Remote Sensing Aplication and Geochemical Studies for Hydrocarbon-Induced Alterations Discoveries in Western Kendeng Zone

The development of satellite imaging technology that has spectral capability has the potential to be utilized in hydrocarbon exploration. The presence of hydrocarbons can be detected through spectral recording of hydrocarbon seepage. Over a long period, hydrocarbon seepage will change the chemical structure and mineralogy of the surrounding soil and rocks, so that it will cause spectral anomalies that are key to the existence of active hydrocarbons and petroleum systems. The West Kendeng zone was chosen as a research location because several hydrocarbon seepage sites were found to contain, either oil or gas in the area. Based on hydrocarbon seepage spectral theory, Landsat 8 imagery has a wavelength spectrum capability that is sensitive to the anomalous object of hydrocarbon seepage. Therefore, this research was conducted to determine the distribution of hydrocarbon seepage areas in the West Kendeng zone by using Landsat 8 imagery. In addition to using Landsat 8, to strengthen the research results a surface geological mapping process was also carried out at the seepage location. Then the samples obtained were analyzed by XRD and XRF. XRD analysis was carried out to determine the types of minerals that became an anomaly around the seepage location. In addition, the XRF analysis is carried out to determine the chemical composition of rocks that have undergone alteration. Based on the results of Landsat 8 data calibration, an altered rock which is an anomaly of hydrocarbon seepage is found in the south and southwest of the study site. These results are confirmed by the location of the discovery of several points of seepage of hydrocarbons in the research area. The XRD test results also showed anomalous clay mineral content in the form of halloysite, albite, and augite in the southwest and south of the study site. Besides this anomaly, magnetite and pyrite were also found at that location. While the XRF test results from the sample also showed the presence of Fe2O3 element at 9.21% and CaO at 7.42% in the south and southwest of the study location. This indicates a reaction between hydrocarbons and rocks that affect the acidity conditions around them, so they will form clay minerals, iron oxides, and iron sulfides. Therefore, based on Landsat 8 image analysis, XRD, and XRF, a hydrocarbon seepage distribution area accumulated in the Bancak, Boto, Wonokerto, and Nyemoh areas in the Semarang Regency.