SOURCE ROCK GEOCHEMISTRY PRA-TERSIER AKIMEUGAH BASIN, PAPUA

SOURCE ROCK GEOCHEMISTRY PRA-TERSIER AKIMEUGAH BASIN, PAPUA

The Akimeugah Basin is located north of the southern Papuan basement high (Merauke Ridge) which separates it from the Arafura Basin to the south. This basin Judging from its association with surrounding basins, the akimeugah basin is associated with basins that have produced hydro-coal in the West Papua Basin and Australian basins. From tracing various journals and articles, the geochemical literature will provide an overview of the active host rocks in the area.

The index map of the Akimeugah and Sahul Basins is based on the Indonesian Sediment Basin Map (Badan Geologi, 2009).

The Akimeugah Basin begins as a passive margin, which is a basin formed by rifting on the northern edge of the Australian continent at the edge of this bank, experiencing cracking due to a part of the mass in its northern part which is about to move and move from Australia. In this crack, horst and graben are formed which in the graben are deposited sediments of Paleozoic and Mesozoic synrifting. Then, when this part is separated and away from Australia (drifting) sediment drifting is deposited which is generally in the form of shale or limestone, this event occurs until Paleogene.

 

Tectonic maps and cross sections of the foreland basin

At the age of Neogen, Akimeugah collided with the Central Range of Papua (Back of Papua). Since that's the type foreland basin Akimeugah. Passive Paleozoic-Neogen margins are bent into the lower Banda line and Central Range. Then at the front of the buckling (foredeep) deposited molassic sediments which are erosional products from nearby heights. However, and burial by the sedimentary part of the passive margin molasses, Akimeugah has ripened Paleozoic, Mesozoic, or Paleogene host rock in the graben. move flips from foredeep to the forebulge (the direction in the direction of the passive margin which is not bent like foredeep) laterally, or moves vertically towards the immobilization deformation zone in the impact area. The main control of the Akimeugah basin is rifting and drifting in the Mesozoic-Paleogene Paleozoicum, and collisions on Neogene (Awang Satyana, in Sabarnas Agus 2011)

Stratigraphy of the Akimeugah Basin

The Akimeugah Basin consists of pre-cambrian-tertiary deposits. The basic rock consists of Gabro rocks aged pre-cambrian and Metamorphic rocks. Followed by the deposition of the Permian Dolomite Modio formation and the Aiduna Formation which are deposited incongruously. Then it was harmoniously deposited on top of Mesozoic clastic formations (Tipuma, Kopai, Woniwogi, Piniya and Ekmai Formations), as well as some carbonate coatings locally. Above the Ekmai Formation, overlaid by clastic and limestone Paleocene-Miocene age (Waripi, Lower Yawee, Adi Members, and Upper Yawee) are out of tune. The last deposition was the final claystone of the late Miocene to Plio-Pleistocene and the uncoated local carbonate, the Buru Formation.

GEOCHEMICAL METHOD

The geochemical approach is the process of identifying active host rocks beginning with evaluating the quantity of organic material using the parameters Petter and Cassa, 1994. Determination of the quality of organic material uses a modified Van Krevelen diagram in Hunt, 1996. And Determination of maturity level using the parameters Petter and Cassa, 1994. used consisted of analysis of TOC content, Rock-Eval Pyrolysis, and Vitrinite (RO) reflection.

Identification of Parent Rock

The process of identifying host rock intervals in the aqueduct basin is carried out in several wells. Where the host rock evaluation focuses on the Woni - Wogi Formation and Aiduna Formation

Organic Material Quantity

The source rock identification begins by analyzing the host rock quantity and the ability to generate hydrocarbon. The quantity of host rock is assessed by looking at the value of total organic content (TOC) expressed in units of the percentage by weight of dry rock. Analysis of the source rock quantity is done by making a TOC curve to the depth at the intervals of each formation, as follows:

a) Woni - Wogi Formation

The Woni-wogi Formation at the Early Cretaceous age with the lithology of sandstone, shale and siltstone consisting of having a value of organic material content is 0.34 wt - 2.9 wt% based on the classification of organic material content into the Poor - V. Good category (Peters and Cassa, 1994). Judging from the ability to generate hydrocarbons with parameters S1 + S2 (Potential Yield) the value is 0.2 mgHC / g - 6.21 mgHC / g which is included in the Poor-Good category (Peters and Cassa, 1994). This data shows that this formation has the potential to become host rock.

TOC content of Woni-Wogi Formation and Ability to generate

Hydrocarbons

b) Aiduna Formation

Aiduna Formation at Permian age with shale lithology has a value of organic material content which is 0.39 wt% - 3.45 wt% based on the classification of organic material content into the Poor - V. Good category (Peters and Cassa, 1994). Judging from the ability to generate hydrocarbons using the parameter value S1 + S2 (Potential Yield) with a value of 0.33 mgHC / g - 10.47 mgHC / g into the Poor-V.good category (Peters and Cassa, 1994). This data shows that this formation has the potential to become host rock

Quality of Organic Materials

The quality of organic material influences whether or not the potential of sedimentary rocks to become host rock, which is represented by the kerogen type of host rock. Kerogen type is influenced by the constituent material and its depositional environment. Kerogen type also determines the final active rock product in the form of oil, oil / gas or gas. Determination of kerogen type in this study using a modified van Krevelen diagram plot. The modification is to replace the plot of the H / C to O / C ratio to the ratio of the hydrogen index (HI) to Tmaks. This is done because there is little analysis that gets H / C, O / C and oxygen index (OI) data. Analysis of the quality of organic material using Tmax Vs HI values, as follows:

a) Woni - wogi Formation

The results of plotting HI vs Tmax data from 49 samples in this formation indicate that the kerogen type in the Woni-wogi formation has kerogen Type II - III (Modified Van Kravelen Diagram in Hunt 1996) which is dominated by kerogen type III (Prone Gas). Tmax data shows that this formation has a mature maturity level

Quality of the Woni - Wogi Formation

b) Aiduna Formation

Kerogen type analysis based on HI Vs Tmaks data conducted on 22 samples in the Aiduna formation shows that this formation has a kerogen type II - III which tends to produce a mixture of oil and gas dominated by type III (gas). Also based on Tmax data, this formation has entered the maturity window. With maturity level not yet mature.

Quality of Aiduna Formation

Maturity

Analysis of the maturity of organic material will determine the depth interval (window of maturity) of active host rock that produces hydrocarbons. Maturity analysis is done by looking at the value of vitrinite (Ro) reflectance. Maturity analysis based on vitrinite reflectance (Ro) is based on reflection values ​​(Ro) derived from kerogen, especially from vitrinite. Maturity analysis using Ro is done by combining the whole well so that the trend of maturity values ​​is obtained in a regional (Figure 6). The results of the Ro value analysis indicate that the maturity window in this basin is 7000 feet below sea level. This proves that the Woni-Wogi Formation and also the Aiduna Formation have entered the maturity window. Ro is done by combining all the wells so that the trend of maturity values ​​can be obtained regionally (Figure 6). The results of the Ro value analysis indicate that the maturity window in this basin is 7000 feet below sea level. This proves that the Woni-Wogi Formation and also the Aiduna Formation have entered the maturity window.

Regional Maturity

Immersion History

The results of modeling the history of 1D immersion in a well show that the maturity of the host rock occurs at the age of miocene at a depth of 1980 m or 6500 ft. It is this sediment yield that has the role of ripening pre-tertiary host rock. Where the speed of sedimentation takes place very quickly due to the large supply of erosion from the high sediment produced by the collusion of neogeneous ferns.

History of Immersion of a Well in the Akimeugah Basin

CONCLUSION

The results of the identification of pre-tertiary host rocks in the Akimeugah Basin indicate that the intervals of the host rock of the Woni-Wogi formation and Aiduna formation have poor organic matter content - good. In addition, the two formations have a kerogen type dominated by type III kerogen which will tend to produce gas and have entered the maturity window. This shows that the woni-wogi and Aiduna formations are active host rocks in the Akimeugah basin.

The maturation of this formation occurs during the middle myoses, where a lot of this fast and sedimentary sediment originates from collusion which occurs at that time which successfully ripens the pratersier host rock of this basin.

Reference:

• Harahap, B.H. 2012. Tectonostratigraphy of the Southern Part of Papua and Arafura Sea, Eastern Indonesia, Indonesian Journal of Geology, Vol. 7
• Huang, W.Y. dan Meinschein, W.G. 1979. Sterol as Ecological Indicators: Petroleum Geochemistry. Bandung. PreConvention short course IAGI : Awang H. Satyana 2004.
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• Peters, K.E. dan Cassa, M.R. 1994. Applied Source Rock Geochemistry, dalam Magoon, L.B. and Dow, W.G., eds., The Petroleum System - From Source to Trap: AAPG Memoir, 60
• Satyana, A. 2015. Petroleum Geochemistry for Exploration and Production of Conventional and Unconventional Hydrocarbons. Short Course: IPA 2015
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• Waghete Dan Sekitarnya, Kabupaten Deiyai Provinsi Papua. Prosiding Hasil Kegiatan Pusat Sumber Daya Geologi Tahun 2011
• Yudha Situmorang, et al, 2017, STUDI GEOKIMIA BATUAN INDUK AKTIF PRA-TERSIER CEKUNGAN AKIMEUGAH, LEPAS PANTAI PAPUA SELATAN, Padjajaran Geoscince Journal
• Waples, D. 1985. Geochemistry in Petroleum Exploration, International Human Resources Development Corporation, Boston.
• http://geomagz.geologi.esdm.go.id/cekungan-akimeugah-dan-sahul-harapan-baru-penemuan-migas/
• https://dzulfadlib.wordpress.com/tag/lapangan-minyak/