Hydrocarbon Accumulation Research Articles

Optimized medium conditions maximize colony regeneration from a single cell of Botryococcus braunii NIES836

Botryococcus braunii is a colonial alga recognized for its slow growth but high hydrocarbon accumulation. Although using genetic engineering to increase the growth rate and hydrocarbon yield of B. braunii is desirable, the presence of an extracellular matrix (ECM) significantly hinders the emergence of a homogeneous colony from a single DNA-transformed cell. Previously, we developed a method to isolate single cells without ECM from colonies. However, following the isolation of single cells, several months are required to regenerate colonies with a sufficient cell mass for subsequent analysis. To shorten the colony regeneration period, we investigated basal media and medium components, along with growth-promoting additives, in a series of single-factor experiments and optimized the concentrations of the medium constituents via response surface methodology (RSM). The results of the single-factor experiments revealed that the nitrogen source (a mixture of NaNO3 and NH4NO3), 1-naphthylacetic acid (NAA) and Fe(III)-citrate significantly increased the growth of B. braunii single cells into colonies. The optimal medium composition identified by RSM included 151.6 mg/L nitrogen source, 2.419 mg/L NAA and 15.3 mg/L Fe(III)-citrate. Verification experiments showed that the optimized medium resulted in a 1.75-fold increase in colony size compared with that of colonies grown in nonoptimized AF6 medium. This is the first report of the optimal medium composition for the regeneration of B. braunii colonies from single cells.

Reactivation of a trap-boundary fault and its impacts on hydrocarbon migration and accumulation in Longkou 7 − 6 structure, Bohai Bay Basin: insights from geology, geophysics and basin modeling

Reactivation of a trap-boundary fault and its impacts on hydrocarbon migration and accumulation in Longkou 7 − 6 structure, Bohai Bay Basin: insights from geology, geophysics and basin modeling

Air pollution from unconventional oil and gas development in the Eagle Ford Shale

Unconventional oil and gas development (UOGD) has experienced substantial growth in recent years with currently unconstrained impacts on air quality. In this work, we describe ambient aerosol and gas-phase measurements during spring 2021 to examine air quality in the Eagle Ford Shale (EFS), a region in southeast Texas with thousands of UOGD wells. NOx, O3, H2S, PM1, and several VOCs were measured at concentrations above expected levels for non-urban regions. Hydrocarbon measurements from gas chromatography (GC) and proton transfer reaction (PTR) mass spectrometry show periodic high concentrations of variable compositions consisting of both saturated and unsaturated (polycyclic and/or aromatic) hydrocarbons, including larger (C > 10) unsaturated hydrocarbons that are often not quantified by GC measurements but are still present at substantial concentrations and relevant for air quality. Hydrocarbon VOCs are expected pollutants from anthropogenic activity and, based on ratios of i-pentane to n-pentane, xylene to benzene, and toluene to benzene, measured VOC ratios were characteristic of UOGD activity. Wind data and back-trajectory analyses show that air predominantly arrived from the S/SE, consistent with UOGD sources as well as shipping emissions from the Gulf of Mexico impacting air quality in the EFS. Analysis of diurnal trends at the site show hydrocarbon and NOx accumulation overnight and highlight diurnal differences in oxidative conditions, with important implications for both SOA and O3 formation. UOGD emissions impact the air quality in Karnes City and more broadly the EFS as well as the nearby urban area of San Antonio, which struggles to meet national air quality standards set by the Environmental Protection Agency.

Kureika–Tunguska Composite Tectono-Sedimentary Element, northern East Siberia

The Kureika–Tunguska Composite Tectono-Sedimentary Element (KT CTSE) is located in East Siberia. Geologically, it is confined to the homonymic basin in the northwestern part of the Siberian Craton. The basement of the basin is composed of Archean–Early Proterozoic metamorphic rocks. The sedimentary cover is composed of Mesoproterozoic, Neoproterosoic and Early Paleozoic predominantly carbonate rocks capped with a succession of Pennsylvanian–Permian coal-bearing sediments overlain by thick section of Early Triassic tuffs and lavas. The entire sedimentary cover, especially its upper part, is saturated with mafic intrusive bodies. The maximum depth to the top basement can exceed 10 km. The KT CTSE is characterized by a very low degree of exploration. The rather scarce prospecting work carried out on oil and gas in the CTSE has not yet yielded positive results. However, indirect data such as, for example, numerous bitumen fields and evidence of the source rocks are promising for potential discoveries including large hydrocarbon accumulations.

Three-dimensional reservoir modeling of the pliocene reservoir based on seismic data advances for new prospect assessment

This study presents a comprehensive characterization of the Pliocene reservoir formation in the Temsah gas field, located 65 km NNW of Port Said in the northeastern Nile Delta Basin. The research integrates seismic data with well log analysis to enhance reservoir characterization. The Temsah gas field is distinguished by its intricate geological structure, featuring numerous normal faults oriented along northeast-southwest and northwest-southeast trends. The field’s stratigraphy is predominantly composed of sandstone and shale facies, which are considered highly prospective for hydrocarbon accumulation. A full geological field analysis was conducted to identify key prospects for enhancing productivity. To accurately delineate seismic features, data from four wells and twenty-nine 2D seismic lines were interpreted. Depth maps of the reservoir layers were constructed, highlighting critical transitions between sandstone and shale facies, which are pivotal for future exploration efforts. A detailed 3D static model was developed to illustrate the impact of lithological composition on reservoir characteristics, with a specific focus on the Upper Sand of Kafr El-Sheikh Formation. Petrophysical properties, including effective porosity (13–23%), shale content (7–31%), and water saturation (30–45%), were meticulously evaluated to inform the creation of a robust 3D property model. This model provides a detailed spatial distribution of rock facies and petrophysical parameters within the Temsah gas field. The integration of these studies identified two promising areas, with estimated original gas in place (OGIP) ranging from 2.86 to 4.04 stock cubic feet (SCF), indicating significant potential for field development and enhancement.

Heterolytic tide-dominated sedimentary facies and depositional environment: An Example from the Boka Bil formation, Sitapahar anticline, Bangladesh

The Baraichari Shale Formation, which is equivalent to the Boka Bil Formation, is well exposed within the Neogene sequence of the Sitapahar Anticline in the Chittagong-Tripura Fold Belt, Bengal Basin, Bangladesh. Regardless of its importance in hydrocarbon accumulation, a comprehensive facies analysis is essential to understand and explain the heterogeneity within different depositional architectural elements. The purpose of this work is to delineate the lithofacies characteristics, depositional environment heterogeneities and propose a generic depositional model for the Middle to Late Miocene shallow marine sediments of the formation. The sedimentary facies were investigated at three outcrops along the Kaptai–Chandraghona road cut sections of the Sitapahar anticline. The formation is composed of dark to bluish-gray shale, silty shale, yellowish brown siltstone, and gray to yellowish brown fine-to medium-grained sandstone. Eight distinct sedimentary facies have been identified and were categorized into three facies associations: subtidal or estuarine, mixed flats with tidal creeks, and tidal mud flats. The subtidal facies, predominant in the middle member, consists of fine to medium-grained ripple cross-stratified sandstone-siltstone, herringbone cross-stratified sandstone, and trough cross-stratified sandstone, indicating sub-tidal channel deposition. Mixed flats with tidal creeks exhibit heterolithic facies, suggesting energy level changes in intertidal to sub-tidal zones influenced by tidal currents. Tidal mud flats are predominantly laminated shale/mudstone and lenticular laminated sandstone-siltstone, reflecting deposition during tide transitions in the intertidal zone. Fining upward cycles within the formation indicate progressive progradation or changes in inner tidal flats conditions during regressive periods. These depositional settings serve as analogs for equivalent subsurface reservoirs and contribute to the construction of reservoir models with greater accuracy.

Studies on the characteristics of polycyclic aromatic hydrocarbons accumulation in lipids and the disturbance of lipid metabolism of Ruditapes philippinarum

Polycyclic aromatic hydrocarbons (PAHs) constitute a class of persistent organic pollutants with strong lipophilicity, which readily accumulate within organisms and have the effect to induce disorders in lipid metabolism. The present study aimed to investigate the accumulation localization and pattern of PAHs in Ruditapes philippinarum, and to reveal the association between PAHs and lipids metabolism. The 21-day exposure experiment was conducted using a mixture of phenanthrene, chrysene, and benzo[a]pyrene (the proportion is 1:1:1) at concentrations of 0.4 μg/L, 2 μg/L, and 10 μg/L. The tissue distribution of PAHs indicated that the digestive gland was the primary site of PAHs accumulation. Meanwhile, fluorescence colocalization suggested that PAHs primarily accumulated within the lipid droplets of digestive gland cells. This study further determined the transcriptomic and lipidomic profiles of the digestive gland to analyze the key genes involved in disrupted lipid metabolism and the major lipids affected. Lipidomic analysis identified the key differential metabolites as triglycerides (TGs). Furthermore, TGs were upregulated in the digestive gland had a total carbon atom number of 50–64 and a total number of 3–9 double bonds in the acyl side chains. Biochemical analysis experiments and oil red O stained frozen sections confirmed that the content of TGs steadily increased in various tissues during the experiment, leading to an elevated digestive gland index. Changes of lipid metabolism associated genes expression level also indicated that the synthesis of lipid in digestive gland were up-regulated while the decomposition was down-regulated. This study is the first to demonstrate the cellular localization of PAHs accumulation in bivalves and confirms the pattern of variation in TGs, providing new insights into the mechanisms of PAHs bioaccumulation and lipid metabolism disruption.

Synthesizing a realistic seismic training data set incorporating prior geologic patterns and seismic imaging features for supervised convolutional neural network-based intracratonic strike-slip fault detection

Intracratonic strike-slip faults play a vital role in hydrocarbon migration and accumulation, making their accurate detection crucial for subsurface structure interpretation and reservoir characterization. Although numerous approaches have been developed for automatic fault interpretation, they are still unable to fully recognize intracratonic strike-slip faults with subtle reflection variations in seismic images. We develop a supervised convolutional neural network (CNN) to automatically and precisely delineate these faults in 3D seismic images. The primary obstacle in using a CNN for this task is the lack of diverse seismic training samples and corresponding high-quality labels. To address this, we develop an efficient two-step workflow for automatically generating a tremendous amount of 3D seismic training sample pairs: (1) guided by the prior geologic structure patterns of the study area, we use parameterized vector fields to simulate various velocity models with accurate fault labels incorporating realistic intracratonic strike-slip faulting features, such as the transtensional, transpressional, and strike-slip translational types and (2) following seismic imaging laws, we synthesize seismic training samples from simulated velocity models through the point-spread function-based convolution method. One synthetic and two field examples demonstrate that the CNN trained with this seismic data set containing prior geologic patterns and seismic imaging features outperforms the conventional fault detection approaches in accurately and continuously delineating intracratonic strike-slip faults.

Prospects for the allocation of Paleorousels in the subsalt complex of the south-east of the Caspian sedimentary basin

development and features of the formation of the sedimentary complex of the south of the Caspian sedimentary basin are presented. The complex geological structure of the region is mainly due to the influence of tectonic, volcanic and denudation processes on sedimentation. The introduction of terrigenous material deep into the sedimentary basin (Matken-Ushmolinsk, Biikzhal and South Embin zones) by paleorubic flows contributed to the emergence of accumulative shafts and interbranch uplifts composed mainly of clay rocks with alternating siltstone-sandstones. In the paleorusls themselves, coarser sediments were deposited – gravelites and sandstones. The reconstruction of the conditions of formation of sand bodies made it possible to predict their facies composition, morphology and identify patterns of spatial placement, and are also of great interest in the search for oil and gas deposits in deep-lying lithological traps. The prospects of these structures and their resource potential are evidenced by the world experience in identifying large deposits of hydrocarbon raw materials. This is a new highly promising direction of large accumulations of hydrocarbons for the Caspian Basin. The results of drilling deep wells conducted in recent years have made it possible to refine the internal structure, substantiate new facilities in the Late Paleozoic sedimentary complex, and reassess the prospects of oil and gas potential and forecast oil and gas resources of the south of the Caspian Basin.

Petrological and geochemical evidences for anaerobic and thermochemical oxidations of methane in petroliferous basins

Methane oxidation affects hydrocarbon accumulation and carbon cycling with important geological and paleoclimatic responses. However, the petrological and geochemical evidences that can clearly discern anaerobic (AOM) and thermochemical (TOM) oxidations in petroliferous basins are unclear, causing the disputes if these two processes can take place in specific conditions. Here, the Baikouquan Formation (T1b) in the Mahu Sag, Junggar Basin, China, was used as the first case study for comprehensive petrological and geochemical analyses to explore this scientific issue. Results indicate that the two main types of T1b calcite cement record different methane oxidation mechanisms. Calcite cements filling intergranular pores were formed during early diagenesis in relatively shallow-burial stages, through AOM with high-valence Mn oxides as electron acceptors, and with compositions of −47.5 ‰ < δ13C < −30.9 ‰, 1.1 wt% < MnO < 5.8 wt%, and 0.02 wt% < FeO < 0.13 wt%. Calcite cements filling intragranular dissolution pores were formed through TOM with high-valence Mn oxides as electron acceptors during mesogenesis during relatively deep-burial stages, with compositions of −39.7 ‰ < δ13C < −14.3 ‰, 0.43 wt% < MnO < 11.00 wt%, and 0.03 wt% < FeO < 0.36 wt%. Thus, methane oxidation underwent a transition from AOM to TOM with increasing depth, as recorded by the calcite cements with different occurrences. This transition may be a common feature of clastic strata in petroliferous basins.

Uranium mobility and enrichment during hydrocarbon generation and accumulation processes: A review

Black shale serve as a new uranium sources and provide reducing agents for uranium deposits through hydrocarbon generation. However, the systematically interplay between the black shale and the formation of uranium deposits is not obscure. This paper provides a comprehensive summary and critical assessment of the depositional control factors of uranium in black shales, the extent of uranium migration during hydrocarbon generation, the enrichment of uranium in oil/gas reservoirs, and the relationship between crude oil-natural gas leakage and uranium. The study show that U-riched constituents within black shale persist through mechanisms of adsorption, reduction, complexation, and absorption within matrices rich in phosphates, iron, carbonate minerals, and organic matter. The U in black shale originates from continental weathering, volcanic eruptions, and seabed hydrothermal activities. The average U concentration in black shale is determined by the U content in atmosphere, while its relative content is controlled by the degree of anoxia during the geological historical periods.. Black shale prior to the Late Neoproterozoic period exhibits minimal migration with hydrocarbon substances, whereas black shale post the Late Neoproterozoic period demonstrates migration, with a migration rate ranging approximately between 55 and 75 %. However, the migrated uranium does not accumulate in (ancient) reservoirs. The correlation between hydrocarbon substances and sandstone-type uranium deposit is attributed to the oxygen uptake by hydrocarbons or the thermochemical sulfate reduction (TSR). The study has fundamental significance for further understand the interaction mechanisms between uranium and hydrocarbon substances.

A study on the accumulation model of the Santos basin in Brazil utilizing the source–reservoir dynamic evaluation method

The exploration potential within deep-water petroliferous basins holds great promise for oil and gas resources. However, the dearth of geochemical and isotopic data poses a formidable challenge in comprehending the intricate hydrocarbon charging processes, thereby impeding the comprehensive understanding of hydrocarbon accumulation mechanisms and models. Consequently, the establishment of robust source–reservoir relationships in deep-water petroliferous basins represents a pivotal challenge that significantly influences the exploration strategies and the comprehension of hydrocarbon enrichment dynamics within such basins. In this study, we introduce a novel approach, termed the “source–reservoir dynamic evaluation method,” tailored to investigate reservoir accumulation models in deep-water petroliferous basins. This method uses basin simulation technology to recover the thermal evolution history and hydrocarbon generation and expulsion history of source rocks, and on this basis delimits the hydrocarbon kitchen range. At the same time, the maturity of source rocks corresponding to crude oil and natural gas in typical reservoirs is calculated. Then, when the thermal evolution degree of source rocks adjacent to the reservoir reaches this maturity, the corresponding geological period is the main charging period of hydrocarbon. As a typical deep-water petroliferous basin, the Santos Basin in Brazil has abundant oil and gas reservoirs under the thick salt rock, but there are still some fundamental problems such as unclear oil–gas accumulation process and model. Therefore, in this paper, the main charging periods of typical hydrocarbon reservoirs are determined based on the internal relationship between the thermal evolution history of the main source rocks and the maturity of crude oil and natural gas, and then the hydrocarbon accumulation process is analyzed and the dynamic accumulation model is established. Finally, the favorable prospecting direction is pointed out. The results show that the oil and gas in the Barra Velha Formation in the Santos basin are mainly derived from the Itapema Formation lacustrine shale source rock, and the source rock is mainly developed in the Eastern Sag of the Central Depression, and its main hydrocarbon generation period is from the deposition period of Florianopolis Formation to the deposition period of Santos Formation. The main hydrocarbon expulsion period was from the deposition period of the Santos Formation to the Early deposition of the Iguape Formation. The oil and gas in the Barra Velha Formation were mainly charged from the Late deposition period of the Santos Formation to the Early deposition period of the Iguape Formation. During this period, the hydrocarbon migrated vertically along the normal fault formed in the rift period to the trap of the adjacent inheritance structural highs and accumulated in the reservoir, which was dominated by the accumulation model of the “lower generation-upper reservoir-salt cap”. Since the Barra Velha Formation has the characteristics of near-source accumulation, based on the hydrocarbon expulsion center and hydrocarbon expulsion intensity of the source rock of the Itapema Formation, the distribution ranges of 85% and 50% Pre-salt accumulation probability in the Santos basin were calculated by using the quantitative analysis model of the hydrocarbon distribution threshold. It is suggested that the next oil and gas exploration should be carried out in the paleo-structural highs and slope of Class I favorable area (the hydrocarbon accumulation probability is more than 85%) and Class II favorable area (the hydrocarbon accumulation probability is 85–50%).

The Strike-Slip Fault System and Its Influence on Hydrocarbon Accumulation in the Gudong Area of the Zhanhua Depression, Bohai Bay Basin

The Gudong area contains abundant petroleum resources. Previous studies have mainly focused on the extension structure in this area, with its strike-slip characteristics remaining poorly understood. In this study, the geometry of the strike-slip faults in the Gudong area was investigated using high-resolution 3D seismic reflection and drilling data, as were their associated releasing and restraining structures. Based on the profile’s flower structure and the plane’s horsetail splay pattern, the Gudong fault in the study area can be characterized as a dextral strike-slip. Three types of strike-slip fault-associated structures can be identified in the study area: (a) a restraining bend occurring in the right-stepping area of the S-shaped Gudong strike-slip fault, (b) a restraining bend identified in the left-stepping, overlapping zone of the Gudong and Kendong faults, and (c) a releasing bend seen in the extensional horsetail splay structure at the southern end of the Gudong fault. The restraining stress induced the formation of a fault-related open anticline, which led to a significant increase in fault sealing efficiency, thereby preserving an estimated 75.479231 million tons of oil and 15.28317145 billion cubic meters of gas. Conversely, releasing transtensional stress has compromised the effectiveness of the traps, preventing hydrocarbon retention. Consequently, oil and gas have migrated upward along the horsetail faults to the top of Cenozoic formations and have then dispersed.

Zyryanka Basin Composite Tectono-Sedimentary Element, northeastern Asia

The Zyryanka Composite Tectono-Sedimentary Element is located in NE Asia. It consists of a synonymous sedimentary basin that is one of the least studied onshore basins in NE Asia due to its remoteness and the scarcity of wells and geophysical data. The basin evolved through four episodes of subsidence and two episodes of contraction. The Late Jurassic–Late Cretaceous subsidence is inferred to be caused by tectonic loading during contraction events within the Verkhoyansk–Kolyma Orogen, which led to the deposition of up to 10 km of predominantly continental siliciclastic strata. In the Cenozoic, the basin evolved in a post-orogenic intracontinental setting and accumulated a 2–3 km-thick succession of continental siliciclastic strata. In the Oligocene–Mid-Miocene, the basin evolved in a contractional setting, caused by a convergence between the Eurasian and North American lithospheric plates, and underwent a contractional deformation in the Middle Miocene. We recognize four individual tectono-sedimentary elements that are related to different stages of the basin's evolution. The basin contains significant coal resources. It was also considered a potential prospective area for the formation of hydrocarbon accumulations, especially in its Upper Jurassic–Cretaceous strata; however, drilled wells did not encounter any oil- or gas-bearing reservoirs.

Study on the Changes and Correlation of Microorganisms and Flavor in Different Processing Stages of Mianning Ham.

(1) Background: Mianning ham is a dry-cured ham from Southwest China, known for its distinct regional characteristics and delicious taste. It is particularly favored by consumers due to its safety, as no artificial nitrites are added during processing. The microbial changes during its different processing stages significantly influence the final product's flavor. This study aims to investigate the changes in microbial communities and flavor compounds across the nine stages of Mianning ham production, from raw material preparation to salting, drying, fermentation, and maturation, using 16S and ITS sequencing, as well as solid-phase microextraction-gas chromatography-mass spectrometry (SPME-GC-MS). The goal is to explore the correlation between these changes and provide a basis for process improvement from the initial raw material preparation. (2) Results: The microbiota of Mianning ham across different processing stages mainly consisted of Proteobacteria, Firmicutes, and Ascomycota. A total of 324 volatile compounds were identified, of which 27 were key contributors to the ham's flavor. Aldehydes contributed the most to flavor, with octanal, trans-2-nonenal, and trans, trans-2,4-decadienal being the most significant contributors at various stages. Mature Mianning ham, fermented for 1-3 years, exhibited fresh grass and earthy aromas, buttery and fatty flavors, and a distinctive roasted potato note. Correlation analysis revealed that Cobetia was the primary bacterial contributor to the main flavor compounds, especially prominent in the second year of fermentation. Among fungi, Yamadazyma and Aspergillus positively influenced several key aldehyde flavor compounds throughout the processing stages, significantly contributing to the flavor profile of Mianning ham. (3) Conclusions: Correlation analysis showed that the Mianning ham that matured for two years had the richest and most characteristic flavor. The positive and consistent impact of fungi on the ham's flavor suggests that they may warrant further research and application in Mianning ham production. This provides a theoretical basis for improving the flavor quality and enhancing the market competitiveness of Mianning ham. One of the key features of Mianning ham is its substantial accumulation of hydrocarbons, which surpasses that of hams from other regions in China. A notable characteristic of Mianning ham processing is the absence of artificially added nitrites as antioxidants and color fixatives. Whether this absence is a contributing factor to the significant accumulation of hydrocarbons warrants further investigation.

Experimental investigation of kerogen structure and heterogeneity during pyrolysis

Kerogen in shale microstructure plays a vital role in hydrocarbon generation, retention and accumulation. However, characterization of kerogen structure is challenging arguably due to a complex microporous structure and chemical heterogeneity. Thus, the role of kerogen molecular structure in controlling porosity and its heterogeneity, as well as its evolutionary processes, remains unclear. In this study, we investigate the chemical and pore structure of heated kerogen samples by employing a range of characterization tools including gas adsorption experiments, high-resolution transmission electron microscopy (HRTEM), Fourier transform infrared (FTIR) spectroscopy, and laser Raman experiments for a broad range of pyrolysis temperatures (420–850 °C). Multifractal theory and peak fitting techniques were used to evaluate the controlling mechanisms of kerogen pore structure and heterogeneity. The results suggest that with increasing thermal maturity, the content of oxygen functional groups and long-chain aliphatic groups in kerogen significantly decreases, while the length of aromatic fringes increases and gradually becomes oriented. Furthermore, with increasing thermal maturity, the pore volume of kerogen exhibits a non-monotonic trend, i.e., a decrease, followed by an increase, and then finally a decrease. This is primarily influenced by processes such as hydrocarbon production weakening, secondary hydrocarbon cracking, and carbonization. The heterogeneity and dispersion of meso to macro-sized pores in kerogen increase with temperature, while the connectivity gradually decreases. The chemical structure and spatial distribution of kerogen significantly affect the heterogeneity, connectivity, and dispersion of meso to macro-sized pores. Specifically, high aromaticity, structural disorder, and short aliphatic chains result in enhanced heterogeneity and dispersion of meso to macro-sized pores, reducing pore connectivity. This study thus contributes to a deeper understanding of the evolution of organic matter pores.

CONTRIBUTION OF SEISMIC AND GEOTHERMAL DATA ANALYSIS TO THE ASSESSMENT OF THE HYDROCARBON POTENTIAL OF THE CENTRAL BASIN OF THE D.R. CONGO

This paper presents an evaluation of the hydrocarbon potential of the Cuvette Centrale basin in the Democratic Republic of Congo (DRC) using an integrated approach that combines seismic and geothermal data. The envelope attribute of seismic data was used to identify different rocks of the petroleum system, including potential gas-prone zones. The interpretation of seismic profiles helped to delineate geological units and determine their lithology. Isobath maps based on seismic data revealed the presence of grabens and anticlines, which are favorable geological structures for hydrocarbon accumulation. Analysis of the geothermal gradient and temperature evolution in the formations allowed us to establish source rock maturity maps, highlighting two distinct zones: an overmature zone favorable for gas and a mature zone favorable for oil. These results suggest a strong hydrocarbon potential in the Cuvette Centrale basin.

Formation temperature of microcrystalline dolomite in oil-rich black shale: Implications for hydrocarbon accumulation in a volcanic-lacustrine rift basin

Lacustrine microcrystalline dolostones in the ancient records have been commonly interpreted as of an evaporitic origin, on the basis of their numerous occurrences in modern evaporative shallow lakes. This interpretation obscures the forming mechanisms of dolostones formed in a deep lacustrine setting, where dolostones interbedded with shale become a focus of hydrocarbon source rocks in recent years. In this study, an alternative non-evaporitic origin of dolomite is interpreted for a Permian lacustrine laminated dolostone. The dolostones are thinly intercalated with tuffaceous shales and composed mainly of volumetrically abundant, low-ordered, subhedral to euhedral, microcrystalline dolomites with a variable amount of pyroclastics. Evidence for evaporation (e.g., the presence of halite, gypsum and shrinkage cracks) and typical methanogenic microfossils is absent. Instead, our dolostones are unevenly and locally distributed as thin beds or lenses and intercalated with tuffaceous shale and have a formation temperature ranging from 31.4 to 73.8 °C, as estimated from dolomite clumped oxygen? isotope thermometry. In addition, the dolostones have a87Sr/86Sr ratio similar to that of the mantle (0.705154 on average) and extremely negative δ18O (−2.9‰ to −24‰) and positive δ13C (5.1‰–10.8‰) values. A lateral trend of increasing formation temperature of the dolostone toward the volcanic center correlates with the trends of: 1) an increasing amount of pyroclastics, euhedral dolomite crystals, Fe, and TOC, and an increasingly positive δEu value, and 2) decreasing values of 87Sr/86Sr and δ18O. The correlation suggests that a local temperature increase and frequent elemental (Fe and Mg) cycling between the conditions of dolomite supersaturation and undersaturation, which are controlled by episodic volcanic-hydrothermal activities are the causes for dolomite nucleation and growth, resulting in the formation of massive dolostone during deposition and shallow burial. The process also affected organic matter accumulation and local transformation to immature or early mature hydrocarbon during deposition and early burial. The results establish a volcanism-controlled temperature range for primary dolomite nucleation and growth, as well as hydrocarbon generation in a deep lake environment during the period of deposition and early burial, and provide insights on shale oil exploration in petroliferous rift basins.

Hydrocarbon accumulation and orderly distribution of whole petroleum system in marine carbonate rocks of Sichuan Basin, SW China

Based on the situation and progress of marine oil/gas exploration in the Sichuan Basin, SW China, the whole petroleum system is divided for marine carbonate rocks of the basin according to the combinations of hydrocarbon accumulation elements, especially the source rock. The hydrocarbon accumulation characteristics of each whole petroleum system are analyzed, the patterns of integrated conventional and unconventional hydrocarbon accumulation are summarized, and the favorable exploration targets are proposed. Under the control of multiple extensional-convergent tectonic cycles, the marine carbonate rocks of the Sichuan Basin contain three sets of regional source rocks and three sets of regional cap rocks, and can be divided into the Cambrian, Silurian and Permian whole petroleum systems. These whole petroleum systems present mainly independent hydrocarbon accumulation, containing natural gas of affinity individually. Locally, large fault zones run through multiple whole petroleum systems, forming a fault-controlled complex whole petroleum system. The hydrocarbon accumulation sequence of continental shelf facies shale gas accumulation, marginal platform facies-controlled gas reservoirs, and intra-platform fault- and facies-controlled gas reservoirs is common in the whole petroleum system, with a stereoscopic accumulation and orderly distribution pattern. High-quality source rock is fundamental to the formation of large gas fields, and natural gas in a whole petroleum system is generally enriched near and within the source rocks. The development and maintenance of large-scale reservoirs are essential for natural gas enrichment, multiple sources, oil and gas transformation, and dynamic adjustment are the characteristics of marine petroleum accumulation, and good preservation conditions are critical to natural gas accumulation. Large-scale marginal-platform reef-bank facies zones, deep shale gas, and large-scale lithological complexes related to source-connected faults are future marine hydrocarbon exploration targets in the Sichuan Basin.

Determination of phase components of impedance in the environments over hydrocarbon accumulation

Abstract The article presents a novel method for hydrocarbon accumulation exploration based on determining the phase components of impedance in environments over hydrocarbons. Experimental studies were conducted at the Rechitsa hydrocarbon field and Osipovichi underground gas storage. The phase characteristics of surface impedance of hydrocarbon accumulation were measured using amplitude-frequency-modulated signals. The results show that determining two components of surface impedance in this mode significantly improves the accuracy of hydrocarbon boundary determination. The developed method can be implemented at frequencies of 0.1-2 GHz, using modulation frequencies of 10-100 MHz, amplitude modulation coefficients of 0.1-1.0, and frequency modulation indices of 20-95. The findings of this research can be applied in electrical exploration for prospecting hydrocarbon accumulation.