Figure - available from: Scientific Reports
This content is subject to copyright. Terms and conditions apply.
(A) Paleocene, (B) early Eocene, and (C) middle Eocene locations studied, including locations with and without recorded sand-rich deep-sea systems. Paleomaps are modified from the PALEOMAP Project of C. R. Scotese³⁵. Location names and references are available in Supplementary Information.
Source publication
The early Eocene (~ 56–48 million years ago) was marked by peak Cenozoic warmth and sea levels, high CO2, and largely ice-free conditions. This time has been described as a period of increased continental erosion and silicate weathering. However, these conclusions are based largely on geochemical investigation of marine mudstones and carbonates or...
Citations
... As an example, the Early Eocene was a hyperthermal characterised by a sea level 70 to 100 m above present (Miller et al., 2020). Despite these highstand conditions, at least 59 deep-water turbidite systems were recognised worldwide (Burton et al., 2023) in both active and passive margins. Evidently, triggering of flood-generated (extrabasinal) highstand turbidites is largely more common in depositional settings characterised by narrow shelves (Burton et al., 2023). ...
... Despite these highstand conditions, at least 59 deep-water turbidite systems were recognised worldwide (Burton et al., 2023) in both active and passive margins. Evidently, triggering of flood-generated (extrabasinal) highstand turbidites is largely more common in depositional settings characterised by narrow shelves (Burton et al., 2023). ...
Deltas are deposits directly accumulated by land-generated
gravity flows in
a standing body of water. The paradigm of deltaic sedimentation has dramatically
changed during recent years, from the popular very simplified ternary models
of marine littoral deltas towards more realistic and comprehensive models,
considering the importance of sediment-laden
river discharges. Ternary delta
models were designed for clean rivers, where a stream flow drags the sediments.
Depending on the basin dynamics, these littoral deposits can be modified, forming
tidal-dominated,
wave-dominated
or fluvial-dominated
littoral deltas. In recent
years, a new classification of delta systems was proposed, based on contrasting
the salinity of the receiving water body with the bulk density of the incoming
fluvial discharge. Rivers are highly dynamic systems, and their discharges can be
very variable in terms of flow duration and sediment concentration. Additionally,
the salinity of the receiving water body can exhibit significant variability, especially
in closed lakes and epicontinental seas, ranging from freshwater to brines.
This scenario allows the distinction of three major delta categories (hypopycnal,
homopycnal and hyperpycnal deltas) which can be in turn subdivided, defining
seven delta types. Hypopycnal deltas form when the bulk density of the incoming
flow is lower than the density of the water in the basin, allowing the definition
of three delta types, corresponding to hypersaline littoral deltas, marine littoral
deltas and brackish littoral deltas. Homopycnal deltas form when the bulk density
of the incoming flow is similar to the density of the water in the basin, defining a
delta type termed homopycnal littoral deltas. Hyperpycnal deltas form when the
bulk density of the incoming flow is higher than the density of the water in the
basin, allowing the definition of three categories termed hyperpycnal littoral deltas,
hyperpycnal subaqueous deltas and hyperpycnal fan deltas.
... The overall geological structure is a west-dipping monoclinic structure, and the underlying geological structure pattern is a west-dipping monoclinic structure. The object of study is the mud shale of the Upper Paleozoic Permian Shanxi Formation in the Sulige area, which is a sea-land transitional phase deposit that developed a series of clastic depositions in the environment of the coastal shallow lake-delta front [23][24][25]. The overall evolution of the shale lithology is relatively stable, consisting mainly of gray-black mudstone and dark mudstone [26]. ...
The mass fraction of total organic carbon (TOC) is one of the key indicators for evaluating the hydrocarbon generation potential of shale source rocks. Experimental measurements to evaluate the TOC content require significant cost and time. Furthermore, the experimental data are often fragmented and may not provide an accurate depiction of the source rocks throughout the entire block. To solve the above problems, this paper proposes to use the combination of conventional logging data and experimental data after an in-depth study of the geophysical characteristics of hydrocarbon source rocks in the Ordos Basin. A quantitative model between logging data and source rocks is established, and then the continuous distribution value of the TOC content in the hydrocarbon source rock interval is calculated. Firstly, the mud shale formation of the Permian–Shanxi Formation in the Upper Paleozoic, located in the Jingbian area of the Ordos Basin, is selected as the research target using the “Jinqiang method”. The model is constructed by selecting appropriate logging curves (acoustic time difference logging, resistivity logging, and density logging) and experimental results based on the response relationship between logging data and TOC data. This method provides more accurate and comprehensive data for source rock studies, combining experimental sampling to contribute to a better evaluation of TOC in source rock. The shale hydrocarbon source rock logging data from 10 wells are selected, and the model is used to realize the full-well section of the logging data to find the hydrocarbon source rock TOC, which is compared with the TOC data from the experimental core tested at a sampling point. The results demonstrate that the model is highly effective and accurate, with a mere 2.7% percentage error observed across 185 sample data points. This method greatly improves the accuracy and completeness of TOC evaluation compared with the results of previous studies and provides a guide for subsequent TOC logging evaluation of source rocks in other areas. With the study in this paper, continuous TOC values of source rocks are obtained, discarding the TOC values representing the whole set of hydrocarbon source rocks with a limited number of sample averages. This method can reflect the contribution of the layers with high and low organic matter abundance, and the calculated reserves are more accurate. By utilizing the measured TOC values of the study area to invert the model to find the parameters, this study contributes to the decision-making of hydrocarbon exploration in domestic and international basins.
... Considering that the target reservoir is buried deep, the horizontal difference stress coefficient is applicable to represent the influence of horizontal stress difference on FI. The calculation method is shown in Equation (9). A small difference coefficient of horizontal stress is beneficial to reservoir fracturing. ...
Reservoir rocks of the Pearl River Mouth Basin’s Lufeng Sag have low porosity (average porosity 12.6%) and low permeability (average permeability 16.5 mD), requiring hydraulic fracturing to obtain economic production of oil and gas. To contribute to the understanding of these reservoirs, and to promote successful production in the region, we analyzed the mechanical properties of tight sandstone. Moreover, we introduced the shear/tensile strength factor, in combination with the fracture toughness and horizontal stress difference coefficient, as an innovative approach to characterize the ease of forming a complex fracture network after reservoir fracturing. Based on this, we established a fracability evaluation model suitable for offshore low-permeability sandstone reservoirs by an analytic hierarchy process from the perspective of whether the reservoir can form an effective transformation volume and complex fracture network after fracturing. The results indicate that the primary minerals of the target reservoir are quartz and clay minerals, and the natural fractures are not developed. The mechanical properties exhibit a high Young’s modulus (ranging from 30.4 to 34.4 GPa) and high compressive strength (with cohesion between 41 and 45 MPa and an angle of internal friction between 31.0 and 33.5°). The relatively low tensile strength and fracture toughness values are conducive to fracture initiation and extension during the fracturing process. Through the fracability evaluation model constructed in this paper, the depth interval at 4155.1–4172.1 m is identified as a high-quality fractured layer. The results of this study not only provide theoretical guidance for target well and formation selection in the Lufeng Sag, but also have important practical implications for increasing oil and gas production from tight sandstone reservoirs.
... As discussed above, PetroMod™ assumes that methane entering the GHSZ and exceeding the solubility limit is instantaneously converted to hydrate, and therefore does not consider the kinetically feasible coexistence of hydrate and free gas phases within the GHSZ (Burwicz et al., 2017) or, for instance, the migration of gas through the GHSZ, invoked at Blake Ridge (Gorman et al., 2002). We make various assumptions by assigning model boundary conditions, as detailed above, including the assumption of constant basal heat flows, sediment-water interface temperatures, and water depths through time, and we do not explicitly consider, for instance, impacts of sea-level fluctuations on variable delivery of organic matter or coarse-grained sediment to our real-world model areas (e.g., Blum & Hattier-Womack, 2009;Burton et al., 2023;Erbacher et al., 1996), though we do seek to replicate coringand geophysical data-based interpretations of stratigraphy and lithology, as detailed above. ...
By harnessing both hypothetical, synthetic basin and gas hydrate (GH) system models and real‐world models of well‐studied salt diapir‐associated GH sites at Green Canyon (Gulf of Mexico) and Blake Ridge (U.S. Atlantic coast), we propose and demonstrate salt movement (and in particular, diapirism) to be a new mechanism for the recycling of marine GH. At Green Canyon, for example, we show that by considering this newly proposed diapir‐driven recycling mechanism in conjunction with previously proposed lithological control on sandy‐reservoir‐hosted hydrate at the base of the GH stability zone (BGHSZ; ∼bottom‐simulating reflector, BSR), modeled GH saturations match drilling data. Overall, salt diapir movement‐induced GH recycling provides a temperature‐driven mechanism by which GH saturations at the BGHSZ may reach >90 vol. % and by which GH volumes near and free gas volumes beneath the BGHSZ may be increased significantly through time. Interestingly, comparison of salt diapir‐driven recycling and sediment burial‐driven recycling scenarios suggests notably higher rates of recycling via diapir‐driven versus burial‐driven processes. Our results suggest that GH and associated free gas accumulations above salt diapir crests represent particularly attractive targets for unconventional and conventional hydrocarbon resource exploration and for scientific and academic drilling expeditions aimed at exploiting GH systems. Salt basins containing GH systems—including passive margin basins of the Gulf of Mexico, southeastern Brazil, and southwestern Africa—are therefore compelling localities for studying salt‐driven GH recycling and for salt diapir‐associated natural gas exploration.
... Paleoclimate can affect parent rock weathering, erosion, and sediment transport, and ultimately control the input of terrestrial nutrients and sediment into an ocean [38,39]. The CIA is a typical parameter for reconstructing paleoclimatic conditions [20,21] and for judging the degree of paleoweathering [40,41]. ...
The organic-rich shale of the Permian Taiyuan Formation (TYF) and Shanxi Formation (SXF) in the Southern North China Basin (SNCB) is considered a potential shale gas source. The shale was formed in a marine-continental transitional sedimentary environment, which has rarely been studied, with the enrichment mechanisms of organic matter (OM) remaining unclear. This study investigated the controlling factors and enrichment mechanisms of OM by analyzing the total organic carbon (TOC) content, paleoclimate, paleoproductivity, sedimentation rate, redox, and paleosalinity. The TOC of the TYF ranged from 0.92 to 7.43 wt.%, with an average of 2.48 wt.%, which was higher than that of the SXF (TOC = 0.36–5.1 wt.%, average of 1.68 wt.%). These geochemical indices suggest that both the TYF and SXF were deposited in warm and humid paleoclimates, with relatively high biological productivity and sedimentation rates. During the deposition process, the TYF experienced frequent transgression and regression events, leading to an enhancement of water reducibility, a relatively high sedimentation rate, reduced OM oxidation, and rapid deposition of OM, which were conducive to the preservation of OM. Moreover, a high biological productivity increased respiratory oxygen consumption in the water column, which could lead to OM accumulation. However, the regression event experienced by the SXF reduced the paleoproductivity and sedimentation rate and increased water oxidation, leading to a decrease in OM. The main controlling factors for the enrichment of OM in the TYF and SXF were the sedimentation rate, paleoproductivity, and redox conditions, thus establishing the enrichment models for OM in the TYF and SXF. This study is conducive to understanding shale enrichment mechanisms and guiding shale gas exploration.
Dashiling Gully, located in Miyun District, Beijing, exhibits a high susceptibility to debris flow due to its unique geological and topographical characteristics. The area is characterized by well-developed rock joints and fissures, intense weathering, a steep gradient, and a constricted gully morphology. These factors contribute to the accumulation of surface water and loose sediment, significantly increasing the risk of debris flow events. Following a comprehensive field geological investigation of Dashiling Gully, key parameters for simulation were obtained, including fluid weight, volume concentration, and rainfall. The formation and development conditions of potential mudslides were analyzed, and numerical simulations were conducted using FLO-2D software (version 2009) to assess scenarios with rainfall probabilities of 1 in 30, 50, and 100 years. The simulations accurately reconstructed the movement velocity, deposition depth, and other critical movement characteristics of mudslides under each rainfall scenario. Using ArcGIS, pre- and post-treatment hazard zoning maps were generated for Dashiling Gully. Furthermore, the efficacy of implementing a retaining wall as a mitigation measure was evaluated through additional numerical simulations. The results indicated that mudslide velocities ranged from 0 to 3 m/s, with deposition depths primarily between 0 and 3 m. The maximum recorded velocity reached 3.5 m/s, corresponding to a peak deposition depth of 4.31 m. Following the implementation of the retaining wall, the maximum deposition depth significantly decreased to 1.9 m, and high-risk zones were eliminated, demonstrating the intervention’s effectiveness. This study provides a rigorous evaluation of mudslide movement characteristics and the impact of mitigation measures within Dashiling Gully. The findings offer valuable insights and serve as a reference for forecasting and mitigating similar mudslide events triggered by heavy rainfall in gully mudslides.
The understanding of the stratigraphic evolution of marine rift basins is important for both “pure” scientific and
economic reasons. From a hydrocarbon exploration point of view the main goal is to develop tools to predict
reservoir location, quality, and extent. Stratigraphic models try to do that, and only historical cases can be used
to test those models. On the other hand, depositional model cannot precisely predict reservoir location as factors
unique to the specific basin under analysis affect sediment distribution (basin physiography, type of flows,
among others). This aspect can be assessed only on a case-by-case basis and can be used for initial hypothesis
generation based on analogues. This paper shows a case history study based on the integration of well logs, and
3D seismic data across the Eastern Dampier sub-basin, Northwester Shelf of Australia. Advanced seismic interpretation techniques, calibrated to well data, enable the definition of a chrono-stratigraphic framework of the
late syn-rift sequence (Late Jurassic) of the Lewis Trough, and the description of the sediment distribution
through the interpretation of geomorphological features. During the Late Jurassic three different channel systems
deliver sandstones to the deep-water part of the basin through multiple entry points. The timing of the sediment
input seems to be linked to variation of sediment input as during that time relative sea-level was slowly rising.
The location of the entry points is related to local physiography and defies any attempt of prediction based on
general “rules.” From a stratigraphic point view, the findings of the study support the idea that, in rift basin,
mechanical subsidence is the primary control for accommodation space, with episodic pulses of extension followed by longer periods of tectonic quiescence. It is during these episodic movements along the basin’s bounding
faults that space for sedimentation is created. This interpretation is in striking contrast with the basic assumptions of the conventional sequence stratigraphy model.
Traditional stress sensitivity experiments are typically conducted under dry conditions, without considering the reservoir’s water content. In reality, the presence of water within pores significantly influences the extent of stress sensitivity damage in tight sandstone oil formations, subsequently affecting the determination of stress sensitivity coefficients during experimentation. By investigating sandstone samples from wells in the Mahu Block of China’s Xinjiang province, we observed that increasing water saturation reduces the stress sensitivity of tight sandstone. By conducting stress sensitivity experiments under varying water content conditions, we found that the stress sensitivity coefficient is not a constant value but decreases as water saturation increases. Based on experimental comparisons, an optimized power-law model for stress-sensitive damage assessment was refined. By conducting stress-sensitive damage assessment experiments under different water content conditions and integrating the concept of comprehensive compression coefficient, an improved stress-sensitive power-law model was established allowing for the influence of water content. The accuracy of this improved model was increased by 46.98% compared to the original power-law model through experimental validation. The research outcomes can enhance the accuracy of permeability and productivity evaluation, providing valuable guidance for unconventional oil and gas development.
Tight sandstone reservoirs are of interest due to their potentially favorable prospects for hydrocarbon exploration. A better understanding of tight sandstone outcrop reservoir characteristics and their influencing factors is thus needed. By laboratory observation, thin section analysis, and experimental analysis, the current work carried out a detailed investigation of densely sampled tight sandstone outcrops of the Shanxi Formation in the Liujiang River Basin, paving the way for further research on rock types, reservoir spatial distribution, physical properties, and their key controlling factors. The application of the Pressure Pulse Attenuation Method made it possible to determine the porosity and permeability, as well as the analysis of debris composition and filling content. The findings indicate that the main rock type of the tight sandstone outcrop reservoirs in the Shanxi Formation in the Liujiang River Basin is lithic quartz sandstone, some of which contains fine sand-bearing argillaceous siltstone, giving them very low porosity (average porosity of 4.34%) and low permeability (average permeability of 0.023 mD) reservoirs. Secondary pores—mostly dissolved pores among and in grains—are widely developed in the target region. In addition, diagenesis primarily includes mechanical compaction, cementation, and dissolution. The main controlling factors of tight sandstone reservoirs in the target region are sedimentation, diagenesis, and tectonics, whereby sedimentation affects reservoir physical properties that become better as the clast size increases, reservoir properties are negatively impacted by compaction and cementation, and reservoir properties are somewhat improved due to dissolution and the impact of tectonism. In addition, the tilt of the crust will produce faults during the tectonic action, generating reservoir cracks that improve the reservoir’s physical properties. This study tends to be helpful in the prediction of high-quality reservoirs in the Permian Shanxi Formation in North China and can also be used for analogy of high-quality reservoirs in similar areas with complete outcrops.
