3D Seismic Reflection Data Research Articles

Architecture and geomorphology of fluvial channel systems in the Arabian Basin

The architecture and geomorphology of fluvial channel system plays an important role in the interpretation of its sedimentary processes and characterization of the ability for subsurface storage. In the Arabian Basin, this system is considered a new petroleum play after a century of carbonate-play dominance with enormous petroleum reserves. In addition, the presence of publicly available 3D seismic refection data in the Arabian Basin is very limited, providing a condition that fluvial channel system knowledge becomes publicly less understood. Therefore, our study utilizes 3D seismic reflection data and aims to (1) interpret seismic facies and architecture, (2) map the unit thickness and lateral distribution, and (3) calculate morphometry of the Late Carboniferous to Early Permian fluvial channel systems in the Arabian Basin, and discuss its sedimentary processes, development and petroleum prospectivity. Seismic facies and seismic attribute analysis revealed three distinct fluvial channel systems including their crevasse-splay and flood plain. The channels are characterized by isolated bright on the RMS amplitudes, spectral decomposition, variance and sweetness with sinuous geomorphology and lobes (crevasse-splay) and variation of amplitude values in hummocky to sub-parallel and parallel (flood plain) reflection configuration. The morphometric analysis shows three clusters on the scaling relationship between maximum channel width and meander belt width, as well as the minor variation on the channel sinuosity index. These results indicated the dominance of the bed-load sediment transport mechanism in the fluvial depositional environment with a single-story channel body architecture. These factors provide the ability for fluvial channel systems in the studied area to act as petroleum reservoir as well as potential source rock, cap rock and stratigraphic traps. Furthermore, a single-story channel body indicated poorly connected among them, both in lateral and vertical extends that required horizontal wellbore for drainage the reservoir. Our study revealed that fluvial channel systems in the Arabian Basin has potentiality both in petroleum prospectivity as well as subsurface storage (carbon dioxide, waste, hydrogen). In addition, the workflow presented here could be applicable to characterize the fluvial channel system from 3D seismic reflection data in other basins, worldwide.

Petroleum system analysis of Fujairah basin, eastern offshore of the United Arab Emirates

The Fujairah basin, located on the eastern margin of the United Arab Emirates, forms part of the hinterland basin of the Oman-UAE mountains. Despite its geological significance, the hydrocarbon potential of this basin remains unexplored. This study aims to address this knowledge gap by using 2D seismic reflection data, three exploration wells, geochemical data from one well, a 2D velocity section, and two pseudo-wells. The study began with the interpretation of the seismic profiles and then proceeded to create depth maps for the most significant units. We used Rock-Eval pyrolysis plots to identify the primary source rocks and to classify their kerogen types. The seismic interpretation formed a basis for the 1D and 2D basin modeling techniques that are used to determine the petroleum system of the basin. Our results identify the Pliocene, Miocene, and Eocene sequences as potential source rocks in the basin with TOC values less than 1 wt% and low expulsion efficiencies. The Pliocene and Miocene source rocks are mainly type-II kerogen, whereas most Eocene samples are characterized as type-III kerogen. The Pliocene and Miocene source rocks are immature in the basin. The Eocene is mature depending on the burial within the sub-basins. The Eocene started expelling hydrocarbons during the Burdigalian, which was linked to the collision of the Arabian and Central Iran plates along the Zagros suture zone. Structural and stratigraphic traps may have entrapped the generated hydrocarbons. The three drilled wells in the basin lack good reservoir rocks. However, low-velocity anomalies and bright spots indicate possible hydrocarbon accumulations in the basin.

The Mundeck Salt Unit: A Review of Aptian Depositional Context and Hydrocarbon Potential in the Kribi-Campo Sub-Basin (South Cameroon Atlantic Basin)

The Kribi-Campo sub-basin, located in the Gulf of Guinea, constitutes the southeastern segment of the Cameroon Atlantic Margin. Drilling in the Aptian salt unit revealed a sparse hydrocarbon presence, contrasting with modest finds in its counterparts like the Ezanga Salt in Gabon and the Rio Muni Salt in Equatorial Guinea. This discrepancy prompted a reassessment of the depositional context and hydrocarbon potential of the Mundeck salt unit. By integrating 2D seismic reflection and borehole data analysis, this study established the structural and stratigraphic framework of the area, emphasizing the salt unit’s significance. Borehole data indicate a localized salt unit offshore Kribi, with seismic reflection data revealing distinct forms of diapir and pillow. This salt unit displays a substantial lateral extent with thicknesses ranging from 4000 m to 6000 m. The depositional context is linked to the following two major geological events: a significant sea-level drop due to margin uplift during the Aptian and thermodynamic processes driven by transfer faults related to mid-oceanic ridge formation. These events were crucial in forming and evolving the Mundeck Salt. Regarding hydrocarbon prospects, this study identifies the unit as being associated with potential petroleum plays, supported by direct hydrocarbon indicators and fault-related structures. The findings suggest that untapped hydrocarbon resources may still exist, underscoring the need for further exploration and analysis.

Major tunnel valleys and sedimentation changes document extensive Early Pleistocene glaciations of the Barents Sea

Sedimentary records of Early Pleistocene (~2.6–0.8 Ma) glaciations are sparse on shelves, yet trough mouth fans on adjacent continental slopes provide a continuous record of ice-sheet and climate development throughout the Quaternary. Here, we interpret high-quality 3D seismic reflection data combined with borehole and chronostratigraphic information from a shelf-slope setting in the southwestern Barents Sea to study meltwater and sediment inputs to the deep ocean, focusing on the onset of Pleistocene glaciations. Sandy deposits were brought to the slopes of the high-latitude Bear Island Fan by a preglacial contourite-turbidite system from ⁓2.6–2.4 Ma. Muddy glacigenic debris flows document the first shelf-edge glaciation at ⁓2.4 Ma. From 1.78–0.78 Ma, muddy turbidity-current- and debris-flow-derived sediments were delivered from shelf to slope via six tunnel valleys measuring up to 12 km in width and 200 m in depth. These tunnel valleys and associated downslope deposits formed during the 41-kyr climate cycles of the Early Pleistocene, and evidence abundant channelized, meltwater discharges from these glaciations. Following the mid-Pleistocene transition to 100-kyr cycles, a change in the style of glaciation is suggested by a change in landform and facies associations consistent with a reduced meltwater contribution. This study shows that the Norwegian-Barents shelf was extensively glaciated in the Early Pleistocene, with a first shelf-edge glaciation from ~2.4 Ma.

Seismic stratigraphy and petroleum prospectivity in the Northern Rovuma Basin, offshore Tanzania

The upper slope area of the Northern Rovuma Basin has been poorly studied and little is known about its development and petroleum prospectivity. Interpretation of wellbore, 2D and 3D seismic reflection data in this area has allowed identification of seismic features reflecting key factors for understanding the development of the Cretaceous-Holocene stratigraphy and distribution of petroleum system elements. Our results show that infill of sediment into the basin was due to an interplay of three major factors. These are the sea level variations, extensional tectonics and sediment gravity flows. The Miocene and Pleistocene-Holocene tectonic events triggered gravity flows that supplied sediments to the basin. The resultant deposits include slides, slumps, debrites and turbidites some of which contain potential reservoirs that are interpreted to have been charged by the Permo-Triassic Karoo shales and Cretaceous-Cenozoic source rocks. These reservoirs are contained in both stratigraphic and structural traps with localized combinations in some places, and are encased by deep marine shales. Some of the potential reservoirs are positively inverted and compartmentalized, and they contain several bright and flat spots suggesting hydrocarbon accumulations within the Miocene and Oligocene intervals. It has also been revealed that major gravity flows and bottom currents, that supplied and distributed sediment to the basin, were confined in three long-lived channelized systems that were initiated during the Cretaceous (due to rapid regression), and the Oligocene and Pleistocene periods (due to rapid uplift). The channels migrated toward the southeast, with some shift toward the northeast, and had overall northeast traverse direction perpendicular to the shoreline. The reported gravity flows eroded previously deposited sediment in most places causing several unconformities in the whole Cretaceous-Holocene stratigraphy. Seismic stratigraphic interpretation and facies analysis have proved useful in the identification of key petroleum system elements and improve understanding of sedimentary fill evolution of the study area.

New understanding on the interplay of longitudinal and transverse sediment dispersal: Combination of 3D seismic profile and u-pb ages of detrital zircons of Paleogene sedimentary rocks in the northern South China Sea

The northern South China Sea (SCS) experienced a significant transition from a lacustrine to marine environment in the Paleogene, and its deep-water basin of Zhu-II Depression is in particular extensively studied due to its richness in oil and gas resources. However, limited number of boreholes in the deep-water area has long constrained a better understanding on the provenance of the Paleogene strata and the associated sediment transport processes. In this study, detrital zircon U-Pb ages and three-dimensional (3D) seismic-reflection data were systematically employed to investigate the “source-to-sink” pathways and interplay of longitudinal and transverse sediment dispersal. Our results indicate that the Zhu-II Depression sediments of the northern SCS were predominantly derived from the surrounding nearby paleo-uplifts in the early and middle Eocene. A significant provenance shift took place in the late Eocene, when the local paleo-uplift source was replaced by a distant source from the western SCS. Sediments were transported from west to east by the “Kontum-Ying-Qiong River” as a longitudinal dispersal. In the Oligocene, the “Kontum-Ying-Qiong River” delivered large amounts of sediments from Central Vietnam to the eastern part of the northern SCS. Meanwhile, the Pearl River gradually evolved through regional tectonic processes and influenced the deep-water area of Zhu-II Depression as a transverse dispersal. Sediments from both “Kontum-Ying-Qiong” and Pearl Rivers converged and deposited as deep-water deltas in the Zhu-II Depression. This dual provenance system in the northern SCS deep-water area was featured by the interplay between longitudinal and transverse sediment dispersal. It was largely controlled by the tectonic-palaeogeographic pattern inherited from the Mesozoic arc system.

Evolution of the transtensional Barreirinhas pull-apart system in the Brazilian Equatorial margin and its correlation with the African conjugate counterpart

The Barreirinhas pull-apart system encompasses marginal basins in divergent and transform margin segments in the central sector of the Brazilian Equatorial Margin and its African conjugate counterpart. This ancient pull-apart system evolved through transtensional strike-slip motion within a highly heterogeneous crystalline basement affected by multiple rift phases. The geometry and development of pull-apart structural elements during the final rifting phase before continental breakup and the mechanisms and extent to which they were influenced by preexisting crustal heterogeneities are comprehensively addressed using an extensive database of potential field (magnetic and gravity) and 2D seismic reflection data. We also assess the lithospheric thermomechanical conditions and their influence on transtensional extension throughout Curie Point Depth, Heat Flow, and Moho depth, derived from potential field data and published seismological models. Plate reconstruction of Brazilian and African equatorial margins based on gravity patterns and comparison with sandbox analog models allow a 3D synoptic model to reveal the Barreirinhas pull-apart system evolution during the Equatorial Atlantic opening. During the rift phase I, the location of major grabens was controlled by favorably oriented Neoproterozoic shear zones, while the cooler, stronger, and thicker crust beneath cratonic areas formed the western barrier to strike-slip rift activity during rift phase II. This same geological domain anchored the onset of the pull-apart system in the last rift phase III, whose principal displacement zones developed along the extensive oceanic fracture zones linked by sigmoidal fault systems. Toward the end of the rift phase, a large asymmetric lozangle to a lazy-Z-shaped, pull-apart basin developed above low overlapping ∼90°, releasing stepover in oblique transtensional strike-slip motion.

Late Cenozoic mass transport deposits in the offshore Tanzania continental margin

Sediment mass movements and their associated Mass Transport Deposits (MTDs) have been widely studied due to their economic and geohazard potentials. This study combines 2D and 3D seismic reflection data with a seismic facies approach and attribute analysis to reveal the presence and distribution of different MTDs in the southernmost region offshore Tanzania. Results of seismic facies analysis show that the study area contains different Late Cenozoic MTDs. The MTDs have limited petroleum reservoir potential and include slides, slumps, debris flow deposits and occasional turbidites. The formation of these MTDs was caused by tectonic events associated with the development of the East African Rift System. Seismic attribute maps have shown the locations of channels, remnant blocks, headwall scars, and grooves confirming downslope sediment mass mobilization. The seabed attribute maps have shown areas where recent mass mobilizations were initiated. Some of these areas coincide with faults which have dissected the seabed, forming potential future gravity failure sites. Other future gravity failure sites include channel banks and slope edges, which may be present over the whole Tanzania continental margin. Sediment mass movements may be catastrophic, and therefore future infrastructure installations in the area must involve detailed mapping of the seabed to assess geohazard risks and act accordingly.

Sedimentation record of a complete glacial-interglacial cycle: Down-slope deposits, contourites and plumites of the North Sea trough mouth fan

Trough mouth fans (TMFs) are major submarine depocentres that form in front of ice streams advancing onto the continental shelf, and they provide extensive records of past glaciations and ice-sheet dynamics. However, early research about TMFs was conducted using primarily 2D seismic data, which limits the insights on the deposit's geometries and internal structures and more recent studies using 3D data have focused on the general depositional history of TMFs. Here, we assess the spatial and temporal changes of the glacio-marine landforms and deposits throughout the last glacial-interglacial cycle (Marine Isotope Stage (MIS) 6 to 1, ∼130 ka to present) recorded in a >550 m thick progradational sequence. We use 3D reflection seismic data with significant vertical resolution (up to 2 m) imaging over 14000 km2 from the uppermost North Sea Fan (NSF) to document the seismic stratigraphy and sedimentary processes, by combining horizon picking and geomorphological analyses. The studied interval comprises five mappable units, four on the slope and one on the shelf, spanning from the modern seabed down to the top of the Tampen Slide (∼130 ka). Five different channel types (here included slide scars), as well as contourite and plumite packages are described based on their seismic facies, morphology, geometry, and stratigraphical position. We propose that contour currents are responsible for sediment delivery after the Tampen Slide deposition during the interglacial period before the onset of the Last Glacial Maximum, when high meltwater influx from the shelf produced turbidites. Sedimentation became debris-flow-dominated towards the end of the period of shelf-edge glaciation. The deglacial interval is characterized by the deposition of plumites on the slope. On the shelf, subglacial tills are deposited during both glacial and deglacial periods. We calculate an average sedimentation rate of <1 m/kyr during the interglacial (MIS 5-3), and around 50–65 m/kyr during the glacial and deglacial periods (MIS2-early MIS1). Thus, we document a change of two orders of magnitude in sedimentation rate during a glacial cycle on the slope of a glaciated margin.

Temporal and spatial characterization of a thermogenic, fault-controlled gas hydrate system, Woolsey Mound, Gulf of Mexico

Woolsey Mound, located at Mississippi Canyon Lease Block 118 (MC118), is the site of the Gulf of Mexico hydrate research consortium’s seafloor observatory, where gas hydrates outcrop at the seafloor. The presence of gas hydrates in the mound is confirmed directly by coring and indirectly by 3D seismic reflection data. Craters, pockmarks, chemosynthetic communities, and authigenic carbonates populate the seafloor at Woolsey Mound. Each crater is characterized by a network of shallow crestal faults that connect the hydrate mound to the underlying allochthonous salt body. We characterize the temporal and spatial evolution of gas hydrates at Woolsey Mound under natural perturbations using four collocated 3D seismic reflection data sets that span over 14 years. Data acquisition differences embedded in the data sets arising from variation in geometry, sample rate, and phase are minimized using the “cross-equalization” method. Our results indicate that hydrate formation and dissociation vary temporally and spatially in close connection to the shallow crestal faults. Evidence of gas hydrate dissociation is observed over a period of three years (2000–2003), where major dissociation occurred along the southern portion of the crestal fault in the southeast crater. The dissociation is less prominent in the southwest crater. Evidence of methane venting is observed between 2000 and 2010, which is mostly concentrated in the southeast crater. The residual amplitude anomalies observed between 2000 and 2014 in the mound are mostly positive, implying that the methane venting had increased significantly. The positive anomalies are correlated with the methane seepage recorded in 2011. Our results indicate the evolution of a fault-controlled gas hydrate system in the northern Gulf of Mexico, which would aid in assessing its impact on the seafloor.

Interaction between active tectonics, bottom-current processes and coral mounds: A unique example in the NW Moroccan Margin, southern Gulf of Cadiz

The NW Moroccan Margin has a complex geological evolution, being located close to the transition zone between the Azores – Gibraltar Fracture Zone and the western front of the Betic–Rif collisional orogen. The interaction between tectonic, halokinetic and fluid flow processes with bottom-current activity shapes the seafloor and influences the distribution of seafloor biological communities (such as the cold-water coral mounds) and deep-water sedimentation. The aims of this work are to study the interaction of the paleo-oceanographic and morpho-tectonic processes that generated the various seafloor features of the NW Moroccan Margin. To achieve this, high-resolution multibeam bathymetry and parasound data acquired in the “ALBOCA II” cruise have been used, complemented by high-resolution 2D seismic reflection data and the EMODnet bathymetric compilation.Several morphological features were identified in the margin, which are related to different processes of sedimentary (contourites and sediment waves), structural (faults and diapirs), gravitational (slide scars, mass transport deposits), fluid migration (mud volcanoes and pockmarks) and biogenic (exposed and buried coral mounds) nature. The structural features (e.g., strike-slip faults) have a major control on the seafloor morphology and, consequently, on the development and evolution of the sedimentary systems in the study area.The evolution of the NW Moroccan Margin during the late Quaternary has been controlled by climatic variations and tectonic activity. The action of these factors has been dominant in distinct parts of the study area where: i) contourite terraces developed when climatic and oceanographic changes were the prevalent factor, ii) mounded and confined contourite drifts and local mass transport deposits formed when the major control was tectonic activity.

Carbonate mounds formed by mud volcanism at the Cretaceous-Paleogene boundary, Saudi Arabia

More than 1000 mound structures have been mapped in shallow marine sediments at the Cretaceous-Paleogene boundary in the Rub’ Al-Khali of Saudi Arabia. Mapping used 3D reflection seismic data in a 37,000 km2 study area. No wells penetrate the mounds themselves. The mounds are at a present-day subsurface depth of approximately 1 km, and they are convex-up with diameters of 200–400 m and elevation of 10–15 m. The mounds display spatial self-organization with a mean separation of approximately 3.75 km. Comparison with mound populations in other study areas with known spatial distribution statistics and modes of origin indicates that the mound population in this study has the characteristics of fluid escape structures, and they are interpreted here as mud volcanoes. The observation that the mounds occur at the Cretaceous-Paleogene boundary demands a singular trigger at that moment in time. We develop a model of seismic energy-related mud volcanism mechanism including the Chicxulub asteroid impact as the energy source that accounts for the timing of the mound structures and a drainage cell model based on producing water wells that provides a mechanism for spatial self-organization into a regular pattern.

The role of ice-sheet dynamics in the Miocene-Pliocene depositional systems of the Ross Sea, Antarctica

The dynamics of the Antarctic ice sheet (AIS) have profound implications for the evolution of the Antarctic continental margin, global ocean currents, and climate changes. Marine sediments from the Antarctic continental margins recorded the history of the advance and retreat of the AIS. In this study, we present an integrated analysis of the sedimentary characteristics of the Early Miocene to Late Miocene of the Ross Sea by using 2D seismic reflection data and cores from International Ocean Discovery Program (IODP) Expedition 374 Sites U1521, U1522, and U1524. The characteristics of the seismic facies and sediments show that the expansion and grounding of the ice sheets across the continental shelf significantly influenced the depositional processes, leading to increased glacial erosion, the formation of prograding wedges, mass transport deposits (MTDs), and mixed (turbidite-contourite) depositional systems since the Early Miocene. The seaward migration of the continental shelf edge and the steepening of the continental slope were mainly influenced by the glaciation of extreme expansion of the AIS. Marked increases in the prograding wedge and MTD are associated with extensive sediment reworking and deposition at the grounding zones and along the continental slope as a result of ice sheet expansion. The development of the mixed (turbidite-contourite) depositional systems was the result of extensive sediment reworking and deposition by gravity flows and bottom currents on the continental slope and the rise. This research provides new insights into the complexity of the ice sheet and the sensibility of marginal sediments in responding to the past climate changes in Antarctica.

Integration of Seismic and Well Log Data for Reservoir Characterization in Offshore Niger Delta, Nigeria

The demand for fossil fuels is continually increasing due to the growing global population and industrialization. It is thus necessary to find hydrocarbon prospects in new fields and those that have previously been classified as marginal fields in order to maximize production. An integrated approach is required to effectively characterize hydrocarbon reservoirs and assess their ability to store and produce hydrocarbons. 3D seismic reflection data and well log data were combined to quantitatively estimate hydrocarbon reserves in a field, offshore Niger delta, Nigeria. The reservoirs were delineated on the gamma ray and resistivity logs which penetrate four wells selected from the field. The petrophysical analysis provided information about the net-to-gross thickness ratio, porosity, shale volume and water saturation of the reservoirs, deduced from well log suites comprising gamma, resistivity, density and neutron-porosity logs through four wells. The seismic interpretation involved mapping of horizons and faults across the wells on the seismic section. Check shot data were used to tie the seismic data to the well log data to generate the synthetic seismogram. The time structural and depth structural maps were generated. The volumetric analysis entailed derivation of the Gross rock volume from the depth structural map, and estimation of the Stock Tank Oil Initially In Place (STOIIP). Four reservoirs were delineated in each of the four wells. The average thickness of the reservoirs ranges from 56.6 m to 232.7 m while the water saturation varies from 0.29% to 0.57%. The average porosities of the reservoirs ranges from 0.18% to 0.22%. The structural interpretation of the eight faults mapped reveals synthetic and antithetic faults, and rollover anticlines. The time- and depth structural maps generated from the mapped horizons show that the reservoirs are penetrated by the different faults. The Stock Tank Oil Initially In Place (STOIIP) of the reservoirs range from 25 MMstb to 468 MMstb. The study shows that the integration of 3D reflection data and well log data can be used effectively to estimate hydrocarbon reserves. The results of the study are expected to contribute to the development of new exploration and production strategies in the Niger delta basin and similar sedimentary environments.

Geohazard features of the Ligurian Sea

ABSTRACT We present the characterization of geohazard-related features of the Ligurian Sea with the map of its physiographic domains (1:250,000 scale) and five maps (1:100,000 scale) of the morphological and morpho-bathymetric elements. These were realized in the framework of the MaGIC (Marine Geohazard along Italian Coasts) project, promoted by the Italian Civil Protection Department. The characterization of submarine geohazards along continental margins, together with mapping of marine geological features are critical for the management of coastal risks. Multibeam bathymetric data combined with high-resolution 2D reflection seismic data, allowed to identify and map the main tectono-sedimentary features related to mass movements along the Ligurian continental margin. A dense grid of seismic profiles allowed to improve the comprehension of the margin structure as well as its recent tectonic activity providing new insights concerning mass wasting processes and active tectonics relationships to plan further, focalized investigations in areas of maximum risk.

3D seismic analysis of complex faulting patterns and fluid escape features and their relation to Late Cenozoic Magmatism in the Bass Basin, offshore SE Australia

Abstract Igneous intrusions in sedimentary petroleum basins are often perceived as having a negative impact on the elements of the petroleum system, though the impact of intrusion-related deformation features on petroleum systems and broader geoenergy applications is not well understood. In this study, we use 3D seismic reflection data to document a variety of deformation styles that are spatially and temporally associated late Cenozoic magmatic activity in the Bass Basin, offshore southeastern Australia; three types of normal fault systems (conjugate faults, concentric faults, radial faults) and fluid escape pipes. These deformation features occur in the overburden up to ∼600 m above underlying igneous intrusions, within the Eocene to Miocene Demons Bluff and Torquay formations. The conjugate faults bound graben and are interpreted to have formed in response to underlying dyke intrusions. The radial faults are interpreted to have formed in response to overburden uplift, though the link between these and associated igneous activity is less clear. We identify 101 fluid escape features that show variation in both the morphology of their surficial depressions and of the seismic reflection characteristics of their infilling deposits. These features are interpreted to be hydrothermal or volcanic vents with underlying pipe-like feeders, depending on their spatial association with adjacent or underlying igneous intrusions. The concentric fault systems are associated with surficial depressions, and quantitative analysis of reflection sags within these depressions suggest that they are a result of subsurface subsidence in response to formation of maar-craters. The intrusion-related deformation features documented in this study may have multiple effects on working petroleum systems, such as providing secondary fluid flow pathways that can either reduce seal integrity, or enabling migration of fluids into shallower reservoirs.

Use of resistivity and density borehole image logs to identify and distribute facies in the Pikka unit — A case study from the Nanushuk Formation, North Slope, Alaska

Over the past few decades, the North Slope of Alaska has yielded several major hydrocarbon discoveries in the deltaic topsets of the Brookian Nanushuk Formation. Together, the Nanushuk topsets and genetically related foreset and bottomset beds of the Torok Formation comprise part of a giant clinothem system that prograded across the Colville Foreland Basin during the lower Cretaceous (the Aptian through the Cenomanian). The Nanushuk Topset Play contains stratigraphically trapped hydrocarbons within multiple fairways trending roughly north to south along the basin’s extent. Inside the Pikka Unit, the Nanushuk Formation represents a shelf-edge delta and attached shoreface system, defined primarily from sedimentological interpretations of conventional cores integrated with 3D seismic reflection data and well-log motifs. In this study, we build a structural and stratigraphic framework for the Nanushuk reservoir across the Pikka Unit through integrated observations of the borehole image logs, seismic data, and core. In the described workflow, the boundaries delimiting dip zones interpreted in the wells are correlated to higher order stratigraphic cycles within the Nanushuk clinothem zone. These boundaries are observed in seismic profiles and provide the basis of the structural framework. In addition, core facies interpretations are calibrated to CT-scan data to establish each facies character and vertical distribution within the wells. In the absence of core data, core-calibrated borehole images are instrumental in guiding sedimentological and structural interpretations. This extrapolation is dependent on the image log quality and resolution. The calibrated facies interpretations are applied to wells without core data and guided by seismic amplitude interpretation to extrapolate reservoir presence and distribution across the area.

Unsupervised machine learning and depth clusters of Euler deconvolution of magnetic data: a new approach to imaging geological structures

We present a novel approach that determines the location and dip of geologic structures by clustering Euler deconvolution depth solutions using Density-Based Spatial Clustering Applications with Noise (DBSCAN). This method and workflow rely on the association of changes in the location and relationships between Euler depth clusters and cluster boundaries with changes in rock susceptibility. We applied our method to global magnetic and high-resolution aeromagnetic datasets over Phanerozoic-Precambrian zone-bounding faults in west and central Victoria. The architecture of these structures at different scales from this imaging technique is comparable to interpreted 2D seismic reflection data. The results from the global magnetic data resolved the architecture of these structures below 5 km, while the aeromagnetic data used were limited to structural information of faults above 2 km depth. Therefore, this method shows the structural relationship of the west-dipping Avoca Fault that soles into the east-dipping Moyston Fault at a depth of ∼22 km in central Victoria and at a shallower depth of ∼15 km southward beneath the Quaternary basaltic rocks of the Newer Volcanic Province. In the vicinity of the Heathcote Zone, the method resolves the location, dip, and overprinting relationship between faults and extrusive rocks, such as the relationship between the Heathcote and Mount William Faults and the granitic Cobaw Batholith. We show how combining magnetic data at various scales can track faults from the near-surface to deeper roots while avoiding possible over-interpretation. We demonstrate how to optimise the DBSCAN parameters and a sensitivity analysis of how to determine clusters and cluster boundaries that are geologically relevant in the absence of geological constraints. Our technique provides an effective and rapid tool for imaging structures and can supplement complex and expensive imaging techniques to resolve the architecture of structures in complex geologic terrains.

Imaging Pleistocene volcanic edifices along the Egyptian Red Sea margin: Insights from reflection seismics and 3D constrained inversion of gravity and magnetic data

Several volcanic buildups have been documented using gravity and magnetic data at specific locations in the Northern Red Sea (NRS). Most of these volcanoes were never sampled, and only a few were imaged by seismic or bathymetry data. Furthermore, the confidentiality of commercial datasets does not allow adequate knowledge of these structures and their morphology and physical properties. In this study, 2D and 3D seismic reflection data and 3D constrained inversion of magnetic and gravity data have been used to infer densities and magnetic susceptibilities of volcanic features in the central part of the NRS and to evaluate the distribution and geometry. This study indicates that the results of the 3D inverted models show a good fit with the volcanic structures inferred from seismic data and, thus, that the inversion technique adopted can be a reliable tool for detecting other edifices where seismic data are missing. The 3D inverted density and magnetic susceptibility models suggest that at least eight isolated structures with similar gravity and magnetic properties exist in the study area. They are associated with high densities and magnetic susceptibility anomalies with average values of 2700 kg/m3 and 0.025 SI, respectively. These magmatic structures are deeply rooted in the sedimentary cover and emerge at elevations of 100 to >650 m relative to the seabed. They developed in a sector interpreted as containing thinned continental crust, accompanied by the ascension of magma through prominent rift-related normal faults. Magmatic activity likely started in the Pleistocene and continues to the present day.

Evolution of Mesozoic paleo-uplifts and differential control on sedimentation on the southern margin of Kuqa Depression, Tarim Basin

The paleo-uplift is an important tectonic element which is key to control the sedimentary system in petroleum basins. The evolution of Mesozoic paleo-uplifts and differential control on sedimentation on the southern margin of Kuqa Depression, northern Tarim Basin, is still unclear, restricting successful petroleum exploration and development. Based on borehole and 3D seismic reflection data on the southern margin of the Kuqa Depression, the parameters of paleo-uplifts, such as residual thickness, eroded thickness, slope height, slope angle, slope height difference were extracted. Combined with the composition of the detrital minerals in the Cretaceous Shushanhe Formation which was one of the target layers and the Paleo-lithofacies map before the deposition of Cretaceous, the paleo-uplifts could be further divided into four sub-uplifts. The paleo-uplifts grew and extended in the Triassic to Jurassic, decreased in the Jurassic to Cretaceous, and transformed into subaqueous low uplift in the upper part of Cretaceous Shushanhe Formation. The evolution of paleo-uplifts controlled strata and facies, resulting in no Triassic strata were deposited in the north of Yaha-Kudong and Luntai sub-uplifts, while the Jurassic strata in the Xinhe and Qiaogu sub-uplifts experienced extensive erosion. The faults in the Xinhe sub-uplift and steep slopes in the Luntai sub-uplift controlled the deposition of alluvial fans and fan deltas, while the gentle slopes of Qiaogu and Yaha-Kudong sub-uplifts controlled the distribution of braided river deltas. The evolution of the paleo-uplifts was synchronized with regional tectonism, including the south Tianshan collision orogeny and the post-orogenic stress relaxation. This study will help elucidate the development and evolution of the paleo-uplifts on the southern margin of Kuqa Depression, northern Tarim Basin, clarify the relationship between provenance and sedimentary system, and guide the oil and gas exploration in Tarim Basin and other basins with the similar background globally.