Publications

Some wells produce hydrocarbons from carbonate reservoirs. Hydrocarbon in the form of fluid is stored in pores of rock. The pores of the rocks may contain gases other than hydrocarbon gases. Not all the gases contained in carbonate reservoirs have economic value. Another gas that has been found in drilling is Carbon dioxide (CO2). When a formation containing a large percentage of CO2 is produced, the CO2 will be produced as well. So the percentage of CO2 in the formation must be known. The method to determine the distribution of CO2 is to find the relationship between Vp, Vs and CO2 saturation, where Vp is compressional velocity and Vs is shear velocity. We use log data that has carbonate characteristic. From the sonic log data we can predict Vp and Vs. We do not have Vs, so we calculate Vs from fluid replacement model and the Castagna formula. After we obtain Vp and Vs, we can use fluid substituion based on Biot-Gassmann formula for knowing the change of Vp and Vs in CO2 saturated condition. Then, we make seismic wave modelling with Amplitude Versus Offset (AVO). We analyze seismic wave to CO2 saturation condition about 0-100% using the zero offset synthetic. From this result modeling, the Vs increase by the increasing CO2 saturation , whereas Vp decrease. Vs data has big increasing when CO2 saturation below 20%. whereas other data the increase is linear. The Vs increase is very small, about 0.100 m/s. We use trace math to analyze the amplitude of anisotropy seismic modeling. Seismic respone in anisotropy and isotropy media has a similar trend in trace but with different characteristic. In anisotropic media the seismic modelling result is more complex and clearly amplitude than the isotropic media. Keywords : CO2, Vp, Vs, Saturation, Anisotropy