pleated ascidian Styela plicata (Lesueur, 1823) is a solitary species commonly found in ports and marinas around the world. It has been recorded in the Mediterranean region since the mid‐19th century. In the present work, the species’ genetic diversity was analysed, employing a 613‐bp portion of the mitochondrial cytochrome c oxidase subunit I (COI) gene from 149 individuals collected in 14 ports along Italian coasts at spatial scales ranging from 1 to approximately 2200 km. Haplotype and nucleotide diversity values were h = 0–0.933 (total h = 0.789) and π = 0–0.145 (total π = 0.0094), respectively. A general southward trend of increasing within‐population genetic diversity was observed. Analysis of molecular variance revealed significant genetic structuring but no significant differences were detected among basins, and no isolation by distance was found. Our data were integrated with the COI sequences available from previous studies and re‐analysed in order to investigate the possible routes of introduction of this ascidian into the Mediterranean Sea. The presence of the two COI haplogroups detected in previous molecular investigations on S. plicata at intercontinental spatial scale was confirmed in the Mediterranean Sea. The results revealed multiple introductions of S. plicata, although some locations appear to have experienced rapid expansion from few founding individuals with reduced genetic diversity. However, continuous introductions would confound the pattern deriving from single founder events and make it difficult to estimate the time needed for gene diffusion into established populations. This mixing of effects creates difficulties in understanding the past and current dynamics of this introduction, and managing this alien invasive ascidian whose genetic structure is continuously shuffled by vessel‐mediated transport.     

The evolving perceptual model of streamflow generation at the Panola Mountain Research Watershed

The Panola Mountain Research Watershed (PMRW) is a 41-hectare forested catchment within the Piedmont Province of the Southeastern United States. Observations, experimentation, and numerical modelling have been conducted at Panola over the past 35 years. But to date, these studies have not been fully incorporated into a more comprehensive synthesis. Here we describe the evolving perceptual understanding of streamflow generation mechanisms at the PMRW. We show how the long-term study has enabled insights that were initially unforeseen but are also unachievable in short-term studies. In particular, we discuss how the accumulation of field evidence, detailed site characterization, and modelling enabled a priori hypotheses to be formed, later rejected, and then further refined through repeated field campaigns. The extensive characterization of the soil and bedrock provided robust process insights not otherwise achievable from hydrometric measurements and numerical modelling alone. We focus on two major aspects of streamflow generation: the role of hillslopes (and their connection to the riparian zone) and the role of catchment storage in controlling fluxes and transit times of water in the catchment. Finally, we present location-independent hypotheses based on our findings at PMRW and suggest ways to assess the representativeness of PMRW in the broader context of headwater watersheds.     

The stereoscopic spatial connectivity of wetland ecosystems: Evaluation method and regulation measures

Currently, the weakened connectivity of wetland ecosystems is the most important factor leading to the destruction, degradation, and disappearance of wetlands. Studying changes in wetland ecosystems connectivity enables the understanding the hydrological processes in wetland ecosystems and provides significant support for the study of ecological water demand. However, recent research on the connectivity of wetland ecosystems has primarily focused on intuitive Heilongjiang River Basin in China (HRBC) connectivity in terms of hydrology and geomorphology, while the impact of wetland ecosystems on habitats has been ignored. The present study applied an innovative method to evaluate and regulate the stereoscopic spatial connectivity (SSC) of the wetland ecosystems in the HRBC. In this method, the water requirements of typical organisms in the region were considered, and the hydrological trends in the wetland ecosystems along with the status of the SSC were analysed using remote sensing images. A regulation mode for improving the stereoscopic spatial connectivity index (SSCI) was proposed. The results revealed that over the past 35 years, the wetland ecosystems in the study area shrank significantly, with the SSCI decreasing from 41.30% in 1980 to 35.08% in 2015. By comparing the correlations among temperature, precipitation, agricultural land, construction land, and the wetland ecosystems during the same period, it was proven that human activity serves as the major driving force behind the observed loss of wetlands in the system. Subsequently, the key protected areas needing protection to maintain the SSC of the wetland ecosystems were clarified, and the key recovery areas were determined based on three scenarios featuring high, medium, and low feasibility, which greatly improved the SSCI and generalization route after regulation. In general, the proposed SSC evaluation and regulation method is widely applicable to all kinds of wetland ecosystems located on animal habitat and migration routes, which can fully reflect the ecological effects of wetland ecosystems, and this method has certain reference significance for the evaluation and regulation of wetland ecosystems in other regions.     

MHYDAS‐Erosion: a distributed single‐storm water erosion model for agricultural catchments

In this paper, we present MHYDAS‐Erosion, a dynamic and distributed single‐storm water erosion model developed as a module of the existing hydrological MHYDAS model. As with many catchment erosion models, MHYDAS‐Erosion is able to simulate sediment transport, erosion and deposition by rill and interrill processes. Its originality stems from its capacity to integrate the impact of land management practices (LMP) as key elements controlling the sedimentological connectivity in agricultural catchments. To this end, the water‐sediment pathways are first determined by a specific process‐oriented procedure defined and controlled by the user, which makes the integration of LMP easier. The LMP dynamic behaviours are then integrated into the model as a time‐dependent function of hydrological variables and LMP characteristics. The first version of the model was implemented for vegetative filters and tested using water and sediment discharge measurements at three nested scales of a densely instrumented catchment (Roujan, OMERE Observatory, southern France). The results of discharge and soil loss for simulated rainfall events have been found to acceptably compare with available data. The average R² values for water and sediment discharge are 0·82 and 0·83, respectively. The sensitivity of the model to changes in the proportion of LMP was assessed for a single rain event by considering three scenarios of the Roujan catchment management with vegetative filters: 0% (Scenario 1), 18% (Scenario 2, real case) and 100% (Scenario 3). Compared to Scenario 2 (real case), soil losses decreased for Scenario 3 by 65% on the agricultural plot scale, 62% on the sub‐catchment scale and 45% at the outlet of the catchment and increased for Scenario 1 by 0% on the plot scale, 26% on the sub‐catchment scale and 18% at the outlet of the catchment. Copyright © 2010 John Wiley & Sons, Ltd.     

Ground‐based thermal imagery as a simple,practical tool for mapping saturated area connectivity and dynamics

The hillslope‐riparian‐stream system is a key functional unit of catchments, yet very difficult to measure and monitor due to its tremendous complexity and high spatio‐temporal variability. Here, we present a simple and practical tool for imaging directly these hillslope‐riparian‐area connections. We used a FLIR b50 infrared camera to produce thermal images at the scale of 140 × 140 pixels over the spectral range 7·5–13 µm. Our IR imaging technique is sensitive to the upper 0·1 mm of the water column. Images were obtained from a constant position on the right bank of the Weierbach catchment in Luxembourg, at an incidence angle of approximately 45° over a 5‐week period. The study site measured 5 × 3 m. Our results show that ground‐based IR imagery can discriminate between areas with snow cover, snow melt, soil seepage, and stream water. More importantly, it can detect when and where variably saturated areas are active and when connectivity exists between the hillslope–riparian–stream system. Our proof of concept suggests that this is a simple, inexpensive technology for sequential mapping and characterisation of surface saturated areas and a useful complement to conventional tracer techniques. Copyright © 2010 John Wiley & Sons, Ltd.     

Semi‐automated GIS techniques for detecting floodplain earthworks

Levees, channels and water storages built on the world's floodplain wetlands control flows for irrigation, flood mitigation and erosion management. Assessing their distribution and hydrological impacts through time and across broad extents is limited by significant costs and technical challenges. We tested the effectiveness of three new semi‐automated geographic information systems and traditional visual interpretation techniques for detecting earthworks. We used commercially or freely available two‐dimensional and three‐dimensional spatial imagery within 19 quadrats in an agricultural floodplain of the Murray–Darling Basin, southeastern Australia. Semi‐automated digital elevation model (DEM) analysis performed best for spatial accuracy (78% of earthworks correctly predicted within 25 m), overall classification accuracy (97.7%) and kappa (0.64), compared with traditional visual interpretation techniques using Landsat TM (52%, 96.3%, 0.39), SPOT (53%, 95.8%, 0.27) and aerial photography (72%, 97.2%, 0.31). DEM analysis also outperformed semi‐automated image segmentation (16%, 93%, 0.29) and integrated analysis (75%, 96.0%, 0.43) that used spectral information. Semi‐automated techniques were slow (DEM analysis: 27 418 s/km²; integrated analysis: 27 737 s/km²; and image segmentation: 1439 s/km²) compared with visual interpretation (Landsat TM: 109 s/km²; SPOT: 166 s/km²; and aerial photography: 276 s/km²); however, processing speed of semi‐automated techniques can be further increased without compromising accuracy. Semi‐automated techniques also offered operational autonomy following model calibration. High quality, cost‐effective earthwork mapping techniques, particularly the semi‐automated techniques in this study, are critical for understanding and managing ecosystem health, flood risk and water security in developed floodplains worldwide and should be implemented by governing institutions. Copyright © 2012 John Wiley & Sons, Ltd.     

The hydrogeomorphic influences on alluvial gully erosion along the Mitchell River fluvial megafan

Hydrogeomorphic processes influencing alluvial gully erosion were evaluated at multiple spatial and temporal scales across the Mitchell River fluvial megafan in tropical Queensland, Australia. Longitudinal changes in floodplain inundation were quantified using river gauge data, local stage recorders and HEC‐RAS modelling based on LiDAR topographic data. Intra‐ and interannual gully scarp retreat rates were measured using daily time‐lapse photographs and annual GPS surveys. Erosion was analysed in response to different water sources and associated erosion processes across the floodplain perirheic zone, including direct rainfall, infiltration‐excess runoff, soil‐water seepage, river backwater and overbank flood inundation. The frequency of river flood inundation of alluvial gullies changed longitudinally according to river incision and confinement. Near the top of the megafan, flood water was contained within the macrochannel up to the 100‐year recurrence interval, but river backwater still partially inundated adjacent gullies eroding into Pleistocene alluvium. In downstream Holocene floodplains, inundation of alluvial gullies occurred beyond the 2‐ to 5‐year recurrence interval and contributed significantly to total annual erosion. However, most gully scarp retreat at all sites was driven by direct rainfall and infiltration‐excess runoff, with the 24‐h rainfall total being the most predictive variable. The remaining variability can be explained by seasonal vegetative conditions, complex cycles of soil wetting and drying, tension crack development, near‐surface pore‐water pressure, soil block undermining from spalling and overland flow, and soil property heterogeneity. Implications for grazing management impacts on soil surface and perennial grass conditions include effects on direct rainfall erosion, water infiltration, runoff volume, water concentration along tracks, and the resistance of highly dispersible soils to gully initiation or propagation under intense tropical rainfall. Copyright © 2012 John Wiley & Sons, Ltd.     

库车坳陷迪那2构造油气运聚模拟实验

为了研究油气运聚过程, 以迪那2构造为地质模型, 在构造特征、储盖组合、油气来源分析的基础上建立油气运聚过程物理模拟的二维实验模型.通过模拟实验, 揭示: (1)断层是迪那2构造中油气运移的主要通道; (2)泄压区是油气运移的有利指向区; (3)毛管力及浮力在渗透性相近的砂岩中起重要作用; (4)油气总是选择优势通道运移, 在沿断层运移的同时, 也向两侧砂体中扩散; (5)油驱水之后的气驱油运移通道具有继承性的特点.      

Multi‐scale assessment of overflow‐driven lateral connectivity in floodplain and backwater channels using LiDAR imagery

Overflow‐driven lateral connectivity significantly influences the spatial distribution and diversity of floodplain habitats and biota. Proper understanding of lateral connectivity in floodplain and backwater channels is therefore critical for assessment of river quality and for targeting management or restoration actions. In this study, we present a methodological framework for spatial and temporal assessments of overflow‐driven lateral connectivity at two spatial scales: bypass reach and backwater channel. Firstly, we compute the relative elevations, as well as overflow discharge, duration, and frequency using a simple, raster‐based method that uses a LiDAR digital elevation model (DEM), rating curves, and streamflow time series. Subsequently, we analyse the accuracy of this approach with respect to the accuracy of a DEM and evaluate its further applications. Altogether, four 10‐km‐long bypass reaches and 11 backwater channels are analysed, located along the Rhône River corridor in France. The results proved the precision of the method to be affected by the LiDAR DEM accuracy, which was on average more precise in a typically homogeneous floodplain setting rather than for backwater channel plugs with pronounced topographic complexity and usually riparian forest canopy. Amongst the four studied reaches, Brégnier Cordon proved to have the greatest flooding dynamics, followed by Belley and Chautagne. The hydrological connectivity pattern of Pierre Bénite differed significantly. Three longitudinal patterns of hydrological connectivity of backwater channels displayed stepwise advancement of the water. The presented results can be used to assess ecological potential of floodplain habitats and their historic and prospective evolution through time. Copyright © 2014 John Wiley & Sons, Ltd.