Coal Potential as Source Rock of Hydrocarbon Warukin Formation Based on Coal Macerals Composition, Central Wara, Tabalong, South Kalimantan

The interest of this research: there is oil seepage at the contact between coal seam-A and sandstone facies of Warukin Formation, so it is necessary to study where is the source rock. The correlation between HI and Tmax as result from rock eval pyrolysis shows that the shale of the Warukin Formation is immature while the correlation between HI and OI shows oil prone. The vitrinite (Ro) reflectance of Central Wara coal is between 0.48% up to 0.5% (immature), the content of the vitrinite group is 68.0 84.8 (% Vol.), Liptinite 3.0 14.0 (% Vol.) and inertinite 0.48 25.0 (% Vol.). The high content of liptinite mineral groups (14% Vol.) and the presence of exsudatinite maceral are as an initial indication of bitumenization of oil formation when there is a change in reflectance and fluorescence. Therefore, Central Wara coal plays an important role as the source rock of the Warukin Formation, although the maturity level is immature, the presence of exsudatinite maceral is believed to be the source of origin for producing oil, where the organic material comes from terrestrial.

(2021) Coal Potential as Source Rock of Hydrocarbon Warukin Formation Based on Coal Macerals Composition, Central tan. It covers an area of 70,000 square km, extending to South Kalimantan Province in the Barito River area.
Based on the petroleum system study, the source rocks in the Barito Basin are shale, claystone, and coal from Tanjung Formation. Yet according to temporary study there is a possibility that source rock of Barito Basin is shale originating from claystone or shale of Warukin Formation. The main reservoir rock is Tanjung Formation and the secondary reservoir rock is Warukin Formation located in East Tapian, South Warukin and Middle Warukin Field. The cap rock in this area is from shale founded in the Upper Tanjung Formation and shale between Warukin Formation [1].
The hydrocarbon traps are structural traps of fold and combination of fold and thrust fault, another trap is sandstone lenses of stratigraphic traps.
The objective of this study is to determine the hydrocarbon generation system by integrating the coal potential source rocks in the Central Wara, Tabalong, South Kalimantan of the Warukin Formation in Barito Basin on previous and recent coal macerals analysis and pyrolysis rock eval. The interest in this research is discharge of oil seepage at contact between coal seam-A and sandstone facies, so it is needed to study where is the source rock of the oil seepage.

Literature Review
Central Wara research location is close to the Tanjung Field located in north east part of Barito Basin, which is one of the largest oil basin in Kalimantan. Geographically in South Kalimantan Province. It is bordered by the core of Sunda Continent in the west which is often known as Sunda Shield that consists of Pre-Tertiary rocks which have been tectonically stable since the Mesozoic era. In the southern part it is separated from the East Java Sea Basin by a relatively stable shelf which is covered by a thin layer of  [3] shows in Figure 2.
The result of the entire tectonic process is the discovery of structural configuration characterized by parallel folds and thrust faults trending southwestnortheast. The fault structure involves bedrock and is increasingly patterned toward the Meratus mountains which are the basis for the tectonic process [3] [4].

2) Berai Formation
The Berai Formation is divided into Upper Berai, Middle Berai and Lower Berai [6] [7]. This division is generally based on differences in lithology. Upper Berai lithology composes of limestone intercalation, claystone and marls, Middle Berai is massive limestone, reefal or skeletal, and Lower Berai is an intercalation of limestone with marls [6].   is based on morphological shape, size, relief, internal structure, chemical composition, color of reflection, intensity of reflection and degree of coalification [7].

3) Warukin Formation
In this study, the division starts from the maceral group (group), the maceral subgroup and the maceral type which refers to the Australian Standard: AS2856 (1986) ( Table 1). The advantage of this Australian Standard system is that the distribution of the mass composition applies to all coal rank, both hard coal and brown coal, and this system is quite simple. Meanwhile, other standard systems are usually distinguished between hard coal and brown coal.    [9]. Based on the morphology and source of origin, the liptinite group can be distinguished such as: sporinite, cutinite, suberinite, resinite, liptodetrinite, exsudatinite, fluorinite, alginite, and bituminite ( Table 1).
The inertinite group macerals are originated from burnt plants (charcoal) and some are thought to be due to oxidation processes from other macerals or decarboxylation processes caused by fungi or bacteria (biochemical processes). With this process, the inertinite group has a relatively high oxygen content, low hydrogen content, and higher O/C ratio than the vitrinite and liptinite group macerals.
The inertinite group macerals has the highest reflectance value among other maceral groups. Under a reflection microscope, inertinite shows a gray to greenish gray color, but in ultraviolet light it does not show fluorescence. Based on the internal structure, level of preservation and intensity of combustion, the inertinite group was divided into several macerals, called fusinite, semifusinite, sclerotinite, micrinite, inertodetrinite and macrinite (Table 1).
Coal contains various forms of organic elements over a range of chemical compositions, and these variations in chemical composition can be combined to determine the geological history of what type HC was produced. coal as the source of origin for gas Hydrocarbon and liquid HC (oil), especially for kerogen and or maceral [10].
Kerogen is a typical classification of hydrocarbons for types I to IV based on chemical composition [10]. Chemically, kerogen is basically classified in the proportions of C, H and O. Petrographically (microscopically), kerogen is directly related to the origin of organic material that has been deposited in sedimentary rocks and the products of mechanical, biological and thermal alteration. In this way, each kerogen type can be characterized using the coal mineral terminology.

Methodology
This research was conducted in the coal mining in Central Wara, Tabalong, South Kalimantan area and its surroundings. The research methods carried out in the field are coal observation and sampling data from outcrop direct.. The main target of coal seam is Seam A Central Wara in Warukin Formation ( Figure  5 and Figure 6).
The method for taking coal samples is carried out directly in the outcrop of coal mine walls at seam-A by the ply by ply method, based on the appearance of the lithotype macroscopically. Then each sample is reduced in size, and a composite is then divided into two for archives and laboratory analysis.
Microscopic analysis of coal identifies mineral composition, minerals and vitrinite reflectance values. Coal samples taken from the outcrop of mining wall then prepared for polishing incisions. In sample preparation several tools and materials are needed such as:   The coal fraction size −16 mesh +20 mesh is then mixed with resin powder (transoptic powder) with a ratio of 1:1. The mixture is then put into the mold and heated to 200˚C. After the temperature reaches 200˚C the heater is turned off and the mold is pressured to 2000 psi. Briquette can be removed after the temperature reaches room temperature. The next stage is briquette polishing which starts with cutting using a polishing tool (grinder-polisher) then smoothed with silicon carbide size of 800 mesh and 1000 mesh above the glass surface. Next polished using alumina oxide measuring 0.3 microns, 0.05 microns, and finally measuring 0.01 microns on silk or silk cloth. The resulting polishing incision is placed on the preparatory glass with the night candle holder then leveling.
Observation of polishing incisions is done using a reflectance microscope both qualitatively and quantitatively to determine the mineral content and minerals in coal. Microscopic research using reflected light with 200 times magnification with observation of 500 points.
The analysis process was carried out at the Coal Petrographic Laboratory, TekMIRA Research Center, Bandung. Coal Mining Classification uses Australian standards (AS 2856(AS , 1986 and the microscope used is Microscope Spectrophotometer Polarization with Fluorescence, type: MPM 100, brand: Zeiss. Organic carbon content (wt%) is measured using LECO CS-344 carbon/sulfur analyzer. Previously, the analysis of powdered coal samples was mixed with dilute hydrochloric acid (10%) to remove carbonates. The samples were washed three times with distilled water and dried for 1 hour at 105˚C. For sample element analysis, coal is mixed with iron flakes and a tungsten accelerator is burned in an oxygen atmosphere at a temperature of 1370˚C. The combustion product causes moisture and dust to disappear, while the solid portion of CO 2 gas is measured by infrared detector. The organic carbon content was used to determine the extract yield (mg extract/g TOC).
Pyrolysis rock eval method used to approach the actual hydrocarbon formation event in nature which occurs at low temperatures but with a very long geological time [11]. The method used is rock eval with the parameters used are S1, S2, S3, maximum temperature (Tmax), Hydrogen Index (HI) and Oxygen Index (OI).

Result and Discussion
The results of the pyrolysis analysis of rock eval samples of Central Wara coal and coaly shale are shown in Table 2. The Tmax of Central Wara Seam-A coal varies between 376˚C -413˚C, HI values are between 155 -238 mg HC/g TOC and OI values between 51 -73 mg HC/g TOC.
The result of depiction of the Hydrogen Index value against the Tmax value indicates that the maturity of the Central Wara Seam-A coal is immature ( Figure  7). Stated that the description of HI value against Tmax for 3 samples of humic coal is generally in kerogen type III (Gas Prone) and 1 sample of coaly shale is in kerogen type II (Oil Prone) [11]. However, the depiction can also be between Open Journal of Geology type II and III kerogens, because generally the way coal responds is not the same as the organic matter in type III kerogen. Likewise, Based on the results study of pyrolysis rock eval from several coal basins, it shows that most of the HI depictions of Tmax are between kerogen types II and III [12]. This condition applies to Central Wara Seam-A coal, that the results of HI depiction of Tmax are in kerogen type III (Figure 7), while the results of depicting HI to OI are included in kerogen between types II and III (Figure 8). Tmaks (<435˚C), the maturity level of the source rock is still immature, so for Central Wara Seam-A coal with Tmax values ranging from 396˚C -410˚C [11], the maturity level is immature ( Table 2).
Based on the lower OI value compared to HI, this supports the fact that reduced oxygen is a character for low rank coal coalification [13]. Thus, it is consistent between the vitrinite reflectance (Rv) value, the Tmax value and the depiction of the Hydrogen Index value against Tmax, that the maturity level of the Central Wara Seam-A coal is immature.   Kerogen or coal maceral as a hydrocarbon occurs during coalification, namely significant changes in both mechanics and chemistry during stockpiling, and these changes are driven by compaction, biological activity and kinetic thermal.  [14].
Liptinite macerals content between 3.0% -14.0% Vol (Table 3)  and the result of bacterial degradation can help increase the hydrogen content of some organic materials wooden. Perhydrous vitrinite is also more strongly associated with coal and shale which is rich in the type of oil-forming organic elements (oil prone). Therefore, the high hydrogen content and the suppression of the reflectance of the pertydrous vitrinite may be explained by the sorption of hydrocarbon oil that has been generated from kerogen types and other macerals in liptinite such as flourinite as a residue to produce hydrocarbon solutions, thus coal has the potential to regenerate oil in large volumes [10].
The immature level of coal maturity indicates that the coal is still in the gelification stage, where during coalification there is vitrinitization accompanied by the formation of liquid bitumen (oil). This clue is seen in the presence of fluorinite alginite sporinite alteration result which is rich in hydrogen content (high Hydrogen Index) to oil forming.
In general, the type of tertiary coal plant in the tropics is an angiosperm containing coniferous rich in resine, latex, oil and fat as a source of resinite [9]. Resinite has a tendency to form exsudatinite at the beginning of the coalification process [9].  [10]. The chemical composition of exsudatinite is thought to be asphaltene [10]. Therefore the presence of exsudatinite maceral as an initial indication of bitumenization of oil formation when there is a change in reflectance and fluorescence.

Conclusion
The presence of exsudatinite maceral in the coal of Central Wara Warukin Formation proves that: -The coal had bituminization, tended to form kerogen type II (oil prone) and as a precursor to oil forming.
-Coal in Central Wara is source rock of Warukin Formation, South Kalimantan.