* Medco E&P Grissik Ltd. IPA22-G-51 PROCEEDINGS, INDONESIAN PETROLEUM ASSOCIATION Forty-Sixth Annual Convention & Exhibition, September 2022 GEOCHEMICAL ANALYSIS IN SUPAT FIELD, SOUTH SUMATRA REVEALED DIFFERENT OIL CHARACTERISTICS FROM THE SAME SOURCE ROCK Budi R. Permana* Ahmad Faisal* Alan A. Gantyno* ABSTRACT Supat is an oil field in Corridor Block in the South Sumatra Basin. This field has two main oil-bearing reservoirs, named the Talang Akar Formation (TAF) and the K-limestone Formation (KLS). These reservoirs are not in pressure communication. TAF Formation has been produced for 28 years while KLS was assessed and proved as an oil reservoir in 2014 and 2015. However, KLS did not have continuous production due to flow assurance problem. This paper discusses the geochemical analyses performed to characterize oil properties from both formations (TAF and KLS). The analysis that consists of SARA (saturated, aromatic, resin, and asphaltene) compositions, API gravity, pour point, WAT (wax appearance temperature) and WDT (wax disappearance temperature) were performed on oil samples. High Temperature Gas Chromatography and Mass Spectrometry (HTGC-MS) was also conducted on the saturated and aromatic fractions of the oils for biomarker analysis. Based on the physical oil characteristic analysis, the oil produced from TAF and KLS is different in term of SARA, API gravity, pour point, WAT and WDT. The analysis describes that producing oil from TAF has a propensity to form wax whereas the producing oil from KLS tend to form asphaltene. Nevertheless, the results of Gas Chromatography and Mass Spectrometry analysis indicate that the oils from both formations have same source progenitor which is terrestrially derived higher land plant (D/E Type organo-facies) source rock. This source rock was deposited in fluvio-deltaic or transitional system. It is then concluded that the variation in oil composition occurred due to alteration during and post migration and accumulation. INTRODUCTION Supat Field is located in the southeastern area of the Corridor Block (Figure-1), in the South Sumatra Basin. This field was discovered in 1984 and developed in 1988 with main production came from the Talang Akar Formation (TAF). Subsequently in 2014 and 2015 well testing programs were conducted at several wells to confirm the oil potential of K- limestone (KLS) Formation (Syukri, et al., 2018). The well test results demonstrated that K-Limestone was proven to be oil bearing reservoir despite of its tight reservoir properties. There are 19 (nineteen) wells targeted the TAF reservoir sands have been drilled, with peak production of 3,400 BOPD. Since oil production commenced, the Supat wells have experienced frequent downtime. Oil has been produced with artificially lifted by jack pump, and rod repairs were the primary driven issue of production. By pulling- out the assembly, it was found out that waxy material has been build-up at the rod, might as well at the tubing. Later, the analysis of formation water also shown that there is a tendency from produced water to form scale. The wax itself is a mostly coming from alkanes hydrocarbon that compositionally ranging from C6 to C60 and mixed with other inorganic material. It is soluble at high temperature but precipitate upon cooling and hence become more solid at room temperature. Other than TAF, a new attractive opportunity in the Supat Field is KLS Formation. This formation was tested, and the production from KLS showing similar signature to the TAF. Perforated was performed at Supat-10 well in January 2014 with initial production of 150 BOPD and rapidly dropped to only10 BOPD within six months. Similarly, Supat-07 well also experienced rapid decline to 100 BOPD from initial the initial production of 280 BOPD in just three months. The production behavior of the TAF and KLS in Supat Field was intriguing to be further investigated.