JCY2019

Kalimantan is one of several areas in Indonesia with potentials in oil and gas production. However, North Kalimantan has its own risks in exploration and development, especially high pressure formation. Overpressured region may cause drilling hazard like mud loss, pipe obstructions and drilling failures. Overpressure mechanism is divided into two major groups: unloading and loading mechanism. The mechanism is identified through density and sonic log, where the constant sonic transit time and density to depth increase signifies loading mechanism while the sonic reversal with increasing density to depth increase indicates unloading mechanism. The unloading mechanism is also usually followed by clay diagenesis. The method used in the research is gamma ray vs resistivity plot in order to get the clay dominated formation interval and sonic vs density log plot to identify the zone of overpressure along with its thickness and mechanism. In two logs observed, the overpressure mechanism was found to be different for each log. In log X, overpressure zone was found from depth 1100 to 1546 meter shown by increasing sonic transit time with increasing density. In log Y, the overpressure with loading mechanism was found from depth 1546 to 1975 m. This research conclude that in the observed field the overpressure unloading mechanism for log X was caused by clay diagenesis and in log Y overpressure loading mechanism was caused by disequilibrium compaction.