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A Comprehensive Geochemical Studies by Using Pyrolysis Analysis and Migration Pathway Map on Evaluating Source Rock Potential in Talang Akar Formation, Jambi Sub-Basin, South Sumatra

Abstract

The Talang akar Formation of the Jambi sub-basin has been a potential contributing source of hydrocarbon for the Gelam Field when drilled at the graben margins, dominated by shales interbed with sands. The main structural elements of the Jambi sub-basin are horst and grabens formed during Paleogene. With structural trends that aligns northeast to southwest, which was then subjected to wrenching and further subsidence, continued with PlioPleistocene compression forming the northwest to southeast trending folds Geochemical approach through pyrolysis analysis is conducted to determine the quantity, quality, and maturity of the source rock and to determine the type of kerogen and hydrocarbon that the organic materials produces as a potential source rock and its contributing factor to the Gelam Field. The shales of the Talang Akar formation of the jambi sub-basin has good TOC values, and a proven Type III Kerogen based on the value of hydrogen index, a gas producing kerogen. Based on vitrinite reflectance and Tmax data, all of the shales of the Talang Akar formation has reached early mature phase, making it a potential source rock. Isopach and Shale Thickness Map are used to determine which location has higher value of total thickness of shale. Shale Thickness map is also used to determine the volume of shale of the Talang Akar Formation. The volume of shale is then used for volumetric calculations, to calculate the total mass of hydrocarbon generated (HCG), using calculated values of mass of organic carbon and mass of hydrocarbons generated per unit mass of organic carbon. The value of HCG is then converted into TCF (considering its gas producing kerogen). Using depth structure map of the Talang Akar Formation and Basement, the pathway of the hydrocarbon can be determined, forming a migration pathway map. It can be concluded that the Talang Akar Formation of the Jambi sub-basin is indeed a potential source rock and contributes to the Gelam field's gas production. Further geochemical analysis through basin modeling should be considered to conclude the full potential of hydrocarbon generation of the Talang Akar Formation shales of the Jambi sub-basin. Keywords: geochemistry, pyrolysis, hydrocarbon, petroleum, source rock, shale, subsurface mapping, Volumetric Calculations.