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It is important to understand both the origin and destruction of H 2 S in petroleum since it is toxic, corrosive andenvironmentally damaging. Sour gas (H 2 S) in the Central and Northern North Sea elastic-dominated basins is locally present at concentrations ≥ 20,000 ppm. The origin and destruction of H2S has been examined using large basin-scale datasets of water, gas and oil geochemistry and fluid inclusion volatile analysis from a sweet oil field. Both thermochemical sulphate reduction (TSR) and organic-sulphur compound cracking have, probably occurred given the depth distribution patterns of H 2 S, the sulphate concentration in formation water and the sulphur content of oils. There is evidence that TSR-derived H 2 S has backreacted with oil so modifying the sulphur isotope ratio of the oil. H2S is precipitated as pyrite in many sandstones and it only accumulates, or is trapped within inclusions, in clean sandstones that have limited available iron. |
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