Identification of Coal Bed Methane Layer in Riau Area Based on Inversion Study of Acoustic Impedance, Spectral Decomposition and Seismic Attribute

Energy diversification is needed to overcome the energy shortage. By diversification, it would require the identification of new energy resources that is methane gas. One of methane gas reservoir is coal layer. Seismic data processing has been done to map a coal layer containing methane gas call as coal bed methane in central Sumatra basin zone, Riau area. It can be identified by acoustic impedance inversion, spectral decomposition and attribute seismic. The seismic inversion is controlled and verified by well data consisting of gamma ray logs, density log, resistivity log and sonic log. The result of data processing shows that there is coal bed methane at 1560 feets depth on Korinci formation. This is determined from well seismic tie so as to obtain gamma ray value of 52-55 API, density of 1.5 - 1.55 g/cc, resistivity of 0.68 to 0.76 ohmmeter, acoustic wave velocity of 5988.3 - 6330.2 ft/s, acoustic impedance of 8000 - 9600 ((ft/s)*(g/cc)) and tuning frequency of 30 Hz. Other data processing result shows that coal bed methane is also found in Telisa formation at 1526 feets depth. By the same process obtained gamma ray value of 28 API, density of 1.28 - 1.49 g/cc, resistivity of 1.33 - 1.44 ohmmeter, acoustic wave velocity of 6616.54 - 6845 ft/s, acoustic impedance of 8,800 - 10,200 ((ft/s)*(g/cc)) and tuning frequency of 34 Hz. The low value of density, acoustic wave velocity and gamma ray indicate coal bed methane at Korinci and Telisa formation. Coal bed methane layer thickness is 65 feets at 1555 to 1620 feets depth in Korinci formation and 78 feets at 1475 to 1540 feets depth in Telisa formation.