Geochemical Characteristic and Correlation of Oil Seepage Boyolali, Center Java, Indonesia

Abstract

Kendeng Zone is an interesting area for many explorationist because of it's hydrocarbon prospect, especially in Boyolali and surrounding areas. The hydrocarbon prospect is indicated by the existence of the production wells since colonialism and some oil seeps in this area that means petroleum system in this area is active. Oil seepages in this area can be generated from the same origin or different oil source rock. To know the origin of these oil seepages, this research are conducted. The aim of this research is to understand the characteristic of the oil seepages including biodegradation level, organic material origin, depositional environment and thermal maturity also determining the correlation of the oil seepages in this area. Three oil seepages were collected by fieldwork activity in Gunungsari, Repaking and Kemusu area. These oil seepages are conducted by geochemical analysis including Liquid Chromatography, Gas Chromatography and Gas Chromatography-Mass Spectrometry analysis in LEMIGAS Laboratorium. The analysis result of Gunungsari oil seepage show high level of biodegradation while oil seepages from Repaking and Kemusu show minor biodegradation. The biomarkers interpretation of these oil seepages show the source input of all oil seepages derived from the higher plants materials that deposited in terrestrial environment with little contact with deltaic system. Thermal maturity of these oil seepages can be considered as thermally mature with Ts/(Ts+Tm) ratio ranging from 0.52-0,59 and C2920S/(20S+20R) ratio ranging from 0.42-0.48. The characteristics of Gunungsari, Repaking and Kemusu's oil seepages has same organic matter origin, depositional environment and thermal maturity which is show a positive correlation.