Publications

Java Island in Indonesia is in the active southern margin of the Eurasian Plate since Cretaceous and has a thick volcanic cover from Paleogene to Recent time. Maja-1, the first exploration well was drilled in 1871 in Majalengka based on the presence of the oil seeps at the surface in the volcanic environment and the finding that an active petroleum system works in this environment. Satyana (2018) conducted a study of hydrocarbon prospects in the volcanic environment and they are North Serayu, Banten Block and Majalengka-Banyumas areas. These three regions are very intriguing and challenging as one of the petroleum systems play concepts in Indonesia that need to be explored in the future. During the exploration stage, the seismic method plays important rules to understand the subsurface, however, there is a challenge when it applies in the volcanic area. A high velocity and high-density properties of volcanic facies can cause large attenuation resulting in a poor quality of the seismic image. Low signal to noise ratio increases uncertainty in velocity analysis that will produce inaccurate reflector position of the seismic event. Therefore, we use the non-seismic method of utilizing and integrating Gravity and Magnetotelluric (MT) to improve the subsurface imaging of the sub-volcanic reservoir. The gravity method is sensitive to the presence of the basement but the image that was given was too ambiguous. The MT method is sensitive to the presence of volcanic facies but has poor information on the basement area while seismic tomography is very sensitive to the presence of the volcanic layer and can provide a highly detailed image. However, the ray path from seismic tomography is unable to reach the area below volcanic facies which resulted in the seismic tomography could not give any information below the volcanic layer. We combine the advantages and disadvantages of non-seismic methods and propose an unconventional integration scheme with Simultaneous Joint Inversion (SJI). We create a synthetic subsurface model of North Serayu Basin, run the inversion simultaneously for each method and constrain each of them by the empirical relationship between resistivity, density, and velocity. The result of the SJI subsurface synthetic model of the North Serayu Basin is encouraging compared to the conventional velocity estimation through Dix conversion. Therefore, an unconventional integration scheme of non-seismic methods and the seismic data are promising. It can be applied to a real dataset and can have a significant impact on the sub-volcanic petroleum system discovery in Indonesia.