Publications

Bunyu is located in the Tarakan Sub-Basin which is a prolific hydrocarbon province where production began in 1971. A total of 234 wells have been drilled in the Bunyu area. The deepest well reached 4000 m in depth and penetrated the Tabul Formation. The hydrocarbon production comes from Tarakan, Santul and Tabul Formation reservoirs, whereas the deeper targets (>4000 m or below 2 seconds of the Bunyu 2D seismic data) have not been explored for yet. Seismic data, the main data for interpretation, has low signal to noise ratio due to the high energy absorption from loose sand and coal on near the surface. This issue has considerably impacted the long standing uncertainty of the seismic interpretation. Furthermore, the presence of a high overpressure shale zone in the Tabul Formation also gives another obstacle in the subsurface interpretation data in Bunyu. To answer the challenge of understanding the potential of the deeper exploration targets in the Bunyu area, four geophysical methods (gravity, magnetotelluric, passive seismic and 2D seismic) were acquired in 2015. These four sets of geophysical data give another perspective of interpretation to the deeper prospectivity of the Bunyu area. New methods in seismic acquisition and processing have given a better resolution of the seismic data. The deeper targets (>2 seconds or >4000 metres), that previously were hard to interpret with any confidence, can now be more easily interpreted. New exploration plays below the high pressure zone in the Tabul Formation can now be described with more confidence. The culmination of these new plays in the Meliat and Naintupo are in the southern part of Bunyu Area as can be interpreted in new 2D seismic data. The high pressure zone in Bunyu area is shown as blurry seismic data. It can be good seal for reservoir below it. The structural interpretation is also confirmed by the 1970 gravity map on a regional scale. Inside the Bunyu area, integration of the gravity and passive seismic data clarify the main faults that are interpreted to later affect the hydrocarbon migration pathways and entrapment. This is proved by the existence of hydrocarbon fields in the southern part of the Bunyu area above the high pressure zone.