OVERPRESSURE, COMPARTMENTALIZATION, AND PROPERTY OF RESERVOIRS IN OIL AND GAS FIELD, BLOCK AA, NORTHERN MADURA PLATFORM, EAST JAVA BASIN

• Main Author: Suryana, Ecep
• Format: Dissertations
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/74486
• Institution: Institut Teknologi Bandung

<p align="justify">The research is conducted in the Northern Madura Platform, East Java Basin, which is Eocene to Miocene in age and is proven as a hydrocarbon producer in the Kujung and Ngimbang Formations. Tectonically, this basin is located in active tectonic regions that may allow overpressure to occur. The plot of pressure data against depth showed that carbonate reservoirs in the Kujung Formation and Ngimbang Formation were subjected to overpressure and hydrostatic conditions. Varying pressure gradient trends in the Kujung and Ngimbang Formations indicate that reservoirs are not connected to each other or compartmentalized. The distribution of pressure regimes in some wells indicates that overpressure is only localized in some wells. The overpressure in both formations is caused by loading (undercompaction). Seismic interpretation of acoustic impedance inversion and attribute shows that reef carbonates overpressure facies in the Kujung I Formation are deposited in the platform interior environment (tidal flat). Meanwhile, reef carbonates hydrostatic are deposited in the margin platform (barrier reef) and the platform interior (tidal flat). Reef carbonate interbedded with shale in the Kujung II, III, and Ngimbang Zone A Formations, which were also under overpressure condition were deposited in the platform interior environment (lagoon and tidal flat). Analysis of carbonate reservoir properties derived from seismic data which were calibrated by well core data showed that overpressure in the Ngimbang Formation of zone A occurred in patch reef carbonate facies that had relatively low to moderate porosity and permeability, while overpressure in the Kujung Formation occurred in the platform carbonate facies that had relatively high porosity and permeability. This means reservoir properties do not affect the overpressure that occurs in the patch reef carbonate facies and the platform carbonate. Pore pressure prediction using the Eaton method on carbonate reservoirs interbedded with shale produces a more accurate pore pressure prediction compared to pore pressure predictions in clean carbonate reservoirs. Overpressure that occurs in the study area is spatially small in value so it cannot be used to predict reservoir compartmentalization. Meanwhile, reservoir quality can be mapped by multiplying the attributes of porosity, permeability, and pore pressure. The greatest value is associated with the excellent quality of the reservoir. Overpressure associated with good reservoir quality is located in the southeast trend which indicates a fluid flow pattern occurs in that direction as an aquifer zone.