Anticlinal Structure Research Articles

Optimizing reservoir characterization: insights from integrated data analysis

The Onshore Hydrocarbon prospectivity of the Niger Delta X-field is examined through the integration of 3D seismic and recorded information from well log data. Probable reservoirs of hydrocarbon-bearing were delineated to tackle the non-uniqueness in the identification of hydrocarbon quantity of concern. Three significant faulting patterns or systems were delineated and their architectural attributes depict a typical Niger Delta embedded anticlinal structural pattern. The study field exhibited both synthetic and antithetic structures, hence only fault on delineated reservoirs was used for structural modeling. All well locations were sited within the fault-supported synthetic and anticlinal structures and the static characteristics within the well coordinates were analyzed through petrophysical assessment. Depicted reservoir sands show low gamma ray readings, low volume of shale, considerate hydrocarbon saturation and low water saturation. The established petrophysical models showed a better net-to-gross (NTG) ratio, for the entire delineated reservoir units. This has contributed to the assessment of hydrocarbon-bearing reservoir units before employing the strategy for field development scenario, in order to eliminate dry hole drilling campaign. These will contribute to the reduction of operational costs, having delineated the accurate geometry and petrophysical model of hydrocarbon reservoir units.

The role of the Messinian evaporites in the identification of potential gas storage sites: A review of the Adriatic foreland basin system (Italy)

AbstractFocusing on the late Miocene succession stratigraphic successions including the evaporite deposits from the Messinian salinity crisis (MSC) of the Adriatic foreland basin, a revision of available boreholes and seismic data allowed us to recognize the presence of reservoirs and seals systems that can be considered of potential interest for the storage of natural and synthetic gas. Potentially good reservoir sites can be found where porous rocks referable to siliciclastic turbiditites (Marnoso‐arenacea and Laga Fms) or shallow‐water carbonates (Bolognano Fm) preferentially involved in anticlinal structures and covered by thick MSC evaporites, which may represent effective reservoir seals. The integrated reconstruction of porous rocks distribution and facies, thickness, and lateral continuity of the overlying evaporites, allows the identification and zonation of geological settings in the Adriatic foredeep, backbulge and foreland with peculiar stratigraphy and deformations, only partially considered before, that may deserve consideration in the research of potential gas storage sites.

Integrated seismic, petrophysical, and geochemical studies for evaluating the petroleum system of the Upper Bahariya-Abu Roash G sequence in the Karama Field, Abu Gharadig Basin, North Western Desert, Egypt

The main aim of this study is to delineate the hydrocarbon potential and evaluate the petroleum system elements of the Cenomanian Abu Roash G (AR/G) and the Upper Bahariya Members in the Karama Field. It lies at the southeast borders of the Abu Gharadig Basin, a well-known basin in the W.D. to the NE of Africa. We accomplish this study by analyzing a total of thirty 2D seismic profiles, a complete data set of well logs for five wells, and their geochemical data. The workflow starts with illustrating the dominant subsurface structural features, defining the main potential reservoirs and their parameters, and checking the maturity of the probable source rocks. The seismic interpretation indicated that the research area had been influenced by a NE-SW anticlinal structure accompanied by a set of WNW-ESE and NW-SE normal faults that are controlled by the positive compression inversion process that dominated during the Late Cretaceous. Analyzing and processing the well log data sets suggest that the reservoirs of the Abu Roash G (AR/G) and the Upper Bahariya Members are characterized by poor to good reservoir settings with net-pay thickness reaching up to 13–50 feet in the different wells (av. Effective porosity (∅eff) = 17.7 % and 15.6% for the AR/G and the Upper Bahariya Members, av. Shale volume (Vsh) = 17.4 % and 13.6 %, av. Water saturation (Sw) = 38.9 % and 39.8 %, while av. Hydrocarbon saturation values (So) = 60.2 % and 61.1%, respectively). The geochemical and maturity analyses assisted in determining the potential mature source rocks of the Jurassic Khatatba Shale (TOC = 0.70–5.67%; S1+S2 = 0.43–5.97 mg/g, Ro = 0.54–1.06 %) with some contribution from the Cretaceous sources (Alam El-Bueib and Bahariya Formations). Studying elements of the petroleum regime of the Karama Field indicates that the trapped hydrocarbons are structurally controlled by three-way dip closures, horst blocks, sealing faults, and vertical sealing by impervious shale and limestone beds. This case study could be applied to similar analogs in other oil fields in the Egyptian Western Desert to delineate their hydrocarbon potential and structural setting.

Deep tectonics and oil and gas prospectives of the kura depression according to geophysical data

According to the sedimentary features, the transfer of the upper, middle and lower case segments of the Kura depression is marked by oil-scientists and researchers. Structure-tectonic signs of these segments are significantly different, and are characterized by favorable conditions for the emergence, migration and gene- ration of hydrocarbons. Emigrate oil and gas products in basins created potential fields in favorable anticlinal structures, oil and gas collectors. Kur-Cabrırrı is the main oil-gas complex plieli-gas complex pliocene sediments in the Lower Kura depression in the Key-Caucasian Mmmatic basin in the Zevabadi Magmathic basin. It is of great importance in terms of monitoring the history of paleostructural development of these complexes, starting the mass generation of oil and gas, to investigate their migration directions, formation and maintenance of oil and gas fields. The official article was dedicated to the results of the complex in recent years in recent years, according to the results of regional geophysical intelligence work carried out by Azerbaijan and foreign companies. Based on a comprehensive analysis of geophysical information on regional profiles, the tectonic structure of Mesozoic-Cenozoic deposits was clarified, the conditions of sedimentation in the basins were assessed, changes in thickness were traced, and new explanations of the geological development of the territory were provided. At the same time, the boundaries of the Mugan monocline with the Jalilabad depression and the Karaja-Gyzylagad uplift zone have been clarified.

Comparison of Seed Morphology and Seed Coat Chemistry in Ophrys (Orchidaceae) Species.

Orchidaceae is the largest flowering plant family in the world and holds significant importance in terms of biological diversity. Many of the species are found in endemic regions, serving as important indicators for the conservation of biological diversity. Therefore, research on the morphology, seed and embryo structures, chemical composition, and taxonomy of orchids is crucial for species conservation, habitat restoration, and the sustainability of natural habitats. This research involves comparing the morphometric and chemical contents of seeds belonging to certain Ophrys L. species and examining interspecies relationships. The micromorphological features of the seeds were analyzed by using light microscopy and scanning electron microscopy (SEM), while their chemical contents were compared by using Fourier transform infrared spectroscopy (FT-IR) analysis. Seed and embryo morphology, morphometric analysis, and seed coat chemistry hold diagnostic significance. In species of the Ophrys genus, features like anticlinal wall structure and periclinal wall reticulation are considered weak taxonomic characters. FT-IR analysis identifies specific chemical groups in orchid samples, revealing significant differences in absorbance values and chemical compositions among the different orchid species. Particularly, Ophrys lycia (Lycian Kaş Orchid) shows distinct separation from closely related species at peak points such as 2917 and 2850, 1743, 1515, 1240, and 1031 cm-1. Common peak points in the fingerprint region (1200- 700 cm-1) indicate similarity between O. apifera and O. reinholdii subsp. reinholdii. O. ferrum-equinum, O. mammosa subsp. mammosa, O. fusca subsp. leucadica, O. reinholdii subsp. reinholdii, and O. iricolor exhibit similar absorbance values in the range of 1500-1000 cm-1. These results provide valuable preliminary information about the structure of orchid seed coats, reticulation presence and pattern, chemical profiles, distribution, and dormancy-germination processes.

Soil-forming accumulation of heavy metals in geological high background areas: Constraints of structure, lithology, and overlying soil geochemistry

Heavy metals (HMs) are often abnormally enriched in soils in geologically high background areas, posing a serious threat to the ecosystem and human health. However, the material origin of HMs in overlying soils is unclear. In this paper, we studied the accumulation control and formation process of HMs (Cd, Hg, As, Pb, Cr, Cu, Ni, and Zn) in soils overlying bedrock from different geological periods in a typical anticline structure area in southwest of Guizhou province. The results revealed that the content of HMs in the bedrock were ranked as Carboniferous carbonate rocks < Permian carbonate rocks < Triassic clastic rocks, while the opposite trend was observed for the HMs content in the overlying soil. The slopes of the EF-Q values of HMs in the soils overlying the Carboniferous, Permian, and Triassic rocks were 0.003, 0.007, and 0.83, respectively, which suggests that HMs enrichment or leaching was more complicated in the process of carbonate weathering soil-forming, whereas it was mainly in situ weathering during the process of clastic weathering soil-forming. The soils overlying the bedrock of the three geological periods experienced similar weathering processes and had the same source of soil-forming matrices, as it was observed that their Fe2O3-Al2O3, Hf-Zr, Nb-Ta, Th/Sc-Zr/Sc and Y/Ho-Y contents were significantly correlated (with R2 values of 0.80, 0.94, 0.72, 0.60, and 0.76, respectively) with very similar REE assignment patterns. The results corroborated the causes of the high background geological heterogeneity of HMs in the overlying soils in karst areas and supported the theory of the source of weathering soil-forming materials from carbonate rocks in karst areas.

Sandstones and red beds in the Lower Cretaceous Sidi Aich Formation, Chotts Basin (Southern Tunisia): facies, architecture and depositional environments

Abstract The Lower Cretaceous deposits of North Africa represent a terrestrial to shallow-marine sandstone-dominated succession often referred to as the ‘Continental Intercalaire’ and Nubian Sandstone informal groups. The upper Barremian Sidi Aich Formation of the Continental Intercalaire is distinguished throughout the Chotts basin of southern Tunisia by sandstone-dominated sequences within conglomerate, calcareous siltstone and palaeosol red bed occurrences. This paper aims to highlight: (1) the facies distribution, internal architecture and depositional environment of the sandbodies; and (2) the origin, spatial distribution and architecture of the red beds that underlined and topped sandbodies. Strata in the Zimlet El Beida anticlinal structure, Chotts basin, offer a good opportunity for detailed field observations and bed-by-bed logging of three representative lithostratigraphic sections. Detailed sedimentological investigation allows the recognition of several lithofacies grouped into three facies associations indicating tidal flat, tidal channel and tidal bar depositional settings characterizing a transgressive tide-dominated estuarine system that developed during an episode of relative sea-level fluctuations in the Early Cretaceous. The high-resolution petrographic, mineralogical and geochemical analyses of the red beds allow the differentiation of three distinct lithofacies sets including: (1) intraformational conglomerates; (2) calcareous siltstones; and (3) palaeosol. Major red beds comprise detrital grains inherited from the host or parent sediment and authigenic minerals (dolomite, calcite and hematite) precipitated during the diagenetic processes. Grain components have been partially or completely cemented and/or replaced by terrestrial phreatic dolomite. The negative δ 13 C and δ 18 O signatures of the dolomite analyses indicate that the dolomitization processes have been influenced by fluctuations of the groundwater table or climate change from semi-arid to semi-humid conditions. This study, therefore, may provide useful data for the better understanding of the internal architecture of the red beds associated with sandbodies that represent the main and significant potential reservoir within the Lower Cretaceous Continental Intercalaire sandstone-dominated groundwater aquifers of the Chotts basin.

Structural and seismic attribute analysis of the Paleocene carbonate reservoir from the Balkassar Field, Potwar Plateau, Pakistan

The structural and seismic properties of the Paleocene carbonate reservoir are re-evaluated, using 3D seismic data multi-attributes, to improve reservoir prediction accuracy rarely documented earlier. This study highlights a number of relevant post-stack seismic attributes for understanding the structural setup and seismic properties of a carbonate reservoir. The structural analysis was carried out using seismic interpretation, combined with multi-attribute analysis for prospect actualization and generation of a 3D structural model to determine the structural aspect. The structural interpretation reveals the presence of faults and an asymmetrical anticlinal structure demonstrating a four-way closure, confirming compressional tectonics. The high amplitude anomaly (-6 to 12) combined with the RMS attribute (23 to 32) suggests bright spots in the Paleocene carbonate reservoir and gas saturated zone, the variance attribute (0.05 to 0.03) highlights the presence of two major faults, and the lower instantaneous frequency demonstrates the presence of hydrocarbons. The attribute results indicate that the Lockhart Limestone possesses good reservoir potential as revealed by DHI (bright spot), gas saturated zone and a trapping mechanism supported by four-way structure closure in the region and can help to understand analogous carbonate reservoirs in similar geological settings around the world.

Olenek–Anabar Composite Tectono-Sedimentary Element, northern East Siberia

Abstract The Olenek–Anabar Composite Tectono-Sedimentary Element (OLA CTSE) is located in the northern part of the Siberian Craton. Its structure and depositional history is controlled by two main tectonic events: (i) Mesoproterozoic rifting and (ii) Ediacaran–Cambrian (to Middle Devonian?) post-rift thermal subsidence. The sedimentary succession is mainly represented by Mesoproterozoic–Cambrian strata, including the black shales of the lower–middle Kuonamka Formation. The hydrocarbon potential of the OLA CTSE is defined by the presence of large superficial bitumen fields, anticlinal structures, large reefal build-ups and direct proximity to the potential source rock (Kuonamka Formation). A very scarce grid of seismic profiles and a lack of exploration wells limit the knowledge of the petroleum potential. The lack of seals and broad occurrences of faults, causing significant vertical permeability of sediment cover, and abundant occurrences of mafic and kimberlite magmatism are limiting factors with regard to the petroleum potential. Wells drilled during the Soviet era did not recover any commercial discoveries.

The influence of an anticline structure on ambient noise spectral anomalies at an underground gas storage

SUMMARY The purpose of this study is to investigate the seismic ambient noise spectral anomalies that occur near gas reservoirs. These anomalies involve a significant spectral amplification of the vertical component for frequencies generally between 1.5 and 4 Hz and have been reported at various hydrocarbon sites worldwide. There are differing views on the mechanisms responsible for these anomalies. The guideline for this study is that many hydrocarbon reservoirs share a common geological feature: an anticline structure. It appears to cause site effects that influence the amplitude of the ambient noise wavefield. This research examines a dense real data set of ambient noise recorded at the Chémery underground gas storage site in France. The analysis identifies stable spectral anomalies between 1.2 and 2.4 Hz that are correlated to the position of the anticline structure, which also corresponds to the position of the gas bubble. We use a beamforming technique to study the composition and the origin of the ambient noise, and show that the variations of the spectral anomalies over time are correlated to changes in the source wavefield. Finally, we perform numerical simulations of Rayleigh wave propagation within a realistic 3-D velocity model of the Chémery site, while using source distributions directly extracted from real data analysis. The comparison of the simulated anomalies with real data yields a satisfactory qualitative fit. We conclude that the fundamental-mode Rayleigh wave site effect on the anticline is the main mechanism of the spectral anomaly.

East Barents Basin and Admiralty High Composite Tectono-Sedimentary Elements, Barents Sea

Abstract The East Barents Sea (E Barents Sea) includes two major tectonic elements, the East Barents Basin (EB Basin) and the Admiralty High, which are, in the context of the volume, characterized as composite tectono-sedimentary elements. Whereas they share some stratigraphy, their early history may differ. The EB Basin is a dominant structural feature of the Barents Shelf, and one of the largest and deepest sedimentary basins in the Arctic. Admiralty High rims the EB Basin in the east. The advance in understanding the E Barents Sea geology was achieved during 1980s and 1990s mainly due to a significant amount of multichannel reflection seismic data and a number of drilled deep exploration wells. These wells tested many large anticlinal structures and made several large gas discoveries including a giant Shtokman gas and gas condensate accumulation. In the following decades, many important geological results were published in the international and Russian literature. In this chapter we provide a summary of the geology and petroleum geology of the E Barents Sea based on published results and public-domain geological reports.

Determine the Reservoir Characterization, Using Seismic Data, Well Logs, Attribute Interpretation, and Static Modelling in the Duhok Province, Kurdistan Region, Iraq

Although the High Folded Zone in the Kurdistan Region of Iraq forms part of the Zagros-Taurus Folds and Thrust belt considered one of the potential hydrocarbon provinces, the oil fields within the zone are still lacking in geophysical exploration and scientific research. So, the rationale behind this study is the prospecting and evaluation of one of the Tertiary carbonate reservoirs at the “WN” oil field in the Duhok area by integrating the 3D seismic and well-log data. The methodology covered seismic interpretation, well logs and their relevant petrophysical analysis, attribute computation, and 3D static property modeling. The constructed reservoir maps revealed a double-plunging rollover anticlinal structure trending in the East-West direction parallel to the Taurus Mountain series. A total of nineteen minor reversal faults trending E-W to ENE-WSW dissecting the northern limb of the anticline were manually interpreted. The isopach map shows various thicknesses ranging from 160 to 330 m, averaging 245 m. The property models show the limited values of their parameters as the effective porosity is limited (0.97-23%), the secondary porosity (0.43-11.7%), permeability (0.00-238.8 mD), the water saturation (12.44-99.8%), and the clay volume (0.00-9.8%). The results of this research indicate that the horizon is a promising reservoir characteristic.

Estimation of Seismic Attenuation and Gas Hydrate Concentration From Surface Seismic Data at Hydrate Ridge, Cascadia Margin

AbstractAn improved understanding of the effects of gas hydrate presence on seismic attenuation is important for accurate hydrate characterization and quantification. Based on a rock‐physics model recently presented for gas hydrate‐bearing fine‐grained clay‐dominated sediments, here we establish an integrated workflow for surface seismic data from extracting seismic attenuation to estimating gas hydrate concentration (Ch) in the sediment. We apply this workflow to the high‐resolution seismic data acquired at southern Hydrate Ridge, offshore Oregon, to reveal the hydrate distribution and clarify the controlling factor of hydrate formation. We first present an adaptive‐bandwidth spectral ratio method to robustly measure attenuation. The attenuation measurements show that the presence of hydrate suppresses the attenuation of the host sediment. We then calculate Ch by applying the rock‐physics model to the attenuation measurements. The estimated Ch are mostly low (&lt;5%) in Hydrate Ridge and agrees well with the in‐situ Ch measured from core‐ or well log‐based data. Our result also suggests that the lithology and stratigraphic structures together control the distribution of gas hydrate at Hydrate Ridge, where relatively high Ch is found in the region where a gas‐charged conduit exists and in an anticlinal structure overlying a strong bottom simulating reflection. Adjacent to the anticline, however, a low amount of gas hydrate appears present, possibly due to the gas migration blocked by the anticlinal structure or the lack of gas conduits. Our study offers an effective strategy for detecting and quantifying gas hydrate in fine‐grained clayey sediments through surface seismic data.

Messinian canyons morphology of the Rhône and Ardèche rivers (south-east France): new insights from seismic profiles

Twelve available two-way time high-resolution seismic reflection profiles located in the central part of the middle Rhône valley are interpreted. In addition, one of the profiles was reprocessed to determine the P-wave velocities of the main geological units and to convert this profile into a depth cross section. The Lower and Upper Cretaceous units are clearly identifiable on all the profiles, along with the Messinian Erosion Surface (MES) carved out during the Messinian Salinity Crisis (MSC) by the paleo-Rhône and its western tributaries, the Ardèche and Cèze paleo-canyons. The Plio-Quaternary fill of these paleo-canyons shows at least 4 main units with an overall transgression. The combination of geological data from geological maps, geological field surveys and borehole data made it possible to model the MES in 3D at the scale of the region, and to produce depth/elevation model. From a geological point of view, the interpretation of the seismic profiles enabled us to reconstruct the stages in the sub-aquatic filling of the Messinian-Pliocene aggradation of the paleo-river. Several Mass Transport Deposits (MTDs) were identified both during the drop and during the rise in the Mediterranean Sea level. From a geomorphological point of view, this study provides new insights in the route and longitudinal profile of paleo-rivers and, in particular, it deepens the profile of the Paleo-Rhône at the latitude of the Tricastin region (up to −700 m b.s.l.) and significantly modifies the course and depth of the Ardèche proposed in previous studies. The N-Ardèche river, known to develop a karstic system during the MSC, is connected to a deep canyon, most likely through a karstic pocket valley, as suggested by the very steep longitudinal profile of the MES. Finally, from a structural point of view, our interpretation of the seismic profiles shows a broad ENE-trending anticline structure associated with a normal fault which apparently did not affect the Mio-Pliocene fill. In the southern part of the area, near the Uchaux anticline, the imaged structures suggest the presence of a recent (syn- to post-Pliocene) fault propagation fold. In addition to all the new information on the geology, morphology and methods of excavation and filling of the Messinian paleo-canyon, the proposed topographic model of the paleo-canyon is crucial for modelling seismic movement in the context of a basin with a complex geometry and, in particular, for the numerical assessment of site effects in a context of low seismicity.

Structural and Stratigraphic Reservoir Characterization of “MONI” Field¸ Niger Delta.

Reservoir characterization of “MONI” field of the Niger Delta has been carried out using well log and seismic data. The study is aimed at delineating structural and stratigraphic features associated with hydrocarbon entrapment of the field. Lithostratigraphic correlation reviewed two main lithologies which are reservoir sands and seal shales. Well log correlation and interpretation across the field indicates – main stratigraphic bounding surface which include two sequence boundaries and one maximum flooding surface. This indicates about three depositional sequences exists in the study area. Stacking patterns (progradation, retrogradation, and aggradation) were delineated and interpreted as lowstand system tract (LST), highst and system tract (HST), and transgressive system tract (TST). The alternation of LST, HST and TST offers good reservoir and seal for the hydrocarbon accumulation. The depositional environment of the reservoirs ranges from subaerial channel deposits, barrier bar, tidal channel sands to delta distributary channel fill. Subaerial channel deposits have a bad reservoir quality, tidal channel sands possess a fair reservoir quality while delta distributary channel fill have a good reservoir quality. Petrophysical analysis shows that three reservoirs delineated have a porosity ranging from 19.37% to 23.62%, permeability ranging from 1408.71 to 1855.36 mD, a Net-to-Gross ranging from 0.46 to 0.88, volume of shale ranging from 11.72% to 24.92%, Water saturation ranging from 37.24% to 47.96% and hydrocarbon saturation ranging from 52.04% to 62.76%. Structural interpretation reviewed four main faults that serves as traps to the accumulation of hydrocarbon. Three hydrocarbon bearing sands were interpreted in the seismic volume. Time and depth structure maps show that the hydrocarbon bearing structure is a fault assisted anticlinal structure. Seismic facies analysis reviewed five facies. The study concluded that structural and stratigraphic features can be used to characterize reservoirs.

Structural and tectonic features of the Transcarpathian trough according to gravity and magnetic data

Based on the analysis and interpretation of gravity and magnetic field anomalies, we studiedthe peculiarities of fault tectonics, structural-tectonic structure (including salt dome tectonics) of the Transcarpathian trough. We identified signs of the manifestation of deep faults and other large structural-tectonic elements in anomalies of gravity and magnetic fields. We then traced these structural-tectonic units by comparing the morphology, intensity, dimensions, and directions of the typical anomalous zones in the gravitational and magnetic fields with the tectonic structure of the region.&#x0D; We used digital maps of gravitational and magnetic fields; averaging transforms and relief-shadow images, we mapped local gravimagnetic anomalies. Analysis of the spatial structure of the original gravimagnetic fields and their transforms and structural-tectonic maps yielded a reflection of large tectonic elements of fault tectonics, anticlinal and salt dome structures in the gravimagnetic fields. Based on gravimagnetic data, the tectonic structure of the Transcarpathian trough was clarified, and the boundaries of tectonic zones and microplates were traced. The zone of the Transcarpathian deep fault is identified as a tectonic zone traced by a band of intense local positive anomalies of the gravity field along the Flysch Carpathians to the border of the Marmarosh massif. It is limited by high gradients from the southwest and northeast and is a reflection of the Pieniny and Marmarosh rock zones. The zone of the Transcarpathian deep fault is considered a suture zone of the Inner and Flysch Carpathians. In the structure of the anomalous gravity field of the Transcarpathian trough, a number of local anomalies associated with salt stocks, as well as individual anomalies, expected to be connected to salt-bearing deposits, werefound.&#x0D; We confirmed the effectiveness of gravimagnetic methods in the geological conditions of the Transcarpathian trough to detect anticlinal structures, basement protrusions, which create favorable conditions for oil and gas traps in sedimentary strata. Interpreting anomalous gravimagnetic fields in combination with geological and tectonic materials is an important condition for the integral process of studying the geological and tectonic structure of the Earth’s crust in the Transcarpathian region.

Evaluation of Carbonate Reservoir with Integration of Petrophysical Analysis and Seismic Impedance Inversion in Banggai Basin, Sulawesi

Banggai Basin is controlled by the collision between Banggai-Sula micro-continent and East Sulawesi ophiolite belt, forming a thrust-sheet anticline structure that has potential to trap hydrocarbon. The Siotu-1 well was drilled right into the thrust-sheet anticline structure targeting Miocene carbonate platform layer. The same structure has proven to be an oil trap at the Tiaka oilfield which is located adjacent to the Siotu-1 well. This study aims to evaluate the presence of hydrocarbon in the Siotu-1 well with characterization of the Miocene carbonate reservoir. It is carried out by integrating petrophysical analysis from the Siotu-1 well log data and 2D seismic impedance inversion of the Tarib-1 line. Five reservoir zones have shale content values range of 21.91-37.53%, effective porosity values range of 9.7-14.62%, water saturation values range of 88.5-98.27%, and permeability values range of 2.53-8.16 mD. The results of the porosity calculation are validated by the model of seismic inversion where the reservoir zone with an acoustic impedance in the range of 7600-13450 ((m/s)/(g/cc)) is a carbonate layer with fair to excellent porosity (10 to> 25%) and reservoir zone with acoustic impedance values range of 13450-16200 ((m/s)/(g/cc)) as carbonate layer with poor porosity (< 10%). The net pay zone in reservoir zone 4 with a thickness of 4.5 feet and a net-to-gross of 0.006 are shown as the lumping result. It is concluded that Miocene carbonate reservoir in the Siotu-1 well met the criteria as a good reservoir rock but insignificant of hydrocarbon potential for further development.

Exploration for Helium in the Phanerozoic

Almost all the helium discovered worldwide has been found by chance in the drilling for hydrocarbons. Targets were usually anticlinal structures located by seismic surveys. The association of helium and natural gas in reservoirs is purely coincidental because the source rocks for each are different—natural gas is mainly produced from diagenesis of carbon rich shale whereas Helium- 4 is derived mainly from the decay of uranium/thorium in the crust. A new geochemical exploration system for helium in the Phanerozoic is considered highly desirable by industry. The current exploration system in the Phanerozoic uses a modified petroleum system concept that has been used successfully for decades to high-grade plays and de-risk oil and gas prospects. Like a petroleum system, the helium system is identified by its source rock, reservoir, trap, seal, and migration pathways. However, this approach is expensive taking years to complete and can be a limiting factor for countries/provinces/states to develop their resources. As a precursor to ground helium/hydrogen surveys for exploration in the Phanerozoic, hyperspectral (satellite) surveys assess huge areas for their helium potential as well as any associated hydrocarbons. These areas may be even devoid of any previous exploration for hydrocarbons. This is followed with geochemical soil gas surveys of the more prospective trends to locate drilling locations. Both methods ascertain whether helium anomalies, which represent helium reservoirs at depth, are associated with hydrocarbons or nitrogen. Helium reservoirs associated with nitrogen are higher in helium content but are deeper, close to the basement. Hyperspectral and geochemical soil gas surveys are also applicable for projects that begin with helium analysis of old wells followed by seismic and drilling. Typically, exploration companies lease vast areas surrounding the legacy well, but their initial focus is on seismic in the area around the legacy well to determine the size and configuration of the helium reservoir and trap penetrated by the well and this is followed by drilling. It is not known at this point whether this reservoir is the best prospect because the helium discovered is usually associated with hydrocarbon (HC), not with nitrogen with much higher helium concentration in the lower Phanerozoic. Rarely do legacy wells penetrate deep enough to this level. Any cost-effective exploration program for helium is best accomplished by hyperspectral and follow-up geochemical soil gas surveys.

Estimation of uplift and erosion in the Miri area of northwest Sarawak, Malaysia: A multidisciplinary approach

The question of uplift in the Sarawak Foreland is addressed in a multi-disciplinary approach, namely by assigning surface vitrinite reflectance measurements to depth, and by vitrinite reflectance-to-depth conversion using functions from two previous studies. Additional erosion and uplift data were obtained by comparing eroded anticlinal crests with adjacent synclines and their preserved sediments. The combined data pool suggests two types of uplift (I) a regional uplift in the Neogene affecting the entire coastal area, and (II) a tectonically focused uplift. The amount of the latter uplift and erosion is directly linked to rise of anticlinal structures during the Upper Pliocene, with a total uplift ranging from 700 to 4,000 m in areas along prominent regional faults. Within a very short time window major sedimentation, folding, trap formation and trap destruction took place both as a consequence of folding and erosion. Only anticlines in the offshore and the proximal onshore appear to have survived without major crestal erosion. Since the end of the Pleistocene, a rise of foreland sections by some 132 m is recognized. The rapid Pliocene burial and the erosion that consequently removed the overburden thereafter may have negatively affected the petroleum system and hydrocarbon accumulation within the Miri area, which was left largely intact only in the Siwa-Seria anticlinal trend. All anticlines were targeted by petroleum exploration. However, only the Siwa-Seria trend has proved to be economically successful. This has highlighted the significance of overburden in relation to depth of burial and the thermal effect needed to mature the source rocks capable to generate hydrocarbons.

Seismic characterisation of multiple BSRs in the Eastern Black Sea Basin

Long offset seismic reflection data reveal the presence of four Bottom Simulating Reflectors (BSR0-3) within folded sediments of the Tuapse Trough, along the NE margin of the Eastern Black Sea Basin (EBSB). Multiple BSRs are observed in other sites worldwide, however, their origin and formation mechanisms are still debated. Here, we investigate the formation mechanisms of the EBSB multiple BSRs based on their seismic character and on their physical properties derived from reflected and refracted arrival seismic velocities. Seismic reflection data are downward continued to enhance refracted arrivals. A 2D travel-time velocity model of the sub-seabed, using combined travel-times from non-downward-continued reflected and downward-continued refracted signals, shows variations in the physical properties at the BSRs and nearby sediments. The P-wave velocity (VP) increase of 1.55–1.72 km/s between the seafloor and BSR0 (258 mbsf) reflects normal compaction trends in sediments, whereas the VP of 1.75–1.83 km/s between BSR0 and BSR1 (360 mbsf) is higher than that expected for sediments at that depth. Beneath BSR1, a VP decrease from 1.83 km/s to 1.61 km/s occurs within a 70-80 m-thick layer including BSR2 (395 mbsf) and extending to BSR3 (438 mbsf). Beneath BSR3, VP increases. Based on an analytical model linking seismic velocity to physical properties, these VP trends can be explained by a gas hydrate saturation from 0 to 2% between the seafloor and BSR0, reaching 4 ± 2% just above BSR1. A free gas saturation of up to 20–25% is estimated within the low-velocity zone between BSR1 and BSR3. BSR1 likely represents the present-day base of the gas hydrate stability zone (BGHSZ), which aligns with the theoretical BGHSZ assuming a geothermal gradient of 26–30 °C/km. Based on seismic polarities and results from travel-time analysis and rock physics modelling, we suggest that hydrate dissociation and recycling processes may explain the negative polarity of BSR2 and BSR3, which are still visible due to the presence of relict gas, and inferred higher gas hydrate saturations close to the present-day base of the stability zone at BSR1. Also, structural and stratigraphic controls seem to have favoured focused free gas flow and hydrate formation at the top of an anticlinal structure, thus likely controlling multiple BSR generation in the EBSB.