抄録
We are now executing a cooperative research project with UNOCAL in order to develop and apply geophysical technology for reservoir characterization and optimizing miscible flood enhanced oil recovery in carbonate reservoirs. This project aims to monitor the fluid behavior in carbonate reservoirs by time-lapse geophysical surveys such as 3-D seismic survey, VSP, cross-well technology and well logging. JNOC and UNOCAL decided to conduct this study at the Reinecke oil field in Texas, U.S.A., operated by UNOCAL, whose reservoir is Paleozoic dolomitic limestones.First, we interpreted the geometrical framework of the reservoir and described the reservoir in terms of P-P reflected wave volume and P-SV converted wave volume, both of which were generated from the data acquired in December, 1997. Based on these methods, we drew a detailed time structure map and found some new structural/sedimentological features of the reservoir.
Second, for reservoir characterization, we calculated the Vp/Vs ratio from the isochron P-P and P-SV 3D volumes and created a distribution map of the Vp/Vs ratio. We evaluated the distribution map as a predictive tool of carbonate lithology by using the relationship between the Vp/Vs ratio and the dolomite content established through well log analysis. Our initial interpretation suggests the correlation between the the seismically deduced Vp/Vs ratio and the dolomite content. There has been, however, difficulties in the evaluation at its advanced stage. Believing that such 3D seismic volume information should include some useful attributes of reservoir, we are continuing to evaluate the data for further reservoir characterization.
Third, we conducted a new 3D survey over the field in December, 1999, after Unocal started to inject CO2 to the reservoir in January, 1998. This is to monior the effect of the CO2 injection using the seismic attributes in those time-lapse data series. We successfully found some differences in and around the reservoir between the previous baseline sections and the rush sections of the monitoring survey. This evaluation will be completed with cross-equalizing the volume data sets calculated from the two, time-lapse surveys.
