Seismic amplitude anomalies by using rock physics and AVO in Sirikit field area, Pitsanulok basin, Changwat Kamphaengphet

Abstract

Seismic amplitude anomalies are the significant tools as a hydrocarbon-indicator; however, these anomalies can be originated by many causes. To investigate the causes of anomalies and classify their AVO (Amplitude-Versus-Offset) classes are the aim of this research. In this study the data from Sirikit petroleum field in Pitsanulok Basin were used. The techniques used in this study are Rock physics and AVO modeling. Firstly the several cross-plots of petrophysical parameters were performed. Then, fluids-substitution was modeled with 100% of water and 80% of gas and oil to observe the variations of impedances with particular fluids. Based on the models, acoustic impedance trends were used to classify classes of AVO responses. Lastly, Synthetic AVO gathers were generated in order to observe the seismic amplitudes with different types of fluids. The interested sand formations in this study area are 868-878 meters and 1280-1430 meters. As the result, the depth trend analysis showed that if we considered the interface at shales overlie sand, both of shallow and deep sands have acoustic impedance of sands lower than shales represented as class 2 or class 3 according to Rutherford’s AVO classification system. In AVO modeling, the two interested sand have intercept and gradient decreasing with angles and give negative reflection coefficient that corresponding with the previous analysis and the geology of the study area, However, the bed thicknesses in this study are mostly thinner that tuning thickness especially at deep depth.