Seismic Stratigraphic Interpretation Research Articles

Seismic stratigraphy analysis of main controlling factors of Lower Wuerhe Formation reservoir in Manan area

Fan delta sedimentary reservoirs developed in the Lower Wuerhe Formation of the Manan Slope in the Mahu Sag of the Jungger Basin have good prospects for oil and gas exploration and development. In order to clarify the high-quality reservoir system and the distribution range of the reservoir plane, a seismic stratigraphic interpretation of the Lower Wuerhe Formation is carried out in combination with geology, logging and 3D seismic data. The Lower Wuerhe Formation is divided into three stratigraphic series, a total of 8 four-level sequences, and 8 water body lifting cycles. Through seismic wave group and sedimentary evolution analysis, combined with pseudo-acoustic impedance amplitude and production test analysis, the high-quality oil-bearing reservoirs of the Lower Wuerhe Formation are mainly the third member of the Lower Wuerhe Formation. Oil-bearing reservoirs are mainly controlled by sedimentary facies belts caused by the ups and downs of water bodies. The well-developed oil-bearing reservoirs are developed in the fan delta plain-fan delta front-shore shallow lake sedimentary system.

Quantitative seismic-stratigraphic interpretation of the evaporite sequence in the Santos Basin

On the account of the absence of modern analogues, the interpretation of evaporite-bearing basins relies extensively on seismic and well data. Recent studies describe the intrasalt kinematic, geometries and compositions, relating the change of reflection patterns in seismic data to variations in evaporite sequences. However, these interpretations are only qualitative. This study describes a step further in proceeding from qualitative to quantitative interpretation of an evaporite-dominated interval. It integrates geophysical and geological foundations by combining rock physics, seismic inversion and statistical techniques to deliver seismic-driven facies volume of the evaporite sequence in the Santos Basin, offshore Brazil. Synthetic seismogram demonstrate the ambiguities and uncertainties in relating the seismic amplitude to salt types. Rock-physics analysis indicates that acoustic impedance is an effective differentiator of salt types in comparison to seismic amplitude. Therefore, we perform seismic inversion to transform interface property into layer property. The acoustic impedance volume mitigated significantly the risk of seismic interpretation in the salt sequence. The Bayesian classification integrates acoustic impedance and rock-physics analysis to deliver the seismic-driven facies volume, which categorizes bittern salts, halite and anhydrite. This enables the refinement of the seismic-stratigraphic interpretation of intrasalt sequences of the Ariri Formation based on the sedimentary cycles of evaporites. Additionally, we calculate proportion maps to evaluate the spatial variability of salt deposition. We observe an increase in bittern salts and anhydrite proportions from the bottom to the top of the sequence. The comparison between well-based and seismic-based proportions testifies to the quantitative potential of seismic data. The approach provides quantitative analysis of the evaporite sequence and can be applied to other salt-bearing basins.

Integrated Morpho-Bathymetric, Seismic-Stratigraphic, and Sedimentological Data on the Dohrn Canyon (Naples Bay, Southern Tyrrhenian Sea): Relationships with Volcanism and Tectonics

Submarine canyons are geomorphologic lineaments engraving the slope/outer shelf of continental margins. These features are often associated with significant geologic hazard when they develop close to densely populated coastal zones. The seafloor of Naples Bay is deeply cut by two incisions characterized by a dense network of gullies, namely the Dohrn and Magnaghi canyons, which develop from the shelf break of the Campania margin, down to the peripheral rise of the Eastern Tyrrhenian bathyal plain. Seismic-stratigraphic interpretation of multichannel seismic reflection profiles has shown that quaternary tectonics and recent to active volcanism have exerted a significant control on the morphological evolution and source-to sink depositional processes of the Dohrn and Magnaghi submarine canyons. The Dohrn canyon is characterized by relatively steep walls hundreds of meters high, which incise a Middle-Late Pleistocene prograding wedge, formed by clastic and volcaniclastic deposits associated with the paleo-Sarno river system during the Mid-Late Pleistocene. The formation of the Dohrn canyon predates the onset of the volcanic eruption of the Neapolitan Yellow Tuff (NYT), an ignimbrite deposit of ca. 15 ka that represents the bedrock on which the town of Napoli is built. Integrated stratigraphic analysis of high-resolution seismic profiles and marine gravity core data (C74_12) collected along the flanks of the eastern bifurcation of the head of Dohrn Canyon suggests that depositional processes along the canyon flanks are dominated by gravity flows (e.g., fine-grained turbidites, debris flows) and sediment mass transport associated with slope instability and failure.

Seismic stratigraphy interpretation by deep convolutional neural networks: A semisupervised workflow

Depicting geologic sequences from 3D seismic surveying is of significant value to subsurface reservoir exploration, but it is usually time- and labor-intensive for manual interpretation by experienced seismic interpreters. We have developed a semisupervised workflow for efficient seismic stratigraphy interpretation by using the state-of-the-art deep convolutional neural networks (CNNs). Specifically, the workflow consists of two components: (1) seismic feature self-learning (SFSL) and (2) stratigraphy model building (SMB), each of which is formulated as a deep CNN. Whereas the SMB is supervised by knowledge from domain experts and the associated CNN uses a similar network architecture typically used in image segmentation, the SFSL is designed as an unsupervised process and thus can be performed backstage while an expert prepares the training labels for the SMB CNN. Compared with conventional approaches, the our workflow is superior in two aspects. First, the SMB CNN, initialized by the SFSL CNN, successfully inherits the prior knowledge of the seismic features in the target seismic data. Therefore, it becomes feasible for completing the supervised training of the SMB CNN more efficiently using only a small amount of training data, for example, less than 0.1% of the available seismic data as demonstrated in this paper. Second, for the convenience of seismic experts in translating their domain knowledge into training labels, our workflow is designed to be applicable to three scenarios, trace-wise, paintbrushing, and full-sectional annotation. The performance of the new workflow is well-verified through application to three real seismic data sets. We conclude that the new workflow is not only capable of providing robust stratigraphy interpretation for a given seismic volume, but it also holds great potential for other problems in seismic data analysis.

Seismic stratigraphy of a deep water basin in the Brazilian equatorial margin: the eastern portion of Potiguar Basin and Touros High

The Brazilian Continental Margin (BEM) deep-water regions contain important geological features, although the area is poorly explored beyond the continental shelf-break. The main objective of this study is to seismically characterize syn- and post-rift sequences and certain seamounts that are part of the Fernando de Noronha Ridge (FNR) in deep-water basins and are off of the shore of northeastern Brazil. We used 2D post-stack high-resolution seismic sections to distinguish syn-rift, post-rift, and drift tectono-depositional phases. Three seismic horizons (R1 to R3) could represent, respectively, the following: an acoustic basement top, a rift top, and a highstand system tract (drift). The syn-rift stage is marked by discontinuous parallel reflectors with low amplitude and low frequency, which are offset by normal faults in half-grabens. The post-rift and drift stages are characterized by continuous parallel reflectors with low to high amplitude and frequency. Chaotic seismic reflections within the seamounts indicate their volcanic origins. Volcanic intrusions affected syn-rift, post-rift, and drift sequences and partially confine the deep-water basin deposition. The magmatic event occurred once the preexistent material and the sediment deposited after the seamount rises were partially confined by the continental slope and the seamounts. Seismic stratigraphy interpretation and its correlation with volcanic activities indicate a relative chronological control relating the emplacement of the seamounts to the Early Eocene to Late Miocene. Volcanic episodes seem to have created volcanoclastic deposits marked by a disorganized/chaotic seismic pattern with few continuous reflectors, indicating interbedded magma flows with sedimentary material. This paper provides an initial observation regarding the deep-water basin deposits on syn- and post-rift stages in the NE portion of the BEM.

Evaporite occurrence and salt tectonics in the Cretaceous Camamu-Almada Basin, northeastern Brazil

The Camamu-Almada basin is located at the South Atlantic Margin and, despite the availability of seismic data and the evidence of its hydrocarbon potential, is still considered a new exploratory frontier. In this study, the authors used fifty 2D seismic lines and twelve wells to: a) present a seismic stratigraphic interpretation of the transitional phase (i.e., the strata between the rift and the drift stages; b) investigate the distribution of evaporite deposits at the study area; b) verify the impacts of salt tectonics in the deep-water region, using basins situated in the same geotectonic context as reference. The development of the South Atlantic margin resulted in the formation of several rift basins - including the Camamu-Almada basin – and occurred through four tectonic phases: pre-rift, rift, transitional and drift. The regional deposition of evaporites marks the transitional phase, with occurrences both in Brazil and West Africa that increases in thickness and width southwardly. This work details that in the study area, the salt moved laterally and vertically, forming a highly deformed deposit that marks salt deflation and salt inflation zones, directly associated respectively with diapirs and mini-basins. Features related to salt tectonics that can be directly related to processes of migration and accumulation of hydrocarbons in the study area are also described.

Tectonic, Oceanographic, and Climatic Controls on the Cretaceous‐Cenozoic Sedimentary Record of the Australian‐Antarctic Basin

AbstractUnderstanding the patterns and characteristics of sedimentary deposits on the conjugate Australian‐Antarctic margins is critical to reveal the Cretaceous‐Cenozoic tectonic, oceanographic, and climatic conditions in the basin. However, unraveling its evolution has remained difficult due to the different seismic stratigraphic interpretations on each margin and sparse drill sites. Here, for the first time, we collate all available seismic reflection profiles on both margins and use newly available offshore drilling data to develop a consistent seismic stratigraphic framework across the Australian‐Antarctic basins. We find sedimentation patterns similar in structure and thickness, prior to the onset of Antarctic glaciation, enabling the basinwide correlation of four major sedimentary units and their depositional history. We interpret that during the warm and humid Late Cretaceous (~83–65 Ma), large onshore river systems on both Australia and Antarctica resulted in deltaic sediment deposition offshore. We interpret that the onset of clockwise bottom currents during the early Paleogene (~58–48 Ma) formed prominent sediment drift deposits along both continental rises. We suggest that these currents strengthened and progressed farther east through the Eocene. Coevally, global cooling (<48 Ma) and progressive aridification led to a large‐scale decrease in sediment input from both continents. Two major Eocene hiatuses recovered by the Integrated Ocean Discovery Program site U1356A at the Antarctic continental slope likely formed during this preglacial phase of low sedimentation and strong bottom currents. Our results can be used to constrain future paleo‐oceanographic modeling of this region and aid the understanding of the oceanographic changes accompanying the transition from a greenhouse to icehouse world.

Improving three-dimensional high-order seismic-stratigraphic interpretation for reservoir model construction: An example of geostatistical and seismic forward modeling of Permian San Andres shelf–Grayburg platform mixed clastic–carbonate strata

The three-dimensionally complex, highly progradational mixed siliciclastic–carbonate strata of the San Andres and Grayburg Formations have long been the backbone of conventional hydrocarbon reservoir production from the Permian Basin, and significant recovery continues via waterflooding and CO2 injection. Besides, nonreservoir equivalents of these formations have recently taken increasing significance as produced water disposal targets. However, seismic-stratigraphic interpretations are challenged by complex internal shelfal-stratal geometries and numerous laterally continuous but vertically thin fluid barriers in overlying platforms. We built a three-dimensional (3-D) geocellular model of Guadalupian 8–13 high-frequency sequences (G8–G13 HFSs) and then conducted forward seismic modeling (35-Hz 0° phase). This allows investigations on the validity of applying conventional reflection-geometry–based interpretation to delineate the G9 HFS top and base, which can potentially serve as bounding/constraining surfaces for upper San Andres shelf–Grayburg platform reservoirs. This study contributes to 3-D modeling methodologies by introducing a query tree to select geostatistical methods for modeling dual-scale heterogeneities and by integrating data from diverse sources for seamless and realistic 3-D models. Our seismic-stratigraphic evaluation demonstrates that conventional reflection–geometry-based interpretation does not adequately resolve the G9 top and base; deviations from the geocellular model reach up to 80 m (260 ft) and are thus well beyond the maximum acceptable error limits of ±0.5 wavelength. We suggest improving conventional interpretations of the G9 base by selective interpolation or mixed-polarity event picking near the error-prone shelf margin and upper slope. Besides, instead of picking the highly discontinuous seismic peak as G9 top, bulk-shifting of a shallower trough horizon near actual G10 top should deliver a more accurate surface representing G9 top.

Full-volume 3D seismic interpretation methods: A new step towards high-resolution seismic stratigraphy

Following decades of technological innovation, geologists now have access to extensive 3D seismic surveys across sedimentary basins. Using these voluminous data sets to better understand subsurface complexity relies on developing seismic stratigraphic workflows that allow very high-resolution interpretation within a cost-effective timeframe. We have developed an innovative 3D seismic interpretation workflow that combines full-volume and semi-automated horizon tracking with high-resolution 3D seismic stratigraphic analysis. The workflow consists of converting data from seismic (two-way traveltime) to a relative geological time (RGT) volume, in which a relative geological age is assigned to each point of the volume. The generation of a horizon stack is used to extract an unlimited number of chronostratigraphic surfaces (i.e., seismic horizons). Integrated stratigraphic tools may be used to navigate throughout the 3D seismic data to pick seismic unconformities using standard seismic stratigraphic principles in combination with geometric attributes. Here, we applied this workflow to a high-quality 3D seismic data set located in the Northern Carnarvon Basin (North West Shelf, Australia) and provided an example of high-resolution seismic stratigraphic interpretation from an Early Cretaceous shelf-margin system (Lower Barrow Group). This approach is used to identify 73 seismic sequences (i.e., clinothems) bounded by 74 seismic unconformities. Each clinothem presents an average duration of approximately 63,000 years (fifth stratigraphic order), which represents an unprecedented scale of observation for a Cretaceous depositional system on seismic data. This level of interpretation has a variety of applications, including high-resolution paleogeographical reconstructions and quantitative analysis of subsurface data. This innovative workflow constitutes a new step in seismic stratigraphy because it enables interpreters to map seismic sequences in a true 3D environment by taking into account the full variability of depositional systems at high frequency through time and space.

Tectonostratigraphic framework and depositional history of the deepwater Ulleung Basin, East Sea/Sea of Japan

AbstractThe Ulleung Basin, East Sea/Japan Sea, is a Neogene back‐arc basin and occupies a tectonically crucial zone under the influence of relative motions between Eurasian, Pacific and Philippine Sea plates. However, the link between tectonics and sedimentation remains poorly understood in the back‐arc Ulleung Basin, as it does in many other back‐arc basins as well, because of a paucity of seismic data and controversy over the tectonic history of the basin. This paper presents an integrated tectonostratigraphic and sedimentary evolution in the deepwater Ulleung Basin using 2D multichannel seismic reflection data. The sedimentary succession within the deepwater Ulleung Basin is divided into four second‐order seismic megasequences (MS1 to MS4). Detailed seismic stratigraphy interpretation of the four megasequences suggests the depositional history of the deepwater Ulleung Basin occurred in four stages, controlled by tectonic movement, volcanism, and sea‐level fluctuations. In Stage 1 (late Oligocene through early Miocene), syn‐rift sediment supplied to the basin was restricted to the southern base‐of‐slope, whereas the northern distal part of the basin was dominated by volcanic sills and lava flows derived from initial rifting‐related volcanism. In Stage 2 (late early Miocene through middle Miocene), volcanic extrusion occurred through post‐rift, chain volcanism in the earliest time, followed by hemipelagic and turbidite sedimentation in a quiescent open marine setting. In Stage 3 (late middle Miocene through late Miocene), compressional activity was predominant throughout the Ulleung Basin, resulting in regional uplift and sub‐aerial erosion/denudation of the southern shelf of the basin, which provided enormous volumes of sediment into the basin through mass transport processes. In Stage 4 (early Pliocene through present), although the degree of tectonic stress decreased significantly, mass movement was still generated by sea‐level fluctuations as well as compressional tectonic movement, resulting in stacked mass transport deposits along the southern basin margin. We propose a new depositional history model for the deepwater Ulleung Basin and provide a window into understanding how tectonic, volcanic and eustatic interactions control sedimentation in back‐arc basins.

High Resolution Seismic for sequence stratigraphy interpretation of shallow sediments in the center Continental Shelf of Vietnam

Seismic stratigraphy analysis based on sequence stratigraphy has been developed strongly over the world. However, due to differences in development system of sedimentary basins, the analysis is different from place to place. In this paper, the authors will present seismic stratigraphy interpretation of sequence stratigraphy on shallow sediments of continental shelf of Vietnam, using HRS, determining the sedimentary system tracts and sequences in 4rd or 5th order, the relationship between sedimentary cycles, sea level change and tectonic movement, facial-paleogeographic characteristics and geological development history of Pliocene-Quaternary in the area. The interpreted seismic stratigraphic features assisted in defining the gross depositional environments, the relative sea level changes, shale/sand ratios, and locations of carbonate reefs and igneous rocks in the area

Characterization of lower Vaca Muerta at Fortín de Piedra in Neuquén Basin, Argentina

The Vaca Muerta Formation in the Fortín de Piedra Block is a current focus of exploration for hydrocarbons. Here, we investigate its deepest levels, La Cocina and El Orgánico. These levels have high average total organic content (TOC) of 4.5 and 3 wt%, respectively, making them the main exploration targets. Seismic stratigraphic interpretation indicates that La Cocina was deposited over a paleo-dune surface, initially covering it as a sheet but later forming discontinuous lenses as the interdune areas filled in. El Orgánico is an aggradational-progradational section, represented mainly by bottomset facies and subordinated foreset facies. The brittleness and TOC distribution, as correlated with well log and laboratory measurement data, suggest that the entire block is prospective for both levels.

Seismic stratigraphy of a Lower Cretaceous prograding carbonate platform (Oman) and implications for the eustatic sea-level curve

The Lower Cretaceous of northern Oman consists of a large carbonate platform that prograded over a distance of 280 km (174 mi) in approximately 23 m.y. The seismic stratigraphic interpretation of this system, based on a regional three-dimensional survey (40,000 km2 [15,400 mi2]), revealed a complicated organization of nested clinoforms with changing depositional dips. The tectonic setting and stratal patterns suggest that different orders of sea-level fluctuations, ranging from 20 to 150 m (66–492 ft) in amplitude, have controlled the overall sedimentation. The Lower Cretaceous Lekhwair, Habshan, and Salil Formations form the lithofacies of this carbonate platform that prograded in a northeastward direction from the United Arab Emirates and Oman to northern Oman, filling in the Rayda Basin. The majority of this system is documented in seismic and well data, whereas the final part of the progradation is visible on outcrops in the Oman Mountains. Cored wells and outcrops have been dated with calpionellids, echinoids, and calcareous algae biostratigraphy; 14 sequences have been identified and are grouped into four sequence sets based on their seismic stratigraphic organization. The differences in stratal patterns between the sets are interpreted to be caused by variations in the amplitude of sea-level fluctuations. The sequence sets indicate a general increase of the amplitude of sea-level fluctuations to a maximum of 150 m (492 ft) in the early Valanginian, followed by a general highstand and low-amplitude fluctuations (20 m [66 ft]) in the late Valanginian. The Oman relative-sea-level curve shows similarities with the one proposed for the Vocontian Basin in France, providing strong evidence for the eustatic nature of these fluctuations. A glacio-eustatic control is invoked to explain this global trend.

Tectonostratigraphic framework of the Lower Keraudren Formation, Bedout Sub-basin: interplay of tectonics and sedimentary systems

Recent drilling activity and new seismic data have contributed to the understanding of the Lower Keraudren Formation in the Bedout Sub-Basin. The Lower Keraudren Formation is a thick (>5 km) succession of strata that was deposited rapidly during the Anisian of the Middle Triassic. Distinctive characteristics related to sediment provenance, sediment supply and accommodation have facilitated subdivision of the Formation into eight informal units: the Milne, Crespin, Baxter, Caley, Hove, Barret, Palma, and Huxley members. Tectonic elements of the East Gondwana Interior Rift and the Bedout High influenced the Sub-basin geometry during deposition of the Lower Keraudren. Extensional tectonics of the East Gondwana Interior Rift generated a series of Palaeozoic tilted fault blocks and grabens, which influenced the stratigraphic architecture, sediment dispersal patterns and distribution of reservoir and source rock facies. The structurally proud Bedout High, a roughly circular (~60 km wide) igneous feature, created a northern boundary to deposition. Seismic stratigraphic interpretation has characterised the interval as a series of north west prograding wedges. Well based data indicates the section is dominated by fluvio-deltaic deposits. Separating the Caley and Hove Members is a significant unconformity that is associated with renewed uplift of the Bedout High and a change in sediment provenance. Chemostratigraphy and petrology indicates the Caley and older strata were derived from a more mature sediment source, whereas the Hove and younger a more immature metamorphic source. Distinct changes in reservoir quality are observed above and below the Caley–Hove unconformity. Below the unconformity, the older, more mature sandstones exhibit superior reservoir quality compared with the younger, more immature sandstones.

Različiti pristupi u seizmostratigrafskoj interpretaciji

This paper presents two basic approaches in seismic stratigraphy interpretation. The first one as starting point have seismic sections, whose interpretation in the later stage correlates with well data. The second one in initial phase analyze the data obtain by deep well drilling which are later correlated with the seismic sections. The chronological order and seismic stratigraphy procedure are explained for both approaches. Those interpretation approaches enabled oil companies a detailed and more precise insight into geological features, reduction of exploration risk and more rational design of development wells.

Nonlinear anisotropic diffusion techniques for seismic signal enhancing - Carpathian Foredeep study

The use of nonlinear anisotropic diffusion algorithm for advanced seismic signal processing in the complicated geological region of Carpathian Foredeep was examined. This technique allows for an improvement of seismic data quality and for more accurate interpretation by the recovery of a significant amount of structural information in the form of a correlating seismic reflections and by preserving true DHI indicators. It also allows searching for more subtle geological structures. Anisotropic diffusion is an iterative image processing algorithm that removes noise by modifying the data by solving partial differential equations. Moreover, it can reduce image noise without blurring the edges between regions of different chrominance or brightness. This filter preserves edges, lines, or other features relevant to the seismic structural and stratigraphic interpretation. The algorithm also enables noise reduction without removing significant information from a seismic section even for high dips values. For a better estimation of anisotropic diffusion structure tensor, the parameterization is done using the depth field and the calculations in the two-way travel time field. The presented research shows the results of using an anisotropic diffusion algorithm for post-stack and migration processing of seismic 3D data collected in Carpathian reservoir rocks of southern Poland.

The pre-Silurian Riachão basin: a new perspective on the basement of the Parnaíba basin, NE Brazil

Abstract We present a new interpretation of the basement immediately below the pre-Silurian unconformity in the mid-western part of the Parnaíba cratonic basin. Regional seismic reflection data, constrained by well and gravity data, have revealed the remnants of a pre-Silurian basin named the Riachão basin. It has a north–south trend and is about 120 km wide with a minimum area of c. 35 000 km 2 and a maximum thickness of 4 km. Seismic interpretation shows the Riachão basin is defined by erosional unconformities at its top (the pre-Silurian unconformity) and base (the top of the pre-Riachão basement). The basin fill is formed of three stratigraphic sequences – Riachão I, II and III – separated by seismic discontinuities and laterally bounded by monoclinal folds and basement uplifts related to thrust faults. Exploration wells show that the Riachão sediments are Ediacaran to Lower Cambrian, clastic and a minimum of 1 km thick, unconformably overlying a heterogeneous metamorphic basement. The mechanism of formation of the basin is unclear. However, our seismic stratigraphic interpretation suggests that Riachão II and III are remnants of marine, clastic, foreland basin sequences of opposed polarity, related to late Neoproterozoic tectonics. The banded, high-amplitude, Riachão I sequence is interpreted as a carbonate platform preceding the main subsidence and clastic input of the Riachão basin.

The Jurassic basin prototypes and episodic sedimentary characteristics of the Hongshan Sag in the eastern segment of the Northern Qaidam Basin, NW China

The Hongshan Sag, located in the eastern segment of the northern Qaidam block, has undergone complicated tectonic evolution, which results in the controversy on the Jurassic basin prototype. Based on field geological investigation, interpretation of seismic stratigraphy, restoration of balanced cross‐section, recognition of stratigraphic contact relationship, observation of lithofacies features, and exploration of basin filling characteristics in the Hongshan Sag, the paper analyses the basin prototype, establishes a sequence stratigraphic framework, and explores episodic sedimentary features. The Hongshan Sag was a small‐scale faulted basin pulled apart by NE‐oriented extensional stress along the margin of the Qaidam Block during the Early Jurassic. During the Middle Jurassic, along with protracted rifting, the Hongshan Sag evolved into a relatively large‐scale faulted basin controlled by NE‐oriented extensional stress. The faulted basin evolved into a compressional sag during the Late Jurassic. The Jurassic strata are subdivided into 2 first‐order sequences, 3 second‐order sequences, and 5 third‐order sequences. Every third‐order sequence corresponds to an episode. The deposits of Episode I(SIII1) mainly contain coarse‐grained clasts of alluvial fan and braided river, which is locally distributed in the eastern sub‐sag. The deposits of Episode II(SIII2) mainly encompass coarse‐grained clasts of shallow water braided delta, which is distributed in discrete eastern and western sub‐sags. During the period of Episode III(SIII3), the isolated eastern and western sub‐sags connect to a whole sag, whose sediments are composed of coarse‐grained clasts of fan delta in steep slope of basin. Deposits of Episode IV(SIII4) comprises fine‐grained clasts, which are distributed throughout the basin. The deposits of compressional Episode V(SIII5) mainly consist of red fine‐grained clasts, but suffer from obvious erosion on the margin of the basin.

Geology and hydrocarbon potential of offshore SE Somalia

Interpretation of a 20 550 line km 2D seismic survey acquired in 2014 by Soma Oil and Gas in the deep water offshore area of SE Somalia has identified three previously undocumented sedimentary provinces – Jubba Deep, Mogadishu Deep and Mid Somalia High – all of which have distinctive geological characteristics. Well and stratigraphic controls are limited, with inferred lithologies largely based on seismic stratigraphic interpretation. The Jubba Deep has a thick Late Cretaceous–Early Tertiary deltaic section deformed by major gravitational collapses in the Paleocene-age Kismaayo Thrust Belt (KTB) and the Pliocene-age Baraawe Thrust Belt (BTB). It is proposed that the KTB has significant hydrocarbon potential in deltaic and pro-delta sands trapped in thrust anticlines and sourced with oil from Mid-Cretaceous mobile shales. The Mogadishu Deep Basin has a thick Mesozoic and Tertiary section but is missing the thick deltaics seen in the Jubba Basin. Volcanics are present in this basin. The Mid Somalia High has a relatively thinner sedimentary section where Cretaceous and Jurassic reservoirs and potential source rocks are at moderate burial depths. An extensive post-rift Mid–Late Jurassic carbonate platform is developed here with potential hydrocarbon targets in interpreted reefs and shoal facies. Supplementary material : Additional seismic examples and map figures are available at https://doi.org/10.6084/m9.figshare.c.3902650

TECTONO-STRATIGRAPHIC EVOLUTION OF LAPA FIELD PRE-SALT SECTION, SANTOS BASIN (SE BRAZILIAN CONTINENTAL MARGIN)

Santos Basin is located in the southeast of the Brazilian continental margin and was created by rifting processes during the Gondwana break up and opening of the South Atlantic, initiated in the Neocomian (Cretaceous). The area gained renewed attention from the oil industry due to recent Petrobras' huge discoveries of carbonate reservoirs below the salt layer (Pre-salt). The discovery of this new play in deep and ultra-deep water opened a new exploratory frontier in Brazil, generating excellent economic prospects for the country. The case study of this work is the Lapa Field, discovered in 2007 by Petrobras, which is located in deep water and represents one of the largest producing fields of the Pre-salt. This research aims to improve the actual model for the tectono-stratigraphic evolution of the Pre-salt section on the Santos Basin (Brazil). The used database includes the public data provided by National Petroleum Agency (ANP; six post-stack 2D seismic lines migrated in time and four wells). Main Pre-salt horizons and faults were mapped considering the Exxon Model to do the seismic-stratigraphy interpretation. A velocity model was constructed for the Lapa field, which enable the generation of isopach maps. All these products allow a better visualization of the tectono-stratigraphic evolution of the region and also show the salt thickness variation, analyzing the reason of its behavior.