Inversion of mud invasion of horizontal layered formation with induction logs in Mahuangshan area

Combining dual induction logging curves and eight lateral logging curves, we establish a two-dimensional resistivity forward model of horizontal layered formation (considering the borehole, the flushed zone, etc.) by Doll geometric factor theory. The resistivity of flushed zone, radius of mud invasion, resistivity of virgin formation are inversed with the least-squares method. For different layers, cyclic variable method is used to complete the inversion of two-dimensional formation. The calculation showed that the combined method is good at the inversion of dual induction logs of Mahuangshan area. Writing the code by FORTRAN language, the inversion is fast and the curves from inversion fit the measured logs well (absolute error is less than 0.001). The affect of mud invasion is removed, meanwhile the differences among oil layer, oil-water layer and water layer is enhanced. The interpretations from the inversion logs fit the tests better.