ANALISIS PETROFISIKA DENGAN METODE DETERMINISTIK DAN PROBABILISTIK SERTA PERHITUNGAN VOLUME HIDROKARBON DENGAN METODE WELL BASIS PADA SUMUR MG-04 DI STRUKTUR MUSI, CEKUNGAN SUMATERA SELATAN PT. PERTAMINA EP REGION SUMATERA

Well logging is a measurement technique to obtain the subsurface data using instrument inserted into wellbore, to evaluate formation and rock characteristics identification beneath the surface. Formation evaluation aims to identify zones of reservoir rock, formation fluid type, and to obtain petrophysical parameters of reservoir rocks such as shale volume, rock porosity, permeability, water saturation at the research area, the well MG-04 were drilled in the Musi Structure, South Sumatra Basin, PT. Pertamina EP. The purpose of this research is identifying productive layer on an exploration well in Musi Structure, South Sumatra Basin. In addition, to determine the value of petrophysical rock parameters which recorded in a log curves generated during logging and calculating the volume of hydrocarbon in exploration well as a consideration, prior to further exploration and exploitation. This research using descriptive methods and petrophysical analysis. The descriptive method includes literature study of the basics concept on determining rock petrophysical parameters to be used. The analytical method using deterministic and probabilistic method to determine petrophysical parameters, also “well basis” method to calculate the volume of hydrocarbons. Based on wireline logs analysis, well MG-04 known has two reservoir zones, namely oil reservoir in zone 2 and gas reservoirs in zone 4. In zone 2, the reservoir rock is shaly sandstone with little amount of glauconite. In zone 4, the reservoir rock is limestone, so this is a necessary to analyze the shaly sandstone with different methods to the interpretation of limestone to obtain the correct value of petrophysical parameters. After calculation of petrophysical parameters in deterministic and probabilistical way with “wet-clay” models, obtained two log plot models that have close values, and it is known that the oil reservoir in zone 2 not potential for production, but gas reservoir in zones 4 the potential to do exploitation/ production. After the interpretation of petrophysical parameters, it is known in zone 4 has a net pay thickness 68.43 m, total porosity percentage 28.42 to 29.72%, effective porosity 25.57 to 26.32%, permeability 56376,2 mD, water saturation 13.49 to 15.35% and shale volume 5 to 10.5%. After obtaining reservoir petrophysical parameters, next step is hydrocarbon volume calculation using the “well basis” method, supported by pressure build up (PBU). Based on this analysis, it is known that total volume of gas in the reservoir hydrocarbon type is estimated at 5088.4 MMSCF. Keywords: physical properties of reservoir parameters, deterministic-probabilistic methods, well basis method, limestones, the volume of hydrocarbon gas type