Artificial Maturation Research Articles

Graptolite reflectance anomaly

Thermal maturation is traditionally evaluated based on vitrinite reflectance (VRo) measurements and its relationship to oil and gas generation and diagenetic transformation are ingrained in many basin modeling tools. However, vitrinite derives from higher land plants that evolved in Devonian. In pre-Devonian rocks graptolite reflectance (GR) is the most significant thermal index for establishing thermal maturation. Currently, conversions of GR to VRo equivalent rely on several established linear relationships. This study investigates a continuous thermal evolution of GR during artificial maturation of the Lower Ordovician (Tremadocian) Alum Shale of Estonia. We observe an anomalous breakdown in the gradient of GR versus thermal maturity. The anomaly trend is characterized as a suppressed GR gradient throughout the entire gas window (VRo: 1.0–2.0%). We attribute the suppressed measured GR trend to surface imperfection caused by the generation and evasion of hydrocarbon gases that generate nano-porosity vacuolation of the graptolite tissues. After the gas window, GR resumes its increasing trend with a similar gradient as observed in the pre-gas window, due to continued aromatization and condensation of the organic molecules. The GR anomaly indicates a potential underestimation of thermal maturity up to 0.52%VRo when applying a linear conversion formula between random GR and VRo directly. Therefore, a significant maturity correction should be applied to all legacy GR-based maturity measurements that indicate a gas or post-gas maturity rank.

Broad Ion Beam–Scanning Electron Microscopy Characterization of Organic Porosity Evolution During Thermal Treatment of Bazhenov Shale Sample

Summary Organic matter-hosted pores are considered as the main type of porosity in organic-rich shales. At the same time, literature indicates the formation of pore space during pyrolysis of oil shales. However, controls, evolution, and types of organic porosity remain controversial. This study aims to experimentally investigate the evolution of organic pores in an organic-rich shale sample during thermal treatment. This paper reports the organic porosity evolution during an artificial maturation experiment of the Bazhenov Formation (BF) shale sample (West Siberian Petroleum Basin). The siliceous-argillaceous organic-rich shale immature nonporous rock sample was treated in an open system in the temperature range of 350–450°C with the step of 10°C. Organic porosity was characterized by the combination of broad ion beam (BIB) polishing and scanning electron microscopy (SEM). After each episode of treatment, the area of 1000×1000 μm was scanned with a resolution of 25 nm. The acquired mosaic SEM images were segmented by the neural network algorithm and quantitatively analyzed. We demonstrate direct experimental evidence that thermal maturation/thermal treatment influence on organic porosity development. Organic porosity evolution is shown within the individual organic matter (OM) particles throughout the experiment. Thermal treatment leads to the formation of two types of organic pores, which are shrinkage and spongy pores. The first shrinkage pores start to form after the evacuation of existing hydrocarbons; they are relatively large and might reach 7 µm. This type of pore dominates at the initial stages of treatment (350–390°C). Porosity at this stage does not exceed 1.4%. The second type is spongy pores, which are up to 3–5 μm in size and are potentially formed due to hydrocarbon generation from the kerogen. This type of porosity becomes major after 400°C. This is confirmed by the pore size distribution analysis. The porosity spikes up to 2.3% after 400°C and rises up to 2.9% after 450°C. Revealing of artificial organic porosity development during thermal treatment experiment shows the crucial importance of the thermal maturity level. The formation of pore space during the treatment is critical during the implementation of thermal enhanced oil recovery (EOR) technologies in shales for fluid flow, and a mandatory aspect that should be accounted during thermal EOR simulations.

Bacterial survey of skin ulcers in Anguilla anguilla L. females during artificial maturation under controlled conditions

Controlled indoor reproduction of European eel is commonly recognized as a prospective tool to prevent extinction of this fish species. There is a little information about diversity of bacterial microflora of European eel during long maturation under controlled but changing thermal and salinity conditions. Characteristics of the composition of the bacterial microflora inhabiting the body surface of fish kept firstly in fresh and then in salt water, may help enhance the survival of spawners and spawning efficiency. Knowledge about the presence of potentially pathogenic bacterial species and their antibiotic resistance is particularly important. Methods: This study analyzed the bacterial microflora of two types of necrotic changes on the skin of eel females during artificial maturation under fresh and saltwater conditions. Results: A total of two hundred and forty bacterial strains were isolated from necrotic dermal changes on fish in freshwater and saltwater conditions. Both the bacterial number and biodiversity were greater in freshwater than in saltwater. Psychrophilic bacterial strains in freshwater were twice as abundant as in saltwater, especially among isolates which were cultured from the mucus or from ulcerative changes around the chip injection point (up to 1010 cfu/mL). 16 S ribosomal RNA gene sequencing of isolates from the freshwater conditions revealed the presence of twenty genera of bacteria, including: Pseudomonas sp., Comamonas sp., Escherichia sp., Aeromonas sp., Citrobacter sp., Burkholderia sp., Pantoea sp., Enterobacter sp., Yersinia sp., Edwardsiella sp., Serratia sp., Bordetella sp., Morganella sp. and Chromobacterium sp. In saltwater conditions, five genera of bacteria were found dominantly: Pseudomonas sp., Aeromonas sp., Yersinia sp., Vibrio sp., Edwardsiella sp. In freshwater conditions, the bacteria were mostly resistant or resistant to all tested antimicrobial drugs. Conclusions: Changes in bacterial microflora during controlled indoor reproduction of European eel predispose fish to bacterial infection especially during the first freshwater step of female maturation. New, alternative to antibiotic therapy, methods should be adopted to prevent infections and enhance spawning efficiency.

Incorporation of water-derived hydrogen into methane during artificial maturation of source rock under hydrothermal conditions

To investigate the origin of CH bonds in thermogenic methane (CH4), a solvent-extracted sample of organic-rich Eagle Ford shale was reacted with heavy water (D2O) under hydrothermal conditions (350 bar) in a flexible Au-TiO2 cell hydrothermal apparatus at a water-to-rock ratio of approximately 5:1. Temperature was increased from 200 to 350 °C over the course of one month and the concentrations of aqueous species and methane isotopologues were quantified as a function of time. In general, production of hydrogen, CO2, alkanes, and alkenes increased with time and temperature. Methane formed during the early stages of the experiment at 200 °C was primarily C1H4 with some CH3D. With progressively higher temperatures, increasing proportions of deuterated isotopologues were produced. Near the end of the experiment, the concentration of CD4 exceeded that of all other isotopologues combined. These results suggest that competition between rates of kerogen-water isotopic exchange and natural gas generation may govern the D/H ratio of thermogenic gases. Furthermore, hydrogenation of kerogen by water may be responsible for hydrocarbon yields in excess of those predicted by conventional models of source rock maturation in which hydrocarbon generation is limited by the amount of organically bonded hydrogen.

Convolutional neural network-based automatic cervical vertebral maturation classification method.

This study aimed to develop a fully automated artificial intelligence-aided cervical vertebral maturation (CVM) classification method based on convolutional neural networks (CNNs) to provide an auxiliary diagnosis for orthodontists. This study consisted of cephalometric images from patients aged between 5 and 18 years. After grouping them into six cervical stages (CSs) by orthodontists, a data set was constructed for analyzing CVM using CNNs. The data set was divided into training, validation, and test sets in the ratio of 70, 15, and 15%. Four CNN models namely, VGG16, GoogLeNet, DenseNet161, and ResNet152 were selected as the candidate models. After training and validation, the models were evaluated to determine which of them is most suitable for CVM analysis. Heat maps were analyzed for a deeper understanding of what the CNNs had learned. The final classification accuracy ranking was ResNet152>DenseNet161>GoogLeNet>VGG16, as evaluated on the test set. ResNet152 proved to be the best model among the four models for CVM classification with a weighted κ of 0.826, an average AUC of 0.933 and total accuracy of 67.06%. The F1 score rank for each subgroup was: CS6>CS1>CS4>CS5>CS3>CS2. The area of the third (C3) and fourth (C4) cervical vertebrae were activated when CNNs were assessing the images. CNN models proved to be a convenient, fast and reliable method for CVM analysis. CNN models have the potential to provide automatic auxiliary diagnostic tools in the future.

Effects of confining pressure and microscale heterogeneity on hydrocarbon retention and pore evolution from artificial maturation of Eagle Ford Shale

Although shale heterogeneity has recently emerged as a key topic in unconventional petroleum systems, hydrocarbon (HC) retention and pore evolution in organic-rich shales still remain poorly constrained. In this study, an organic-rich Eagle Ford Shale sample (EqVRo = 0.92%) from a shale-oil prospecting well in South Texas was selected for gold-tube pyrolysis experiments to investigate organic matter (OM) -hosted pore development versus confining pressure during thermal maturation. Before heating, the OM-type heterogeneity and associated pore characteristics in the sample were examined by thin section and scanning electron microscopy imaging, combined with elemental mapping by X-ray energy-dispersive spectroscopy. Four forms of OM occurrence that are closely associated with different mineral matrix domains are distinguished, including the ductile oil-bearing primary OM and rigid primary OM in the siliceous-argillaceous seams, as well as the secondary OM in coccolith-rich lenses and in foraminifera chambers. From heating experiments, the pressure effect on pore evolution was found to be pronounced for the secondary OM in the foraminifera chambers, in which the coalescence of small pores to larger pores upon OM maturation was accelerated by increasing fluid pressure, accompanied by arrangement and densification of OM structures. However, the expulsion effect as a function of confining pressure seems to be evident only for the secondary OM in the coccolith-rich lenses. In contrast, the two types of primary OM in the siliceous-argillaceous seams do not show any apparent changes in pore development over the investigated pressure range of 10 to 120 MPa, probably due to stiffer mechanical properties of primary OM as compared to secondary OM. The discrepancies in pore evolution of different OM types as a response to the variation in confining pressure upon maturation primarily depend on the physical-chemical properties of these various OM materials.Of further importance, observed differences in OM evolution and associated pore characteristics in response to the variation in confining pressure imply that the microscale heterogeneity of shale fabric controls the extent of oil retention and pore evolution. In contrast to the intragranular pores in the foraminifera chambers, the intergranular pores in the coccolith-rich lenses from the Eagle Ford Shale sample are relatively smaller, yet more likely interconnected. Thus, these coccolith-associated pores may provide not only significant storage space but also a major flow pathway for HC production. Our investigation at the microscopic scale provides concepts indicating that HC retention and OM-hosted pore evolution occur differently in two contrasting types of mineral matrix pores, which is critical to successful unconventional shale oil and gas exploration in sedimentary basins.

Maturation and migration processes in intact source rock micro plugs induced by chemical and thermal treatment: A new approach combining Rock-Eval pyrolysis and organic petrography

This study proposes a new approach to investigate hydrocarbon generation and migration processes in petroleum source rocks under laboratory conditions. For the first time, programmed open-system pyrolysis using a Rock-Eval 6 instrument is applied on small, polished source rock plugs to induce changes in the type and distribution of solid bitumen, which are qualitatively investigated by means of organic petrography before and after different pyrolysis experiments. This approach allows us to directly visualize the evidence of solid bitumen (SB) formation and distribution after the following treatments: (1) thermal extraction at 300 °C for 3 min, (2) chemical extraction of the surface using dichloromethane (DCM), and subsequently (3) artificial maturation by applying the standard procedure of Rock-Eval programmed pyrolysis up to a temperature of about 400 to 500 °C (depending on the initial thermal maturity of the sample). After each step, the surface of the treated micro plugs was digitally scanned to allow a comparison of specific areas of interest before and after the respective treatments and alterations. For this study, core samples of the Eagle Ford Shale Formation are used, which are suitable for such investigation, as the Eagle Ford Shale exhibits a variety of different initial thermal maturities from immature to overmature. Furthermore, the presence of large intraparticle porosities provides suitable voids where changes in SB distribution can easily be observed. After the thermal extraction, the volume of observed SB in the early- and moderately mature samples slightly increased, while most of the thermally mobilized bitumen from inside the plug was evaporated and thus lost from the sample. The initial solid bitumen was not or hardly affected by thermal extraction at 300 °C for 3 min, i.e. it was thermally stable at this temperature. Solid bitumen reflectance was slightly higher than in the initial sample showing a minor maturation. In contrast to thermal extraction, solid bitumen in the early mature samples was almost completely dissolved after DCM treatment. These petrographic observations on micro plugs are in agreement with the pyrolysis results of powdered fractions, where the initial Rock-Eval S1 and to a much lesser extent also the S2 signal decreases after the chemical extraction in DCM. While the SB in early mature sample was almost entirely dissolved by DCM, only about half of it is was dissolved in the moderately mature sample showing more mature and more stable SB. After the artificial maturation, the volume of SB in early- as well as in moderately mature samples clearly increased within the intraparticle pores, indicating presence of new SB due to bitumen migration from the deeper part of the micro plug to the surface. In contrast, SB in initially overmature sample is mainly present as thermally-highly stable pyrobitumen, indicated by no change in the SB distribution after chemical and thermal treatments representing a stable type of SB at the very end of petroleum generation.

Semi-closed artificial thermal maturation of type I source rock with the presence of natural formation water: hydrocarbon generation and individual n-alkane stable carbon isotope partitioning pattern

Hydrous pyrolysis is a significant laboratory method to investigate oil generation with the presence of water. Generally, distilled water is utilized in hydrous pyrolysis but not natural formation water, which is ubiquitous in oilfields and has elevated salinities. To understand the influence of formation water on hydrocarbon generation and stable carbon isotopic ratios of expelled oils, two series of semi-closed hydrous pyrolysis experiments were conducted in a wide temperature range (250–550 °C) for the type I Green River Shale source rocks using distilled water and formation water with a salinity of 76 g/L. Oil generation peak occurred at a lower temperature (325 °C) in experiments using formation water compared to experiments using distilled water (375 °C), suggesting that the presence of formation water has facilitated the oil generation. The presence of formation water also promoted the hydrocarbon expulsion at lower temperatures in hydrous pyrolysis (325–350 °C). Stable carbon isotopic fractionation between unpyrolyzed kerogen and n-alkanes (n-C17 to n-C28) generated during the primary stage of oil generation (325–375 °C) is minor (<2.6‰) in the presence of formation water, but smaller relative to those in experiments using distilled water at individual temperature points. Positive correlations between pyrolysis temperatures and δ13C ratios of n-C17, n-C18 and n-C19 during oil generation were observed in the experiments using formation water, which is consistent with the knowledge that 12C–12C bonds are more readily to be cleaved than 13C–12C bonds. Outcomes of this study not only support that stable carbon isotopic analysis of n-alkanes is a powerful tool for fingerprinting oil source in sedimentary basins, but also highlight the significance of using formation water as a medium in hydrous pyrolysis to improve the understanding of chemical/isotopic variations during hydrocarbon generation.

Does grain size influence hydrocarbons generation and mesoporosity during artificial thermal maturation of an organic-rich mudstone?

To assess how the grain size/rock fabric of laboratory-matured shale samples impact oil, gas production, and the formation of pores during laboratory thermal maturation, cores (4.5 mm*1 cm) of bulk rock, millimetric equidimensional rock fragments (3*3 mm), and fine grind powder (<200 μm) were obtained from an organic-rich mudstone (Kimmeridge Clay Fm. “KCF”, Yorkshire, UK) and artificially matured under anhydrous conditions. The composition of the organic matter (OM), porosity, and thermal maturity were characterized using nitrogen adsorption, Rock-Eval® VI pyrolysis, GC/TCD (Gas-Chromatography/Thermal Conductivity Detector), and GC/MS (Gas Chromatography/Mass Spectrometry). While only a few differences in geochemical composition and porosity exist between rock fragments and powders, a greater gap is observed with the cores. Probably due to lower surface contact between the organic components themselves and clay mineral surfaces (which can act as a catalyst of oil and gas generation) less intense OM thermal degradation processes were observed for the cores. The use of cores rather than powder and fragments results in: (i) the production of lower extractible OM concentrations; (ii) lower amounts of gas (C1–C5 and CO2); (iii) lower pore volumes and smaller pore sizes during maturation. This preliminary work highlights the importance of considering the fabric of the rock being artificially matured and shows that the use of cores with an intact rock fabric (e.g. cores), closer to natural conditions, could be more suitable when studying OM thermal degradation and porosity. In comparison with previous works, this also demonstrated that depending on the maturation system used (e.g. semi-confined, confined) the differences in the amount of hydrocarbons generated and porosity observed between powder and cores during maturation could differ significantly and find their origin in different processes.

Effects of Confining Pressure and Microscale Heterogeneity on Hydrocarbon Retention and Pore Evolution from Artificial Maturation of Eagle Ford Shale

Effects of Confining Pressure and Microscale Heterogeneity on Hydrocarbon Retention and Pore Evolution from Artificial Maturation of Eagle Ford Shale

Geochemical Characteristics of Expelled and Residual Oil from Artificial Thermal Maturation of an Early Permian Tasmanite Shale, Australia

Lipid biomarkers play an important role in defining oil-source rock correlations. A fundamental assumption is that composition (or ratios) of biomarkers in oil is not significantly different from that in bitumen in the source rock. In order to compare the geochemical characteristics of expelled oil and residual oil, a Permian Tasmanite oil shale was used for an artificial maturation experiment to simulate the oil generation period. The results show that the Tasmanite oil shale generated high amounts of hydrocarbons (731 mg HC/g TOC) at low maturation temperatures (340 °C). The hydrocarbon (HC) group compositions are different between the expelled oil (with more aromatic HC and saturated HC) and the residual oil (with more resin fraction and asphaltene). The Pr/Ph ratio (up to 4.01) of the expelled hydrocarbons was much higher than that in residual oil (&lt;1.0). Maturity-related biomarkers Ts/(Ts + Tm), and αααC29-20S/(20S + 20R) and C29-αββ/(ααα + αββ), also showed complicated variations with pyrolysis temperature, especially at post peak oil generation. C27-, C28-, and C29- sterane distributions showed variations with pyrolysis temperature. Therefore, without considering the influence of maturity on the abundance of compounds, either source, maturity and/or organic matter type from the chemical characteristics may not be correct.

Defining kerogen maturity from orbital hybridization by machine learning

Kerogen is the primary material for oil and gas. Its maturity is used to determine the potential for hydrocarbon generation. Nowadays, kerogen maturity is mainly measured experimentally and characterized by its chemical composition. The fundamental reason for the change in its chemical composition during the maturation is the breaking and recombination of chemical bonds, manifested by the transformation in atomic hybridization based on quantum mechanics. While traditional methods are time-consuming and labor-intensive, machine learning technique has been introduced to clarify the relationship between hybridization and maturity. A kerogen maturity prediction model based on hybridization is constructed. The average error of the predicted values is only 4.91%, and more than 87% of the test samples have an error of less than 10%. The results demonstrate that the model can accurately predict the maturity of kerogen. As the evolution of kerogen maturity increases the proportion of sp2 hybridized carbons, the orbital hybridization maturity index (OrbHMI) is proposed. The chemical changes in the thermal evolution and pyrolysis mechanism of kerogen can be explained and understood more essentially by OrbHMI. The results provide a basis for guiding artificial maturation and pave a promising path toward studying the kerogen structure and predicting hydrocarbon generating potential.

Role of zooclasts in the kerogen type and hydrocarbon potential of the lower Paleozoic Alum Shale

This study investigates the role of zooclasts in the bulk organic matter composition, kerogen type, and hydrocarbon generation potential of the lower Paleozoic marine Alum shale in Baltoscandia, northwestern Europe. The results show that graptolite periderm is composed of non-granular cuticles and granular filling. The graptolite cuticle is non-fluorescing and has a well-polishing measurable surface, while the graptolite granular fraction is semi-translucent and has brownish fluorescence, suggesting remaining hydrocarbon generation potential. The graptolite granular fraction shows similar optical characteristics to fluorescing diagenetic solid bitumen. Both the graptolite granular fraction and diagenetic solid bitumen have low intensity yellow to brown fluorescence and contribute to generative potential (Rock-Eval S2). The sum of semi-quantitative zooclastic cuticle (non-granular graptolite cuticle, chitinozoan cuticle, and vitrinite-like) and diagenetic solid bitumen content, obtained from maceral point-counting, correlates with the non-generative organic carbon content. Enrichment of zooclastic cuticle in the samples is displayed as enrichment of inert organic carbon, and hence bulk geochemical kerogen of type III. This refractory carbon-rich maceral enrichment results represents autochthonous ‘refractory organic carbon dilution’ and will lead to Hydrocarbon Index (HI) underestimation. Confined hydrous pyrolysis was used to compare the hydrocarbon generation process of a zooclastic cuticle-lean sample (0.2 vol%) and a zooclastic cuticle-rich (1.6 vol%) sample. Results indicate that there are four stages of hydrocarbon generation in the artificial maturation of unconventional source rock of the Alum Shale. The zooclastic cuticle-lean sample has higher hydrocarbon generation potential and more oil-prone than the zooclastic cuticle-rich sample, which is gas-prone and generates more CO2. This difference in hydrocarbon generation is attributed to differences in the organic constituent composition.

Hydrous pyrolysis of New Albany Shale: A study examining maturation changes and porosity development

The characterization of nanoscale organic structures has improved our understanding of porosity development within source-rock reservoirs, but research linking organic porosity evolution to thermal maturity has generated conflicting results. To better understand this connection, an immature (0.25% solid bitumen reflectance; BRo) sample of the New Albany Shale was used in four isothermal hydrous pyrolysis (HP) experiment sequences at 300°, 320°, 340°, and 370°C, with residues collected periodically for a maximum of 103 days. The HP residues, along with the original immature sample and two naturally matured (1.49 and 1.56% BRo) New Albany Shale samples were analyzed for organic petrology, total organic carbon (TOC) content, and organic porosity evaluation using correlative light and electron microscopy (CLEM). All of the HP series increased in thermal maturity with increasing duration of pyrolysis, though reflectance for each series plateaued within 25 days of maturation. Initially, TOC in the HP residues decreases (from 14.24 wt. %) with increasing thermal maturity until ∼1.0% BRo where TOC remains at ∼9–10 wt. % for all remaining residues. Qualitative CLEM observations within the 50–100 day 300° and 340°C HP sequences (0.95–1.70% BRo), and the naturally matured samples, develop organic porosity in smaller (<5 μm in diameter), void-filling solid bitumen that occurs in spaces between clays and other fine-grained minerals. The 370°C HP residues developed significant organic porosity, relative to the other HP temperature series in all solid bitumen accumulations regardless of size. Overall, the study indicates that temperature and duration of artificial maturation play an important role in the abundance of pores in the HP residues. This work expands on our understanding of the conditions needed for the generation and development of organic porosity in the New Albany Shale and potentially in other marine source-rock petroleum systems.

Molecular structure evolution of Type I kerogen during pyrolysis: Case study from the Songliao Basin, NE China

To characterize molecular structure evolution of Type I kerogen, we performed gold tube pyrolysis experiments on a Cretaceous Qingshankou lacustrine mudstone in the Songliao Basin during artificial maturation. The hydrocarbons generated at 320–600 °C at two heating rates, 2 and 20 °C/h were quantified, and the maximum yields of C14+, C6-14 and C2-5 gaseous products corresponded to vitrinite reflectance (Ro) nodes of 1.18%, 1.76% and 2.5%, respectively. Chemical compositions of solid residues (pyrolysis products remaining after extraction by dichloromethane and methanol) with Easy%Ro values ranging from 0.49 to 2.5% were studied by elemental analysis and nuclear magnetic resonance. With increasing temperature, the solid residues presented sharp decreases in aliphatic fractions and significant increases in aromatic fractions, while a condensation reaction occurring in the residue was related to secondary coking and cracking reactions occurring after the peak oil window. Four structural models of the residues were investigated, demonstrating that three positive nonlinear stages occurred between fused aromatic carbon (XE BP) structures and hydrocarbon generation. At Easy%Ro < 0.89, the XE BP numbers were relatively stable, and the generated hydrocarbons mainly attributed to cleavage of heteroatomic functional groups (NSOs) of kerogen. During the peak hydrocarbon-generating stage (Easy%Ro values of 0.89–1.76), the XE BP numbers exhibited an obvious increase due to breaking of carbon chains and cyclization reactions, which was accompanied by formation of large quantities of C14+ oils and C6-14 hydrocarbons derived from direct cracking of kerogen. The XE BP numbers were growth slowing and highly cross-linked features at Easy%Ro values of 1.76–2.5% due to polycondensation, and a large amount of C2-5 gas generation was mainly attributed to oil cracking. A good coupling relationship between H/C atomic ratio and polycondensation of aromatic structures in evolution further strengthens research of molecular structure evolution in Type I kerogen. Moreover, comparison of the number of aromatic structures caused by alkyl bond breakage and condensation showed that the number of the former was higher than that of the latter before the peak of oil generation, whereas the number of the latter was obviously dominant after the peak of oil generation.

Enhancing oocyte maturation and fertilisation in the black-foot limpet Patella candei d′Orbigny, 1840 (Patellidae, Mollusca)

Limpet species are subjected to pressures of high exploitation. In the Madeira Archipelago (Portugal), the limpes are an economic and traditional fishing resource whose exploitation is regulated, to reduce the impact over the native populations. The effectiveness of the NaOH-alkalinized seawater baths to enhance the artificial maturation of Patella candei (D′orbigny, 1840) oocytes and fertilisation success in laboratory has been studied. First, the optimal combinations of pH and activation time to obtain the active oocytes were tested. Then, the viability of those oocytes was studied in a three factorial assay (pH x activation time x fertilisation time). Finally, the results obtained in the previous assays were cross tested to find a relationship between both. The viability of the oocytes over time were tested for methodology improvement. Results showed that the optimal conditions for the production of larvae was a pH of 9.5, activation time between 2 and 3 h and fertilisation time of 24:00 h, obtained a ratio of development between 0.65 and 0.75. The refrigeration could help to maintain the oocyte viability over time, but further research is required. This study establishes a foundational step towards the study the larval biology of Patella candei in laboratory, which is required to understand the ecological requirements for the early life stages of this species and promote aquaculture production.

Superimposed secondary alteration of oil reservoirs. Part II: The characteristics of biomarkers under the superimposed influences of biodegradation and thermal alteration

Petroleum biomarkers could be altered to varying extents under the influence of biodegradation and thermal alteration in reservoir, and their respective influence has been well documented. However, the superimposed influence of successive biodegradation and thermal alteration has not been systematically studied so far. In this study, a sequence of crude oils and oil sands that are of identical origin but at different biodegradation levels from the Liaohe Basin of China were artificially matured via closed-system pyrolysis. The distributions of biomarkers such as steranes and hopanes in the variably biodegraded oil samples and in their pyrolyzates at varying artificial thermal maturities were compared. The results showed that the presence of normal (n-) alkanes in crude oil does not necessarily excludes the possibility of previous moderate–severe biodegradation as n-alkanes can be further generated under advanced thermal stress. Besides, biomarkers in the oils that have suffered superimposed alterations could be derived not only from the modifications of free biomarkers in the oils, but also from the release of biomarkers bound in the asphaltenes. The mix of these two sources complicated the biomarker profiles in this type of oils. Most source related parameters based on steranes and tri-, tetra- and penta-cyclic terpanes seem to be reliable only when the oil reservoir has suffered biodegradation not beyond moderate level and the maturity of the crude oil is below 0.91 Easy%Ro. The TT23/(TT23 + TT24) ratio, however, was found to remain constant even after severe biodegradation and thermal alteration, making it applicable in oil-source correlation in superimposed oil reservoirs. In addition, isomerization-based maturity parameters such as methylphenanthrene index of crude oils are reliable if subsequent thermal alteration reached above 0.91 Easy%Ro despite prior moderate–severe biodegradation, because the related isomerization reactions would approach the same level observed for the non-biodegraded oil after subsequent thermal alteration.

The Optimal Harvest Decisions for Natural and Artificial Maturation Mangoes under Uncertain Demand, Yields and Prices

This study focuses on the decisions of picking, inventory, ripening, delivering, and selling mangoes in a harvesting season. Demand, supply, and prices are uncertain, and their probability density functions are fitted based on actual trading data collected from the largest spot market in Taiwan. A stochastic programming model is formulated to minimize the expected cost under the considerations of labor, storage space, shelf life, and transportation restrictions. We implement the sample-average approximation to obtain a high-quality solution of the stochastic program. The analysis compares deterministic and stochastic solutions to assess the uncertain effect on the harvest decisions. Finally, the optimal harvest schedule of each mango variety is suggested based on the stochastic program solution.

Cyclic Subcritical Water Injection into Bazhenov Oil Shale: Geochemical and Petrophysical Properties Evolution Due to Hydrothermal Exposure

In situ shale or kerogen oil production is a promising approach to developing vast oil shale resources and increasing world energy demand. In this study, cyclic subcritical water injection in oil shale was investigated in laboratory conditions as a method for in situ oil shale retorting. Fifteen non-extracted oil shale samples from Bazhenov Formation in Russia (98 °C and 23.5 MPa reservoir conditions) were hydrothermally treated at 350 °C and in a 25 MPa semi-open system during 50 h in the cyclic regime. The influence of the artificial maturation on geochemical parameters, elastic and microstructural properties was studied. Rock-Eval pyrolysis of non-extracted and extracted oil shale samples before and after hydrothermal exposure and SARA analysis were employed to analyze bitumen and kerogen transformation to mobile hydrocarbons and immobile char. X-ray computed microtomography (XMT) was performed to characterize the microstructural properties of pore space. The results demonstrated significant porosity, specific pore surface area increase, and the appearance of microfractures in organic-rich layers. Acoustic measurements were carried out to estimate the alteration of elastic properties due to hydrothermal treatment. Both Young’s modulus and Poisson’s ratio decreased due to kerogen transformation to heavy oil and bitumen, which remain trapped before further oil and gas generation, and expulsion occurs. Ultimately, a developed kinetic model was applied to match kerogen and bitumen transformation with liquid and gas hydrocarbons production. The nonlinear least-squares optimization problem was solved during the integration of the system of differential equations to match produced hydrocarbons with pyrolysis derived kerogen and bitumen decomposition.

Thermal evolution behavior of the organic matter and a ray of light on the origin of vitrinite-like maceral in the Mesoproterozoic and Lower Cambrian black shales: Insights from artificial maturation

The overmature Precambrian to Lower Paleozoic marine shales from China contain relatively simple organic matter (OM) composition, which is dominated by in-source solid bitumen (i.e., solid bitumen in the hydrocarbon source rocks). The thermal evolution behavior of the original OM and the determination of thermal maturity in the Precambrian to Cambrian marine shales have been challenging for decades. The vitrinite-like maceral (VLM) is widely present in these marine shales, and its origin is still unknown. To address these issues, the immature Proterozoic Xiamaling shales from China and the immature Cambrian Alum shales from Sweden, and a Chinese immature Carboniferous coal were heat-treated at temperature range of 300 °C to 550 °C. The carbonized residue of the artificially matured samples was examined for their morphological and reflectance variation, and the results were compared with data on the other overmature natural shales from China and Sweden.OM components are similar in the Xiamaling and Alum immature oil shales, consisting of filamentous algae, matrix bituminite, bituminite, VLM and liptodetrinite, and rare thucholites are present in the Xiamaling shales. The algal-derived OM decomposed gradually due to hydrocarbon generation at 300–350 °C. OM is mainly composed of the in-source solid bitumen in the artificially heated shales after 350 °C, similar to the overmature Precambrian to Cambrian natural shales, and the in-source solid bitumen gradually loses its mass with increasing thermal maturity. The in-source solid bitumen is derived from the thermal cracking of the retained oil or the direct conversion of algal-derived liptinite macerals (e.g., the bituminite) or their mixture. VLM in the Xiamaling oil shales can not be observed after 350 °C, but VLM is still present in the Alum oil shales. It can be inferred that there is a different source of VLM in these shales, and VLM in the Xiamaling oil shales contains more volatile material. The VLM in the Xiamaling shales may be biodegradation products of liptinites under anoxic environments. The origin of VLM in the Cambrian Alum shales requires further study to be verified, although it is certain that graptolites are not its sources. The reflectance of in-source solid bitumen (SBRo) increases with heat-treated temperature in both the Xiamaling shales and the Alum shales, but at different rates, which may be due to the difference of the original kerogen composition in these shales. VLM reflectance (VLMRo) and SBRo in sections perpendicular to bedding can be used to determine the maturation level of the Precambrian-Cambrian sediments. Their relation to equivalent vitrinite reflectance (EqVRo) can be expressed by the following equations: EqVRo = 1.07 × VLMRo – 0.18, EqVRo = 0.87 × SBRo + 0.25 (in the Precambrian sediments) and EqVRo = 1.15 × SBRo + 0.01 (in the Cambrian sediments).