Gas Inclusions Research Articles

Investigating the effects of natural gas, nuclear energy, and democracy on environmental footprint and energy risk in France: Does financial inclusion matter?

To alleviate their energy poverty, most European nations, including France, import the bulk of their oil, natural gas, and coal needs, damaging the environment. The government has expanded its nuclear energy industry to lessen its reliance on imported fossil fuels and for energy security. The current investigation analysis the influence of natural gas, nuclear energy, democracy, and financial inclusion on carbon footprint and energy security from 2000Q1 to 2018Q4. The results of the Bounds test demonstrate that there are long-term interactions between the variables studied. Based on the estimates of the Auto Regressive Distributed Lag (ARDL) model results, nuclear energy, natural gas, and financial inclusion contribute to environmental degradation by increasing the carbon footprint. However, democracy has a role in mitigating long and short-term emissions. Nuclear energy and democracy, on the other hand, help to reduce energy risks while increasing energy costs. The outcomes of the Competition Competence Reports (CCR) test show that all findings are robust and consistent. Moreover, the study results confirmed the existence of the U-shaped EKC hypothesis. The study provides significant policy suggestions that improve energy security and enhance environmental quality. The study suggests that policymakers should exploit the productive capabilities of nuclear energy so that it can achieve energy security. Moreover, it does not have to be at the expense of the quality of its environment. The policy maker should use natural gas as a bridge that accelerates the energy transition since natural gas is the least emitting fossil energy. Likewise, within the framework of democracy, associations and political parties must be encouraged to consider environmental sustainability in their political programs.

Fluid evolution and petroleum accumulation in the precambrian gas reservoirs of the Sichuan Basin, SW China

Deep marine carbonates comprise one of the most significant reservoir types globally. Reconstruction of Precambrian oil reservoirs and the complex tectonism that affected Precambrian carbonate reservoirs demonstrate the complexity of the natural gas enrichment mechanism. A comparison between the fluid evolution of the well-preserved reservoirs in the central Sichuan Basin and the poorly preserved reservoirs in the southeastern Sichuan Basin offers insights into the factors that control the preservation of ancient reservoirs. We conducted geochemical analysis of the multistage cementation sequence, Raman quantitative analysis on fluid (gas) inclusions, and rare earth element (REE) analysis of diagenetic fluid environments. Hydrocarbon migration can cause variations in the diagenetic environment. Quantitative Raman measurements of the trapping pressure, trapping temperature, and composition of fluid (gas) inclusions are also useful in defining periods of gas accumulation. In situ U–Pb dating results of dolomite veins indicate that extensive dolomitization in the Sichuan Basin began during the early Cambrian. In the central Sichuan Basin, reservoir pressure evolved from normal during the Middle Jurassic to strongly overpressured during the mid-Cretaceous. Overpressure generated before Himalayan tectonism appears to be positively correlated with gas preservation. Overpressure within inclusions bearing hydrogen sulfide indicates that thermochemical sulfate reduction (TSR) does not produce intense dissolution that increases the porosity of carbonate reservoirs and reduces pore pressure. Poorly preserved reservoirs were intruded by exogenous and hydrothermal fluids but remained normally pressured. Secondary methane-rich gas inclusions record normal pressure conditions during the early Paleogene.

Electroslag heating and additional melt feed of steel ingots of semi-continuous casting

The issues related to the continuous compensation of metal shrinkage during its crystallization are studied. Based on the evaluation of ways to reduce the size of the shrinkage shell, aimed at maintaining the liquid phase for a long time, the most effective ways to reduce the size of the shrinkage shell and reduce the head trim are selected. The influence of electroslag heating and recharge technology on the length of the shrinkage shell and the quality of the metal of the sub-shrinkage area of semi-continuously cast ingots has been studied. The study was carried out on ingots with a diameter of 500 mm weighing 3.5 tons of carbon and alloy steels. The installation consisted of 3 electrodes with a diameter of 75–100 mm, connected to the transformer TSH-3000-3. The transformer power was 570 kVA, the current per phase was 1000–3000 A, the voltage on the electrodes was 40–60 V. Temperature measurements were carried out in the copper sleeve of the mold. For comparison, the temperatures in the walls of the mold were recorded during the cooling of the ingot in the mold without heating. The cooling curves showed that the process of electroslag heating does not cause overheating of the mold walls. This is explained by the appearance of a side metal crust in the upper part of the ingot, which does not melt with liquid slag and protects the walls of the mold. The surface of the ingots had no visible defects (crust inversions, film and slag inclusions). Additional surface treatment (stripping, stripping) was not required. The macrostructure of the ingots is dense, without visible defects, including in the axial zone. Sulfur liquation on sulfur prints according to Bauman was not detected. Electroslag heating had a significant impact on the length and shape of the shrinkage shell. The results obtained show that electroslag heating with graphite electrodes, feeding with consumable steel electrodes of the same composition with the resulting ingot and electroslag casting of steel can improve the structure, density and chemical homogeneity of cast metal, reduce the content of non-metallic and gas inclusions and significantly increase the yield of usable compared to conventional casting.

Fluid evolution and paleo-pressure recovery by Raman quantitative analysis in the Shahejie Formation of the western slope belt in Dongpu Sag, Bohai Bay Basin, China

Inorganic and organic fluids are widely found in sedimentary basins during oil and gas migration and accumulation. This research investigates two types of sandstone reservoirs with different pressure states and fluid evolution of the Shahejie Formation in the western slope belt of Dongpu Sag. Based on petrographic observations, micro-Raman spectroscopy, and fluorescent spectrometry, petroleum inclusions, CH4-bearing inclusions, and CO2-bearing inclusions were discovered in quartz-hosted minerals. The pressure–temperature–time–composition (P–T–t–X) properties of the CH4 and CO2 inclusions were obtained by quantitative Raman analysis and thermodynamic models. Minimum trapped pressure was predicted by the thermodynamic modeling of petroleum inclusions. Saffron yellow petroleum inclusions represent an early Oligocene oil-charging event (∼32–30 Ma), and the two kinds of reservoirs were all kept in moderate-overpressure conditions (average pressure coefficient: 1.26). Due to rapid uplift and denudation (Dongying movement) in the middle Oligocene in step II, crude oil degrades into CH4 and CO2 (density of CH4 gas inclusions: 0.1010–0.1339 g/cm3; density of CO2 gas inclusions: 0.450–0.612 g/cm3) and retains low-maturity (0.67–1.04%) bitumen in situ. Tectonic destruction causes the reservoir to be released to normal pressure. With the reburial of the Es3 Formation, step II entered the middle stage of oil generation again (average pressure coefficient: 0.90). However, in step I, with secondary hydrocarbons occurring, second-stage oil (performance for pale blue fluorescence in petroleum inclusions) accumulated at ∼12–0 Ma (late Miocene–Pliocene). The second oil charging event in step I remains a reservoir under high-overpressure conditions (average pressure coefficient: 1.67).

Vapor mixing in turbulent vaporizing flows

Scalar mixing and evaporation processes are analyzed in a compressible two-phase homogeneous and isotropic turbulence configuration. To this end, the fully compressible Navier–Stokes equations are solved using a pressure-based method and a mass-conservative interface capturing method (CLSVOF). Temperature and vapor mass fraction transport equations are coupled with the momentum equation via the evaporation rate: i.e. heat and mass transfer has an effect on the flow dynamic through the generation of a Stefan flow at the interface. In this formalism, a pressure equation is developed to include the acoustic, thermal dilatation and compressibility effects. Moreover, the method can consider several gas structures in the same domain, each with independent temperature, density, and thermodynamic pressure. The latter is important to simulate atomization, where interaction among the liquid structures (such as breakup or coalescence) can generate multiple gas inclusions. This work is one of the first to describe with high fidelity the vaporization and turbulent mixing occurring in dense two-phase flows.A statistical analysis of the vapor mass fraction field is performed. The obtained results reveal the influence of the non-homogeneous scalar source at the interface, which depend directly on the local interface temperature, on the PDF shape. Under these conditions, the vapor mass fraction PDF deviates from the Gaussian and beta PDF shapes, frequently used for turbulent combustion modeling. Furthermore, access to the local surface averaged vapor mass fraction and evaporation rate at the interface allows a statistical analysis of these variables. Results show a large dispersion of both quantities, especially at the early times of the simulations, which contradict the usual assumption of a constant vapor mass fraction (or vaporization rate) at the interface used in the literature in standard vaporization models. Finally, the influence of the mean interface curvature on the evaporation rate is quantified and discussed. Large evaporation rate are present when the interface is convex (positive mean curvature). On the contrary, local saturation zones are present near concave interface (negative mean curvature), reducing the evaporation rate magnitude.

Surface quality improvement at selective laser melting AlSi10Mg by optimizing single point diamond turning parameters

Abstract Selective laser melting allows aluminum-silicon alloy mirrors further lightweight for aerospace applications. The reflective surfaces based on Selective laser melting aluminum-silicon alloy substrates are commonly machined by single point diamond turning. However, many surface defects on single point diamond turning machined surfaces may limit their direct applications in optical system. In the paper, single point diamond turning parameters (cutting depth, feed rate, and cutting speed) are optimized orderly to improve its surface quality. The single point diamond turning machined surface morphologies are measured by using white light profilometer. In our selective laser melting AlSi10Mg substrate, scratches and holes mainly damaged single point diamond turning surface. Scratches are caused by inclusions while holes are generated by gas pores and inclusions. Single point diamond turning parameters optimization reduces the density of such surface defects, but these defects cannot be eliminated totally.

Biomethane as an energy resource for achieving sustainable production: Economic assessments and policy implications

Circular bioeconomy models aim to reduce dependence on non-renewable and unsustainable use of resources, involving also the inclusion of gas in the green taxonomy. Thus, biomethane represents a flexible and clean resource for combating climate change. This work aims to show that biomethane is a feasible energy resource that can meet sustainable production requirements. We perform an economic analysis on biomethane plants, obtained from the organic fraction of municipal solid waste (OFMSW) varying from 100 to 500 m 3 /h capacity, based on Net Present Value for two distinct policy scenarios in Italy: i. Certificate of Emission of Biofuel in Consumption (Baseline Policy Scenario) and ii. Tariff Premium (Alternative Policy Scenario). In addition, the Break Even Point will be calculated for the critical variables. The results show that the cost of biomethane production varies from 0.54 to 0.78 €/m 3 and the profitability changes depending on the policy scenario. The 200 m 3 /h plant is the one in which the minimum profitability condition is achieved, which significantly depends on variables such as, the size of the plant, the type of incentive, the value of the incentive, the selling price of biomethane, and the net revenue associated with the treatment of OFMSW. In addition, this work quantifies the potential for unused biomethane in Italy associated with OFMSW, which ranges from 464 to 678 million m 3 , showing that could generate economic profits from about 41 to 2068 million € and from about 59 to 3027 million € in two different scenarios (characterized by a higher rate of separate collection). Policy implications are provided to enable further penetration and development of this renewable resource.

ФОРМИРОВАНИЕ МАРШРУТА МАГИСТРАЛЬНОЙ ТРЕЩИНЫ РАЗРУШЕНИЯ В МНОГОУРОВНЕВОЙ СТРУКТУРЕ КОНГЛОМЕРАТНЫХ СТРОИТЕЛЬНЫХ КОМПОЗИТОВ

In the publication, conglomerate building composites (concrete) are identified as heterogeneous solids with a hierarchically organized spatial-geometric structure with a characteristic dimension from 10-10 to 10-1 m, with a minimum of 5-6 scale levels and three types of substructure design that differ in scale, genesis and mechanics of properties manifestation. The first type is characteristic of the macro-, meso- and microscale levels and is taken in the form of a two-component “construction” of a spatially continuous matrix and discrete solid and gaseous (macropores) inclusions deterministically and stochastically distributed in it; the second type refers to the submicro-, ultra-micro- and nanoscale levels and is believed to be in the form of a “microscale spatial structure” of new formations of a cementitious substance from consolidated individual crystalline differences; the third type, finally, corresponds to the atomic-molecular structure of new formations of the cementing substance. Characteristics of the distinguished types of substructures are given according to the scale of their components, the peculiarities of formation, the mechanics of manifestation of properties, design criteria and means of synthesis of each substructure. The patterns of formation of the fracture route in substructures of all types and substances of each scale level are analyzed. In this case, the development of the stress-strain state of the conglomerate composite according to the principle of energy dissipation, localization and increase (concentration) of stress is realized in the direction from the macro- to the atomic-molecular level of the structure of the composite, and the destruction itself and, accordingly, the formation of the crack route in time and in space of the composite passes in the direction from the atomic-molecular level to the macrolevel in a cascade through all intermediate structural levels. Within the framework of an integrated mechano-physico-chemical approach, the place of thermofluctuation theory (fracture physics) at the stages of breaking single atomic-molecular bonds and crack mechanics at the stages of development of micro- and macrodamage is shown. The possibilities of using theoretical principles of crack route formation to formulate and solve practical problems of designing and synthesizing optimal structures of conglomerate building composites are discussed.

GAS LIQUID FLOW IN HILLY TERRAIN PIPELINES-SINGLE AND MULTIPLE SECTIONS

A new way of calculating severe slugging behavior for hilly terrain pipe lines is presented. Analysis is based on the analytical solution of a single line/riser system and treats each section as a single system, using the results of the analytical solution. Yet interaction is needed since the "outlet pressure" in each section is calculated iteratively. The present modification leads to a more elegant and reliable solution. In addition, the modified model takes into account the inclusion of gas within the liquid in the risers. The solution presents the variation of pressure and liquid level in each inclined line with time, the maximum inlet pressure, the cycle time (frequency), the maximum penetration of liquid into the inlet section, and the pressure in each line. The solutions of multiple sections are compared to the case of a single line/riser case.

ФРИКЦІЙНІ ЯВИЩА У ВУГІЛЬНИХ ШАХТАХ: ПРИЧИНИ, НАСЛІДКИ ТА ВПЛИВ НА ГАЗОДИНАМІЧНІ ЯВИЩА

Coal mines are objects of increased danger, since dynamic, gas-dynamic and thermal phenomena occur in them. These phenomena lead to violations of the operating regime, the failure of mining equipment, the death of miners, an increase in the cost of coal mining and other consequences. The purpose of the article is to present the results of studies of the conditions for the formation of thermal effects in coal mines and the reasons for their occurrence, which has both scientific and applied relevance. The conducted studies made it clear that sparking can occur under the influence of both man-made and natural factors. Friction phenomena leading to thermodynamic effects have been recorded in many mines and countries of the world. The main part of explosions and fires of methane occurs during frictional sparking of rocks containing sulfides. The latter produce sparks of a sufficiently high temperature, which can lead to the ignition of combustible gases, as well as the release of hydrogen sulfide, which has a low ignition temperature. In world practice, cases of ignition of combustible materials during the landing of the roof in the absence of coal have been described. British researchers concluded that the methane-air mixture can be ignited by a spark generated by the friction of sandstone against sandstone or mudstone against sandstone. According to the literature data, the ignition of combustible materials and coals can occur as a result of: emissions and explosions, rock collapse during landing, when a spark discharge occurs in quartz during a tribo- or piezoelectric effect; the presence of sulfides in coals or rocks, pyroelectric effect; electrification of coals. At the micro level, in quartz grains of sandstones, the formation of static charges by dislocations, which are decorated with dust, has been established. A particularly strong effect can occur if, in addition to methane, carbon monoxide, hydrogen, hydrogen sulfide, and acetylene are present in the air. An increase in sparking during frictional friction of quartz in the presence of coal dust has been established. The presence of gas inclusions in sandstone minerals during shear deformations leads to the appearance of additional concentrations of hydrocarbons. As a result of contact of such a mixture with a heated area, a short-term small flash occurs, which is a spark.

Підхід до чисельного моделювання просторових рухів газорідинного сере-довища в паливному баку космічного ступеня в умовах мікрогравітації з урахуванням гарячої зони

Space propulsion systems ensure multiple startups and shutdowns of the main liquid-propellant rocket engines in microgravity conditions for spacecraft preset motions and reorientation control. During the passive flight of a space stage (after its main engine shutdown), the liquid propellant in the tanks continues moving by inertia in microgravity and moves as far away from the propellant management device as possible. In this case, the pressurization gas is displaced to the propellant management device, which creates the potential danger of the gas entering the engine inlet in quantities unacceptable for multiple reliable engine restarts. In this regard, the determination of the parameters of fluid movement in propellant tanks under microgravity conditions is a pertinent problem to be solved in the designing of liquid-propellant propulsion systems. This paper presents an approach to the theoretical calculation of the parameters of motion of the gas–liquid system in the propellant tanks of today’s space stages in microgravity conditions. The approach is based on the use of the finite element method, the Volume of Fluid method, and up-to-date computer tools for finite-element analysis (Computer Aided Engineering - CAE systems). A mathematical simulation of the spatial motion of the liquid propellant and the formation of free gas inclusions in passive flight was performed, and the motion parameters and shape of the free liquid surface in the tank and the location of gas inclusions were determined. The liquid motion in a model spherical tank in microgravity conditions was simulated numerically with and without account for the hot zone near the tank head. The motion parameters of the gas-liquid interface in a model cylindrical tank found using the proposed approach are in satisfactory agreement with experimental data. The proposed approach will significantly reduce the extent of experimental testing of space stages under development.

Correspondence Between Charge Accumulated in Voids by Partial Discharges and Mapping of Surface Charge With PEA Detection

Partial discharge (PD) dynamics in gaseous inclusions are related to the memory effects that originate from surface charge accumulation. In this article, the correspondence between a deposited charge that is inside a void during the PD activity with the surface potential mapping and space charge quantity that are obtained through the pulsed electroacoustic (PEA) method was investigated. The experiments were performed in the configuration of an asymmetric void that is embedded in a polyethylene (PE) material. Since the air gap in a void blocks acoustic wave propagation, the measurements were focused on one dielectric void wall (opposite to the metallic electrode). It was discovered that the polarity of the last period in a PD sequence influences the polarity of a deposited charge. Two types of readout pulsers were investigated and compared with the PEA method. In the surface charge decay process, a faster rate for negative charges was noticed as compared with positive ones. The experimental results showed a good quantitative correspondence between a real charge that was deposited by a PD during the phase-controlled sequence with an accumulated charge value that was obtained from surface mapping as well as charge detection—both being performed by means of the PEA method on the same layer of a void wall. The presented experimental results and analysis help extend the insight into PD mechanisms and quantitative surface charge accumulations.

Investigation of the possibility of controlling the formation of physical and mechanical properties of aluminum alloys under pressure crystallization

The study of scientific and technical materials showed that the existing control systems for technological processes of casting with crystallization under pressure are not effective enough. The paper presents a control system capable of real-time measurement, control and correction of the main technological parameters of the process, such as the time and nature of the temperature distribution in the tooling and casting, the rate of pressure imposition on the crystallizing metal, the magnitude of the applied pressure. These parameters have a direct impact on the formation of the properties of the final product. The paper defines the parameters of the response of the control system to fast crystallization processes for the timely prediction of the properties of the final product. The paper proposes a technology for metal processing by pressure prior to the onset of crystallization. In the process of conducting experimental studies in castings, it was possible to achieve the same uniform distribution of components, gas and non-metallic inclusions, as in a superheated liquid metal, bypassing the development of diffusion. As a result of ultrafast application of pressure to a level of 500 MPa on the liquid metal, it was possible to realize the process of compression of the crystal lattice to such limits at which it was possible to exclude the diffusion of components along structural defects. Due to the programmed application of pressure on the liquid and crystallizing one, the idea of controlling the processes of distribution of intermetallic compounds, non-metallic and gaseous inclusions has been realized.

Acoustic Waves in Liquid with Gas Inclusions Having a Liquid Layer and a Viscoelastic Shell

Acoustic Waves in Liquid with Gas Inclusions Having a Liquid Layer and a Viscoelastic Shell

In-line measurement of multiphase flow viscosity

The transportation modes depend entirely on the viscosity of the oil. To date, none of the viscometric methods are able to provide measurements to meet all the requirements of oil flow, features of main oil pipelines, and trends in the oil industry, such as decarbonization and digitalization. The method of inline viscosity measurement of multiphase flow through a metal pipeline can be based on direct gamma ray measurement. It is stipulated by the ability of gamma-radiation to penetrate through the pipeline material without destroying it, as well as by the ability to work with flows containing free gas and the high capability to be introduced into automatic control systems. The authors consider the physical forces acting on the gas inclusions in the oil flow. They determine the physical dependence between the parameters determined by the radioisotope method and the viscosity of oil in the three-phase flow. These studies show good agreement with the work of other scientists. The prospect of further research will be to clarify the mathematical model of gas-oil flow, to increase the accuracy by reducing the number of assumptions made.

The approach to numerical simulation of the spatial movement of fluid with forming free gas inclusions in propellant tank at space flight conditions

The space propulsion systems ensure se veral start-ups and shutdowns of main liquid-propellant rocket engines under microgravity conditions for the spacecraft program movements and reorientation control. During the passive flight of the space stage (after its main engine shutdown), the liquid propellant in the tanks continues to move by inertia in microgravity away from the propellant management device as much as possible. In this case, the pressurization gas is displaced to the propellant management device, which creates the potential danger of gas entering the engine inlet in quantities unacceptable for the reliable engine restart. In this regard, determining the parameters of fluid movement in propellant tanks in microgravity conditions is an urgent problem that needs to be solved in the design period of liquid propulsion systems. We have developed an approach to the theoretical computation of the parameters of the motion of the ‘gas — fluid’ system in the propellant tanks of modern space stages in microgravity conditions. The approach is based on the use of the finite element method, the Volume of Fluid method and modern computer tools for finite-element analysis (Computer Aided Engineering — CAE systems). For the passive leg of the launch vehicle space flight, we performed mathematical modeling of the spatial movement of liquid propellant and forming free gas inclusions and determined the parameters of movement and shape of the free surface of the liquid in the tank as well as the location of gas inclusions. The numerical simulation of the fluid movement in an experimental sample of a spherical shape tank was performed with regard to the movement conditions in the SE Yuzhnoye Design Bureau ‘Drop tower’ for studying space object s in microgravity. The motion parameters of the ‘gas — fluid’ interface obtained as a result of mathematical modeling are in satisfactory agreement with the experimental data obtained. The use of the developed approach will significantly reduce the amount of experimental testing of the designed space stages.

Method for analyzing in-situ volume change of large format lithium-ion hard case cells

To achieve high volumetric energy density in li-ion battery systems, it is relevant to predict the required space for reversible and irreversible volume change of the battery cells. In prismatic hard case cells, a locally inhomogeneous change in thickness occurs due to the rigid housing, which makes geometric analysis much more difficult. This publication highlights the challenges of analyzing prismatic hard case cells with existing test benches. In addition, an innovative test method is presented, in which the cells are both, compressed by air pressure and measured three-dimensionally. Influences such as gas inclusions between the electrode layers or plastic deformations of the housing can be reduced or even eliminated. This method enables a clear description of the local cell thickness at defined pressure, state of charge (SOC) and energy throughput (ETP). The resulting data can be used for a 3D simulation to estimate the required installation space within a battery system and the resulting force and pressure.

Effect on Diesel Engine Performance Parameters Using Hydrogen and Oxygen Produced on Demand

Hydrogen is seen as a future energy carrier since its chemical compounds make up a large part of the Earth’s surface. This study sought to analyze the impact related to the inclusion of hydrogen and oxygen gases produced on demand by an alkaline electrolyzer to the engine added directly through the fuel intake line. For this purpose, performance parameters were monitored, such as liquid fuel consumption and greenhouse gas emissions, and correlated to any effect observed on the engine’s power output and combustion behavior. A 58 kVA nominal power motor-generator was used, coupled with a resistive load bank (20 kW), where two fuel configurations were tested (diesel injection only and a mixture of diesel, hydrogen and oxygen) and compared. A total of 42 tests were performed considering both the admission gases into the fuel intake line and also diesel supply only for baseline. A substantial decrease in fuel consumption was observed (7.59%) when the blend configuration was used despite a decrease in the engine’s work (1.07%). It was also possible to see a common pattern between NO and NO2 emissions for both fuel configurations, while the behavior of the CO2 and CO emissions indicated a higher complete diesel burning fraction when using the gases on demand. Therefore, we can verify that the use of hydrogen and oxygen gases produced on demand in the fuel intake line is a promising alternative to provide a decrease in liquid fuel consumption and an overall improvement in engine combustion.

Determining the gas accumulation period using fluid inclusion observations: Xiang Zhong Basin, China

Abstract There are a large number of natural gas shows in the Upper Paleozoic of the central Hunan Basin. However, the hydrocarbon accumulation process was complicated due to the strong tectonic reformation in this area. A study of the natural gas accumulation period is of significance for determining gas accumulation models. In this research, the fluid inclusion samples were tested, the fluid inclusion occurrence characteristics, uniform temperature data, and reservoir evolution were analyzed, and four diagenetic periods and four diagenetic periods and three hydrocarbon accumulation periods were identified. (i) For the syntaxial stage, the filling is dark and nonluminous, and the fluid captured by the overgrowing cement around the particles is mainly seawater; (ii) for the (Early) Mesogenetic burial stage, the calcite cement grows around the particles or micritic calcite matrix, and the fluid captured is mainly brine; (iii) for (Late) Mesogenetic burial stage, two sets of decomposed fissures developed in massive calcite colloids with non-luminous gas-rich hydrocarbon inclusions within the crystals; and (iv) for Telogenetic burial stage, weakly fluorescent pure gaseous hydrocarbon inclusions are developed in luminescent calcite veins. The result indicates that the organic inclusions in the Lower Carboniferous of the central Hunan Basin are dominated by weakly fluorescent and nonfluorescent rich gas inclusions and pure gas-phase inclusions, with three stages of hydrocarbon filling. By integrating the average homogenization temperatures on burial curves, the three charging orders correspond to 260–250 Ma during the Late Permian, 249–245 Ma during the Early Triassic, and 208–170 Ma during the Late Triassic. Dense reservoir characteristics reveal deep basin gas reservoir in deep basin.

Superimposed hydrocarbon accumulation through multi-source and multi-stage evolution in the Cambrian Xixiangchi Group of eastern Sichuan Basin: A case study of the Pingqiao gas-bearing anticline

The Xixiangchi Group in eastern Sichuan Basin has great potential for natural gas exploration. However, there is a lack of in-depth studies of the hydrocarbon sources and the formation and evolution of gas reservoirs in this Group. Systematic investigation about the gas reservoir in Pingqiao anticline was consequently carried out in terms of characteristics of reservoir bitumen, the geochemical characteristics of natural gas, diagenetic minerals, and fluid inclusions. Based on this, combined with the reconstruction of the burial history, thermal evolution history and uplifting history of strata, and analysis of the regional tectonic settings, the hydrocarbon sources were identified and the formation and evolutionary processes of the gas reservoirs in Xixiangchi Group was revealed in this study. It was shown that the gas reservoirs have mixed gas sources from the shale source rocks in the Lower Cambrian Qiongzhusi Formation and in the Upper Ordovician Wufeng Formation-Lower Silurian Longmaxi Formation, and experienced several evolutionary stages, including the paleo-oil reservoir stage from the Late Siliurian to the Middle Permian, the paleo-gas reservoir stage from the Late Permian to the Early Cretaceous, and the superimposed accumulation and mixed-source gas reservoir stage since the Late Cretaceous. The mixed-source gas reservoir is formed by the adjustment of the Xixiangchi Group paleo-gas reservoirs and depressurization of the overpressure Wufeng-Longmaxi shale gas reservoirs and the charging of gas into the Xixiangchi Group reservoir of the Pingqiao anticline since the Late Cretaceous, which show obvious superimposed accumulation characteristics. There are different accumulation patterns in different geological periods. The accumulation pattern of the “old source - young reservoir” (i.e. hydrocarbons generated from older source rocks accumulating in younger reservoirs) dominates before the Late Cretaceous, and that of “juxtaposed young source - old reservoir” (i.e. hydrocarbons generated from younger source rocks accumulating in juxtaposed older reservoirs) dominates after the Early Cretaceous. Moreover, faults acted as critical vertical pathways for hydrocarbon migration during the evolution of the Xixiangchi Group gas reservoirs. This model provides new insights and theoretical basis for evaluation and mapping of the Xixiangchi Group play fairway in eastern Sichuan Basin.