Light Hydrocarbon Gases Research Articles

Titania Supported Ru Nanoclusters as Catalysts for Hydrodeoxygenation of Pyrolysis Oils

This study evaluates: (1) Ru-containing catalysts for low temperature hydrogenation of acetic acid in aqueous medium to simulate hydrogenating bio-derived oils, and (2) the development of the role of ruthenium–titania (Ru–TiO2) catalytic interaction for this system. A series of 9 catalysts was screened, and a comparison of selectivity versus conversion indicated that selectivity was a function of conversion, with ethanol being the predominant product at low conversion, and light gases being favored at higher conversion by secondary reactions. Exponential trend curves for ethanol (decay) and methane (increase) with conversion were fitted. On a per gram catalyst basis, the most active catalyst under study in the temperature range of 120° through 220 °C with a hydrogen partial pressure of 1000 psi (7.0 MPa) was 5 % Ru on carbon; however, its selectivity for the conversion to ethanol was exceptionally low (5 % selectivity at ~70 % conversion and 180 °C) with the primary products being ethane and methane. This catalyst formulation displayed a negative deviation from the trend curve for ethanol and a higher methane selectivity deviation. On the other hand, a catalyst of Ru prepared by atomic layer deposition (i.e., Ru(ALD)/Ti(ALD)/Nb/Si) was also highly active (~55 % conversion at 180 °C) but displayed a significant positive deviation from the trend curve (~40 % selectivity). These results combined with those of EXAFS suggest that the interface between the deposited Ru and the titania support may be responsible for the increase in selectivity to ethanol. In general, the catalysts prepared by ALD were more active on a per gram catalyst basis than the catalysts prepared by standard aqueous impregnation. Samples of catalyst that were observed using transmission electron microscopy confirmed that the Ru was well dispersed in that no Ru nanoparticle morphology was observed within the resolving power of the JEOL JEM-3010 TEM instrument. Regarding the nanostructure of the support, TEM measurements revealed that the ALD method resulted in support domain sizes that were significantly smaller ( 10 nm), promoting defect formation. EXAFS characterization indicated that the best ALD catalyst (i.e., Ru(ALD)/Ti(ALD)/Nb/Si) had higher dispersion (i.e., smaller nanoparticles and thus greater metal-support interface) than the reference catalysts prepared by aqueous impregnation. A Ru-Osupport contribution was required in order to obtain an acceptable EXAFS fit (‘the long metal–oxygen bond’). Increases in Ru–Ru coordination along with decreases in Ru-Osupport coordination were observed for longer catalyst aging times and higher treatment temperatures. In summary, the selectivity to ethanol during hydrogenation of acetic acid was promoted by preparing finely dispersed Ru particles in close interaction with nanoscale titania domains. The hydrogenation of the bio-model compound, acetic acid, over Ru-deposited catalyst leads to ethanol and methane/ethane. Based on XANES/EXAFS results, the reaction on finely dispersed Ru interacting with titania leads to the preferred product, ethanol, while larger Ru metal particles in the absence of contact between Ru and titania leads towards the formation of light hydrocarbon gases.

Solvent‐Dependent Synthesis from Layer to Microporous Pillared‐Layer Framework for Selective Sorption of Gas Light Hydrocarbons

AbstractThree metal‐organic frameworks, [Zn3(bdc)3(DMA)2] (1) (H2bdc = terephthalic acid; DMA = N,N‐dimethylacetamide), [Zn3(bdc)3(DMA)(DMPU)] (2) (DMPU = 1,3‐dimethylpropyleneurea), and [Zn3(bdc)4(Hdma)2] (3) [Hdma = protonated dimethylamine (Me2NH2)] were synthesized by using different solvents. The solvents determine the framework architectures range from layer to microporous pillared‐layer framework. The microporous framework has 8‐connected bcg topology and shows selective sorption ability for gas light hydrocarbons.

Conversion of sugarcane bagasse to gaseous and liquid fuels in near-critical water media using K2O promoted Cu/γ-Al2O3–MgO nanocatalysts

Bagasse conversion to H2, CO and light gaseous hydrocarbons as gaseous fuels, and higher alcohols and ethers as liquid fuels and fuel additives were performed in a basic water medium with near-critical condition in presence of potassium promoted Cu/γ-Al2O3–MgO catalysts. The catalysts were extensively characterized using ICP, XRD, TPR, BET, CO chemisorption and TEM techniques. In order to investigate support stability at reaction condition, XRD test also was carried out for used catalysts. Maximum dispersion of 48% and minimum average particles sizes of 8.4 nm were obtained for Cu20–K7.5/γ-Al2O3–MgO catalyst. Copper and potassium effects on quality and quantity of gaseous and liquid products were investigated. The maximum amounts of H2 (10 mmol g−1 of bagasse) and total produced gases (41 mmol g−1 of bagasse) were obtained with unpromoted Cu20/γ-Al2O3–MgO catalyst. Addition of K increased the bagasse conversion to liquid fuels. Potassium made the process more selective for alcohols and ethers production. Maximum amount of alcohols and ethers (83.3 mmol g−1 of bagasse) was obtained for Cu20–K7.5/γ-Al2O3–MgO catalyst.

Cost analysis model for catalytic conversion of syngas in to light hydrocarbon gases

Bio-gasification is a new technology and considered as a more efficient way to utilize bio-energy. The economic feasibility becomes one of the greatest issues when we apply this new technology. Evaluation of economic feasibility of a bio-gasification facility needs better understanding of its production unit cost under different capacities and different working shift modes. The objective of this study was to evaluate the unit cost of biofuel products (Liquid HCs, Light HCs and Oxygenates CxHyOz) under different capacities using a modeling method. The cost analysis model was developed using Visual Basic Microsoft 2008, computer programming language and mathematical equations. The modeling results showed that the unit costs of biofuel product from bio-gasification facility were significantly affected by production capacities of facilities. As the facility capacity increased from 65 to 10,000Nm3h−1, the biofuel production unit cost of gas (Light HCs), oil (Liquid HCs), and aqueous (Oxygenates CxHyOz) decreased from $38.92 per MMBTU, $30.89 per gallon and $25.74 per gallon to $2.01 per MMBTU, $1.59 per gallon, and $1.33 per gallon, respectively. The results of the sensitivity analysis showed that feedstock cost was the most sensitive cost factor on unit costs for all biofuel products at high capacity. The cost analysis model developed in this study could be used to optimize production unit costs of bio-fuel products from bio-gasification facility.

A method for characterization of bitumen

Characterization of bitumen is a necessary step to perform phase equilibrium computations involved in bitumen production and processing. This study presents a methodology for bitumen characterization using a residue curve map. A fugacity–activity coefficient approach is applied to model the thermodynamic equilibrium of the species in the gas and liquid phases. The Peng–Robinson equation of state (PR-EoS) and NRTL activity model are utilized to calculate the fugacity and activity coefficients in the gas and liquid phases, respectively. The proposed model was evaluated using experimental simulated distillation (SD) data as well as experimental solubility data of light hydrocarbon (CH4, C2H6) and non-hydrocarbon gases (CO2, N2) in bitumen. The molecular weight, specific gravity, and SD curves were represented using defined pseudo-components. The tuned EoS was able to regenerate the solubility data with an acceptable accuracy (AARD less than 5.6% and 4.5% for hydrocarbon and non-hydrocarbon solvents, respectively). The proposed method can be applied for bitumen characterization and to predict the solubility of the light gases in bitumen.

Diagenesis to very low-grade metamorphism in lower Palaeozoic sediments: A case study from deep borehole Tobolka 1, the Barrandian Basin, Czech Republic

The diagenetic grade of a 2.7km thick sequence of lower Palaeozoic marine sediments in the Tobolka 1 deep exploration borehole was investigated by analysing organic and mineral components and fluid inclusions embedded in vein minerals.The reflectance of organic matter (Rr %) increases down-section from values of about 0.77% at the top of the Devonian Srbsko Formation to values around 3% at the base of the Ordovician Letná Formation. In the Devonian and Silurian sediments the reflectance values of vitrinite-like and graptolite fragments (0.77–1.13% Rr and 1.09–1.46% Rr respectively) and the composition of fluid inclusions entrapped in vein minerals (CH4+CO2+complex saline solutions±light gaseous hydrocarbons±liquid petroleum; Th=170–230°C) collectively indicate organic maturation within the high-temperature part of the oil window to the wet gas stage. In the Ordovician sediments below 1000m, chitinozoan reflectance values (1.38–3.03% Rr) and the CH4-dominated composition of the fluid inclusions (Th=250–310°C) indicate a wet gas/condensate stage to an advanced dry gas stage.The clay mineral assemblage remains uniform throughout the whole succession and consists of illite, mixed-layered illite–smectite (IS), chlorite and kaolinite. Below 1400m the illite content gradually increases down-hole, forming up to 45–55% of the clay fraction in the deeply-buried Ordovician sediments. Throughout the borehole, the IS displays uniformly low expandability (7–12±3% of smectite layers) and an ISII ordering. The illite crystallinity broadly correlates with organic matter reflectance values and improves with depth (from 1.1 to 0.54° Δ2θ according to the Crystallinity Index Standard (CIS) scale) indicating high-grade diagenesis to incipient anchimetamorphism. The chlorite crystallinity (ChC index), however, shows no systematic correlations with depth.The combined evidence from organic matter, clay minerals and fluid inclusions points to maximum paleotemperatures of ~100–230°C in the Silurian–Devonian strata, and up to ~250°C or even higher in the Ordovician strata. Apatite fission track analysis (AFTA) data suggests that maximum heating occurred between 340 and 380Ma, i.e. during Variscan orogenic deformations. These paleotemperatures and the degree of diagenesis may have been produced by a post-Middle Devonian burial or tectonic load that was subsequently eroded, or by higher paleogeothermal gradients, or by a combination of both.

Hydrogen production via supercritical water gasification of bagasse using Ni–Cu/γ-Al2O3 nano-catalysts

Biomass gasification in supercritical water media is a promising method for the production of hydrogen. In this research, Cu-promoted Ni/γ-Al2O3 nano-catalysts were prepared with 2.5– 30 wt% Ni and 0.6– 7.5 wt% Cu loadings via the microemulsion method. Nano-catalysts were characterized by inductively coupled plasma (ICP), Brunauer Emmett Teller (BET) technique, X-Ray Diffraction (XRD), H2 chemisorption and Transmission Electron Microscopy (TEM) technique, as well as Carbon-Hydrogen-Nitrogen-Sulfur (CHNS) analysis was carried out for elemental analysis of bagasse. Nano-catalysts were assessed in a batch micro-reactor under 400°C and 240 bar. The microemulsion method decreased the catalyst average particle size and increased the percentage dispersion and reduction of the catalysts. The total gas yield increased with an increase in Ni and Cu loadings up to 20 wt% Ni and 5 wt% Cu and then started to decrease. Using the microemulsion technique for the preparation of Ni–Cu/γ-Al2O3 nano-catalyst, increased the hydrogen yield to 11.76 (mmol of H2/g of bagasse), CO yield to 2.67 (mmol of CO/g of bagasse) and light gaseous hydrocarbons to 0.6 (mmol of light gaseous hydrocarbons/g of bagasse). Promotion of Ni/γ-Al2O3 with copper increased the mole fraction of hydrogen in the final gasification products to 58.1 mol%.

Effect of char on co-pyrolysis of biomass and coal in a free fall reactor

Fast pyrolysis and co-pyrolysis of pine sawdust (SD) and sub-bituminous coal (SB) were carried out in a free fall reactor. There is a gas–solid separator at the bottom of the reactor, where a controlled re-contact of the primary volatiles with the nascent char could be achieved. The experiments of the individual fuels with the volatiles–char re-contact resulted in increased tar yield and decreased the light hydrocarbon gas concentrations compared with that without the volatiles–char re-contact. During the co-pyrolysis of SD and SB, synergies were observed to have produced more tar at different biomass blending ratios (BR). Particularly, the re-contact of the volatiles–char effectively enhanced tar generation and suppressed water formation. The volatiles–char interactions promoted the tar generation mainly at the char bed temperature range from 600°C to 700°C. At the optimum condition with the BR of 0.50 and char bed temperature of 700°C, the tar yield increased up to 28.7%. The co-pyrolysis and volatiles–char interactions favored the acidic components generation in the liquid products. Especially, the volatiles–char re-contact during co-pyrolysis improved the quality of tar by decreasing its asphaltene content.

An improved viscosity model based on Peng–Robinson equation of state for light hydrocarbon liquids and gases

Recently, a PRμ viscosity model was developed by Fan et al. It is applicable to both the liquid and gas hydrocarbons, but some large deviations might be obtained when applied to some multi-component mixtures. This short communication proposes an improvement method to enhance the accuracy of this model. The method replaces the universal critical compressibility factor in the original model with each component's real critical compressibility factor. The experimental viscosity data of pure methane, pure propane and thirteen light liquid hydrocarbon mixtures were adopted to validate the improved model. The results show the improved model is suitable to both the light hydrocarbon liquids and gases with satisfactory accuracy. The average ARD of the PRμ model was enhanced 4.78% when applied to thirteen hydrocarbon mixtures. Additionally, when applied to five complicated Qatari synthetic natural gas mixtures, the improved PRμ model is essentially comparable in predictability to five other viscosity prediction models.

Application of geo-microbial prospecting method for finding oil and gas reservoirs

Microbial prospecting of hydrocarbons is based on the detection of anomalous population of hydrocarbon oxidizing bacteria in the surface soils, indicates the presence of subsurface oil and gas accumulation. The technique is based on the seepage of light hydrocarbon gases such as C1–C4 from the oil and gas pools to the shallow surface that provide the suitable conditions for the development of highly specialized bacterial population. These bacteria utilize hydrocarbon gases as their only food source and are found enriched in the near surface soils above the hydrocarbon bearing structures. The methodology involves the collection of soil samples from the survey area, packing, preservation and storage of samples in pre-sterilized sample bags under aseptic and cold conditions till analysis and isolation and enumeration of hydrocarbon utilizing bacteria such as methane, ethane, propane, and butane oxidizers. The contour maps for the population density of hydrocarbon oxidizing bacteria are drawn and the data can be integrated with geological, geochemical, geophysical methods to evaluate the hydrocarbon prospect of an area and to prioritize the drilling locations thereby reducing the drilling risks and achieve higher success in petroleum exploration. Microbial Prospecting for Oil and Gas (MPOG) method success rate has been reported to be 90%. The paper presents details of microbial prospecting for oil and gas studies, excellent methodology, future development trends, scope, results of study area, case studies and advantages.

Organic geochemistry of the Vindhyan sediments: Implications for hydrocarbons

The organic geochemical methods of hydrocarbon prospecting involve the characterization of sedimentary organic matter in terms of its abundance, source and thermal maturity, which are essential prerequisites for a hydrocarbon source rock. In the present study, evaluation of organic matter in the outcrop shale samples from the Semri and Kaimur Groups of Vindhyan basin was carried out using Rock Eval pyrolysis. Also, the adsorbed low molecular weight hydrocarbons, methane, ethane, propane and butane, were investigated in the near surface soils to infer the generation of hydrocarbons in the Vindhyan basin. The Total Organic Carbon (TOC) content in shales ranges between 0.04% and 1.43%. The S1 (thermally liberated free hydrocarbons) values range between 0.01–0.09 mgHC/gRock (milligram hydrocarbon per gram of rock sample), whereas the S2 (hydrocarbons from cracking of kerogen) show the values between 0.01 and 0.14 mgHC/gRock. Based on the Tmax (temperature at highest yield of S2) and the hydrogen index (HI) correlations, the organic matter is characterized by Type III kerogen. The adsorbed soil gas, CH4 (C1), C2H6 (C2), C3H8 (C3) and nC4H10, (nC4), concentrations measured in the soil samples from the eastern part of Vindhyan basin (Son Valley) vary from 0 to 186ppb, 0 to 4ppb, 0 to 5ppb, and 0 to 1ppb, respectively. The stable carbon isotope values for the desorbed methane (δ13C1) and ethane (δ13C2) range between −45.7‰ to −25.2‰ and −35.3‰ to −20.19‰ (VPDB), respectively suggesting a thermogenic source for these hydrocarbons. High concentrations of thermogenic hydrocarbons are characteristic of areas around Sagar, Narsinghpur, Katni and Satna in the Son Valley. The light hydrocarbon concentrations (C1–C4) in near surface soils of the western Vindhyan basin around Chambal Valley have been reported to vary between 1–2547ppb, 1–558ppb, 1–181ppb, 1–37ppb and 1–32ppb, respectively with high concentrations around Baran-Jhalawar-Bhanpur-Garot regions (Kumar et al., 2006). The light gaseous hydrocarbon anomalies are coincident with the wrench faults (Kota – Dholpur, Ratlam – Shivpuri, Kannod – Damoh, Son Banspur – Rewa wrench) in the Vindhyan basin, which may provide conducive pathways for the migration of the hydrocarbons towards the near surface soils.

Thermal cracking of free fatty acids in inert and light hydrocarbon gas atmospheres

The aim of this work was to study the pyrolytic conversion of free fatty acids to renewable hydrocarbons in the presence of short-chain alkane and alkene hydrocarbon gases. Oleic acid (cis-9-octadecanoic acid) was used as model for fatty acids produced from hydrolysis of lipids from animal and plant feedstock. Batch pyrolysis reactions were conducted at 410°C for 2h at an initial pressure between 130psi (896.3kPa) and 500psi (3447.4kPa) under constant agitation. Identification and quantification of the pyrolysates in the gas and liquid phase were carried out using gas chromatography and mass spectrometry. Under inert N2 atmosphere liquid product yields were between 74 and 81wt% of feed with lower pressure giving the highest product yields. Liquid product was composed mainly of alkanes and alkenes ranging in carbon number from 6 to 19 and fatty acids from carbon numbers 4 to 18. Pyrolysis reactions conducted in the presence of short-chain alkane gases did not appreciably influence the liquid product yield and the composition compared to the inert atmosphere. On the other hand, pyrolysis reaction in presence of short-chain alkene gases resulted in a marked increase in the liquid product yield, the production of branched alkanes and alkenes and increased fatty acid decarboxylation. This work demonstrates a novel approach to concurrently increase the liquid product yield in pyrolysis of free fatty acids and produce highly valuable branched hydrocarbons for fuel and solvent applications.

Geochemical characterization of adsorbed light gaseous alkanes in near surface soils of the eastern Ganga basin for hydrocarbon prospecting

This study aims to assess the hydrocarbon potential of Ganga basin utilizing the near surface geochemical prospecting techniques. It is based on the concept that the light gaseous hydrocarbons from the oil and gas reservoirs reach the surface through micro seepage, gets adsorbed to soil matrix and leave their sig� natures in soils and sediments, which can be quantified. The study showed an increased occurrence of meth� ane (C1), ethane (C2) and propane (C3) in the soil samples. The concentrations of light gaseous hydrocarbons determined by Gas Chromatograph ranged (in ppb) as follows, C1: 0-519, C2: 0-7 and C3: 0-2. The carbon isotopic (VPDB) values of methane varied between -52.2 to -27.1‰, indicating thermogenic origin of the desorbed hydrocarbons. High concentrations of hydrocarbon were found to be characteristic of the Muzaf� farpur region and the Gandak depression in the basin, signifying the migration of light hydrocarbon gases from subsurface to the surface and the area's potential for hydrocarbon resources.

Correlation of Trace Elements with Hydrocarbon Microseepage

Abstract Direct correlation have been observed between certain trace element and hydrocarbon anomalies in the near subsurface soils of Vindhyan basin, India. This relationship with hydrocarbon is very useful in hydrocarbon exploration. 52 soil samples from Vindhyan basin were collected from a depth of 2.5m. All the soil samples were analyzed for light hydrocarbon, isotope and trace element concentrations. The adsorbed light gaseous hydrocarbon analyses show the presence of methane (8 - 328 ppb), ethane (0 - 27 ppb) and propane (0 -11 ppb) respectively and these values indicate the presence of hydrocarbon micro-seepage in the study area. The carbon isotopic values determined for methane and ethane for these soil samples are (-26.41 to -47.70 ‰ PDB) and (-20.07 to -35.30 ‰ PDB) respectively and they are thermogenic in nature. The trace element concentrations of nickel (33-220 ppm), vanadium (72-226 ppm), copper (20- 131 ppm), chromium (94-205 ppm), zinc (66-561 ppm) and cobalt (9-39 ppm) have higher than the normal concentrations in soils. Trace element concentrations are used to plot with the data obtained from light gaseous hydrocarbon concentrations and carbon isotopic values of soil samples of the Vindhyan basin. Trace element anomalies have been observed around the hydrocarbon anomalies in the study area.

Geochemical features of natural gas in the Qaidam Basin, NW China

Based on the results of natural gas components, carbon isotopes, and light hydrocarbon components analyses, this paper studied geochemical features of natural gas in the Qaidam Basin. These analyses include the intersection relationships of (1) natural gas methane carbon isotopes (δ13C1) and ethane carbon isotopes (δ13C2); (2) natural gas ethane carbon isotopes (δ13C2) and hydrocarbon exclusive of methane contents (C2+); (3) natural gas methane carbon isotopes (δ13C1), ethane carbon isotopes (δ13C2) and propane carbon isotopes (δ13C3); (4) natural gas light hydrocarbon components and carbon isotopes; and (5) natural gas light hydrocarbon carbon isotopes. Natural gas consists mainly of (1) pyrolysis gas derived from type I and type II kerogen and mixed gas in the southwestern Qaidam Basin; (2) pyrolysis gas derived from type II and III kerogen and mixed gas in the northwestern Qaidam Basin; (3) coal- derived gas in the northern Qaidam Basin; and (4) biogenic gas in the eastern Qaidam Basin.

Surface geochemical data evaluation and integration with geophysical observations for hydrocarbon prospecting, Tapti graben, Deccan Syneclise, India

The Deccan Syneclise is considered to have significant hydrocarbon potential. However, significant hydrocarbon discoveries, particularly for Mesozoic sequences, have not been established through conventional exploration due to the thick basalt cover over Mesozoic sedimentary rocks. In this study, near-surface geochemical data are used to understand the petroleum system and also investigate type of source for hydrocarbons generation of the study area. Soil samples were collected from favorable areas identified by integrated geophysical studies. The compositional and isotopic signatures of adsorbed gaseous hydrocarbons (methane through butane) were used as surface indicators of petroleum micro-seepages. An analysis of 75 near-surface soil-gas samples was carried out for light hydrocarbons (C1–C4) and their carbon isotopes from the western part of Tapti graben, Deccan Syneclise, India. The geochemical results reveal sites or clusters of sites containing anomalously high concentrations of light hydrocarbon gases. High concentrations of adsorbed thermogenic methane (C1 = 518 ppb) and ethane plus higher hydrocarbons (ΣC2+ = 977 ppb) were observed. Statistical analysis shows that samples from 13% of the samples contain anomalously high concentrations of light hydrocarbons in the soil-gas constituents. This seepage suggests largest magnitude of soil gas anomalies might be generated/source from Mesozoic sedimentary rocks, beneath Deccan Traps. The carbon isotopic composition of methane, ethane and propane ranges are from −22.5‰ to −30.2‰ PDB, −18.0‰ to 27.1‰ PDB and 16.9‰–32.1‰ PDB respectively, which are in thermogenic source. Surface soil sample represents the intersection of a migration conduit from the deep subsurface to the surface connected to sub-trappean Mesozoic sedimentary rocks. Prominent hydrocarbon concentrations were associated with dykes, lineaments and presented on thinner basaltic cover in the study area, which probably acts as channel for the micro-seepage of hydrocarbons.

Geo-microbiological studies in conjunction with different geo-scientific studies for the evaluation of hydrocarbon prospects in Proterozoic Vindhyan Basin, India

Abstract The Proterozoic Vindhyan Basin is considered to be prospective for hydrocarbons and is grouped under category III sedimentary basins of India. The major part of the study area is covered by the Deccan Traps, hindering the exploration of Mesozoic hydrocarbon targets, surface geochemical prospecting based on microseepage of hydrocarbons from subsurface accumulations, which could be advantageous in such areas. Geo-microbiological study was carried out in conjunction with different geo-scientific studies to characterize the seeping natural gases and to evaluate the hydrocarbon prospects of the study area. Total 70 soil samples were collected in reconnaissance pattern, and the study revealed the presence of high bacterial counts for methane (3.7×10 5 cfu/g), ethane (3.2×10 5 cfu/g), propane (3.0×10 5 cfu/g) and butane oxidizing bacteria (2.3×10 5 cfu/g), which signify the seepage of hydrocarbons from the subsurface. The compositional characteristics of the hydrocarbon gases desorbed from soil samples of study area indicate the presence of light gaseous hydrocarbons methane through butane, thus suggesting that hydrocarbon generation has taken place in the basin probably of thermogenic origin. The trend followed by the hydrocarbons C 1 >C 2 >C 3 > i C 4 > n C 4 further confirms the petroliferous nature of the gases. The stable carbon isotope values of light hydrocarbons desorbed form the soil samples indicate a clear signature of thermogenic gas. The concentrations of TOC and TIC in the soil samples of Sagar vary from 0.09% to 0.93% and 0.003% to 0.82% respectively. The TOC and TIC correlates poorly with the adsorbed soil gases ( r =0.3, r =0.2), representing a lack of association of adsorbed soil gases with the surfacial organic matter thus indicate seepage related surface anomalies. The study revealed the presence of high concentrations of hydrocarbon oxidizing bacteria and adsorbed soil gases near Sagar area of Vindhyan Basin. The integrated geo-scientific studies showed excellent correlation and suggests that the Sagar area is considered to be potential for hydrocarbon generation and entrapment.

Near surface hydrocarbon prospecting in Mesozoic Kutch sedimentary basin, Gujarat, Western India—A reconnaissance study using geochemical and isotopic approach

Abstract The Mesozoic Kutch sedimentary basin in the western continental margin of India has known accumulations of oil and gas. However, the multilayered thick Deccan Traps of Late Cretaceous overlie the Mesozoic targets, thereby imposing inherent problems in imaging sedimentary layers below the traps for exploratory studies. One of the unconventional techniques, the near surface geochemical prospecting study, has been carried out in the onland and offshore Kutch to understand the microseepage and sources of the light hydrocarbon gases (methane through butane) observed in the soils and sediments from the basin. The geochemical and isotopic compositions of the soil samples from the Kutch onland vary in the range of C1 (methane)=3–582 ppb, C2 (ethane)=0–39 ppb, C3 (propane)=0–15 ppb and the δ13C1 (methane)=−24.9‰ to −35.7‰. The offshore sediments showed the presence of butane along with the lower hydrocarbons and the concentration ranges as C1=36–475 ppb, C2=5–27 ppb, C3=5–27 ppb, iC4=2–6 ppb, nC4=0–4 ppb, and their δ13C values are characterized as δ13C1=−37.7‰ to −44‰, δ13C2=−24.6‰ to −30.5‰ and δ13C3=−26.1‰ to −34‰. The compositional ratios and carbon isotopic signatures of light gaseous hydrocarbons suggest their thermogenic origin. The δ13C1–δ13C2 signatures of samples from offshore Kutch indicate the gases to be non-associated, originating from sapropelic liptinitic organic matter. The concentration distribution pattern of light hydrocarbons indicates the areas Bhuj, Anjar, Mandavi and Mundra to have higher values for these gases. The anomalies are also coincident with the active faults, the Bhuj Fault (BF), the Katrol Hill Fault (KHF) and the Sandsra Dungar Fault (SDF) passing through the area, which may serve as a preferential migratory pathway for the light hydrocarbon gases. The results of this study support the generation, preservation, migration and the near surface manifestation of thermogenic hydrocarbons in Kutch basin, particularly in the northern and southern regions of the study area.

Monitoring of near-surface gas geochemistry at the Weyburn, Canada, CO2-EOR site, 2001–2011

Soil gas and CO2 flux measurements were conducted above and in the vicinity of the Weyburn oil field during the period 2001–2005 and in 2011 to determine baseline values and distributions, and to monitor for surface leaks, above this well-established and intensely studied CO2-Enhanced Oil Recovery (CO2-EOR) project in southern Saskatchewan, Canada. Multiple sites were studied which had sample spacing that ranged from 25 to 200m, including a 360 point regional grid above the CO2 injection field, a background site off the oil field, and a new site where a landowner claimed CO2 leakage on his property from the storage reservoir. Typically 400–500 points were sampled during each of the seven field campaigns and analysed for a wide range of components, thus yielding a large and varied database collected during different seasons and years. Results show no sign of leakage of the injected CO2. Spatial and seasonal trends and measured values from discrete sampling of soil gas CO2, O2+Ar, N2, δ13C-CO2, He, Rn, and CH4, from continuous monitoring of soil gas CO2 and Rn, and from discrete sampling of CO2 flux can all be explained by the interplay between near-surface biochemical processes, seasonal environmental conditions, and soil properties. Other light hydrocarbon gases, like C2H4 and C2H6, were generally near or below the instrument detection limit. Lessons learned during the research are described to help improve future near-surface gas geochemistry surveys for site assessment, baseline definition, and leakage monitoring at active CCS sites.

Geochemical evidences of trace metal anomalies for finding hydrocarbon microseepage in the petroliferous regions of the Tatipaka and Pasarlapudi areas of Krishna Godavari Basin, India

The long-term seepage of hydrocarbons, either as macroseepage or microseepage, can set up near-surface oxidation reduction zones that favor the development of a diverse array of chemical and mineralogical changes. The bacterial oxidation of light hydrocarbons can directly or indirectly bring about significant changes in the values of pH and Eh of the surrounding environment, thereby also changing the stability fields of the different mineral species present in that environment. The paper reports the role of hydrocarbon microseepage in surface alterations of trace metal concentrations. In this study trace metal alterations were mapped that appear to be associated with hydrocarbon microseepages in the oil/gas fields. A total of 50 soil samples were collected near oil and gas fields of the Tatipaka and Pasarlapudi areas of the Krishna Godavari Basin, Andhra Pradesh. The soil samples were collected from a depth of 2–2.5 m. The paper reports the chemical alterations associated with trace metals in soils that are related to hydrocarbon microseepages above some of the major oil and gas fields of this petroliferous region. Trace metals, such as scandium (Sc), vanadium (V), chromium (Cr), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), barium (Ba) and strontium (Sr), in soil samples were analyzed using inductively coupled plasma-mass spectrometry (ICP-MS). The concentrations of Sc (8 to 40 mg/kg), V (197 to 489 mg/kg), Cr (106 to 287 mg/kg), Co (31 to 52 mg/kg), Ni (65 to 110 mg/kg), Cu (88 to 131 mg/kg), Zn (88 to 471 mg/kg), Ba (263 to 3,091 mg/kg) and Sr (119 to 218 mg/kg) were obtained. It was observed that the concentrations of trace elements were tremendously increased when they were compared with their normal concentrations in soils. The analysis of adsorbed soil gas showed the presence of high concentrations of ΣC2+ (C2H6, C3H8 and n-C4H10) ranging from 7 to 222 μg/kg respectively. Integrated studies of trace elements over adsorbed light gaseous hydrocarbons (ΣC2+) anomalies showed good correlation with the existing oil and gas wells. The carbon isotopic composition of δ13C1 of the samples ranges between −36.6‰ to −22.7‰ (Pee Dee Belemnite) values indicate thermogenic origin, which presents convincing evidence that the adsorbed soil gases collected from these sediments are of catagenetic origin. The increase in the concentrations of trace metals near oil/gas producing areas, suggests a soil chemical change to a reducing environment, presumably due to the influence of hydrocarbon microseepage, which could be applied with other geoscientific data to identify areas of future hydrocarbon exploration in frontier areas.