Concentrations Of Hydrocarbon Gases Research Articles

Geochemical characteristics, genetic types, and source of natural gas in the Sinian Dengying Formation, Sichuan Basin, China

The Sinian Dengying Formation is a key target for deep oil and gas exploration in the Sichuan Basin, China. Natural gas was mainly distributed in the Ziyang–Weiyuan area (ZWA) and the Gaoshiti–Moxi area (GMA). At present, the genetic types and sources of natural gas are still unclear and controversial. The chemical composition, stable carbon isotopes, and biomarkers were used to analyze geochemical characteristics, genetic types, and gas–source relations. The results showed that the composition and content of hydrocarbon gas in the ZWA and GMA were similar. Natural gas was a typical dry gas with an average dry coefficient (C1/C1+) of 0.9991, which reflected higher methane (CH4) content and lower heavy hydrocarbon gas (C2+) content. For nonhydrocarbon gas, CO2 (0.01%–26.34%), N2 (0.03%–24.95%), H2S (0.10%–3.19%), and He (0.01%–0.37%) were mainly distributed. Compared with the GMA, the ZWA was characterized by higher N2 content and lower CO2 content. Although the carbon isotopes had not been reversed, the values of δ13C2–δ13C1 were different between the ZWA and GMA, with the GMA having the higher value. The assemblage relation between the natural gas composition and carbon isotopes indicated that the natural gas type was dominated by oil-cracking gas. Mud-shale in the high maturity stage of thermal evolution greatly influenced on the content of N2 and He. H2S mainly belonged to thermochemical sulfate reduction (TSR), and most of CO2 was formed by deep carbonate metamorphism and TSR. The gas–source relation showed that natural gas in the ZWA was derived from the Cambrian Qiongzhusi Formation and that the gas in the GMA mainly originated from the Sinian Dengying Formation and the Cambrian Qiongzhusi Formation. The established hydrocarbon generation model indicated that the Sinian Dengying Formation is potentially gas-rich.

Simulation Study of Hydrocarbon Generation Characteristics in Siliceous Rock

Late Triassic-early Jurassic silica rocks are widely developed in Northeast China. To evaluate the silica rock hydrocarbon generating capacity, we have simulated the hydrocarbon evolution process by thermal simulation experiments and analyzed the hydrocarbon generation characteristics. The experiments were carried out at six temperature points 250, 270, 290, 310, 330, and 350°C, and the content of the gaseous and liquid products was measured. The experiments results showed that the organic-rich siliceous rocks are characterized by a relatively high hydrocarbon-generating capacity. The gaseous products are generated at different temperatures, while natural gas is mainly generated when the peak period of oil generation is completed. Natural gas includes hydrocarbon and non-hydrocarbon gases. Hydrocarbon gases include methane, ethane, propane, butane, pentane, and other heavy hydrocarbon gases. Non-hydrocarbon gases include hydrogen, nitrogen, carbon monoxide, and carbon dioxide. Carbon dioxide is the main component of the gas products, followed by hydrogen, methane, nitrogen, and other gases, but the total content of other gases is extremely low. Carbon dioxide generated during all stages of the oil generation process accounts for the vast majority, but in geological conditions, it will eventually be consumed by hydration. Nitrogen is mainly produced in the early stage. The content of hydrogen and hydrocarbon gases increases with increase in temperature, but hydrogen is usually depleted in the actual reservoir due to its strong chemical activity.

ГЕОДИНАМІКА

Purpose. Our research main purpose is to demonstrate the use of entropy maximization method for calculating the geochemical system composition, which consist of solid and gaseous organic substances. Changing the geodynamic situation is the driving force of elements redistribution between compounds in such systems. According to thermodynamic apparatus the main factors influencing this redistribution are pressure, temperature and the initial number of elements. Methods. Gibbs energy minimizing, maximizing the entropy, independent chemical reactions constants, Lagrange's method of undetermined multipliers, Newton–Raphson iterative method. It is well known that the fossilized organic matter, which is mainly represented by many types of kerogen, is an irregular polymer with structure, which cannot be described definitely. To calculate the equilibrium in the kerogen/gas system and obtain reliable results, it is necessary to apply a new model, without using the model structures of kerogen. We have proposed and described in detail a method of applying the Jaynes' formalism and maximizing entropy method to calculate the change in the composition of the kerogen/gas system with geodynamic regimes changing. Software in the Excel macros form and a compiled dynamic library, written in Visual Basic language, was created for calculations. Results. To verify the reliability of the proposed method and algorithm, we calculated the composition of the geochemical system, consisting of type II kerogen, methane to pentane hydrocarbons (including isomers), carbon dioxide, water and hydrogen sulfide. The calculation result is the molar fractions of hydrocarbon components and additive groups that make up kerogen, for different depths of the earth's crust. The calculations were performed for three heat fluxes: 40, 75 and 100 mW/m2, lithostatic pressure taken in account. Scientific novelty. It is established that the geodynamic situation changing in a complex way affects the distribution of elements between gases and kerogen in a closed thermodynamic system; modeling the kerogen/gas system behavior by method of entropy maximization provides results that do not contradict to study the structure of type II kerogen at different stages of maturity; the character of changes in the concentrations of hydrocarbon gases in equilibrium with type II kerogen indicates the inconsistency of the "oil window" hypothesis with the postulates of equilibrium thermodynamics. Practical significance. The entropy maximization method can be successfully used to calculate the composition of various geochemical systems consisting of organic compounds. The method is suitable for determining chemical composition of the irregular polymers, such as kerogen, bitumen, humic, in equilibrium with organic and inorganic gases and liquids.

Methane Flows and Gas Hydrates in the Transition Zone Between the Western Slope of the Kuril Basin and Offshore from Sakhalin Island

The results of integrated studies in the southwestern part of the Sea of Okhotsk obtained during cruise 74 of the R/V Akademik M.A. Lavrentiev in 2016 are presented. Gas hydrates, carbonate crusts and nodules in bottom sediments and more than 100 gas flares in the water column were recognized. Great attention has been paid to the gas composition of the water column and bottom sediments. Anomalous concentrations of hydrocarbon gases, helium, and hydrogen were revealed in the Kuril Basin–Terpeniya Bay transition zone.

Basalt–sediment configuration in the Tapti rift of central Indian region as derived from magnetotelluric (MT) studies and hydrocarbon prospects

Geochemical studies in Deccan syneclise have identified anomalous concentration of light hydrocarbon gases in the surface soil from the Tapti rift region in Narmada–Son Lineament, India. We have reanalysed and modelled broadband MT data from this region to delineate basalts and underlying sediment configuration, which is favourable for hydrocarbon accumulation. We carried out 1D and 3D modelling of the MT data for this purpose. Modelling studies brought regions of thick sub-basaltic sediments towards NW and SW of Nepanagar. But very less anomalous light hydrocarbon gas concentration is observed along NW of Nepanagar. This may be due to the presence of thick basalt cover in that area, which prevents the leakage of gaseous hydrocarbons on to the surface soil. We observed a comparatively thin basalt layer and high sediment thickness with a high concentration of light hydrocarbon gases near to Burhanpur area, which strongly suggests better hydrocarbon prospects in the area. It is inferred that the relatively thin and fractured/vesicular nature of basalt in this region facilitates the upward migration of light hydrocarbon components to the surface soil.

The Origin of Hydrocarbon Gases in the Lovozero Nepheline-Syenite Massif (Kola Peninsula, NW Russia), as Revealed from He and Ar Isotope Evidence

The occurrence of hydrocarbon gases (HCG) in unusually high concentrations for magmatic complexes, in the Lovozero and some other alkaline massifs, is of both geochemical and practical interest. The nature of these gases, despite the long history of research, remains the subject of debate. As an approach to solving this problem, we studied the coupled distribution of occluded HCG and the recognized tracers of various geological processes, such as helium and argon isotopes. The extraction of the gas components trapped in fluid micro-inclusions was carried out by the mechanical crushing of rock and mineral samples. A positive correlation was found between the 3He/4He and CH4/C2H6 ratios, whereas a negative correlation of the latter was found with the 36Ar concentration, which in turn was directly related, in varying degrees, to the content of HCG and most strongly with pentanes. Conjugacy of the processes of the heavier gaseous hydrocarbons, a loss of the deep component of the fluid phase and dilution of it with the atmogenic component was established. In the absence of a correlation between CH4 and 3He, the value of the CH4/3He ratio in the Lovozero gas substantially exceeded the estimates of it in gases of a mantle origin, and mainly corresponded to the crustal values. However, in some samples, a small fraction of mantle methane was allowed. The peculiarities of the relationships between hydrocarbon gases and the isotopes of noble gases indicate a sequential process of abiogenic generation and transformation of HCG at the magmatic and post-magmatic stages during the formation of the Lovozero massif. The obtained results confirm the usefulness of this approach in solving the origin of reduced gases in alkaline igneous systems.

Improved sampling technique to collect natural gas from hydrate-bearing pressure cores

High quality gas compositional data are an important factor in interpreting the genetic source of natural gas hosted in hydrate-bearing sediments and other subsurface systems. In order to accurately characterize the composition of gas samples degassed from hydrate-bearing pressure cores, one must use a reproducible sampling technique that minimizes artifacts of the sampling process. Herein, we review sediment core degassing techniques and compare data obtained from a commonly used degassing approach, which we term the standard quantitative degassing (SQD) technique, to our newly developed modified quantitative degassing (MQD) method designed to minimize atmospheric contamination and gas-water interactions. The SQD method allows sample gas to interact with water in a bubbling chamber, which we hypothesize could alter the gas composition following mixing with water or dissolved gases in the bubbling chamber. Whereas, the MQD method allows for the collection of sample gas prior to the bubbling chamber. To compare the SQD and MQD methods, we performed a side-by-side comparison of noble (He, Ne, Ar, Kr, and Xe), major (H2, N2, O2, and CO2), and hydrocarbon (CH4, C2H6, C3H8, i-C4H10, C4H10, i-C5H12, C5H12) gas concentrations and select isotopic compositions obtained using both sample collection techniques. Gas samples were collected from hydrate-bearing pressure cores recovered and maintained under hydrate stable conditions from the northern Gulf of Mexico during the UT-GOM2-1 Expedition. The MQD method displayed significantly lower concentrations of atmospheric gases, higher proportions of hydrocarbon gases, lower ratios of C1/C2+, and heavier stable carbon and hydrogen isotopes of methane than the SQD method. These results demonstrate that the MQD method reduced air contamination and minimized alteration of the hydrocarbon gases. Therefore, we conclude this method may be important for future work that seeks to determine the composition of natural gas from pressure cores using quantitative degassing experiments, especially those seeking to measure major (e.g., N2) and noble gases.

Dehydration Leads to Hydrocarbon Gas Formation in Thermal Degradation of Gas-Phase Polyalcohols

To understand the molecular mechanisms of hydrocarbon gas formation in biomass gasification, gasification of simple polyalcohols (glycerol, propylene glycol, and ethylene glycol) were studied at 400, 600, and 800 °C (residence times: 0.9–1.4 s) from the viewpoint of dehydration reactions that form aldehydes with various substituents as intermediates to produce hydrocarbon gases. The results were also compared with those of glyceraldehyde and dihydroxyacetone, which are reported to produce syngas (H2 and CO) selectively. All polyalcohols became reactive at 600 °C to form condensable products in 15.7–24.7% yields (C-based), corresponding to 33.9–38.4% based on the amounts of reacted polyalcohols. These condensable products, mostly aldehydes, act as gas-forming intermediates, because the polyalcohols were completely gasified at 800 °C (hydrocarbon gas contents: 20.3–35.3%, C-based). Yields of the intermediates bearing alkyl groups at 600 °C were proportionally correlated to the yields of hydrocarbon gases at 800 °C, suggesting that the alkyl groups are further converted into hydrocarbon gases via the fragmentation of acyl radicals. Dehydration reactions were suggested to occur in both heterolytic and radical mechanisms by theoretical calculations. Glyceraldehyde tended to fragment directly into CO and H2, instead of forming a dehydration intermediate. These results are informative for controlling the product gas composition in biomass gasification.

Palynomorphs in surface sediments of the North-Western Black Sea as indicators of environmental conditions

Most previous Black Sea palynology studies have used pollen-spore assemblages as proxies for climate and landscape changes, and dinocyst assemblages as proxies for surface water salinity. However, there are few data on within-region variations in these assemblages using large sets of surface samples and a full suite of palynomorphs, including terrigenous pollen + spores, freshwater algal spores, and organic remains of marine microplankton, micro- and meiobenthos. Here we fill this knowledge gap, using results from a palynological study of 43 surface samples from water depths of 71–905 mbsl on the Ukrainian Shelf and adjoining continental slope, NW Black Sea. The palynology samples were collected in conjunction with water and sediment chemistry data, grain-size, micropaleontological and meiobenthos data from the EU-FP6 project HERMES “Hotspot Ecosystems Research on the Margins of European Seas”. This dataset uniquely covers shelf and upper slope areas east and west of the Odessa-Sinop Fault Zone (OSFZ) that delimits areas of lower and higher hydrocarbon gas contents, respectively.The new data show that on the wide shelf with a shallow (ca. 80 m) oxycline, pollen assemblages differ from classical models for marine pollen transport. On the Ukrainian Shelf, pollen concentrations are extraordinarily high far offshore and the grains are often pyrite-infilled. These features apparently reflect high pollen preservation potential in low oxygen sediments, probably enhanced by cross-shelf transport of land-derived particulate organic matter. The new data have important consequences for accurate modelling of carbon burial and storage in epicontinental seas, and they provide a baseline for evaluating marine pollen concentrations expected to reflect the early Neolithic farming on the Ukrainian shelf. Furthermore, although large concentrations of dinocysts comprise more than half of the total Non-Pollen Palynomorphs (NPP), the high pollen concentrations skew the P:D index (pollen:dinocyst ratio) commonly used to evaluate changes in paleo-shoreline (proxy sea-level) positions. Despite the discharge of several large rivers to the Ukrainian Shelf, there are negligible traces of freshwater algae in the HERMES samples except at Sta. 15 where Pediastrum is abundant. Overall, palynomorphs of terrestrial origin make up about half (52%) of the acid-resistant organic-walled particles on the outer NW Black Sea Shelf and adjacent slope.The abundances of the major micro- and meiobenthic palynomorph groups show the same trends east and west of the OSFZ as the micropaleontological data reported for the HERMES samples taken at the same sites. The combined microzooplankton and zoobenthos surface assemblage data provide an important new baseline for evaluating historical and past changes in biodiversity and aquatic foodweb structure in the now polluted NW Black Sea. Comparison can also be made with foodweb reconstructions for Permian black shales.

The origin of high and variable concentrations of heavy hydrocarbon gases in coal from the Enhong syncline of Yunnan, China

The composition of coalbed methane (CBM) in the Enhong syncline of Yunnan China has abnormally high concentrations of heavy hydrocarbon gases (C2+). The distribution of the C2+ gases is variable in the syncline, some areas contain high concentration of C2+ gases from 2.9 to 36.98% which are called “wet gas area”, and in some areas, C2+ gases can't be examined which are called “dry gas area”. The reason for the high concentration of C2+ gases is connected with the coal maceral composition, the barkinites. The barkinites have the oil-prone character and have generated a lot of oil and exsudatinite in the process of coal maturation, which have been observed under the microscope. Accompanied by the oil and exsudatinite, many C2+ gases are generated from the coal, which can be proved by a large amount of C2+ gases generated from coal in Enhong syncline during the pyrolysis simulation experiments (Py-Gc). The reason of the uneven distribution of C2+ gases in the study area may be caused by different degrees of microbial degradation. The gases in the “dry gas area” become drier because of more microbial degradation and presenting biogenic gases character with little wet gas and lighter carbon isotopic methane, while gases in the “wet gas area” keep the character of thermogenic gases. The different degrees of microbial degradation may be caused by different gas preservation conditions such as coal pore structure. Mercury injection experiments show that coals in the “wet gas area” have larger pore specific surface areas and more micropores but fewer macropores. The larger pore volume of micropore and transitional pore may help the coal in the “wet gas area” protect the wet gases, maybe avoid the wet gases being degraded by the microorganisms.

ТЕРМОДИНАМІКА ТРАНСФОРМАЦІЇ КЕРОГЕНУ ІІ ТИПУ

The article reviews the chemical structure of type II kerogen. The changes that occur with the structure of type II kerogen as it passes through the stages of catagenesis from immature to post-mature are evaluated. Structural models of type II kerogen at different stages of catagenesis are presented: both obtained empirically after studying the structure by physical and chemical methods and the results of modelling by molecular dynamics method. Methods of equilibrium thermodynamics are used to calculate the composition of the kerogen–gas system for crust sections in the range of 1–20 km with a heat flux of 40 to 100 mW/m2. The composition of kerogen/fluid geochemical system is calculated using the E. T. Jaynes formalism. It boils down to determining the optimal distribution of 5 elements (C, H, O, N, S) among the 44 additive constituents of the solid phase (i. e., type II kerogen) and other individual components that are included in the system (CO2, H2O, H2S, NH3, CH4, C2H6, C3H8, i-C4H10, n-C4H10, i-C5H12, neo-C5H12, n-C5H12). Comparison with the experiments showed that the results of the calculations do not contradict the experiments, with study the structure and changes in type II kerogen with increasing degree of catagenesis. In the analysis of changes in the concentrations of water, carbon dioxide and hydrogen sulfide, it is founded that kerogen could be not only a donor of atoms for gas components, but also their acceptor in contact with a high-energy fluid stream. It is shown that the determination of sulfur-containing atomic groups of kerogen by thermodynamic modelling yields gives more reliable results than molecular dynamics methods. Established is that the concept of “methane-graphite death”, which takes place in the state of thermodynamic equilibrium in the transformation of organic matter, is erroneous. The calculation shows that the composition of the kerogen–gas system, in addition to methane and carbon, includes solid-phase heteroatom groups, various additive components of aromatic structures and gases, both organic and inorganic. The distribution of elements between the additive components of kerogen and gases in this system controls the pressure and temperature in a complex way. The nature of changes in hydrocarbon gas concentrations in equilibrium with type II kerogen indicates the presence of an “oil window” in low-warmed zones within 2–4 km depths.

Composition and origin of natural gases accumulated in the Upper Triassic tight sandstone reservoirs in the Western Sichuan depression, China: Gaseous hydrocarbons, noble gases and carbon dioxide

In this paper, the gas composition and isotopic characteristics of the tight sandstone of the Upper Triassic Xujiahe Formation in the western Sichuan depression were analyzed, and the origin of hydrocarbon gas, rare gas and CO2 in natural gas were determined. The hydrocarbon gas content in the tight sandstone gas of the Xujiahe Formation is the highest, ranging from 96.43% to 99.44 vol.%, while the non-hydrocarbon gas content is only 0.34–2.73 vol.%. The hydrocarbon gas has the highest content of CH4, which is distributed from 88.52% to 97.86 vol.%, and the content of other hydrocarbon gases is relatively low. The studied natural gas is mainly dry gas, and a small part is wet gas. According to the hydrocarbon gas component and carbon isotope analysis results, it showed that the natural gas of the Xujiahe Formation was a thermogenic gas, and there was no mixing of biogenetic gas. The natural gas was derived from the thermal degradation of the humus kerogen. Moreover, the rare gas in the natural gas of the Xujiahe Formation is a crustal origin organic gas, and there is no mantle origin gas, which indicates the lack of inorganic components in the natural gas. We also found that the CO2 in the natural gas is mainly inorganic gas, which is derived from the dissolution of carbonate minerals; and only a small part is organic thermogenic gas, which is derived from the thermal maturation process of organic matter.

Hydrocarbon gases in seafloor sediments of the TATAR strait, the northern sea of Japan

The distributions of hydrocarbon gases (HCGs) from C1-C5 in seafloor sediments of the South Tatar sedimentary basin (northern Sea of Japan) were obtained during five research cruises from 2012 to 2017. As a result of this work, areas of gas hydrates, gas flares, and anomalous gas concentrations were discovered. The concentration of HCGs in seafloor sediment, as determined by the “headspace method” varied from 0.38 to 149,000 ppm, with a median of 177 ppm (N = 1420). The median values of HCGs for the Western, Central, and Eastern part of the South Tatar sedimentary basin are 11.7, 99, and 1134 ppm, respectively. Maximum values and gradients in concentrations of HCGs were found in the central and eastern parts of Tatar Strait, where multiple cores contain gas hydrates and gas-saturated sediments. The predominant gas component in all samples was methane, but relatively high concentrations of ethane (up to 789 ppm) and propane (up to 111 ppm) occur. Methane concentrations below 5.25 ppm can be considered as regional background for near seafloor (0–15 cm) sediments from the South Tatar sedimentary basin. The С1/(С2 + С3) ratio across all samples ranges between 2.6 and 345,000, with a median value of 219. The presence of a large-scale degassing zone exists in the northeastern part of Tatar Strait, which coincides with areas of gas hydrates and gas anomalies in the sediments and gas flares in the water column.

Catalytic pyrolysis of chemical extraction residue from microalgae biomass

Pyrolysis characteristics of chemical extraction microalgae residue in the presence and absence of catalysts (KCl, KOH, K2CO3, Al2O3, CaO, MgO and pyrolysis char of microalgae residue) were evaluated using a thermal analyzer and a tube furnace reactor. These catalysts can effectively improve the oil yield during microalgae residue pyrolysis. The order of the strength on increasing the oil yield was: pyrolysis char of microalgae residue > Al2O3>CaO > K2CO3>MgO > KCl > KOH. The addition of all the catalysts can effectively reduce the potential ecological risk of heavy metals in pyrolysis chars. The addition of KCl, MgO and Al2O3 can increase the content of gasoline components in pyrolysis oil. All the catalysts can reduce the content of CO2 in the pyrolysis gas, and increase the content of CO and hydrocarbon gases. KCl addition showed considerable increase in both yield and quality of pyrolysis oil and gas with a proportion of 5 wt % during microalgae residue pyrolysis.

Parameters of the Native Hydrocarbon Status of Soils in Different Bioclimatic Zones

To characterize the native component of the hydrocarbon status of soils in different bioclimatic zones, representative soils were studied in the East European Plain within the middle and southern taiga, forest-steppe, and semidesert zones. The samples were analyzed for the contents of hexane-soluble bitumens (bitumoids), normal and iso-alkanes (C14–C35), individual polycyclic aromatic hydrocarbons (PAHs, polyarenes), and soil hydrocarbon gases. It was found that the parameters of the native hydrocarbon status of soils are rather similar in different bioclimatic zones. For the background (uncontaminated) soils forming on interfluves, the following concentrations of native hydrocarbons were determined: up to 25 ppm (often, less than 5 ppm) of hexane bitumoid, no more than 60 ppb of the sum of 11 PAHs, and no more than 1 ppb of individual n-alkanes. Polyarenes were represented mainly by the lightest two- and three-ring compounds. The content of hydrocarbon gases retained by the soils varied widely. In 100% of cases, methane was the most common gas (from 1.8 to 3994 ppmv, 5.14 ppmv on average). Ethylene was less common (0.04–54.5 ppmv, 4.1 ppmv on average). Heavier alkane gases were less common and were present in amounts ranging from 0.02 to 4.09 ppmv (on average, 0.53 ppmv).

Accumulation Conditions and an Analysis of the Origins of Natural Gas in the Lower Silurian Shiniulan Formation from Well Anye 1, Northern Guizhou Province

The origin of natural gas and the mechanisms that lead to gas accumulation in the marine calcareous mudstone of the Lower Silurian Shiniulan Formation in northern Guizhou province are special and complicated. According to a combination of qualitative and quantitative methods, including the reconstruction of hydrocarbon generative potential and gas content’s measurement, in the context of some geochemistry information—the origins of the natural gas of Shiniulan Formation is suggested to be mixed gas. Furthermore, the accumulation of the natural gas can be proposed combined with some geological information. Results indicated that the volume of the in-place gas content of Shiniulan samples, reinstated by the formulas’ computation, reaches a yield of 3.67 m3·t−1 in rock. The theoretical gas content for Shiniulan Formation mudstone ranges from 1.6 to 5.8 m3·t−1 using the indirect calculation of gas content, and the total gas contents of those samples range from 0.065 to 0.841 m3/t, according to the United States Bureau of Mines’ (USBM) direct method. According to the combination of the reconstructed in-place gas content and the gas content, even mudstone in the Shiniulan Formation has potential to generating gas but could not satisfy the actual gas content in Shiniulan Formation. In addition, according to the composition, the carbon and hydrogen isotope charts of gaseous hydrocarbons further indicate that the gas origin of Shiniulan Formation is a mixed gas, which also means that the gas is not just generated in the layer, but has partly migrated from other formations, such as the Wufeng–Longmaxi Formation. The lower Shiniulan Formation in the study area is characterized by frequent interbed of limestone and calcareous mudstone. The geological information shows that well-developed fractures of mudstone and faults can be used as main pathways for the upward migration of gases from the underlying strata to the Shiniulan Formation. The limestone with fairly low porosity and permeability hinders the migration of natural gas as much as possible and keeps that efficiently reserved in the horizontal fractures of calcareous mudstone. This migration pattern implies that the interbedded rock association is also favorable for gas accumulation in the Shiniulan Formation.

Significance of Absorbed Natural Gas for Petroleum Exploration. Ukhta-Izhma Region Case Study

The article offers a brief overview of geochemical methods for petroleum prospecting and testing results of the exploration method based on hydrocarbon gas content in soil. For interpretation of the materials a new criterion developed by the authors was used— the naphtide coefficient. As a result of the testing high efficiency of the method is confirmed and it lead to localizing prospects within the Ukhta-Izhma region. Use of this method can contribute to the expansion of the hydrocarbon resource base in the region and demonstrate petroleum potential of unconventional structures of the Timan ridge. Analog to this, structures of the Rocky Mountains thrust belt and other oil and gas-bearing regions in the world, might demonstrate unexpectedly high hydrocarbon potential.

Geochemical response of produced water in the CBM well group with multiple coal seams and its geological significance-A case study of the Songhe well group in Western Guizhou

The geochemical response of produced water from coalbed methane (CBM) well group with multiple coal seams has rich geological significance. Taking 8 CBM wells of Songhe well group in western Guizhou as an example, the geochemical response characteristics and productivity significance of the CBM well group with multiple coal seams when inter-well interference or inter-layer interference appears have been examined mainly based on analyzing conventional ions, hydrogen and oxygen isotopes (δD and δ18O) of 7 batches of produced water samples in the stable production period of 1 year and 4 months, and dissolved inorganic carbon (DIC) stable isotopes (δ13CDIC) of 5 batches of produced water samples by cluster analysis and geological analysis methods. The study found that the change in dynamic fluid level has a good correlation with the Q-type clustering of δD-δ18O of produced water in the process of forming inter-well interference. With the formation of inter-well interference, the δD and δ18O clustering coefficient gradually decreases, and the fluids produced from the wells become more and more similar in property. In addition to the influence of drainage time, another main geological factor affecting inter-well interference is the buried depth of the coal seam. The larger the buried depth is, the larger the cumulative production of water, the faster the water circulation, the larger the Cl− concentration in produced water, the smaller the d-excess value (δD surplus index), and the smaller the cumulative production of CBM will be. In commingled CBM production of multiple coal seams, with larger span and multiple layers, inter-layer interference is likely to occur, resulting in unbalanced productivity contribution of the layers hard to tell. Because the δ13CDIC value in produced water from a well has a positive anomaly, the producing coal seams in the well are in the middle-upper layer of coal bearing strata; these coal seams have better permeability and higher water content, higher CO2 concentration and lower heavy hydrocarbon gas concentration offsetting each other, together with other geological conditions, it is concluded that the relatively large amount of CO2 formed by microbial reduction is the main cause of the positive δ13CDIC abnormality. Taking this well as the calibration well, combined with the Q-type clustering result of the δ13CDIC in produced water from the well group, considering the distribution of the developed coal seams and the change of the dynamical liquid level during the stable production period of the well group, the contribution of multi-coal layers in each well were estimated. If the cluster distance between the calibration well and another well is farther, the lower layer makes a larger contribution to the CBM productivity. If the cluster distance between the calibration well and another well is closer, the middle and upper layer contribute more to the CBM productivity, and it is mainly the production layers under the liquid level that produce CBM. This provides a unique hydrogeochemical analysis method for analyzing and identifying the contribution of production layers.

Enhanced hydrogen-rich gas production from waste biomass using pyrolysis with non-thermal plasma-catalysis

Abstract A pyrolysis-non-thermal plasma-catalytic system for the increased production of hydrogen-rich gas from waste biomass has been investigated. Plasma processing of the hydrocarbon pyrolysis gases produced a marked increase in total gas yield with plasma-catalysis producing a further modest increase. The product gases were mainly composed of H2, CO and CO2, which were all increased under plasma and plasma-catalyst conditions. For example, H2 yield increased from 1.0 mmol g−1biomass in the absence of plasma to 3.5 mmol g−1biomass with plasma and to 4.0 mmol g−1biomass with plasma-catalysis. In addition, in the absence of plasma, the hydrocarbon tar content in the product gas was 420 mg m−3, but, for non-catalytic plasma conditions, this was reduced to 325 mg m−3 and for plasma-catalytic steam reforming, the tar hydrocarbons were markedly reduced to 150 mg m−3. The effect of increasing input power for the plasma processing (no catalyst) showed a large increase in total gas, H2, CO and CO2 yield and corresponding decrease in hydrocarbon gas concentration. Plasma-catalysis showed that higher power input had only a small effect on gas yield. Plasma-catalysis was shown to produce lower catalyst coke deposition compared to non-plasma catalytic processing.

Effect of Hydrothermal Activity on Organic Matter Enrichment of Shale: A Case Study of the Upper Ordovician and the Lower Silurian in the Lower Yangtze, South China

The effect of organic matter on hydrocarbon potential, storage space, and gas content of shale is well-known. Additionally, present-day content of sedimentary organic matter in shale is controlled by depositional and preservation processes. Therefore, a study of the enrichment mechanisms of sedimentary organic matter provides a scientific basis for the determination of favorable areas of shale gas. In this study the Upper Ordovician Xinkailing Fm. and the first member of the Lower Silurian Lishuwo Fm. were examined. Stratigraphic sequences were identified through conventional logs and elemental capture spectrum data. Oxygen isotope analysis was applied to recover paleotemperature of seawater in the study area. The excess silicon content was calculated and the origin of the silica was determined by the Fe-Al-Mn ternary plot. The enrichment mechanism of organic matter was analyzed by two aspects: redox conditions and paleoproductivity. As a result, the stratigraphic interval was divided into two 3rd-order sequences. Through oxygen isotope, the paleotemperature of seawater was 62.7–79.2 °C, providing evidence of the development of hydrothermal activity. Analysis of excess siliceous minerals identified two siliceous mineral origins: terrigenous and hydrothermal. It also revealed an upwards decreasing tendency in hydrothermal activity intensity. Strong hydrothermal activity during the Late Ordovician, recognized as TST1, formed a weak-oxidizing to poor-oxygen environment with high paleoproductivity, which promoted organic matter enrichment. During the Late Ordovician to the Early Silurian, identified as RST1, TST2, and RST2, weakening hydrothermal activity caused the decline of paleoproductivity and increased oxidation of bottom waters, leading to a relative decrease of organic matter content in the shale. Therefore, favorable areas of shale gas accumulation in the Upper Ordovician and Lower Silurian are determined stratigraphically as the TST1, with a high total organic carbonate content. Geographically, the hydrothermally-active area near the plate connection of the Yangtze and the Cathaysian is most favorable.