Advanced Inversion Strategies using a New Geophysical Inversion and Modelling Library

Geophysical inverse problems often suffer ambiguity and yield fuzzy subsurface images. Often satisfactory results can only be obtained if additional information is incorporated in the inversion. The latter can be structural information about known boundaries or information about the parameters or their limits. However, this is rarely done by the available inversion software packages. We present an extremely versatile inversion and modeling framework for solving inverse problems on arbitrary geometries. Irregular meshes are used to incorporate known discontinuities. The generalized minimization scheme allows for controlling every model cell and every cell boundary individually. Moreover the subsurface can be subdivided into regions that represent different geological units or different physical properties. For each region the model transformation function can be set, e.g. for incorporating petrophysical relations, logarithmic barriers or a combination of it. The constraint type, e.g. smoothness, and the strength and characteristics can easily by varied in the course of iterations. Different joint inversion schemes are easily derived from that. By hand of a synthetic ERT study we show how the approach can be used to imagine small contrasts within a contrasted environment and to monitor small changes with time-lapse inversion.