Publications

The Early Miocene reefal carbonate of Kujung-1 is the main hydrocarbon reservoir in JS-1 Ridge Area, North East Java Basin. The varying heights of hydrocarbon columns affect the success rate of exploration in Kujung-1 Formation. The shale of Rancak Unit acts as a regional seal of the Kujung-1 Reservoir. This study aims to understand the character, capacity of seal, and its relationship with hydrocarbon column height, to improve the chances of exploration success. The methodology in this study includes estimation of pore pressures, capillary seals, hydrofracturing seals, seal geometry, and natural fractures modeling. The data used in this study include 41 well, laboratory (Mercury Injection capillary pressure, vitrinite reflectance and X-ray diffraction), and 3D seismic data. The pore pressure of Rancak Unit indicates that it is slightly overpressured by loading mechanism. The presence of slight overpressure increases sealing capacity of Rancak Unit to 1.95 MPa or 221 m gas column equivalent. Hydrofracturing seal does not play an important role in Rancak Unit. The seal geometry of Rancak has good to very good qualitative capabilities to hold hydrocarbon in Kujung-1 Reservoir. Present-day stress magnitudes and orientations have been determined from bore-hole breakout, drilling-induced fractures and LOTs from two wells. Interpretation of borehole breakout and drilling-induced tensile shows that average maximum horizontal stress direction is northeast-southwest. The geomechanically model shows that predominant stress regime at KD-1 and KD-3 Wells is normal stressregime. Fracture distribution based on natural fracture modeling is consistent with the percentage of hydrocarbon filling in Kujung-1 Reservoir. However, the fractures are in a stable condition under present-day stress. Based on further analysis, the natural fractures in the Rancak Unit are the main factor affecting the height of the hydrocarbon column in the Kujung-1 Reservoir. The Neogen compressional tectonic period is estimated to be the period of fracture in the study area in critical condition, and leakage occurred in the Kujung-1 Reservoir at that time.