Hydrogen sulphide represents an undesirable component of hydrocarbon reservoir fluids and its presence poses not only a significant risk for health and life of a personnel involved in hydrocarbon production and transportation, but also may drastically affect the field development strategy and economics, especially in an offshore environment.

The paper demonstrates the results of an assessment of risk of a hydrogen sulfide-containing gas breakthrough into the upper reservoir during its development at one of the fields of the Caspian oil and gas province. The assessment was performed using a coupled reservoir geomechanics modeling that allowed to estimate the changes in in-situ stresses state with field development. During production, differential and non-uniform pressure changes, caused by different depletion levels, result in differential deformation due to the change in effective stress, leading to reservoir rock failure, reservoir compaction and ground surface subsidence. Excessive localized deformation may also result in potential issues in cap and underlying rock integrity and fault seals.

A comprehensive mechanical core testing was carried out to correctly describe the rock failure criteria, which revealed the behavior of upper-layer cavernous carbonates similar to the behavior of the chalk formations of the North Sea, which are known to be prone to significant compaction during field development (J.P. Johnson et al, 1988).

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