The Application of Dispersion and Attenuation Seismic Attributes to Determine the Gas Saturation in the Low-Impedance Sandstone: A Case Study in the Sadewa Field, Indonesia

A porous low-impedance gas-saturated sandstone, can cause P-wave seismic signals to experience dispersion and attenuation. This phenomenon is commonly referred to as Wave-Induced Fluid Flow (WIFF). This paper discusses a methodology to determine gas saturation in the low impedance sandstone using dispersion and attenuation attributes. The Zoeppritz (AVO) approximation by Shuey is used to calculate the attributes from the partial angle stack seismic data. The methodology is applied to the seismic data from Sadewa Deepwater Field in, East Kalimantan, Indonesia. As it is observed that the density parameter also has a good relationship with the porosity of gas-saturated rocks, then the combination of dispersion, attenuation, and density attributes is used to determine the gas saturation. Based on cross-plot analysis at the Sadewa well, it can be concluded that the dispersion and attenuation attributes calculated from near-angle gather and mid-angle stack seismic data have a good correlation with the gas saturation log values. A more detail analysis shows that the best correlation is obtained when a combination attribute calculated by the equation of (AVFDp)0.5 / Dn is used, where AVF is the attenuation attribute, Dp is the dispersion attribute, and Dn is density. Gas saturation values in this study were computed using the linear regression equation derived from the cross-plot analysis between the (AVFDp)0.5 / Dn attribute and gas saturation (Sg), which is expressed as Sg=(AVFDp)0.510.3337.Dn−0.0086.