Seismic Attributes and Acoustic Impedance Inversion Analysis to Deliniate Miocene Net-Pay Sands in Deep-Water Sadewa Field, Kutai Basin, Indonesia

Abstract The deep-water Sadewa Field is located about 45 km east-northeast offshore of the Mahakam delta, North Kutai Basin, East Kalimantan Indonesia, at water depths of 1,000 to 2,800 feet. Most of the producing reservoirs in Mahakam delta were the Early Miocene sand reservoirs deposited in shallow water of shelf delta. During Miocene the study area was submerged under shallow sea level and there were multiple small-scale low-stand system-tracts deltas deposited along the Sadewa shelf slope. The coarse-grain clastic sediments were fed the shelf slope onto the channels and local fans of the deltas. The local fans were filled with thicker, cleaner, and more porous sands as they had bigger accommodation space and higher depositional energy than the channels. Seismic stratigraphy analysis, guided by seismic attributes, identifies and maps the channel and fan facies. This research focuses on delineating the Sadewa Miocene net-pay sand reservoirs using seismic attributes and inversion. The post-stack AI inversion is applied to mapping the associated lithology, porosity, and pore fluids. The net-pay sand was calculated based on the stratigraphic thickness between the two top target zones (gross sand) with cut-off values of VCL < 40%, POR > 10%, and SW < 70% for each target reservoir. Based on the cross plot between seismic attributes and net-pay thickness, shows that net-pay thickness is associated with high RMS seismic amplitude and low attribute variance. The result shows that RMS seismic amplitude is related to the presence of hydrocarbon fluid and the variance is related to the facies and reservoir geometry in terms of continuity and reflector alignment. Thus, using the RMS amplitude*1/Variance attribute can provide answers for hydrocarbon production needs and determine which geometry and sediment are more prioritized. Later, this attribute can be used to see the distribution of net-pay sand with facies and reservoir geometries with high thicknesses.