APPLICATION OF STOCHASTIC SEISMIC INVERSION AND SEISMIC STRATIGRAPHY FOR MAPPING LTAF THIN SAND RESERVOIRS IN THE COMPARTMENTALIZED UNTUNG FIELD, JABUNG BLOCK, SOUTH SUMATRA

• Main Author: Jocelynn Untung, Ilona
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/69105
• Institution: Institut Teknologi Bandung

Untung Field located in the Jabung block, South Sumatra basin, to be exact, about 50 km southeast of Jambi City. This study focuses on the Lower Talang Akar formation (LTAF), based on well data, this formation deposited in three types of environments; Braided River, Meandering Channel, and Anomostosing Channel or Coastal Plain. LTAF compartmentalized into three compartment due to the major fault that divides Untung Field. The target reservoir in the LTAF is thin sandstone intercalate by coal, it is difficult to identify by the seismic data only. Therefore, a geostatistical approach is needed by performing a stochastic inversion to analyze the LTAF reservoir in the Unutng field in order to be able to resolve thin layers of sandstone and see the direction of the distribution of deposition. This study was used 3D Pre-Stack Time Migration (PSTM) seismic data, with 64 data wells and two wells for validation. Based on the tuning thickness analysis, the thickness of individual sandstones in the LTAF is below the vertical seismic resolution, with the stochastic inversion, the unresolved sandstone can be resolved. The stochastic inversion process carried out with 30 realizations and 150 iterations. From these results the best realization is selected based on the smallest error map value with a percentage of truth 83.6%. In this study, the results of the stochastic inversion focus on the density 3D volume where the density can best separate the lithology of sandstone, shale, and coal. The density value used is based on the results of sensitivity analysis. In addition, the direction of deposition of the reservoir is Northeast – Southwest and North-South. By integrating seismic stratigraphy and stochastic inversion results, channel fill and floodplain sediment patterns can be seen as facies of the LTAF reservoir.