Hydrocarbon compounds and plausible mechanism of gas generation in “shale” gas prospective silurian deposits of Lviv paleozoic depression
Journal Title: Геодинаміка - Year 2017, Vol 22, Issue 1
Abstract
Purpose. Investigations of composition of gas within closed porosity (fluid inclusions and closed pores in rocks) of prospective gas-bearing Silurian graptolitic argillites of Lviv Paleozoic depression and ground of plausible mechanism and dynamics of gas generation during “shale” gas formation in productive strata of black-shale formations of the region. Methodology. The composition of volatile fluid inclusions and closed pores of rocks, and their relative gas saturation and water saturation were determined by mass spectrometric chemical method. Inclusions and closed pores were opened by crushing a standard sample (sample weight 200 mg, +1-2 mm fraction) in a small metal cylindrical mortar between two plane-parallel hard carbide alloy (pobedit) surfaces in high vacuum (approx. 1×10-3 Pa). Results. According to data for mineral-fluidological research, methane prevails (up to 100 vol.%) with minor content of ethane, carbon dioxide and nitrogen in gas phase of fluid inclusions and closed pores of Silurian graptolitic argillites of Lviv Paleozoic depression. Lack of the steam may indicate “dryness” of hydrocarbon-bearing systems, and low values of relative gas saturation – the conversion of organic matter as a source of volatile hydrocarbon compounds at the low (mainly, litostatic) pressures. This indicates the reality of passage of processes of gas production during the transformation of organic matter of argillite strata. Higher by one order the relative gas saturation of inclusions in calcite, which healed subvertical fractures in argillites, had the appearance of the steam indicates the likely influx of deep-seated migrating fluids via powerful crack systems. It was grounded that the plausible mechanism and dynamics of gas generation followed by capture of gas in free state and sorption and occlusion within rocks, intensified by influence of deep-seated fluids. It is based on a comparison of data on the composition of volatile compounds of fluid inclusions and closed pores of prospective gas-bearing argillites and sorption-generation processes of methane generation in coal, based on the principle of unity of nature of transformation of dispersed and concentrated form of organic matter. Originality. For the first time relics of renewable, almost substantially hydrocarbon anhydrous (dry) fluids in fluid inclusions and closed pores (cavities, cracks) of shale gas prospective graptolitic argillites of the Paleozoic of the Volyn-Podillya there were found. This indicates the presence geo-fluid-dynamic conditions, both for the generation of hydrocarbons in the conversion of organic matter, absorbed and occluded by mineral and organic component of rocks at the stage of katagenesis, and the influx of deep-seated hydrocarbon fluids, and thus confirms shale gas potential of mineral resources of the region. Practical significance. The influence of volatile compounds in closed porosity (fluid inclusions and closed pores of host rocks (graptolitic argillites)) for the total gas-bearing potential of shale-bearing strata is estimated, which will be significant, regardless of other aspects of the problem (especially social and environmental issues), for the eventual estimate of shale gas resources (reserves).
Authors and Affiliations
I. Naumko, I. M. Kurovets, M. I. Zubyk, N. Batsevych, B. E. Sakhno, P. S. Chepusenko
Keywords
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- EP ID EP455350
- DOI 10.23939/jgd2017.01.036
- Views 87
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