One-Dimensional Consolidation of Sedimented Stowed Pond Ash

Use of fly ash locked in the ash ponds in geotechnical applications such as stowing or backfilling of the mines is an attractive alternative to solve the disposal problem. Before it is used as a stowing or backfilling material, the response of the fly ash?to imposed load must be determined in order to assess its load taking ability. The present study examines the effect of time and incremental load on the consolidation characteristics of the sedimented stowed pond ash using a fixed ring consolidometer. The important parameters, viz. rate of settlement, consolidation coefficients and void ratio, etc. of the hydraulically stowed pond ash collected after 7, 14, 21, 28 and 35?days of stowing under step incremental loads are determined. The study revealed that 60.42–84.87% settlement of the sedimented stowed pond ash takes place in the initial 1?min of the loading. In addition, it is observed that the coefficient of consolidation of the sedimented stowed pond ash, which varies in the range of 0.0195–0.1882?cm²/min, is comparatively low and decreases with the increment of applied load and time. This indicates that the structures lying above the stowed pond ash mass will undergo gradual settling and not suffer large deformation.     

Geochemical exploration for hydrocarbons in the soils of southeast of Krishna-Godavari Basin, Andhra Pradesh

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 (??¹³C_methane). 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.     

Stable carbon isotope geochemistry of adsorbed alkane gases in near-surface soils of the Saurashtra Basin,India

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.     

Soil Iodine Determination in Deccan Syneclise,India: Implications for Near Surface Geochemical Hydrocarbon Prospecting

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.     

A study of arsenic,iron and other dissolved ion variations in the groundwater of Bishnupur District,Manipur, India

The presence of arsenic (As) in groundwater and its effect on human health has become an issue of serious concern in recent years. The present study assessed the groundwater quality of the Bishnupur District, Manipur, with respect to drinking water standards. Higher concentrations of pH, iron and phosphate were observed at several locations. Phosphate and iron levels were highest in the pre-monsoon, followed by monsoon and post-monsoon seasons. The arsenic concentrations were highest during post-monsoon (1–200 μg L⁻¹) as compared to pre-monsoon (1–108 μg L⁻¹) and monsoon (2–99 μg L⁻¹). Kwakta and Ngakhalawai show higher levels of arsenic concentration as compared to the prescribed World Health Organization (WHO) and Bureau of Indian Standards (BIS) norms. Arsenic showed a strong positive correlation with phosphate and negative correlation with sulphate, suggesting a partial influence of anthropogenic sources. The study suggests that the Bishnupur area has an arsenic contamination problem, which is expected to increase in the near future.     

Correlation of trace elements with hydrocarbon microseepage

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.     

Remote sensing and GIS application for land quality assessment for coffee growing areas of Karnataka

An assessment of land quality was carried out for coffee-growing areas of Karnataka using satellite image, toposheets and soil studies. The investigation focused on monitoring soil processes that control the land quality using satellite data in order to identify the land qualities that are ideal for coffee-growing; to identify the status of land qualities of coffee-growing areas using satellite imageries, toposheets and soil resource maps and to characterise land quality using soil studies in selected areas. The land quality was characterised using climatic data, terrain analysis and soil attributes. From the study it was observed that coffee growing lands of Gabbugal and Kelagur have best land qualities and coffee-growing areas of Balur and Nellikkad have moderate land qualities. Satellite image and aerial photographs were successfully used for monitoring the land quality and its changes in these areas. For optimum utilization of available natural resources on a sustainable basis, timely and reliable information on soils regarding their nature, extent and spatial distribution along with their potential and limitations is very important. The efficiency and accuracy of data are improved when remote sensing data products such as aerial photographs and satellite image are used.