STUDI KARAKTERISASI DAN KORELASI HIDROKARBON TERHADAP BATU LEMPUNG EOSEN-OLIGOSEN DI CEKUNGAN SUMATERA UTARA: POTENSI FORMASI PARAPAT SEBAGAI BATUAN INDUK

• Main Author: Budiman Ustiawan, Arief
• Format: Theses
• Language: Indonesia
• Subjects: Geologi, hidrologi & meteorologi
• Online Access: https://digilib.itb.ac.id/gdl/view/80190
• Institution: Institut Teknologi Bandung

Oil production in Indonesia has started since 1885 when the first oil well in Indonesia succeeded in production. The low recovery factor means that oil production in Indonesia has declined since 1995 due to a lack of exploration and investment in the petroleum sector. The oil production targets set by the government at the beginning of each year always fails to be achieved because most of the oil production in Indonesia comes from oil fields which are already included in the old field category. An integrated exploration effort is needed between geological, geophysical and hydrocarbon geochemical aspects to discover possible new hydrocarbon reserves in Indonesia. The high level of demand compared to the level of oil and gas production can cause an energy crisis. The North Sumatera Basin is one of the productive oil fields in Indonesia. The Baong and Bampo Formations with marine environments have been considered regional source rocks in the petroleum system in the North Sumatera Basin. However, several oil discoveries in the North Sumatera Basin tend to have lacustrine and fluvial environments based on hydrocarbon geochemical data. The formation that has a continental environment is the Parapat Formation. However, geochemical analysis has not been carried out in detail, especially on the Parapat Formation. Research was carried out on the Bampo and Parapat Formations in the North Sumatera Basin which are thought to have potential as source rocks. The data used is geochemical and geological data from 11 wells. The available geochemical data are Total Organic Carbon (TOC), Rock Eval Pyrolysis (REP), Vitrinite Reflectance (VR), Gas Chromatography (GC), and Gas Chromatography–Mass Spectrometry (GC-MS). The aim of this research is to determine the characteristics of the source rock, including quantity, quality, type and level of maturity and hydrocarbon character based on geochemical data in the Bampo and Parapat Formations. TOC in the Bampo Formation has values varying from 1.04%-2.5% and the Parapat Formation has a value range of 0.5%-2.7%. The dominant kerogen type is type II (oil) in the Bampo Formation and type II/III (oil and gas) in the Parapat Formation. The maturity level of the Bampo and Parapat Formations is in the immature to overmature stage and is strongly influenced by the burial depth of the formation. In general, maturity begins at a burial depth of about 6000 feet. The graben area has a maturity level of mature to overmature, especially in the deeper graben, for example Graben Lhosukon, Graben Jawa, and Graben Timpang. The Bampo Formation has a shallow marine to deep marine depositional environment, while the Parapat Formation has a depositional environment in the form of lacustrine to fluvial-deltaic plains. The deposition organofacies interpretation of the Parapat Formation is located in organofacies type D and E or transition areas. Organofacies types D and E have the characteristics of a low sulfur element composition, are predominantly composed of organic material in the form of higher plants, resins, cuticles and bacteria, and predominantly produce hydrocarbons in the form of gas. Hydrocarbons in the study area belong to two families. The first and second oil families are characterized by a mixture of organic materials from higher plants and algae, anoxic–suboxic conditions, and shale source rocks. The difference between the two oil families is that the first oil family was deposited in an estuarine environment, while the second oil family was deposited in a lacustrine-estuarine environment. Both oil families are positively correlated with the Parapat Formation. However, based on carbon isotopes, the oil samples do not correlate with the Parapat Formation rock samples. This can be caused by the fact that the location of the wells is generally in the horst area, while the oil comes from the graben area so it already has slightly different characteristics.