Gas source of the Middle Jurassic Shaximiao Formation in the Zhongjiang large gas field of Western Sichuan Depression:Constraints from geochemical characteristics of light hydrocarbons

The Zhongjiang gas field is a typical large gas field in terrigenous strata of the Western Sichuan Depression.It remains debatable which member of the Upper Triassic Xujiahe Formation served as the source rocks and how significant the member contributed to the gas accumulations in the Zhongjiang gas field.In this study,we analyzed the essential characteristics of the Lower Jurassic source rocks and the geochemical features of light hydrocarbons in natural gas from the 2nd(T_(3)χ^(2))and 4th members(T_(3)χ^(4))of the Upper Triassic Xujiahe Formation(T_(3)χ),as well as the Middle Jurassic Shaximiao(J_(2)s)and Qianfoya(J_(2)q)formations.Based on this,we explored the sources of the natural gas in the Zhongjiang gas field and determined the natural gas migration patterns and their effects on the properties of light hydrocarbons in the natural gas.The results indicate that the Lower Jurassic lacustrine source rocks of the Zhongjiang gas field contain humic organic matter,with vitrinite reflectance(R_(0))values ranging from 0.86%to 0.98%.Samples meeting the criterion for effective source rocks[total organic carbon(TOC)content≥0.75%]exhibited an average TOC content of merely 1.02%,suggesting significantly lower hydrocarbon generation potential than source rocks in the underlying T3x,which show higher thermal maturity and TOC contents.For natural gas samples from T_(3)χ^(2),T_(3)χ^(4),J_(2)s,and J_(2)q reservoirs,their C_(5-7)iso-alkane content was significantly higher than their n-alkane content,and their methylcyclohexane(MCH)index ranged from 59.0%to 77.3%,indicating the predominance of methylcyclohexane in C_(7)light hydrocarbons.As indicated by the origin identification and gas-source correlation based on the geochemical features of light hydrocarbons,the natural gas in the Zhongjiang gas field is typical coal-derived gas.The gas from the primary pay zone of the Shaximiao Formation,with significantly high K_(1),(P_(2)+N_(2))/C_(7),and P_(3)/C_(7)values,predominantly originated from the 5th member of the T3x and migrated in the free phase,with a small amount possibly sourced from the Lower Jurassic source rocks.The dissolution and adsorption during gas migration led to a decrease in the aromatic content in C_(6-7)light hydrocarbons and an increase in the isoheptane values.Therefore,their effects must be considered when determining the gas origin and thermal maturity based on the aromatic content in C_(6-7) light hydrocarbons and iso-heptane values.

Tracing of natural gas migration by light hydrocarbons:A case study of the Dongsheng gas field in the Ordos Basin,NW China

Based on the analysis of light hydrocarbon compositions of natural gas and regional comparison in combination with the chemical components and carbon isotopic compositions of methane,the indication of geochemical characteristics of light hydrocarbons on the migration features,dissolution and escape of natural gas from the Dongsheng gas field in the Ordos Basin is revealed,and the effect of migration on specific light hydrocarbon indexes is further discussed.The study indicates that,natural gas from the Lower Shihezi Formation(Pix)in the Dongsheng gas field displays higher iso-C5-7contents than n-C5-7contents,and the C6-7light hydrocarbons are composed of paraffins with extremely low aromatic contents(<0.4%),whereas the C7light hydrocarbons are dominated by methylcyclohexane,suggesting the characteristics of coal-derived gas with the influence by secondary alterations such as dissolution.The natural gas from the Dongsheng gas field has experienced free-phase migration from south to north and different degrees of dissolution after charging,and the gas in the Shiguhao area to the north of the Borjianghaizi fault has experienced apparent diffusion loss after accumulation.Long-distance migration in free phase results in the decrease of the relative contents of the methylcyclohexane in C7 light hydrocarbons and the toluene/n-heptane ratio,as well as the increase of the n-heptane/methylcyclohexane ratio and heptane values.The dissolution causes the increase of isoheptane values of the light hydrocarbons,whereas the diffusion loss of natural gas in the Shiguhao area results in the increase of n-C5-7contents compared to the iso-C5-7contents.

Correction Method of Light Hydrocarbons Losing and Heavy Hydrocarbon Handling for Residual Hydrocarbon (S_1) from Shale

In China, hot researches on shale oil were raised by the important breakthrough of shale oil in America. Obviously, the first important issue is the actual shale oil resource potential of China, and the selection of the key appraisement parameter is vital to the shale oil resource amount. Among the appraisement parameters, the oil content parameter（S1） is the key one, but the evaluation result is generally lower because of light hydrocarbon losing and heavy hydrocarbon handling. And the more important thing is that the light hydrocarbon with small molecular weight is more recoverable, and therefore its amount is important to the total shale oil yields. Based on pyrolysis experiments and the kinetic model of hydrocarbon generation, correction factors and a model of light hydrocarbon losing and heavy hydrocarbon handling were established. The results show that the correction factor of heavy hydrocarbon handling is 3.2, and that of light hydrocarbon losing is controlled by kerogen type, maturity and hydrocarbon generation environment（closed or open）.

4-Pyrazolecarboxylic Acid-based MOF-5 Analogs Framework with High Adsorption and Separation of Light Hydrocarbons

One porous framework [Zn4（μ4-O）（μ4-4-pca）3]·2（DEF）·2（H2O）（1, 4-H2Pca = 4-pyrazolecarboxylic acid, DEF = N,N-diethylformamide） with MOF-5 type topology has been synthesized solvothermally. Significantly, this compound exhibits high capacity of C2 hydrocarbons. C2H2 capacity could compare with the highest value of the reported MOFs, far exceeding that of MOF-5, as well as the high selectivity adsorption of C2s over C1.

The effect of slight to minor biodegradation on C_6 to C_7 light hydrocarbons in crude oils: a case study from Dawanqi Oilfield in the Tarim Basin,NW China

Light hydrocarbons （LHs） are one of the main petroleum fractions in crude oils, and carry much infor- mation regarding the genetic origin and alteration of crude oils. But secondary alterations--especially biodegrada- tion--have a significant effect on the composition of LHs in crude oils. Because most of the LHs affected in oils underwent only slight biodegradation （rank 1 on the biodegradation scale）, the variation of LHs can be used to describe more the refined features of biodegradation. Here, 23 crude oils from the Dawanqi Oilfield in the Tarim Basin, NW China, eleven of which have been biodegraded to different extents, were analyzed in order to investigate the effect of slight to minor biodegradation on C6--C7 LHs. The study results showed that biodegradation resulted in the prior depletion of straight-chained alkanes, followed by branched alkanes. In slight and minor biodegraded oils, such biodegradation scale could not sufficiently affect C6- C7 cycloalkanes. For branched C6--C7 alkanes, generally, monomethylalkanes are biodegraded earlier than dimethylalkanes and trimethylalkanes, which indicates that branched alkanes are more resistant to biodegradation, with the increase of substituted methyl groups on parent rings. The degree of alkylation is one of the primary controlling factors on the biodegradation of C6-Cv LHs. There is a particular case： although 2,2,3-trimethylbutane has a rela- tive higher alkylation degree, 2,2-dimethylpentane is more resistant to biodegradation than 2,2,3-trimethylbutane. 2,2- Dimethylpentane is the most resistant to biodegradation in branched C6-C7 alkanes. Furthermore, the 2-methylpen- tane/3-methylpentane and 2-methylhexane/3-methylhexane ratios decreased steadily with increasing biodegradation, which implies that isomers of bilateral methyl groups are more prone to bacterial attack relative to mid-chain iso- mers. The position of the alkyls on the carbon skeleton is also one of the critical factors controlling the rate of biodegradation. With increasing biodegradation, Mango＇s LH parameters K1 values decrease and K2 values increase, the values of n-heptane and isoheptane decrease, and the indices of methylcyclohexane and cyclohexane increase. LH parameters should be applied cautiously for the biodegraded oils. Because biodegraded samples belong to slight or minor biodegraded oils, the values of n-heptane and isoheptane from Dawanqi Oilfield can better reflect and determine the ＂Biodegraded＂ zone. When the heptane value is 0-21 and the isoheptane value is 0-2.6, the crude oil in Dawanqi Oilfield is defined as the ＂Biodegraded＂ zone

Light Hydrocarbons in Fluid Inclusions and Their Constraints on Ore Genesis:A Case Study of the Songxi Ag(Sb)Deposit,Eastern Guangdong,China

The Songxi deposit is a newly discovered large Ag (Sb) deposit. By using a suite of high-vacuum quadrupole gas mass spectrometer systems, the authors have recognized many kinds of light hydrocarbons in fluid inclusions of minerals. These hydrocarbons are mainly composed of C1-C4 saturated alkanes, while the contents of C2-C4 unsaturated alkenes and aromatic hydrocarbons are quite low, suggesting that the metallogenic processes have not been affected by magmatic activities. Chemical equilibrium studies show that these hydrocarbons may be a mixture of organic gases generated by microorganism activity and those by thermal cracking of type-n kerogens (kukersite) in sedimentary host rocks, and the former may constitute more than two-thirds, implying that microorganism might have played an important role in the metallogenesis. The equilibrium temperature of the latter is about 300℃, which is much higher than the geothermal temperature at the estimated depth of metallogenesis. Thus, the light hydrocarbons generated by thermal cracking of kerogens probably originated in the deep part of the sedimentary basins and then migrated through a long distance to shallower horizons of the basin. Based on the composition of light hydrocarbons in fluid inclusions, the authors infer that the Songxi deposit was formed in a continental rift. The analytical data presented in this paper support from one aspect the genetic model that the Songxi deposit may be a sedimentary hot brine transformed deposit instead of a submarine basic volcanic exhalation and low-medium temperature volcanic hydrothermal fluid filling deposit proposed by most previous researchers.

Coupling pinch analysis and rigorous process simulation for hydrogen networks with light hydrocarbon recovery

In refineries,some hydrogen-rich streams contain considerable light hydrocarbons that are important raw materials for the chemical industry.Integrating hydrogen networks with light hydrocarbon recovery can enhance the reuse of both hydrogen and light hydrocarbons.This work proposes an automated method for targeting hydrogen networks with light hydrocarbon recovery.A pinch-based algebraic method is improved to determine the minimum fresh hydrogen consumption and hydrogen sources fed into the light hydrocarbon recovery unit automatically.Rigorous process simulation is conducted to determine the mass and energy balances of the light hydrocarbon recovery process.The targeting procedures are developed through combination of the improved pinch method and rigorous process simulation.This hybrid method is realized by coupling the Matlab and Aspen HYSYS platforms.A refinery hydrogen network is analyzed to illustrate application of the proposed method.The integration of hydrogen network with light hydrocarbon recovery further reduces fresh hydrogen requirement by463.0 m^(3)·h^(-1) and recovers liquefied petroleum gas and gasoline of 1711.5 kg·h^(-1) and 643 kg·h^(-1),respectively.A payback period of 9.2 months indicates that investment in light hydrocarbon recovery is economically attractive.

Synthesis of light hydrocarbons from CO hydrogenation over Co_xMn_(0.06)/SiO_2

A series of CoxMn0.06/SiO2 catalysts were prepared by an impregnation method for catalytic hydrogenation of CO to Light Hydrocarbons(LHCs).The catalysts were characterized by XRD,SEM,N2 adsorption and NH3-TPD techniques.Catalyst activities were evaluated in a high-pressure micro reactor.The results show that the performance of the catalysts was significantly affected by the amount of Co loaded onto the substrate.The activity of the Co0.10Mn0.06/SiO2 catalyst was stable with time-on-stream.The CO conversion and LHCs selectivity were 95.3% and 98.1%,respectively,for this catalyst at 400 °C.

Permeation Characteristics of Light Hydrocarbons Through Poly（amide-6-β-ethylene oxide） Multilayer Composite Membranes

In this paper, poly(amide-6-β-ethylene oxide) (PEBA1657) copolymer was used to prepare multilayer polyetherimide (PEI)/polydimethylsiloxane (PDMS)/PEBA1657/PDMS composite membranes by dip-coating method. Permeation behaviors of ethylene, ethane, propylene, propane, n-butane, methane and nitrogen through the multilayer composite membranes were investigated over a range of operating temperature and pressure. The permeances of light hydrocarbons through PEI/PDMS/PEBA1657/PDMS composite membranes increase with their increasing condensability, and the olefins are more permeable than their corresponding paraffins. For light hydrocarbons, the gas permeances increase significantly as temperature increasing. When the transmembrane pressure difference increases, the gas permeance increases moderately due to plasticization effect, while their apparent activation energies for permeation decrease.

Geochemical Characteristics of C_5–C_7 Light Hydrocarbons in Gas Hydrates from the Permafrost Region of Qilian Mountains

As an important part of gas hydrates, light hydrocarbons （LHs）, especially C5 to C7 hydrocarbons with various monomer compounds, provide a wide variety of geological and geochemical information, which have received much attention from organic geochemists and petroleum geologists.

Compositional characteristics and geochemical significance of light hydrocarbons for crude oils in Tarim Basin, China

Light hydrocarbons, especially C-7 isoalkanes, cyclopentanes, cyclohexanes and n-heptane in 540 oils from the Tarim Basin were studied systematically. The results suggested the K-1 values [(2-MH+2,3-DMP)/(3-MH+2,4-DMP)] of crude oils vary from a lowest value of {0.78}, to a highest value of {1.54}, but the K-1 values of the majority of oil samples (80%) range from {0.90} to {1.20}. However, the absolute contents of (2-methylhexane+ 2,3-dimethylpentane) and (3-methylhexane+2,4-dimethylpentane) in the total light hydrocarbons (C-4-C-7) show a similar variation trend. The variation of K-1 values of crude oils can suggest a typical sedimentary environment for source rocks. Therefore, according to the compositional characteristics of C-7 light hydrocarbons in light of the steady-state catalytic hypothesis, non-marine oils from the Yingmaili area and marine oils from the Tazhong uplift in the Tarim Basin were genetically classified.

Compositional and geochemical characteristics of light hydrocarbons for typical marine oils and typical coal-generated oils in China

Different types of crude oils have different light hydrocarbon compositional and geochemical character-istics. Based on the light hydrocarbon data from two kinds of oils,i.e.,coal-generated oils and marine oils in China,light hydrocarbons in marine oils in the Tazhong area are generally relatively enriched in n-heptane,and coal-generated oils from the Turpan Basin are enriched in methylcyclohexane . The K1 values,reported by Mango (1987),range from 0.97 to 1.19 in marine oils,basically consistent with what was reported by Mango on light hy-drocarbons in terms of the majority of the crude oil data. But the K1 values of coal-generated oils are particularly high (1.35-1.66) and far greater than those of marine oils; heptane values in marine oils,ranging from 32.3% to 45.4%,and isoheptane values,ranging from 1.9 to 3.7,are respectively higher than those of coal-generated oils,in-dicating that the oils are in the high-maturity stage. In addition,expulsion temperatures of coal-generated oils from the Turpan Basin are obviously lower than those of marine oils from the Tazhong area.

Oil geochemistry derived from the Qinjiatun–Qikeshu oilfields:insight from light hydrocarbons

A suite of 27 oils from the Qinjiatun–Qikeshu oilfields in the Lishu Fault Depression of the Songliao Basin was analyzed using whole oil gas chromatography.In combination with the relative distribution of C27, C28,and C29 regular steranes, detailed geochemical analyses of light hydrocarbons in oil samples revealed crude oils characterized by the dual input of lower aquatic organisms and higher terrestrial plants. Several light hydrocarbon indicators suggest that the liquid hydrocarbons have maturities equivalent to vitrinite reflectances of around0.78%–0.93%. This is consistent with the maturity determination of steranes C2920 S/(20 S ? 20 R) and C29 aab/(aaa ? abb). Crude oils derived from the two distinct oilfields likely both have source rocks deposited in a lacustrine environment based on light hydrocarbon parameters and on higher molecular weight hydrocarbon parameters. The results show that light hydrocarbon data in crude oils can provide important information for understanding the geochemical characteristics of the Qinjiatun–Qikeshu oils during geologic evolution.

Synthesis and Evaluation of Microporous Metal Organic Frameworks for Light Hydrocarbon Adsorption

Five microporous MOFs were synthesized and their static adsorption properties for light hydrocarbons were experimentally investigated at 298 K and 150 kPa.Among the five MOFs,HKUST-1 and Ni(bdc)(ted)0.5 exhibited much higher uptakes of ethane and propane than PCN-250,UiO-66,and ZIF-8.Breakthrough experiments were carried out at 298 K and atmospheric pressure on HKUST-1 and two commercially used adsorbents.HKUST-1 exhibited a much lower dynamic than static adsorption capacity.Moreover,HKUST-1 and the two traditional adsorbents could effectively separate binary(ethane/propane)and ternary(ethane/propane/toluene)mixtures.

Calculation and application of partition coefficients of light hydrocarbons in oil-based mud system

To find out the relationship between the oil-based mud,the formation fluid and the extracted gas,we use a thermodynamic approach based on static headspace gas chromatography technique to calculate the partition coefficients of 47 kinds of light hydrocarbons compounds between nC5 and nC8 in two kinds of oil-based mud-air systems,and reconstruct the original formation fluid composition under thermodynamic equilibrium.The oil-based drilling mud has little effect on the formation fluid compositions in the range of nC5-nC8(less than 1%for low-toxicity oil-based mud and less than 10%for oil-based mud).For most light hydrocarbon compositions,the partition coefficients obtained by vapor phase calibration and the direct quantitative methods have errors of less than 10%,and the partition coefficients obtained by direct quantitative method are more accurate.The reconstructed compositions of the two kinds of crude oil have match degrees of 91%and 89%with their real compositions,proving the feasibility and accuracy of reconstructing the composition of original formation fluid by using partition coefficients of light hydrocarbon compositions between nC5 and nC8.

Recovery Process for Lighter Hydrocarbon of Natural Gas in Liaohe Oilfield

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The Variance of Mango's Light-Hydrocarbon Parameter K

The analyses of light hydrocarbons in oils from the Tarim Basin show that the Man-go’s parameter K is about unity except those oils trapped in the eastern part of the Tazhong (Central Tarim) Fault Uplift. The regular variance of K may indicates the accumulation and admixture of the oil populations in the eastern part of the Tazhong Fault Uplift.

AB044.Phototoxic stress induced in retinal pigmented epithelium cells by the synergy between polycyclic aromatic hydrocarbons and blue light

Background:Lesion to the retinal pigment epithelium(RPE)is a crucial event in age-related macular degeneration(AMD)development.Although the pathogenesis of this complex disease is poorly understood,sunlight exposure and smoking are major environmental risk factors associated with AMD.High-energy visible blue light(HEV;400-500 nm)is the most energetic and potentially harmful solar wavelengths reaching adults retina.On the other hand,RPE cells can be exposed to a large range of pollutants from cigarette smoke,with polycyclic aromatic hydrocarbons(PAH)being among the most toxic.Some PAH from cigarette smoke can absorb HEV light.This led us hypothesize that in RPE cells,the combination of PAH and HEV could synergize to exacerbate the stress caused by either factor alone.We thus investigate the combined effect of PAH and HEV light in RPE cells.Methods:Confluent RPE immortalized cells(ARPE19)were exposed to nanomolar concentrations of benzo[a]pyrene(BaP)or indeno[1,2,3-cd]pyrene(IcdP).While IcdP efficiently absorbs HEV wavelengths,BaP,the most studied PAH,does not significantly absorb HEV light and was used as a control.BaP or IcdP contaminated ARPE19 were then irradiated with increasing sub-lethal doses of HEV light(150-500 J/cm2)using a setup that mimics the light spectrum normally reaching the retina.Cytotoxicity,apoptosis and reactive oxygen species(ROS)generation were assessed in each condition.Results:In presence of low concentrations of IcdP,sub-lethal amounts of HEV light trigger,in a dose-dependent way,up to 70%of apoptotic cell death.Co-exposure to IcdP and HEV also leads to a synergistic ROS generation in ARPE19 cells,thus inducing oxidative stress.None of these effects were observed with BaP.Efficient inhibition of ROS production by specific antioxidants only decreases death by 20%in cells simultaneously exposed to both IcdP and HEV light.Conclusions:Low concentrations of IcdP synergize with HEV light to induce phototoxicity in ARPE19 cells.An increased oxidative stress results from the interaction between both agents and partially explains the enhanced HEV phototoxicity in IcdP contaminated ARPE19 cells.This suggests that another major mechanism is involved in the synergetic toxicity.For smokers,this synergy between HEV and PAH may accelerate RPE cells loss and contribute to their greater risk of developing AMD.

Origin of hydrocarbon fluids and discussion of abnormal carbon isotopic compositions in the Lishui-Jiaojiang Sag,East China Sea Shelf Basin

The hydrocarbon gases in the L1 gas field of the Lishui-Jiaojiang Sag have been commonly interpreted to be an accumulation of pure sapropelic-type thermogenic gas.In this study,chemical components,stable isotopic compositions,and light hydrocarbons were utilized to shed light on the origins of the hydrocarbon fluids in the L1gas pool.The hydrocarbon fluids in the L1 gas pool are proposed to be a mixture of three unique components:mid-maturity oil from the middle Paleocene coastal marine Lingfeng source rock,oil-associated(late oil window)gas generated from the lower Paleocene lacustrine Yueguifeng source rock,and primary microbial gas from the paralic deposits of the upper Paleocene Mingyuefeng source rock.Here,for the first time,the hydrocarbon gases in the L1 gas pool are diagnosed as mixed oil-associated sapropelic-type gas and microbial gas via four pieces of principal evidence:(1)The abnormal carbon isotopic distributions of all methane homologues from C_(1)(CH_(4)or methane)to C_(5)(C_(5)H_(12)or pentane)shown in the Chung plot;(2)the diagnostic~(13)C-depleted C_(1)compared with the thermogenic sapropelic-type gas model,whileδ^(13)C_(2)(C_(2)H_(6)or ethane)andδ^(13)C_(3)(C_(3)H_(8)or propane)both fit perfectly;(3)the excellent agreement of the calculated carbon isotopic compositions of the pure thermogenic gas with the results of the thermal simulated gas from the type-II1 kerogen-rich Yueguifeng source rock;and(4)the oil-associated gas inferred from various binary genetic diagrams with an abnormally elevated gas oil ratio.Overall,the natural gases of the L1 gas pool were quantified in this study to comprise approximately 13%microbial gas,nearly 48%oil-associated sapropelic-type gas,and 39%of nonhydrocarbon gas.The microbial gas is interpreted to have been codeposited and entrained in the humic-kerogen-rich Mingyuefeng Formation under favorable lowtemperature conditions during the late Paleocene-middle Eocene.The microbial gas subsequently leaked into the structurally and stratigraphically complex L1 trap with oil-associated sapropelic-type gas from the Yueguifeng source rock during the late Eocene-Oligocene uplifting event.A small amount of humic-kerogen-generated oil in the L1 gas pool is most likely to be derived from the underlying Lingfeng source rock.The detailed geological and geochemical considerations of source rocks are discussed to explain the accumulation history of hydrocarbon fluids in the L1 gas pool.This paper,therefore,represents an effort to increase the awareness of the pitfalls of various genetic diagrams,and an integrated geochemical and geological approach is required for hydrocarbonsource correlation.