Hydrocarbon Prospectivity Research Articles

Formation evaluation of Deccan (basalt) trap basement of Kutch Offshore basin, Gulf of Kutch, India

Deccan basalt trap that serves as basement rock for a large sedimentary expanse in western India has long been expected to be a hydrocarbon prospect. In the last decade or so, the Kutch Offshore basin, located in western India and towards the outer extends of these traps, has reported gas indications in some of the drilled wells. These indications have sufficed the need to characterize these fractured basements for commercial hydrocarbon potential. Deccan basalt trap is a combination of multiple lava flows where the base of each flow is massive, and the top is weathered or vesicular or brecciated. The present study identifies these textural variations within basalt using conventional open hole logs and delineates the zones with good reservoir properties. Various methods such as the density-neutron cross plots, density-sonic travel time overlay, and weathering scale generated using deep resistivity values have proven to be useful in differentiating weathered and fresh basalt intervals. The ratio of deep and shallow resistivity was used to identify permeable zones within the basalt. The weathered and fresh basalt zones were integrated with permeable zones to identify four reservoir facies (Fractured basalt, Massive basalt, Weathered basalt having permeability, and Weathered Basalt with no permeability) in the studied wells. The micro resistivity image data proved to be of great help in identifying vesicular and brecciated basalt facies along with weathered/fractured basalt and the conventional log signatures of these basalt facies were standardized in this study. Two sets of natural fractures were also identified from resistivity image data in Deccan basalts. The main trend has strike orientation in NE-SW and the other set in NW-SE direction. Maximum and minimum stress directions estimated from drilling-induced fractures and borehole breakouts are 10–40° N and 100–130° N, respectively. This study has given key insights into the various facies present in the Deccan trap and standardizes a methodology to identify interesting reservoir zones within the basalt. The study helps to reduce the uncertainties in the formation evaluation of the Deccan trap extends of the Kutch Offshore.

Improving Hydrocarbon Prospect Evaluation at Badr El Din-3 and Badr El Din-15 Oil Fields by Integrating 3D Structural Modeling and Petrophysical Analysis for Abu-Gharadig Basin, North of Western Desert, Egypt

The BED-3 and BED-15 oil fields are situated in the northwestern portion of the Abu-Gharadig sedimentary basin. The Basin is an E–W trending intracratonic rift basin and ranges in age between the Late Jurassic and Early Cretaceous. Significant extension events, followed by subsidence, took place throughout the Middle Jurassic and continued to the Cretaceous. The relative movement of Africa toward Laurasia in the Jurassic changed from eastward to westward between the Early Cretaceous and the Santonian. Therefore, a compressive force due to the change in direction affected the African plate and gave rise to the reversal of basins (such as the Abu-Gharadig sedimentary basin). Inverted anticlines are important structural traps for hydrocarbons that were formed by the compressional forces acting on the Abu-Gharadig sedimentary basin. This study primarily focuses on understanding the BED-3 and BED-15 fileds' structural style, in addition to the subsurface structure that has participated in the petroleum accumulation in the Abu-Roash C Member (Abu-Roash Formation) in the oil fields, in order to maximize oil recovery in these two fields through new wells. The aim of this study was achieved based on information from 30 two-dimensional seismic profiles integrated with well log data from nine boreholes. The Abu-Roash C reservoir represented by two horizons, in addition to minor and major faults, are recognized and marked. Structural trend in the study area ranges from ESE–WNW to NW–SE, and structures consist of folds and faults, forming horsts, grabens, and half-grabens, all of which are favorable for hydrocarbon accumulation. The petrophysical analysis performed on the BED3-8 well shows approximately 87.4% hydrocarbon saturation within the reservoir rock, while the hydrocarbon saturation of the available wells in BED-15 is calculated to vary between 56.1 and 78.8%. Hence, this study suggests that BED-3 and BED-15 oilfields have an excellent chance of producing hydrocarbons.

Oil biomarker signature and hydrocarbon prospectivity of Paleozoic versus Mesozoic source rocks in the Faghur–Sallum basins, Egypt's Western Desert

Exploration campaigns focusing on Paleozoic plays in the Egyptian north Western Desert Sallum and Faghur basins have been limited to date, and little has been done to investigate their hydrocarbon generation potential. A total of 284 shale, calcareous shale, coaly shale and siltstone side-wall core and cuttings samples, covering the rock succession that ranges from the Silurian Kohla Formation to the Turonian Abu Roash Formation were analyzed for source rock potential. In addition, eight reservoired Paleozoic–Mesozoic oil samples were geochemically analyzed. This paper systematically investigates (1) organic enrichment, hydrocarbon generation potential, and thermal maturity of Mesozoic as well as possible Paleozoic source rocks, and (2) composition and biomarker characteristics of crude oil samples in the study area from the far north Western Desert basins of Egypt.The Silurian Kohla and Basur and the Carboniferous Desouqy and Dhiffah siltstone and shale rock samples show overall poor and fair to good source rock potential for the Lower and Upper Cretaceous rock units, respectively. In contrast, high TOC (up to 4.83 wt%) and Rock-Eval S2 (up to 6.57 mg HC/g rock) for the Devonian Zeitoun Formation samples indicates fair to very good source potential. The Middle Jurassic Khatatba Formation samples, compared with the Devonian Zeitoun Formation or other rock units in the stratigraphic column of the study area, have the highest TOC (30.1 wt%) and the highest S2 (26.9 mg HC/g rock), indicating fair to excellent source rock potential. These high values of the Khatatba Formation are locally related to organic-rich coaly shales and calcareous shale intervals. The Rock-Eval results indicate an overall dominance of Type-III kerogen with strongly varying OI values. This highly gas-prone character for most samples was confirmed petrographically by abundant vitrinite phytoclasts and recycled organic matter. Coals and coaly shale facies from the Alam El Bueib and Khatatba formations that contain liptinitic materials may represent Type-III kerogens that are capable of generating gas with minor oil. Based on Rock-Eval Tmax and HI results, the Zeitoun and Khatatba samples range from early to peak oil window. This is consistent with the Ro measurements of the Paleozoic Zeitoun samples (0.65–1.02%) and the Middle Jurassic Khatatba samples (0.59–1.01%).The Faghur oils are light (35°–46° API gravity), belong to a single genetic family and are non-biodegraded based on wide-ranging n-alkanes. Abundant tricyclic diterpanes, C24 tetracyclic terpane, C27 Ts trisnorneohopane, diahopane, cyclohexanes, C29 steranes and rearranged steranes and low to very low gammacerane and extended hopanes are common molecular signatures of the analyzed light oil and condensate samples. These findings indicate a relatively oxic fluvio-deltaic environment for the corresponding clay-rich coaly shale and calcareous shale source rocks that contain predominantly higher land-plants with negligible algal/bacterial organic materials. Based on saturated- and aromatic-maturity parameters, the analyzed oils were inherited from peak–late mature source rock.

Characteristics of late reformation and petroleum prospect of Carboniferous strata in the Bayanhot Basin, N. China

The Bayanhot Basin is located at the intersection of the Alxa Block, Ordos Basin, and Corridor Transitional Zone. Although the Carboniferous palaeo‐sedimentary and tectonic features are of great significance in discovering the scientific issues of the influential range of the Qinlin‐Qilian Ocean and palaeo‐Asian Ocean and the relationship of the North China Block and Alxa Block, as well as in evaluating hydrocarbon prospects, it is difficult to restore the Carboniferous features because of intense late reformation. It is necessary to systematically discuss the late reformation characteristics. It is shown in this paper that Carboniferous strata have mainly experienced two extensive tectonic movements during the Late Hercynian–Indosinian and Yanshanian periods and had four reformation types: structural compression, uplift to erosion, superimposed and deep burial, and thermodynamic reformation, based on comprehensive analysis of seismic profiles, wells, aeromagnetic data and tectonic characteristics of the surrounding regions. Carboniferous strata were partly eroded by the compressional folding during Late Hercynian–Indosinian movement, and were forcefully eroded by thrusting and uplift during Yanshanian movement, especially movement in the Late Jurassic, which determined the present thickness of the Carboniferous strata. The deep overlap of the overlying Jurassic, Lower Cretaceous, Palaeogene, and Neogene rocks in different areas was beneficial to the maturation of Carboniferous source rocks. The magmatic rocks exposed by well drilling and shallow aeromagnetic anomaly belts show heating reformation, which accelerated the maturation of source rocks to some extent. The total strength of the Carboniferous late reformation was stronger in the western area than in the eastern area and greater in the northern area than in the southern area. The multiple periods and various types of reformation were closely related to the regional closure of the Palaeo‐Qinling‐Qilian Ocean in the south, Palaeo‐Asian Ocean, and Mongolia–Okhotsk Ocean in the north and the subduction of the Palaeo‐Pacific Plate in the east. The Carboniferous strata in eastern and southern basins will be the prospective favourable areas for the petroleum exploration.

About this title - Sedimentary Successions of the Arctic Region and their Hydrocarbon Prospectivity

This volume contains an unparalleled summary of the geology and hydrocarbon potential of all Arctic sedimentary successions. The successions are organised into 67 ‘tectono-sedimentary elements’ according to deformational and lithostratigraphic characteristics, and described in an easy-to-navigate standardized framework. Includes over 800 illustrations and 6 foldout Circum-Arctic maps.

Unscrambling the source kitchen and hydrocarbon prospect information of the ultra-deepwater area in southern Pearl River Mouth basin, South China Sea: Insights from the first ultra-deepwater exploration well W21

Recent breakthroughs in Pearl River Mouth basin (PRMB) regarding offshore hydrocarbon exploration have shifted the focus from deepwater area to ultra-deepwater area (>1500 m water depth), and the southern sub-sag of Baiyun sag, Liwan sag, and the Shunhe Uplift between them constitute the front area for PRMB ultra-deepwater hydrocarbon exploration. This study investigated the source-rock strata (i.e., Eocene Wenchang Formation and Enping Formation) and reservoir fluids (mainly CO2 with small amounts of oil and alkane gas) in the first exploratory well (namely W21, drilled at Shunhe Uplift), aiming to unscramble the source kitchen and hydrocarbon prospect information in this ultra-deepwater area. Biomarker and transgressive history analysis of source-rock strata jointly determined the Wenchang Formation and Enping Formation to be marine sediments in the Liwan sag, while marine and lacustrine sediments in the Baiyun southern sub-sag, respectively. The oil biomarkers and isotopes of alkane gas evidenced prospect for mature oil and oil-associated gas in this ultra-deepwater area, and the correlated source analysis determined the source rocks in the two sags have an advantage of aquatic organic input, indicating a good hydrocarbon-generating potential. Additionally, the regional distribution of terrestrial source-specific biomarkers (i.e., oleanane and bicadinanes) in PRMB deep to ultra-deep water areas traced the terrestrial source area and revealed a significant less input of terrigenous organic matter at the two ultra-deepwater sags. The isotopic analysis of reservoir non-hydrocarbon gases determined the CO2 to be mantle-derived magmatic origin. The present reservoirs are a result of displacement of early charged oils by posterior migrated CO2. In conclusion, this PRMB ultra-deepwater area has a considerable prospect for mature oil; however, the frequent volcanism since the Pliocene poses great risks to hydrocarbon exploration.

Unlocking the Hydrocarbon Potential of the Mannar Basin (Sri Lanka) Based on New Data and New Ideas

The Mannar Basin is a failed rift basin located between Sri Lanka and India. Massive flood basalts have been deposited during latest Cretaceous/earliest Paleocene magmatic activity that is also represented by numerous igneous sill intrusions. The two discoveries are associated with this magmatism: Barracuda and Dorado, both discovered in 2011, have been drilled in the northern part. One of the key challenges for hydrocarbon exploration in volcanic provinces is sub-basalt imaging due to the velocity contrast between basalts and siliciclastics. To unlock hidden play types and identify geological features within Mesozoic intervals we utilized both infill 2D seismic data acquired in 2018 and vintage 2D seismic data reprocessed in 2021. These provide new insights for hydrocarbon exploration and the tectono-stratigraphic evolution of Sri Lanka’s offshore basins. We integrated these new study results into a regional 2D petroleum system modelling study. Modelling results indicate hydrocarbon potential for several play types: Cretaceous reef, turbidite and fan plays. Since the tectonic evolution of the Mannar Basin is still a matter of debate, especially related to timing and duration of extension and Sri Lanka’s position during Gondwana breakup, we created different heat flow scenarios to validate the impact on the hydrocarbon prospectivity.

Backthrust play of the Chernyshev swell, Timan-Pechora Basin: Reentry into a legacy exploration site based on multidisciplinary study

We have developed a new interpretation of the Povarnitsa High, located in the southern part of the transition zone between the Chernyshov swell and the Kosyu-Rogov trough in the Polar Urals foreland. Petroleum exploration in this area took place in the 1980s and resulted only in an uneconomical oil deposit. Reprocessing and reinterpretation of vintage data and a newly acquired 3D seismic survey along with nonseismic geophysical data provided new insight into the geologic setting of the area. It found a subthrust extension of the Povarnitsa High, overlain by a backthrust sheet floored by upper Ordovician evaporites. This backthrust sheet interpretably resulted from the squeezing of the salt diapir during the late Permian contraction. Stratal patterns of the Silurian-Carboniferous section adjacent to the salt structures suggest early precontraction initiation of the halokinetic deformation, which influenced the distribution of reservoirs such as reefs and oolites. We consider the salt-cored subthrust structural culmination a principal hydrocarbon prospect. It includes multiple reservoir-seal pairs in the Silurian-Permian section at depths ranging from 1 to 4 km. The updated structural model of the Povarnitsa High area suggests that the vintage wells penetrated prospective intervals at the periphery of the closure approximately 1 km downdip from the subthrust crest of the prospect.

Multifractal properties of oil and gas indices in the Songnan Low Uplift of the Qiongdongnan Basin deepwater area

Recently, a high-quality reservoir was discovered in the Songnan Low Uplift in the eastern deepwater area of the Qiongdongnan Basin, northern South China Sea. To establish whether this area has good exploration prospects, this paper uses the multifractal moment method to analyse 2689 data points acquired from the basin in the SE of the southern low bulge. It is pointed out that the fractal behaviours of different types of geochemical indices are often distinguished by multifractal spectra of different shapes, therefore multifractal spectrum function analysis is used in this paper. These data were considered within the context of 13 oil and gas indices describing the multifractal spectrum function morphological characteristics. The results show that these indices can be divided into three types according to the multifractal spectrum. Indices with a strong multifractal spectrum function in the Songnan Low Uplift have the characteristics of a wide and continuous multifractal spectrum function, forming a right-skewed arc shape, while the other indices show weak or single-fractal characteristics. The results are in good agreement with principal component analysis results, where the spectral function of each principal component shows that the gas source of the C1, C2, C3, nC4, nC5, and heavy hydrocarbon indices in the Songnan Low Bulge has multifractal characteristics. The weight of these indices with strong multifractal characteristics shows that the principal components C1, C2 and C3, and heavy hydrocarbons, are important indices for delineating hydrocarbon prospects in the Songnan Low Uplift. Multifractal and spatial analysis techniques provide new ideas for index selection and comprehensive information extraction for oil and gas exploration. Thematic collection: This article is part of the Applications of Innovations in Geochemical Data Analysis collection available at: https://www.lyellcollection.org/cc/applications-of-innovations-in-geochemical-data-analysis

Basement cross‐strike Bomdila Fault beneath Arunachal Himalaya: Deformation along curved thrust traces, seismicity, and implications in hydrocarbon prospect of the Gondwana sediments

Structural mapping and fieldwork in the Lesser and Higher Himalayan sequences in the western Arunachal Himalaya reveal crucial deformation fabrics in the Main Central Thrust (MCT) and Dirang Thrust (DT) zones. The top‐to‐SW ductile shear in the MCT and DT zones is correlated with the swing in the trend of MCT and DT from NE to NNW. The curved MCT and DT as traced by previous authors on the regional map of Arunachal Himalaya are studied. It is found that at places where these faults swing, shear senses developed at the meso‐scale. These shear senses are studied in meso‐ and micro‐scales. Seismicity in the western Arunachal Himalaya is influenced by basement cross‐strike crustal‐scale NW‐trending buried Bomdila Fault (BF). Landslides occur frequently along the Bhalukpong‐Bomdila–Sela traverse are also linked with the transverse BF. In its southern part, the BF coincides with the Dhansiri Lineament and is the basin margin fault in the upper Assam shelf. The Gondwana sediments extended further south below the Brahmaputra alluvium along the fault is to be explored for hydrocarbon exploration.

Structural Mapping Inferred from Gravity Data to Image the Upper Lithospheric Structures and its Hydrocarbon Implication from Gwandu Formation NW, Nigeria

Presently a digitized composite satellite gravity data covering the Gwandu formation in Sokoto Basin were acquired and processed with a view to interpret the Bouguer anomalies as well to equally image the upper lithospheric structures beneath the Study area and its environs. The research work was aim to study the structural settings of crustal movement in the Gwandu formation. A least-square fitting polynomial surface of a third-degree order was applied in separating regional and residual gravity components from the Bouguer anomaly. The attributed low gravity sedimentary infill from the residual anomalies were tectonically trends NE -to- SW about the vicinities of Tambuwal, Goronyo, Gada and Argungu, Kolmalo and about Yauri, Koko and Jega, Kamba as well as Bagudo. Data enhancement techniques such as first vertical derivative, total horizontal derivative (THDR), analytic signal, spectral depth analysis, and the standard Euler deconvolution (SED) were applied to enhance deep-seated structures. Results from the Spectral Analysis revealed that the average thickness of the sediments varies from 1.679 km to 4.181 km, outsized enough for hydrocarbon prospect. The derivative maps revealed parallel to sub-parallel trending NW –to- SE, E -to- W fracture zones within the sedimentary infill underlying the study area, coinciding with the cretaceous zones. Hence, the identified lineaments (faults or lithologic contacts) and structures in the area can be attributed to the tectonic setting of the area and probable migratory routes for hydrocarbon migration. More detailed ground gravity and seismic studies may lead to discoveries of structural or stratigraphic traps.

Tectonostratigraphic evolution of the Sohar Basin, exploration concepts and emerging plays offshore on the UAE's east coast

The Sohar Basin, located offshore the East Coast of the Arabian Peninsula, is an area that has seldom been the focus of international oil companies. While all commercial discoveries in the UAE and Oman have been made to the west and south of the Oman Mountains, the Sohar Basin is underexplored and remains prospective. This lack of activity is primarily because the Thamama reservoir, which has yielded huge success to the west of the Oman Mountains is likely not present within the Sohar Basin. However, potential traps, reservoirs, and source rocks are present within the Tertiary succession. The Sohar Basin formed in the late Cretaceous after the obduction of the Semail Ophiolite onto the Arabian Plate. Following a period of tectonic quiescence, which lasted until the Early Eocene, the gravitational collapse occurred along the eastern edge of the present-day Oman Mountains.Interpretation of both 2D and 3D seismic reveals that the subsurface is comprised of three tectonostratigraphic units, defined as pre-, syn-, and post-tectonic packages. North-South trending thrust faults generate distinct mini-basins within the pre- and syn-tectonic sequences. The post-tectonic sequence is defined by the development of prograding systems in a tectonically quiescent margin formed in the Lower Miocene and which persists to the present day. Deep-water depositional systems dominate the undrilled far-east and south of the basin where the presence of submarine canyon systems and associated basin floor fans is supported by 3D seismic data. In recent times, the Sohar Basin has been subject to extensional faulting likely driven by sediment load caused by a prograding delta system.The results of this work reveal that multiple untested play types exist within the Sohar Basin, which are comprised of both structural and stratigraphic elements. This paper integrates both a structural and sequence stratigraphic interpretation to provide insights into the tectonostratigraphic evolution of the Sohar Basin. Consequently, the fundamentals of play fairway mapping have been employed to unlock the hydrocarbon prospectivity offshore the UAE's East Coast.

Seismic-stratigraphic analysis and depositional architecture of the Cenozoic Kribi-Campo sub-basin offshore deposits (Cameroon): Seismic attributes approach and implication for the hydrocarbon prospectivity

The offshore deposits were formed the main part of the Kribi-Campo sub-basin, which is one of the three Cameroonian coastal margin basins formed during the progressive opening of the South Atlantic margin. Determination of the seismic facies and their architecture in seismic units are lacking in the Kribi-Campo sub-basin and calibration of the stratigraphic unit and the hydrocarbon prospectivity of Cenozoic offshore deposits remains unclear. Therefore, the seismic stratigraphic unit, data from five boreholes, and seismic attributes of 2D seismic data were analysed to determine the seismic stratigraphic distribution, the paleoenvironment evolution, and to assess the hydrocarbon prospectivity of the Cenozoic offshore deposits of the Kribi-Campo sub-basin. Five main seismic facies include parallel to subparallel, hummocky, chaotic, sigmoidal, and oblique, and four major seismic stratigraphic units SSU1, SSU2, SSU3, and SSU4 have been identified. The seismic stratigraphic unit has been divided into five major unconformities dated Upper Paleocene, Lower Eocene, Middle Miocene, Upper Miocene, and Pliocene to Pleistocene. The depositional environments evolve from delta to prograding continental shelves, both influenced by high and low energy processes, controlled by relative sea-level change. The offlap-breaks in the SSU4 seismic unit show the presence of both the Low Stand Systems Tract (LST) or Shelf Margin Systems Tract, and retrograding Transgressive Systems Tract (TST). The presence of potential source rocks, reservoirs, seals, and structural and stratigraphic traps throughout the studied seismic intervals highlight the prospective nature for oil and gas exploration within the offshore Cenozoic of the Kribi-Campo sub-basin.

Concurrent 17. Presentation for: Stratigraphic framework and structural architecture of the Upper Cretaceous in the deep-water Otway Basin – implications for frontier hydrocarbon prospectivity

Presented on Wednesday 18 May: Session 17 Geoscience Australia has undertaken a regional seismic mapping study that extends into the frontier deep-water region of the offshore Otway Basin. This work builds on seismic mapping and petroleum systems modelling published in the 2021 Otway Basin Regional Study. Seismic interpretation spans over 18 000 line-km of new and reprocessed data collected in the 2020 Otway Basin seismic program and over 40 000 line-km of legacy 2D seismic data. Fault mapping has resulted in refinement and reinterpretation of regional structural elements, particularly in the deep-water areas. Structure surfaces and isochron maps highlight Shipwreck (Turonian–Santonian) and Sherbrook (Campanian–Maastrichtian) supersequence depocentres across the deep-water part of the basin. These observations will inform the characterisation of petroleum systems within the Upper Cretaceous succession, especially in the underexplored deep-water region. To access the presentation click the link on the right. To read the full paper click here

Geoscience Poster G5: Stratigraphic framework and structural architecture of the Upper Cretaceous in the deep-water Otway Basin – implications for frontier hydrocarbon prospectivity

Poster G5 Geoscience Australia has undertaken a regional seismic mapping study that extends into the frontier deep-water region of the offshore Otway Basin. This work builds on seismic mapping and petroleum systems modelling published in the 2021 Otway Basin Regional Study. Seismic interpretation spans over 18 000 line-km of new and reprocessed data collected in the 2020 Otway Basin seismic program and over 40 000 line-km of legacy 2D seismic data. Fault mapping has resulted in refinement and reinterpretation of regional structural elements, particularly in the deep-water areas. Structure surfaces and isochron maps highlight Shipwreck (Turonian–Santonian) and Sherbrook (Campanian–Maastrichtian) supersequence depocentres across the deep-water part of the basin. These observations will inform the characterisation of petroleum systems within the Upper Cretaceous succession, especially in the underexplored deep-water region. To access the poster click the link on the right. To read the full paper click here

Sequence stratigraphic framework of ‘AKOS’ field, Niger Delta

The aim of this study is to investigate the sequence-stratigraphic framework of a hydrocarbon prospect of ‘AKOS’ Field, Niger Delta, using well logs, and 3-D seismic data. To achieve this, the researchers identify the various sand/shale and seismic facies, build a sequencestratigraphic framework of the oilfield, and assess the petroleum play of identified system tracts. A fault analysis reveal twelve (12) fault sets (Fault 1-12) mapped across the seismic volume. These faults are picked on an increment of 50 and examined for consistency using time slice and variance attributes. Faults-1 and 2 are major faults. The other ten (10) are minor faults. The mapped faults are normal growth faults common in the Niger Delta, as most trend approximately E-W direction. Sequence-stratigraphic analysis of the prospect based on chronostratigraphic correlation reveal two (2) sequences. Sequence-1 is between Sequence Boundary (SB) 0 to SB-1. Sequence-2 is between SB-1 to SB-2. Results from interpreted and analyzed system tracts reveal all three (3) present in Sequence-1. However, the Lowstand System Tract (LST) is absent in Sequence-2. The Lowstand Systems Tracts (LST) identified by shallowing and coarsening-upward succession, and progradational and aggradational parasequence sets are major hydrocarbon-producing intervals within the oilfield. The Transgressive Systems Tract (TST) typified by dirtying-upward seal the Lowstand Reservoirs. The upper section of the Highstand Systems Tracts (HST) has reservoir potential.

Alpine tectonic movements and salt tectonics of Eastern Ukraine

Within Eastern Ukraine, in the course of previous studies, neotectonic movements were established, caused by both salt tectonics and Attic (post-Miocene - pre-Pliocene) thrust dislocations of northeastern vergence. They are partially displayed in modern relief. The aim of the study was to reveal the structural results of the interaction of post-Pliocene fold-thrust deformations and modern salt tectonics of Eastern Ukraine. Research methodology. The base of the Cenozoic deposits of Eastern Ukraine was chosen as an indicator surface reflecting both those and other movements. Its initial orientation is horizontal. Deviations from the horizontal reflect the direction and amplitude of deformations. The morphology of this surface was depicted by isolines with a vertical step of 20 m. To build a map of the supporting surface, state geological maps and data from more than 2,100 wells drilled in this area were used. Research results. A map of the shape of the Cenozoic base in tectonic blocks between the Attic thrusts and beyond their development has been constructed. Uplifts of this surface, which are not associated with thrust movements, have been revealed. The dimensions of such uplifts are 8÷30 × 6÷15 km with vertical amplitude of 40 - 100 m or more. The uplifts are usually contoured by ring or arc compensation troughs a few kilometers wide and 20-100 m deep. Some of these uplifts are associated with the known salt domes of the area. Other uplifts do not contain such domes. It is possible that they formed over salt "pillows", which did not have enough salt reserves to form salt diapirs. The area of distribution of such uplifts approximately corresponds to the area of distribution of Devonian salt deposits at a depth of 5-10 km or more. Scientific novelty. Neotectonic uplifts were discovered, similar in shape and size to those caused by salt tectonics, but located outside the areas of distribution of known salt-bearing strata. It is hypothesized that this is related to the older Hercynian overthrusts. The uplifts are located above the hanging blocks of the Hercynian overthrusts in the north and south of the study area. These thrusts were formed on the northern and southern sides of the former Dnieper-Donetsk depression during its destruction by the Hercynian folding. It is possible that the nappes over thrusts the Devonian salt-bearing deposits with metamorphic rocks of the crystalline basement. The decrease in the level of the World Ocean in the Quaternary period further increased the lithostatic load on the salt-bearing strata. This activated the isostatic upwelling of salt and the formation of gently sloping neotectonic uplifts. Practical significance. These results clarify the geological structure of the territory and make it possible to expand the area of hydrocarbon prospecting.

Conditions for the formation of non-anticlinal hydrocarbon traps in zones around salt stocks of the south-eastern part of the Dnepr-Donetsk depression

Formulation of the problem. The southeastern part of the Dnieper-Donetsk depression has a large-scale formation of underground salt structures (stocks). The stocks are the reason for the formation of many layer structures. The authors divide these layer structures near the stocks into three types - above-stock, inter-stock, and near-stock. The most promising targets for exploration drilling are anticlinal structures (of the first and second types). Many industrial accumulations of hydrocarbons (Shebelinskoe, West-Krestishchenskoe, Efremovskoe) were found in anticlinal structures. The aim of the work is to determine the genetic relationship between lithological structures and hydrocarbon traps. This is the basis for the search for a non-anticlinal form of hydrocarbon traps. Presentation of the main research material. On the territory of the Dnieper-Donetsk depression, different models of structure of salt stock zones were found. The most promising for the search for hydrocarbon deposits are areas with satellite blocks near the underground salt stock. These blocks were formed concurrently with the process of breaking through the rock stock. In this study, salt stocks have been divided into activity types. Only active stocks have satellite blocks. This makes it possible to make predictions in trough zones (stock compensation troughs). The authors have divided found traps for hydrocarbons into: plumes from salt stocks in P1sl - C33 rock formations; rocks raised by salt stocks at the time of formation P1 - C3; tectonic satellite blocks from rocks of age C3, C2b, C1s; carbonate structures of organisms P1. These structures can be hydrocarbon deposits themselves with personal water contact. Often these structures share a common water contact. This is the basis for the allocation of the entire area around the stock for hydrocarbon prospecting. To search for hydrocarbons near stocks, you need to use special techniques. The detailed description of the theory of the search method have been given in the work. Conclusions. Prospective objects for the search for hydrocarbons are located near the salt shafts with the greatest activity. This conclusion was made on the basis of the reconstruction of salt tectonics in the research area. Hydrocarbon traps are non-vaulted forms near the salt object. The objects of the first rank for the search are uprooted blocks, satellite blocks and plume formations. The authors single out Novosanzharsk-Malopereshchepinska, Tarasivska, Elizavetivska, West-Chutivska, Lannivska, South-Khrestishchenska (Berestovenkivska), West-Efremivska, Oleksiivska, Kopylivska and some other areas as promising.

Sedimentary geochemistry of Late Cretaceous-Paleocene deposits at the southwestern margin of the Anambra Basin (Nigeria): Implications for paleoenvironmental reconstructions

The Campano-Maastrichtian deposits of the Nkporo and Mamu formations of the Anambra Basin represent prospective hydrocarbon resources in southern Nigeria. In order to reveal the paleoclimate, sediment recycling and paleoenvironment during the deposition of these formations in the southwestern portion of the Anambra Basin, a detailed geochemical analysis was performed using major elements, trace elements and rare earth element data, as well as the mineralogical characterization of 20 samples from two wells. The combination of geochemical ratios (Rb/Sr, Th/U, and C-value) and weathering indices (CIA, CIW, and PIA) demonstrates that the region experienced a warm, humid tropical paleoclimate throughout the Late Cretaceous. Furthermore, West Africa experienced strong precipitation during the Cretaceous, leading to intense chemical weathering in the region, as documented by the geochemically matured sediments.The paleosalinity (Sr/Ba) and paleoproductivity (Ba/Al and P/Ti) proxies show that the studied mudrocks were deposited primarily in brackish to shallow-marine settings, with poor primary productivity due to terrestrial clastic influx and hydrodynamic influence. Using multiple paleoredox indicators, deposition under oxic conditions is detected. The low authigenic U enrichment and depleted V and Cr values normalized to UCC standards further support oxic bottom water conditions. Wavy laminations observed in the mudrocks indicate retreating seawater and high hydrodynamic conditions. Ultimately, the southwestern Anambra Basin reveals Late Cretaceous-Paleocene deposits of a shallow sea controlled by a strong hydrodynamic regime.

Stratigraphic framework and structural architecture of the Upper Cretaceous in the deep-water Otway Basin – implications for frontier hydrocarbon prospectivity

Geoscience Australia has undertaken a regional seismic mapping study that extends into the frontier deep-water region of the offshore Otway Basin. This work builds on seismic mapping and petroleum systems modelling published in the 2021 Otway Basin Regional Study. Seismic interpretation spans over 18 000 line-km of new and reprocessed data collected in the 2020 Otway Basin seismic program and over 40 000 line-km of legacy 2D seismic data. Fault mapping has resulted in refinement and reinterpretation of regional structural elements, particularly in the deep-water areas. Structure surfaces and isochron maps highlight Shipwreck (Turonian–Santonian) and Sherbrook (Campanian–Maastrichtian) supersequence depocentres across the deep-water part of the basin. These observations will inform the characterisation of petroleum systems within the Upper Cretaceous succession, especially in the underexplored deep-water region.