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11.
M. Lakshmi M. A. Rasheed T. Madhavi B. Rajeswara Reddy M. S. Kalpana D. J. Patil A. M. Dayal 《Journal of the Geological Society of India》2012,80(5):641-652
Surface adsorbed gas surveys and geo-microbiological surveys are known techniques of petroleum exploration and aim towards risk reduction in exploration by way of identifying the areas warm with hydrocarbons and to establish intense exploration priorities amongst the identified warm areas. The present investigation aims to explore correlation between the adsorbed gas distribution pattern with the distribution of the counts of methane, ethane, propane and butane microbial oxidizers in the sub soil samples to establish the role of the latter in identifying the upward migration of hydrocarbons especially in the known petroliferous Krishna-Godavari Basin, India. A total of 135 soil samples were collected near oil and gas fields of Tatipaka, Pasarlapudi areas of Krishna Godavari Basin, Andhra Pradesh. The soil samples were collected from a depth of 2?C2.5 m. The samples collected, were analyzed for indicator hydrocarbon oxidizing bacteria, adsorbed light gaseous hydrocarbons and carbon isotopes (??13Cmethane). The microbial prospecting studies showed the presence of high bacterial population for methane (3.94 × 105 cfu/gm), ethane (3.85 × 105 cfu/gm), propane (4.85 × 105 cfu/gm) and butane oxidizing bacteria (3.63 × 105 cfu/gm) in soil samples indicating microseepage of hydrocarbons. The light gaseous hydrocarbon analysis showed 83 ppb, 92 ppb, 134 ppb, 187 ppb and 316 ppb of C1, C2, C3, nC4 and nC5, respectively, and the carbon isotopic composition of ??13C1 of the samples ranged between ? 36.6 ?? to ?22.7?? (Pee Dee Belemnite) values, which presents convincing evidence that the adsorbed soil gases collected from these sediments are of thermogenic origin. Geo-microbial prospecting method and adsorbed soil gas and carbon isotope studies have shown good correlation with existing oil/ gas fields of K.G basin. Microbial surveys indicating microseepage of hydrocarbons can, therefore, independently precede other geochemical and geophysical surveys to delineate areas warm with hydrocarbons and mapped microbiological anomalies may provide focus for locales of hydrocarbon accumulation in the K.G basin. 相似文献
12.
The stable carbon isotopic compositions of light hydrocarbon gases adsorbed in near-surface soil and sediments from the Saurashtra basin were characterized for their origin and maturity. Saurashtra is considered geologically prospective for oil and gas reserves; however, a major part of the basin is covered by the Deccan Traps, hindering the exploration of Mesozoic hydrocarbon targets. Surface geochemical prospecting, based on micro-seepage of hydrocarbons from subsurface accumulations, could be advantageous in such areas. In light of this, 150 soil samples were collected from the northwestern part of Saurashtra, around the Jamnagar area, where a thick sedimentary sequence of about 2–3 km exists under 1–1.5 km of Deccan basalt. The concentration of acid desorbed alkane gases from soil samples was found to vary (in ppb) as: methane (C1) = 3–518; ethane (C2) = 0–430; propane (C3) = 0–331; i-butane (iC4) = 0–297; n-butane (nC4) = 2–116; i-pentane (iC5) = 0–31 and n-pentane (nC5) = 0–23, respectively.Fifteen samples with high concentrations of alkane gases were measured for their δ13C1; δ13C2 and δ13C3 compositions using gas chromatography–combustion-isotope ratio mass spectrometry (GC–C-IRMS). The values for methane varied from ? 27 to ? 45.4‰, ethane from ? 20.9 to ? 27.6‰, and propane from ? 20.4 to ? 29.1‰ versus the Vienna PeeDee Belemnite (VPDB). The carbon isotope ratio distribution pattern represents isotopic characteristics pertaining to hydrocarbon gases derived from thermogenic sources. Comparisons of carbon isotopic signatures and compositional variations with the standard carbon isotopic models suggest that hydrocarbon gases found in the shallow depths of the study area are not of bacterial origin but are formed thermally from deeply buried organic matter, likely to be mainly a terrestrial source rock with a partial contribution from a marine source. These gases may have migrated to the near-surface environment, where they represent an admixture of thermally generated hydrocarbon gases from mixed sources and maturity. The maturity scale (δ13C versus Log Ro %) applied to the surface sediment samples of the Jamnagar area indicated the source material to be capable of generating oil and gas. The detection of thermogenic alkane gases in near-surface sediments offers the possibility of hydrocarbons at depth in Saurashtra. 相似文献
13.
Devleena Mani T. Satish Kumar M. A. Rasheed D. J. Patil A. M. Dayal T. Gnaneshwar Rao V. Balaram 《Natural Resources Research》2011,20(1):75-88
The association of iodine with organic matter in sedimentary basins is well documented. High iodine concentration in soils
overlying oil and gas fields and areas with hydrocarbon microseepage has been observed and used as a geochemical exploratory
tool for hydrocarbons in a few studies. In this study, we measure iodine concentration in soil samples collected from parts
of Deccan Syneclise in the west central India to investigate its potential application as a geochemical indicator for hydrocarbons.
The Deccan Syneclise consists of rifted depositional sites with Gondwana–Mesozoic sediments up to 3.5 km concealed under the
Deccan Traps and is considered prospective for hydrocarbons. The concentration of iodine in soil samples is determined using
ICP-MS and the values range between 1.1 and 19.3 ppm. High iodine values are characteristic of the northern part of the sampled
region. The total organic carbon (TOC) content of the soil samples range between 0.1 and 1.3%. The TOC correlates poorly with
the soil iodine (r
2 < 1), indicating a lack of association of iodine with the surficial organic matter and the possibility of interaction between
the seeping hydrocarbons and soil iodine. Further, the distribution pattern of iodine compares well with two surface geochemical
indicators: the adsorbed light gaseous hydrocarbons (methane through butane) and the propane-oxidizing bacterial populations
in the soil. The integration of geochemical observations show the occurrence of elevated values in the northern part of the
study area, which is also coincident with the presence of exposed dyke swarms that probably serve as conduits for hydrocarbon
microseepage. The corroboration of iodine with existing geological, geophysical, and geochemical data suggests its efficacy
as one of the potential tool in surface geochemical exploration of hydrocarbons. Our study supports Deccan Syneclise to be
promising in terms of its hydrocarbon prospects. 相似文献
14.
P. Lakshmi Srinivasa Rao D. Srinu M. A. Rasheedd M. S. Kalpana D. J. Patil A. M. Dayal 《Journal of the Geological Society of India》2013,82(6):666-674
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. 相似文献
15.
Edison Caballero Fernando A. Rochinha Marcio Borges Marcio A. Murad 《国际地质力学数值与分析法杂志》2019,43(2):482-500
In this work, we construct a new methodology for enhancing the predictive accuracy of sequential methods for coupling flow and geomechanics while preserving low computational cost. The new computational approach is developed within the framework of the fixed-stress split algorithm procedure in conjunction with data assimilation based on the ensemble Kalman filter (EnKF). In this context, we identify the high-fidelity model with the two-way formulation where additional source term appears in the flow equation containing the time derivative of total mean stress. The iterative scheme is then interlaced with data assimilation steps, which also incorporate the modeling error inherent to the EnKF framework. Such a procedure gives rise to an “enhanced one-way formulation,” exhibiting substantial improvement in accuracy compared with the classical one-way method. The governing equations are discretized by mixed finite elements, and numerical simulation of a 2D slab problem between injection and production wells illustrate the tremendous achievement of the method proposed herein. 相似文献
16.
E. Dayal 《GeoJournal》1990,20(3):293-299
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