On the Distribution of Hydrogen Sulphide in the Carbonate Oil and Gas Fields of the Russian Platform
The hydrogen sulphide content in the gases of the sulphate-carbonate complexes of the oil- and gas-bearing regions of the Russian plate varies over a wide range. Analysis of the regularities of these variations shows that the concentration of the hydrogen sulphide in the gases depends on the type of carbonate bodies, their thickness and areal extent. The most favourable conditions for hydrogen sulphide accumulation exist within large carbonate bodies, such as carbonate shelves (Pre-Caspian region) or barrier reef systems (Timano-Pechora region, etc.). Within the carbonate shelves the most sulphurous gases are confined to traps which lie farthest from the contact with terrigenous facies. i.e. when both the rocks containing the hydrocarbon pools and the rocks in contact with them vertically and laterally are of predominantly carbonate composition. The most sulphurous gases in the barrier-reef system are concentrated in their rear parts.
In thin carbonate beds and also in single reef bodies the content of hydrogen sulphide in gases, other things being equal, is less by a factor of 10 as compared with its content in gases which are confined to large carbonate bodies. This is likely to be due to the greater rate of sour gas diffusions from pools at the contact with terrigenous rocks and the greater influence on the gas composition of the inflow of non-sulphurous fluids from terrigenous rocks into carbonate traps.
The established regularities are important for subdividing regions with sulphate-carbonate complexes into zones of presumed higher or lower hydrogen sulphide concentrations prior to the discovery of the hydrocarbon pools.
KeywordsHydrogen Sulphide Terrigenous Rock Hydrocarbon Accumulation Lower Devonian Russian Platform
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