Publications

The research area is located in Kenduruan, Tuban, Rembang Zone, East Java Basin, where several anticlinoria aligned in E-W direction, stretching from Purwodadi to Madura Island. It is further divided into North and South Rembang Anticlinorium. During the fieldwork, the authors found several spots of oil seepages. The oil seeps found around thrusted folds, and it is interpreted to be originated from hydrocarbon trapped within the anticline that leaked along the fault. This process is known as tertiary migration. The leakage may reduce the oil volume trapped in its reservoir. The study is conducted by field mapping includes measured section; microfossils, petrography, structural analysis, and combined with information from published paper as references. Folds in the study area formed a left-stepping en-echelon pattern. It is controlled by NNE-SSW basement sinistral strike-slip faults. This structural deformation formed micro-fractures in the carbonate rocks and could be observed on the outcropped section. The Bulu Formation consists of grainstone, packstone, and wackestone bedded with shallow open marine environments. Furthermore, the reef buildups were developed in certain areas during Middle Miocene. Whereas the Wonocolo Formation consists of fossiliferous sandy marl, bioclastic limestone and intercalated thin-bedded grey fossiliferous calcarenites, that was deposited in the outer neritic, during Late Miocene. The occurrences of these hydrocarbons leak out from faulted anticlines is a positive sign as it proves the presence of working petroleum system. However, at the same time, one could question whether the remaining accumulation is large enough to be produced commercially.