Geochemical study of Tar-mat formation in Bangestan reservoir in Kupal oil field

Kupal anticline is elongated and almost symmetric. This structure is located in Northwest of Ahwaz city and consists of two reservoir including Bangestan and Asmari. Kazhdumi, Pabdeh and Gurpi formations are probable source rocks and Gachsaran Formation constitutes the cap rock. Because project topic is defined on Bangestan Group, so reservoir studies of Bangestan is focused on Sarvak Formation. Rock-Eval and geochemical analyses conducted on source rocks indicated that Pabdeh Formation is at early stage of oil generation window in the Kupal oil field. Kazhdumi Formation has not been drilled at this field, so geochemical and maturity assessment of this formation has been evaluated using samples from adjacent oil fields including Marun and Haftgel. Geochemical analyses indicated that Kazhdumi Formation is mature enough and is considered to be the main source rock. The aim of this project is investigating Tar-mat in Bangestan reservoir in Kupal field. It is thought that Tar-mat layer was formed in vicinity of oil-water contact and can be related to processes including natural deasphaltening, gravity segregation and oil-mixing. Based on Rock-Eval pyrolysis, pyrolysis-GC performed on Sarvak oil, it is suggested primary asphaltene formed from source rock does not exist in the studied oil but it is derived from secondary asphaltene by chemical reactions occurring due to oil-mixing in production well. In addition, analysis performed on asphaltene in oil zone, oil-water contact and water zone suggest that Tar-mat was formed in oil water contact region due to oxidation process. This layer acts as impermeable seal and prevents water flow to oil