The BA-WELL01-06 well is located in BA Field, Kutai Basin and is the Working Area of PT. Pertamina Hulu Indonesia Region 3 Zone 9. The formation in this study is the Balikpapan Formation. The method used in this research is subsurface geological mapping, with data in the form of wireline logs, seismic and other supporting data. Analyzes were carried out to produce facies and correlation analysis, petrophysical analysis, subsurface maps and calculating initial reserves (OOIP) in the study area. Based on the results of subsurface interpretation, there are five (5) identified facies, Distributary Channel Sandstone Facies, Distributary Mouth Bar Sandstones, Mud Flat Shales, Crevasse Splay Sandstones and Coal Facies. Four (4) identified Facies Associations, Channel Distributary Facies Association, Mouth Bar Facies Association, Mud Flat Facies Association and Crevasse Splay Facies Association. There are anticline folds trending northeast-southwest and thrust faults trending northeast-southwest. The calculation results of Original Oil in Place reserves with a Bulk Reservoir Volume of 4268.91 acre.feet and BOI 1.08, the first calculation using the petrophysical parameters of the BA-WELL01 well, the reserves are 2,564.7 (MSTB) and the second calculation using the petrophysical parameters of all wells, the reserves are 2,152,68 (MSTB).

Keywords: Facies, Subsurface Geology, Original Oil in Place