The genesis of H2S associated with heavy oils in Hendijan and Bahregansar oilfields, Sarvak reservoir

Abstract

ABSTRACTBahregansar and Hendijan oilfields are located in the northwest of the Persian Gulf. Ghar/Asmari and Sarvak Formations are the main productive reservoirs, which contain sweet and sour gas, respectively. The oilfields are considered as a component of a petroleum system due to proximity and large number of geochemical similarities between them. Four gas samples, as well as oil and water samples, were collected in order to study and determine the hydrogen sulfide production mechanisms in the Sarvak reservoir. The prevalent mechanism of sourness in the reservoir, such as thermal sulfate reduction, thermal cracking, bacterial sulfate reduction, and migration from deeper intervals, have been investigated by studying relevant parameters, such as temperature, oil and water composition, lithology, and stable isotope of sulfur and carbon in hydrogen sulfide, asphaltene, and methane. Reservoir temperature as well as isotopic signature and geological data negate the possibility of thermal sulfate reduction, thermal cracking of oil, and migration from deeper intervals as the main reason of sourness. Bacterial sulfate reduction, by contrast, is considered as the main mechanism for hydrogen sulfide production in Sarvak reservoir of Bahregansar and Hendijan oilfields supported by reservoir temperature, water composition, and sulfur isotope ratio.