Geochemical investigation of Sarvak oil reservoir in the west of Abadan Plain and biomarker correlation with Mishrif oil reservoir of Iraqi oil fields

IntroductionUntil now, many researchers have used organic geochemistry to increase exploration efficiency by accounting for many variables, including source rock quality and richness, thermal maturity, and the timing of generation-migration-accumulation relative to trap formation. The Sarvak and Mishrif Formation is one of the main Cretaceous carbonate promising reservoirs in the Abadan Plain and Mesopotamian Basin. Considering limited studies describing the Abadan plain petroleum system and lack of oil-oil correlation between Sarvak and Mishrif oil reservoirs, in this study, initially the quantity, quality and maturity of organic matter in candidate source rocks were investigated and then the geochemical properties of Sarvak oils were evaluated. Finally correlation study was performed on Sarvak and Mishrif oils.Materials and MethodsTwo oil samples in the Cretaceous Sarvak Formation from the west of Abadan Plain oil fields have been analyzed using Gas Chromatography (GC) and Gas Chromatography-Mass Spectrometry (GC-MS). In addition, twenty cutting samples from candidate source rocks in the area from the lower Cretaceous and the upper Jurassic have been studied for source rock analysis.Results and DiscussionThe final interpretations of rock evaluation data for candidate source rocks in Abadan plain are as follows:Garau formation has good to excellent potential for hydrocarbon generation (mostly oil and less gas).Fahliyan formation has poor to fair potential to generate hydrocarbons. Although it is mature but the organic richness of the rocks are not enough and have generated relatively low amounts of hydrocarbons.Gadvan formation is evaluated as having poor potential source rocks and no oil could have been generated from these clastic rocks.Kazhdumi formation evaluated as fair to very good potential source rock, but being thermally immature and no hydrocarbon could have been generated from this rock.The biomarker analysis shows that Sarvak oils have been sourced from mature carbonate rocks containing Kerogen type II and were deposited in a low salinity environment. Also, based on C28 and C29 steranes and ETR, Sarvak oils were generated from Jurassic source rocks. According to biomarker and source rock studies, Sargelu and Garau formations were introduced as main source rocks in the west of Abadan plain, which generated Sarvak oils in maturity levels of early to middle oil window. On the other hand, biomarker data of five Mishrif oils from Iraqi oil fields (taken from released paper) were collected to compare them with Sarvak oil biomarkers.ConclusionThe observations have been suggesting excellent correlations between Sarvak and Mishrif oil biomarkers, so according to close proximity of oil fields and rock evaluation data similarities, all generation levels, migration and accumulation of hydrocarbons in Sarvak and Mishrif reservoir located in the west of Abadan Plain and Mesopotamian basin respectively, are similar to each other. Finally, Sargelu and Garau formations generated hydrocarbons and are likely to have charged upper traps such as Sarvak reservoir, probably during Miocene, along faults and fractures.