Abstract
The presence of oil seepage to the surface indicates that at least an active petroleum system is present subsurface. Oil seepage that occurred in Plantungan, Kendal, Central Java, has been known since 1971 and still produces seepage until today. On the research area, three oil seepages point were found. Plantungan region is located in East Serayu Zone underlain by volcanic area, and based on the Geology Map, the research area is located in Banjarnegara-Pekalongan Sheet. To understand the geology condition of the research area, a subsurface mapping is needed, even though the mapping does not provide the depth of bedrock and reservoir, data recording using HVSR (Horizontal to Vertical Spectrum Ratio) method that has been done in 18 points is able to provide Vp and density profile to understand the distribution of oil seepage. The oil seepage is most prominent close to SB09 location, however the result from crossplot found that the value of highest Vp×density is on SB12A with 4,306,197 kg/m2s, and lowest Vp×density in on SB17A with 302,305.3 kg/m2s.
Highlights
Oil seepage is a presence of oil at the surface which migrated from the high pressure condition to low pressure through rocks fracture [1]
Data collection was done in an area of 560m x 400 m with 18 points at first and 4 additional points around the seepages they are SB09A, SB12A, SB13A, and SB17A (Fig 3 and 4)
According to Horizontral to Vertical Spectral Ratio (HVSR) curve analysis, at research site crossplot has been did around oil seepage points by crossing Zone I which showed dominant frequency with range of 0.20-0.35 Hz and Zone II has low dominant frequency in range of 0.08-0.19 Hz
Summary
Oil seepage is a presence of oil at the surface which migrated from the high pressure condition to low pressure through rocks fracture [1]. According to Zheng et al (2018), types of seepage are divided into two, which are macroseepage; oil, gas, volcanic mud, and bitumen. Petroleum oil itself, both offshore and onshore, is predicted to have more than 1,150 seepage points in 84 countries in the world, including Indonesia [2]. In Java Island itself, oil and gas seepage is focused on three main area, which are Banten, Majalengka, and East Serayu. These three area are located in volcanic area, based on the petroleum geology, all of them have a different petroleum system [3]
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