POROSITY CHARACTERIZATION OF CARBONATE RESERVOIR FROM LINEAR PROGRAMMING SPARSE SPIKE ACOUSTIC IMPEDANCE INVERSION RESULT USING SINGLE ATTRIBUTE (CASE STUDY FIELD 'X' NORTH EAST JAVA BASIN)

摘要

Field "X" is located in the North East Java Basin. It has carbonate build up reservoirs interspersed with low acoustic impedance shales. Seismic inversion using linier programming sparse spike algorithms is used to evaluate the acoustic impedance distribution of the limestone lithology, the main reservoir in this field. Shale and limestone lithologies of the Kujung I formation show good separation on crossplot data from the ALFA-2 well. However, the crossplots of the Kujung II and III formations show poor distinction between the shale and limestone lithologies due to shale interbeds in these reservoirs. Low Acoustic Impedance (AI) values indicates gas is present in the reservoirs of the Top Kujung I Reef + 40ms, i.e. Zone 1, Zone 2, and Zone 3 where AI distribution ranges are 23000-28000 (ft/s)* (g/cc), 24500-28000 (ft/s)*(g/cc) and 25500- 28000 (ft/s)*(g/cc) respectively. While the potential of oil reservoirs in the Kujung III Formation + 40ms lies in Zone 1, Zone 2, Zone 3 and Zone 4 exhibit higher AI values with ranges of 27000-32800 (ft/s)*(g/cc), 26500-32500 (ft/s)*(gcc), 27500- 32000 (ft/s)*(g/cc) and 26000-32000 (ft/s)*(g/cc) respectively. Porosity characterization using a 1/AI attribute was performed to determine the relationship between neutron porosity and AI inversion results from the ALFA-2 well. The derived relationship had a correlation coefficient of 0.72 with an error of 0.069%. Potential gas reservoirs in Zone 1, Zone 2, and Zone 3 have porosities of 20-29%, 21-26% and 22-26%, respectively. While the potential oil reservoirs of Kujung III Formation in Zone 1, Zone 2, Zone 3, and Zone 4 exhibit porosity distributions of 20-25%, 20-26%, 20-24% and 20-27% respectively. Zone 1, Zone 2, Zone 3, and Zone 4 with the distribution of porosity distributions of 20-25%, 20- 26%, 20-24% and 20-27%.