Reservoir evaluation method of the BSEM through the inversion constrained by seismic and well log information

Electrical logging information is the foundation for evaluating the oil saturation of the reservoir. Through the resistivity/conductivity data, the oil saturation can be calculated through Archie's law, Waxman-Smits model, or other conductivity models (Archie, 1942, Waxman and Smits, 1968). Since the well log is regarded as 'a partial view' for the whole exploration area, it's difficult to detect the oil-saturation variation far away from the borehole for the complex petroleum reservoir. Thus, the estimation results based on the log information are inevitably restrained by the well location.

The borehole-surface electromagnetic method (BSEM), which excites electromagnetic waves in the borehole and receives signals on the ground, is a promising technique owning the advantages of flexible deployment and large exploration area compare to the logging method. Combining with the seismic and electrical log information, the constrained inversion over the electromagnetic data is implemented in data processing, and the high-resolution results of the electrical properties can be obtained (He et al. 2010). Therefore, potential benefits would be had if we use the BSEM to calculate the oil saturation.

In this study, we deployed the BSEM in the exploration area, and the electrical resistivity and polarizability of the reservoir were inverted using the Cole-Cole model (Pelton et al., 1978). By means of Archie's law, the oil saturation of the reservoir was calculated. The saturation level of the reservoir is perfectly revealed as a form of section diagram in the vertical depth as well as lateral direction. Ultimately, the result is verified by the production testing in the well.