Automatic invasion correction of elastic logs or “let the tools speak by themselves”
Guilherme Fernandes Vasquez, Lúcia Dillon, Carlos Lopo Varela, Júlio Justen, Guenther Schwedersky Neto, Cassiane da Silva Oliveira Nunes, CLEIDE JEANE RIBEIRO BACELAR · 2005
Mud filtrate invasion may be a major issue in quantitative well-to-seismic calibration. Sonic and density log corrections for water and oil based mud invasion is easily implemented through Gassmann fluid substitution, once the real virgin and invaded zone saturations are known. In general, this can be achieved with deep and shallow resistivity logs. Nevertheless, there is not a common place regarding the depth of investigation of sonic tools beyond the borehole wall. In this paper we present a method of invasion correction based only on the elastic logs (compressional and shear sonic and density) that has an advantage of making no assumption on the saturation. In fact, the method extracts the saturation information from the elastic logs.