Understanding the origin of hydrogen sulphide in South-Western Gissar, Southern Uzbekistan

Hydrogen sulphide (H2S) concentrations across three adjacent gas condensate fields in Southwestern Gissar produced from fractured Middle-Upper Jurassic reef-carbonates with anhydrite-bearing beds have been analysed. Wellsite testing measurements followed by iodometric titration showed concentrations of H2S below 0.2 mole%. Statistical analyses and cross plots of H2S vs. depth, reservoir temperature, porosity, anhydrite content, well tests and water saturation did not reveal linear correlations. Uniform gas condensate compositions and constant souring levels through time rule out secondary bacterial or/and technogenic processes, while temperatures bellow 90–110°С are against thermochemical sources. Low H2S values could result from mineral-fluid interactions within the host rock. However, low abundance of H2S and carbon dioxide (CO2) (