Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

N. Bhattacharya ¹

Affiliations
1 Institute of Petroleum Exploration, Oil & Natural Gas Commission, Dehra Dun, IN

Abstract

265 analyses from 108 selected samples of Subathu, Dharmsala and Siwalik sediments by X-ray diffraction, emission spectroscopy, flame spectrophotometry and gamma ray spectrography are presented in this report. Dominant clay minerals of the Subathu, Dharmsala and Siwalik sediments are respectively moderately degraded illite and chlorite; degraded illite, vermiculite and expandable mixed-layers; and montmorillonite, kaolinite and highly degraded illite/chlorite. Trace and minor elements in clays are divided into non-detrital diadochic substitutions (B, Ba, Sr, Ga, Sc, Zn, Ge and Pb) and detrital elements as diadochic impurities (Be, P, Mn, Cu, Mo, W, Zr and V). Distribution of Li, Na, K, Rb and Cs and that of U and Th seem to be related primarily to weathering in source areas. It appears that mineralogy and crystal chemistry of clay minerals have dominating influence in selective geochemical partition of trace elements.

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C. Gundu Rao ¹, N. Bhattacharya ¹

Affiliations
1 Institute of Petroleum Exploration, Dehra Dun, IN

Abstract

No Abstract.

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N. Bhattacharya ¹

Affiliations
1 Institute of Petroleum Exploration, Oil and Natural Gas Commission, Dehradun, U. P., IN

Abstract

The clays are generally rich in montmorillonite, kaolinite, expandable mixed-layers and degraded illite. Laboratory data indicate two types of sections depending on response of clay minerals to potassium saturation. A partially truncated weathering profile developed under continental conditions is suggested.

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N. Bhattacharya ¹

Affiliations
1 Institute of Petroleum Exploration, Oil and Natural Gas Commission, Kaulagarh, Dehra Dun, IN

Abstract

Studies by X-ray diffraction and scanning electron microscopy of the matrix material from these sands indicated that both allogenic and authigenic clays are present in the reservoir. Matrix of Barail sands are characterized by illite, chlorite and kaolinite which have undergone pronounced diagenetic changes. Montmorillonite and expandable mixed-layers are important clay minerals associated with reservoir sands belonging to the Tipam series. Grains, pores and channels are all heavily coated with expandable clays in Tipam sands; the grains, pores and pore throats are partially coated with matrix clays in Barail sands with rare development of bridges in permeability channels.

Barail sands were deposited in a transitional environment (deltaic/estuarine) while the environment of deposition was fluviatile for the Tipams. Clay minerals in the Tipam sands are very sensitive to formation damage while those in the Barails could result in permeability barriers if the particles are dislodged in the sands. Accordingly, precise control of salinity of formation water in steps during production and development is suggested.

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N. Bhattacharya ¹

Affiliations
1 Sedimentology Laboratory, Institute of Petroleum Exploration, Oil and Natural Gas Commission, Dehradun, IN

Abstract

Recent marine sediments coupled with sea-bottom cores, parting shales and insoluble clay residues of carbonate reservoirs in northeastern continental shelf of the Arabian Sea were investigated for studies of clay mineral diagenesis to evaluate respective roles of source conditions and environment of deposition. The material was also compared with those from selected weathering profiles on basalts and/or diabases. The data indicate an uniform distribution of montmorillonite and expandable mixed-layers with little kaolinite over the continental shelf diluted by sporadic occurrences of degraded illite and chlorite off the Saurashtra coast and beyond in the north and northwest upto the international boundary. These clays were derived by weathering from basalts/diabases and so have not responded to diagenetic changes even at depth. Occurrence of illite and chlorite mixed with montmorillonite and expandable mixed-layers could have resulted from material brought in by the Indus river. The factors of source and inheritance seem to have been the governing criteria for structural failure of these clays against diagenetic processes. However, clay mineral diagenesis indicates that hydrocarbons discovered in this area are independent of the associated clay mineral characters with regard to their genesis and entrapment.

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N. Bhattacharya ¹, V. Raiverman ¹

Affiliations
1 Institute of Petroleum Exploration and Directorate of Geology, Oil & Natural Gas Commission, Dehra Dun, IN

Abstract

Clay mineral distribution in Dharmsala sediments over a region extending from Palampur to Mandi and Sarkaghat in northwest India was studied using standard X-ray diffractometer techniques. Lower Dharmsala sediments show uniform clay mineral distribution over the region and contain partially degraded illite and chlorite with minor amounts of kaolinite. Upper Dharmsala sediments seem to vary in clay mineralogy from one part of the region to another. They are characterized by the presence of illite, chlorite and vermiculite at Palampur-Baijnath. The clay minerals are mainly degraded illite, vermiculite and expandable mixed layers at Jogindernagar-Mandi and Rewalsar areas. Upper Dharmsala clays at Sarkaghat consist of montmorillonite, expandable mixed layers and minor amounts of highly degraded chlorite. Differences in clay mineral distribution over the region is explained here by variations in the characters of source rocks, weathering intensity, sediment transport, drainage and topography. The present findings are compatible with information obtained from paleocurrent investigalions.

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