A study on the geochemical characteristics of natural gas and gas sources in the Bozhong sag

Natural gas is composed largely of hydrocarbon gas, especially wet gas in the Bozhong sag. The carbon isotopic composition shows that the gas is of organic origin. The carbon isotopic values of ethane indicate that the natural gas is dominated by mixed gas with minor coal-generated gas and oil-type gas. A gas-source correlation study showed that the source rocks of natural gas are those of the Lower Dongying Formation, the Shahejie Formation and the pre-Tertiary. The natural gas is characterized by multi-source and continuous generation in the study area, indicating that gas exploration potential is good in the Bozhong sag.     

Evolution of oil and gas generation in the Earth’s history and petroleum prediction in sedimentary basins

Oil and gas generation is a basic problem of geology and natural sciences, which is associated with energy resources as well as with the origination of life on the Earth. The evolution of hydrocarbons is controlled by the evolution of the biosphere and is an issue of phylogeny. Organic matter (OM) buried in sediments since the Early Precambrian consists mostly of phytoplankton, the main carrier of lipids producing hydrocarbons. Organic matter accumulates in marine sediments according to the law of periodicity. Middle Paleozoic fossilized OM is largely composed of zooplankton. Zooplanktonic OM, classified as sapropelites, had interfered with the process of oil and gas generation since its origin, e.g., tentaculites of the Domanik formation increased oil content. The inception of low-lipid macrophytes gave rise to introduction of humic OM into water bodies and formation of mixed-type OM. The larger the humic component in OM, the higher its gas potential. However, instead of replacing oil generation, enhanced gas generation had come on the scene since the Mesozoic, and their scales were approximately equal. The actual oil/gas ratio in sedimentary basins depends both on phylogenetic factors and on the evolution of each separate basin.     

Generation and accumulation of Quaternary shallow gas in eastern Qaidam Basin, NW China

1INTRODUCTION SHALLOW(MOSTLYBIOGENIC)GASACCOUNTSFOROVER20%OFTHEWORLD’SDISCOVEREDGASRESERVES(RICEAND CLAYPOOL,1981;CLAYPOOLANDKAPLAN,1974),AND REPRESENTSONEOFTHEUNCONVENTIONALENERGYSOURCES THATINCREASINGLYATTRACTTHEATTENTIONOFPETROLEUMGEOL OGISTS.NUMEROUS…     

“Source-Diagenesis-Accumulation” enrichment and accumulation regularity of marine shale gas in southern China

After the breakthrough of shale gas exploration and development in the Ordovician Wufeng Formation (Fm.) and Silurian Longmaxi Fm. of Chongqing Jiaoshiba area, Changning-Weiyuan area, etc. in Sichuan basin, a series of discovery and breakthrough were obtained by China Geological Survey in the Cambrian Niutitang Fm. and Sinian Doushantuo Fm. shale of the areas with complicated structure outside Sichuan basin. Based on the understanding of the law of shale gas enrichment in Longmaxi Fm. in the basin, this paper puts forward three elements of the formation and enrichment of shale gas, which are the “Source”, the “Diagenesis” and the “Accumulation”, after deeply studying the law shale gas enrichment and accumulation in Sinian-Cambrian reservoir of the complex structure area outside the basin. The “Source” means the sedimentary environment and petrological characteristics of organic shale. The “Diagenesis” means the basin tectonic subsidence and hydrocarbon generation and expulsion process of organic matter. The “Accumulation” means the tectonic uplift and shale gas preservation. It is proposed that the Sinian-Cambrian and Ordovician-Silurian black shale series in the middle and upper Yangtze region of southern China were both formed in the deep-water shelf environment of rift trough and foreland basin respectively. The dessert intervals were formed in the strong reduction environment under transgressive system tract. The shale lithology belongs to calcium-siliceous and charcoal-siliceous respectively. Based on the summary of structural evolution in Yangtze area, the correlation of structural burial depth with shale diagenesis and the coupling evolution of organic matter with pore structure are discussed. Combining with structural styles, the preservation conditions of shale gas are discussed. Five types of shale gas reservoir control models are further described. Two types of future exploration directions, which are reverse fault syncline and paleo-uplift margin in complex structural area outside the basin, are proposed.     

The application of chromatographic gas ratio analysis in reservoir fluid evaluation of “Beta” field in the Congo basin

This study assessed the hydrocarbon generation potentials/timing of the Awgu source rock horizons encountered in Igbariam-1, Iji-1 and Ajire-1 wells drilled in the southern Benue Trough; using one-dimensional (1D) Genesis Zetaware basin modelling software. This software enabled the integration of burial and thermal influences on Awgu source rocks with kinetic parameters. Thermal and burial history models indicate that the Awgu source horizons encountered at 3249m in Igbariam-1 well (northern part of the basin), expelled 85mg/gtoc of oil and 12 mg/gtoc of gas and hydrocarbon generation began in early Eocene with maximum expulsion in the mid-Eocene (52my) at the rate of 7mg/gtoc/my. To the south of the basin, the Awgu source horizons were encountered at greater depths in Iji-1 and Ajire-1 wells and hydrocarbon generation began in the mid-Palaeocene and peaked in the late Palaeocene (58my) at the rate of 32–38mg/gtoc/my. This resulted in an increase in generated hydrocarbon volume to the south due to (a) increased burial depth and early maturation, and (b) changing source lithofacies -more marine. The fault system linking potential reservoirs such as the Agbani sandstone and the overlying Owelli sandstone to the source rock suggests a possible migration of the generated hydrocarbons to those reservoirs at that time.     

Adaptive numerical simulation of the remediation of soil contamination by in‐situ gas venting

This paper describes a mathematical model and adaptive numerical simulation of the time‐dependent multiphase, multicomponent flow which occurs when a gas venting process is used to remove a volatile contaminant from a porous medium. The numerical simulation is adaptive in both space and time and involves the use of a finite element spatial discretization and the SPRINT2D software [6] for time integration. Results are presented which demonstrate the high quality of the simulation, both in terms of the length scales of the features that are resolved and the efficiency of the solutions relative to those obtained on fixed grids. This revised version was published online in July 2006 with corrections to the Cover Date.     

Sedimentation control over the oil and gas contents in the cretaceous deposits of the Russkoe–Chaselka Mega-Arch (West Siberian oil and gas basin)

Most of the hydrocarbon resources of the Russkoe–Chaselka Mega-Arch are related to the Pokur Formation reservoirs. They are generally composed of alluvial sandstones and shales. Due to their genesis the Pokur reservoirs have a complex structure and a localized spread within ancient alluvial plains. The performed integrated interpretation of the well and 3D seismic data made it possible to estimate new perspective fields and to geometrize the oil and gas deposits.     

Formation Conditions and Distribution Regularities of Oil—gas Pools in Tertiary Volcanic Rocks in Western Huimin Depression,Shandong Province

The formation conditions and distribution regularities of oil-gas pools in volcanic rocks in western Huimin Depression have been studied in terms of geolgic,sesmic and well logging information,This paper discusses the types and lithofacies,development and distribution of Tertiary volcanic rocks in the area.The results demonstrate that volcanic activity occurred mainly during the period from the Sha-4 stage to the Guantao episode,i.e.,before the oil-generating period(before the end of the Guantao episode and the Minghuazhen episode).The activity did not destroy oil and gas formation and accumulation,but was favourable for the concentration of organic matter and its conversion to hydrocarbons;besides,volcanic rocks can serve as reservoir rocks and cap rocks,playing a role very similar to that of a syndepositional anticline,The volcanic rocks are distributed near the margins of the oil-generating depression;there are many secondary interstices in the rocks,which are connected with each other.These are the leading conditions for the formation of oil-generating period and their self-sealing or good combination with other cap rocks are important factors for forming volcanic rock-hosted oil and gas pools.The oil-gas pools associated with volcanic rocks in western Huimin are mainly distributed around the deep oil-generating depression,in the central up lift or the high structural levels on the margins of the depression.In particular,the sites where several faults cross are usually locatons where hith-yielding oil-gas pools in volcanic rocks are concentrated.     

Generation of hydrogen ions and hydrogen gas in quartz–water crushing experiments: an example of chemical processes in active faults

To understand the fundamental chemical processes of fluid–rock interaction during the pulverization of quartz grains in fault zones, quartz grains were crushed within pure water. The crushing experiments were performed batch style using a shaking apparatus. The crushing process induced a decrease in pH and an increase in hydrogen gas with increased shaking duration. The amount of hydrogen ions generated was five times larger than that of the hydrogen gas, which was consistent with the amount of Si radicals estimated from electron spin resonance measurements by Hochstrasser and Antonini (1972). This indicates that hydrogen gas was generated by consuming most of the Si radicals. The generation of hydrogen ions was most likely related to the presence of silanols on the newly formed mineral surface, implying a change of proton activities in the fluid after pulverization of quartz.     

The isotopic evidence of gas source of the cold mineral springs with high pCO_2 in Wudalianchi

Active volcanoes are often associated with thermal springs, but some cold mineral springs exist near the active volcanoes in Wudalianchi, Heilongjiang Province, China, and these cold spas are rich in CO2. Water analysis shows that these HCO3- type mineral…     

Heavy metals contamination and assessment in gas station dust of Xi’an,a mega-city of China

The dust samples from 30 gas stations located in Xi’an are analyzed for Mn, Ni, Co, Cr, Cu, Cd, Pb and Zn by using atomic absorption spectrometry. The concentration, spatial distribution, source and the contamination levels provide scientific basis for urban planning and environmental renovation in Xi’an. The results indicate that the mean values of Ni, Cr, Co, Cu, Pb, Zn and Cd in the dust are 1.15, 1.19, 8.13, 3.94, 4.42, 5.09 and 15.62 times higher than the corresponding background values of Shaanxi soil, respectively. The high concentration of heavy metals is located in the inner and second ring road of Xi’an, China. Furthermore, the contents of metals in the south are higher than in the north. In addition, the concentrations of the gas station dust metals in the west are higher than in the east, particularly in the southwest. Three main sources of heavy metals of gas station dusts are identified in Xi’an. Mn and Ni mainly originate from a natural source; Cr, Cu, Pb, Cr and Zn mainly originate from traffic flow; and Co is mainly from industrial sources. The results of the potential ecological risk assessment indicate that the potential ecological risk index (RI) of Co is moderate; Cd is very high ecological risk, and the other analyzed metals belong to low ecological risk. The mean RI value of eight heavy metals in the gas station dusts from Xi’an is considerable ecological risk.     

Selenium enrichment in Carboniferous Shales,Britain and Ireland: Problem or opportunity for shale gas extraction?

The Carboniferous Bowland Shale in England, and its correlatives in Ireland, contain anomalously high concentrations of trace elements, including selenium (Se), molybdenum (Mo) and arsenic (As). High levels of these elements reflect high sulphur contents as these elements occur as trace constituents of pyrite. Anomalous Se in particular may have a volcanic provenance, from contemporary volcanic activity and/or drainage from Ordovician volcanogenic sulphide deposits. Following concern over the release of Se and As into groundwater during shale gas extraction in the US, the potential fate of Se and As during any future shale gas extraction from the Bowland Shale merits attention. It is at least an environmental issue that must be managed, but at best it could be an opportunity for extraction of Se in an environmentally sensitive manner.     

Discussion on “sandwich” structures and preservation conditions of shale gas in the South Yellow Sea Basin

In order to make a breakthrough in Mesozoic-Paleozoic shale gas exploration in the South Yellow Sea Basin, a comparison of the preservation conditions was made within the Barnett shale gas reservoirs in the Fortworth Basin, the Jiaoshiba shale gas reservoirs in Sichuan Basin and potential shale gas reservoirs in Guizhou Province. The results show that the “Sandwich” structure is of great importance for shale gas accumulation. Therein to, the “Sandwich” structure is a kind of special reservoir-cap rock assemblage which consist of limestone or dolomite on the top, mudstone or shale layer in the middle and limestone or dolomite at the bottom. In consideration of the Mesozoic-Paleozoic in the Lower Yangtze, and Laoshan Uplift with weak Paleozoic deformation and thrust fault sealing on both flanks of the Laoshan Uplift, a conclusion can be drawn that the preservation conditions of shale gas probably developed “Sandwich” structures in the Lower Cambrian and Permian, which are key layers for the breakthrough of shale gas in the South Yellow Sea. Moreover, the preferred targets for shale gas drilling probably locate at both flanks of the Laoshan Uplift.     

Greenhouse gas emissions from soils—A review

Soils act as sources and sinks for greenhouse gases (GHG) such as carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O). Since both storage and emission capacities may be large, precise quantifications are needed to obtain reliable global budgets that are necessary for land-use management (agriculture, forestry), global change and for climate research. This paper discusses exclusively the soil emission-related processes and their influencing parameters. It reviews soil emission studies involving the most important land-cover types and climate zones and introduces important measuring systems for soil emissions. It addresses current shortcomings and the obvious bias towards northern hemispheric data.When using a conservative average of 300 mg CO₂e m⁻² h⁻¹ (based on our literature review), this leads to global annual net soil emissions of ≥350 Pg CO₂e (CO₂e = CO₂ equivalents = total effect of all GHG normalized to CO₂). This corresponds to roughly 21% of the global soil C and N pools. For comparison, 33.4 Pg CO₂ are being emitted annually by fossil fuel combustion and the cement industry.     

Observation of the seismoelectric effect in a gas condensate field in the Earth’s natural electromagnetic and seismic noise of 0.1-20 Hz

The first experimental measurements of the cross-correlation function (CCF) of the Earth’s seismic and electrical noise were carried out in two areas of the Minusinskoe gas condensate field in 2014 and 2015 using a VPEMPZ-M1 (Shum-6) two-channel geophysical device developed at Siberian Federal University. The Earth’s seismic noise and electrical noise in the frequency range 0.1-20 Hz were received by a geophone and an electric dipole, respectively. In both cases, a productive pool at depths of 1800-2000 m had a maximum CCF value five to seven times higher than the normal background, indicating the occurrence of the seismoelectric effect in passive fields.     

The application of gas chromatography fingerprint technique to calculating oil production allocation of single layer in the commingled well

1Principle SincetheGCfingerprinttechniquewasfirstused tomonitortheproductionofoilfieldsbyAmericansci entists(KaufmanandAhmed,1990;Kaufmanetal.,1987)inthe1980s,manyresearchershavetentatively appliedthismethodinseveraloilfields(HeWenxiang etal.,1996;2001;WangZhengpingetal.,2000;ChenShijiaetal.,1999)andhaveachievedsatisfac toryresults.Butthereappearsomeobviousdeficien ciesinthecourseofexplorationanddevelopment.Takinganthraceneasinternalstandard,wecalculated theabsoluteconcentrationsoffingerp…     

Interaction between source rock and evaporite： A case study of natural gas generation in the northern Dongying Depression

It is well known that oil generated from source rocks of saline-lake facies is characteristic of low Pr/Ph ratio and high contents of gammacerane. The authors found that gas generated from the same source rocks was high in benzene and cyclohexane contents and had light carbon isotope compositions. In this study, a series of thermal simulations of gas generations on source rock with/without evaporites (such as carbonate, gypsum, and sodium chlorite, respectively), were conducted. It was found that the gypsum played an important role on the catalyzsis of gas generation in the thermal simulations. Compositions of the gaseous hydrocarbons generated from source rocks with evaporites are very similar to those of natural gases discovered from northern Dongying Depression. Meanwhile, in the thermal simulations, it was found that the carbon isotopic compositions of gaseous hydrocarbons generated from source rocks with evaporites are lighter than those of the gases from source rocks without evaporites. Therefore, it is concluded that natural gases discovered from northern Dongying Depression are the product of interaction between source rocks and evaporites (especially gypsum) of the saline facies.     

Pyrite characteristics and shale gas significance of the Niutitang Formation in Cengong area,Guizhou ProvinceSCIEI北大核心CSCD

黄铁矿特征研究可为页岩沉积环境恢复与页岩气富集保存规律预测提供依据。以贵州岑巩地区岑页1井牛蹄塘组为研究对象,基于岩心、薄片、扫描电镜及微量元素、硫同位素地球化学,确定牛蹄塘组页岩沉积环境及页岩气富集地质条件。研究表明,牛蹄塘组页岩黄铁矿发育为草莓状、自形-半自形及他形(主要为胶状他形)三种形态,不同形态的黄铁矿形成于不同沉积环境,草莓状黄铁矿形成于缺氧还原环境,自形-半自形黄铁矿形成于贫氧环境,胶状他形黄铁矿指示沉积过程有热液活动的参与。测试井牛蹄塘组整体处于较开放的沉积水体,上段为含氧-贫氧环境,硫同位素整体变轻且发生负漂;中段为较缺氧环境,硫同位素跨度大且发生正漂;下段为还原性更强的沉积环境,硫同位素小幅度负漂。黄铁矿含量与有机质富集密切相关,与黄铁矿有关的孔隙为页岩气吸附、保存及运移提供载体,且草莓状黄铁矿指示的缺氧硫化环境更利于有机质保存。研究工作系统梳理了黄铁矿对牛蹄塘组页岩沉积环境及储层页岩气富集的指示作用,为页岩气勘探提供指示。     

Determination of fuel combustion product in airport runoff water samples using liquid–liquid extraction with gas chromatography–spectrometry

Determination of xenobiotics in samples of airport runoff water is both a complex and indispensable task due to an increasing threat resulting from the activities of numerous airports. The aim of this study was to develop, optimize, and validate a procedure based on liquid–liquid extraction (LLE) coupled with gas chromatography–mass spectrometry (GC–MS) for the determination of polycyclic aromatic hydrocarbons (PAHs). So far, no procedure was available that would ensure reliable data about concentration levels of these toxic pollutants in a new type of environmental samples, such as airport stormwater. The most difficult step in the analytical procedure used for the determination of fuel combustion products in airport stormwater samples is sample preparation. In this work, eight different protocols of sample preparation were tested. The evaluation of the LLE demonstrated that the best extraction conditions were as follows: dichloromethane (extraction solvent), solvent volume of 15 mL and sample volume of 250 mL. The percent recovery values ranged from 66 to 106 %, which shows that the LLE technique is a powerful method for extracting PAHs from airport runoff water samples with a complex matrix composition. Moreover, the developed procedure was characterized by satisfactory selectivity and a relatively low LOQ (0.17–0.52 μg/L). The procedure has been successfully applied to the analysis of stormwater samples collected from different sites at international airport in Poland. The procedure can thus be used as a tool for tracking the environmental fate of these compounds and for assessing the environmental effect of airports.