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Getting Big Production Gain in Mature Field by Identifying the Hydrocarbon Potential From Layers With Anomalous Log Reading and Complex Reservoir Architecture: A Case Study From Bunyu Field, Tarakan Basin


Bunyu Field is one of the backbone field of Pertamina EP – the Indonesia government-owned oil and gas company. The production of this field started since 1937 until today. Interestingly nearly 80 year of production, this field experience its second peak of production since 2010 by primary recovery of its deltaic reservoirs. Completion of reservoirs with anomalous log reading is the key to this success. Reinterpretation of cores with regard to the newest facies model and modern sedimen; well logs as input for sequence stratigraphy correlation; 3D seismic for building the faults and geometry framework; and petrophysical properties to know hydrocarbon content of sand layers - was conducted as an integrated study to challenge the unique character of the reservoir. Facies analysis from core and log concluded that deltaic reservoirs are widely distributed in this field with 5 major litofacies that developed as three different depositional facies association: distributary channel (proximal and distal), bars and delta plain deposit. The well correlation and seismic study of this area showing that the sand bodies having high degree of compartmentalization, making it possible to have different hydrocarbon contact to one another. Among all the re-interpretation result, the Petrophysical properties is the most pristine result because of its unique anomaly. This anomalies is low resistivity zone. A deeper analysis of core that include SEM, XRD, Petrography, its litofacies and subsurface analogue showing that the low resistivity anomaly in log is mainly contributed from the conductive ferromagnesian mineral including Pyrite and Siderite that deposited as replacement mineral or pore filing cement. Based on the idealized facies model in bunyu, there is a relation between parasequence stacking pattern to detail mineralogy content, and now the low resistivity zone can be well-predicted.