Basin Research最新文献

In foreland fold-thrust belts, tectonically deformed aquifers remain underexplored, largely due to the complex architecture of their hydrogeological reservoirs. This limited understanding prevents the development of sustainable management policies to face the current decline in groundwater availability. In the southwestern Subalpine Chains, we characterised the structure of the folded Senonian karst aquifer of the Dévoluy Massif, which is transected by the Median Dévoluy Thrust. Using surface structural data, we performed an original 3D structural model of the massif. Quantitative analyses of this model indicate a total Senonian package volume of 114 km³, of which 25 km³ lie below the elevation of Gillardes Spring, the main karst discharge. A structural restoration of the base of the Senonian indicates Alpine shortening of ~4.4 km in the southern part of the massif and ~1.2 km in the northern part. The deformation of the karst reservoir into two N-trending synclines, separated by the Median Dévoluy Thrust, is identified as a key control on the northward groundwater drainage pattern, culminating at Gillardes Spring. This 3D structural modelling approach also allowed for identification of suitable areas for the exploration of new deeper resources. Finally, this study highlights the potential of a hydrostructural approach and 3D structural modelling for assessing the hydrogeology in tectonically deformed karst reservoirs.

Mineral-chemical stratigraphy and provenance analysis are applied to aid diagnostics of a sandstone body of uncertain origin in the northern North Sea. The main Gamma discovery sandstone (well 24/9-3), hosted by fine-grained strata in the Balder Formation (early Eocene), has many characteristics of sandstone intrusions, such as discordant upper and lower surfaces and significant jack-up of overlying strata. However, the gross volume and high net-to-gross in boreholes (75% and 85% in 24/9-3 and 24/9-14S, respectively) are unusually high compared with sandstone intrusions known from the subsurface or outcrop examples. To constrain the origin of intra-Balder Fm sandstones in the Gamma area, their heavy mineral assemblages (HMAs) and garnet chemistry are compared with those preserved in depositional Heimdal, Hermod S2, Odin and Frigg Member sandstones found in stratigraphic and geographic proximity. Mineral-chemical characteristics in the Gamma Sandstone are similar to those in depositional sandstone of the Odin Member, a sandstone unit in the Balder Formation. All other depositional sandstone units analysed have dissimilar mineral-chemical features, or other factors preclude them as parent units for the Gamma Sandstone. We conclude that the intra-Balder sandstones in the Gamma discovery occupy their original stratigraphic position and can be assigned to the Odin Member, despite the intense changes to internal and external features caused by in situ remobilisation and sand fluidisation.

Seismic modelling of outcrop data from a sand injection complex enables detection of subseismic sandstone intrusions, but the geometry and orientation of individual intrusions remain unresolved. Sand injection complexes are increasingly recognised as a common shallow-crustal process, comprising millimetre- to decametre-scale, close to bedding-concordant sills and strongly bedding-discordant dykes, as well as intrusions with less regular geometry. These features can act as basin-scale fluid migration conduits, hydrocarbon reservoirs and possible sites for CO₂ sequestration. This paper presents 2D point-spread function (PSF) seismic modelling of a digital outcrop model containing a wide range of intrusion geometries, including thin, complex and interconnected features. The results provide insights into the seismic response of subseismic (unresolved) geological features and enable evaluation of the effects of illumination, lateral resolution, dominant frequency and noise on seismic imaging. Multiple densely spaced thin intrusions generate interference as a function of wavelength, producing complex seismic patterns caused by the dense spacing and cross-cutting geometry of intrusions. The seismic patterns show little resemblance to the geometry of the intrusions. Increases in dominant frequency improve the resolution and interpretation of large intrusions from seismic data and preferentially intensify some seismic characteristics, sometimes creating bedding-like, sub-horizontal features that do not exist in the outcrop data. This ambiguity caused by enhancement of sub-horizontal intrusions relative to sub-vertical intrusions can lead to misinterpretation of sandstone presence and distribution. Individual intrusions with a thickness of 1 m may be detected under favourable conditions but are not directly resolvable in seismic data and increased dominant frequency does not necessarily result in improved geological interpretation. High-angle dykes (> 45^o) display linear zones with amplitude dimming, which are attributed to their cross-cutting character, thus facilitating their interpretation. Seismic amplitudes from host strata interact with those of intrusions, diminishing the clarity of the seismic response of intrusions. Limited illumination reduces the accuracy of interpretation. The addition of noise increases the complexity of intrusion-related seismic responses, both enhancing and reducing amplitudes associated with intrusions, specifically in intervals with complex intrusion networks.

To achieve net-zero carbon emissions by 2050, gigatonnes of CO₂ must be captured and stored in the subsurface. Screening and exploration of prospective storage sites have thus gained momentum in recent years. The Miocene-age Lille John Member in the Danish Central Graben represents a promising, yet underexplored, CO₂ storage candidate due to its lack of commercial hydrocarbon potential. This study integrates high-resolution 3D seismic data, core analyses, and wireline logs within a sequence stratigraphic framework to characterise the depositional environment within the targeted Miocene interval. Seismic attributes such as RMS amplitude and spectral decomposition are used to define the three-dimensional architecture of the geobodies and evaluate their potential for CO₂ storage by comprehending reservoir distribution, heterogeneity, and connectivity. The reservoir consists of two unconsolidated sand units, informally termed the lower and upper sand units, separated by a mudstone interval. The lower sand unit represents a basin floor fan emplaced by gravity flows during the falling stage systems tract, while the upper unit comprises unconfined gravity flow deposits associated with the lowstand systems tract. The reservoir sands of the Lille John Member are predominantly localised in the southeastern portion of the Central Graben at depths suitable for storing supercritical CO₂. Theoretical P50 storage capacity is estimated at approximately 1108 million tonnes for the lower sand unit and 51 million tonnes for the upper unit. Heterogeneities such as silt beds, mudstones, and carbonate concretions may act as flow baffles, enhancing storage efficiency through plume dispersion, residual trapping, CO₂ dissolution, and geochemical interactions. This study situates the Lille John Member within a broader regional framework by integrating a larger 3D seismic dataset with advanced seismic interpretation workflows, extending beyond the scope of previous investigations. The results provide new insights with implications for unlocking CO₂ storage potential in analogous depositional settings.

High impedance (hard) mudstones are sometimes observed in association with sand injection complexes in the Paleogene petroleum province of the northern North Sea. A hard mudstone surrounding a water-bearing sandstone can give a similar acoustic response to an oil-bearing sandstone surrounded by low impedance (soft) mudstone. The presence of hard mudstone thus impacts the ability to predict hydrocarbon presence directly from seismic data during exploration. To establish the mechanism of ‘hardening’ to better predict the presence of variable mudstone characteristics, we examine three cored wells from the Beryl Embayment. Well logs and core were examined to characterise the structure, petrology, petrophysical properties and spatial distribution of both hard and soft mudstones. The results indicate that mudstone hardening is most likely associated with mechanical compaction and efficient dewatering of mudstones into the sand injection complex. This process is enhanced where sand injection complexes transect primary overpressure zones, that promote dewatering from basal overpressured mudstone into the injection network. This study highlights that seismic response needs careful investigation in the context of the complexity of the injectite complex along with variable mudstone attributes. Additionally, this process highlights the role sand injection complexes play in efficient dewatering through lateral transfer in overpressured basins.