Geophysics Over High Enthalpy Fields: Lessons from RLM-3D Magnetotelluric and Joint Inversions

Abstract

Practical data QC and 3D inversion workflows are now routinely available to reliably handle multiphysics datasets in quantitatively integrated 3D modeling. These result from direct project experience and related software development during hundreds of 3D projects with magnetotelluric (MT) and gravity data sets from many of the world’s producing and prospective high enthalpy geothermal fields – as well as in other natural resource exploration markets. Our 3D inversion engine RLM-3D has evolved to address typical shortfalls and challenges of MT data sets, like separate locations for electric and magnetic sensors (sparse, telluric/T-MT surveys), or static distortions of electric fields: the code allows for accurate modeling of inter-station impedances, and joint inversions of galvanic distortion parameters along with the 3D resistivity. A number of regularization options allow tuning smoothing control to the specific exploration case; e.g. regularization tear surfaces to correctly account for sharp discontinuities at faults or other horizons. RLM-3D also contains solvers for CSEM, gravity, gravity gradiometry, magnetics, and MEQ data (Vp, Vs, event re-locations), and therefore when available, these can be incorporated into the inversion modeling workflow, using a cross-gradient technique that promotes structural similarity between the inverted properties within a joint inversion. The same technology also provides for structural constraints from other sources, like geological, concept model scenarios under investigation, near surface dip and strike data to constrain shallow structural trends, fault surfaces, and seismic reflection volumes when available.