17:15 〜 18:45
[SEM12-P02] 3-D joint inversion framework with hybrid structural and petrophysical couplings
キーワード：Joint inversion, Magnetotellurics, Seismic tomography, structural similarity, petrophysical relationship
Joint inversion that utilizes multiple geophysical datasets is a practical way to produce models with reduced uncertainty and improved resolution. Different from single inversion, joint inversion needs to establish the correlation between different geophysical parameters. One of the keys to unlocking the advantages of joint inversion lies in devising a reasonable coupling mechanism. Currently, mainstream coupling mechanisms fall into two categories: "petrophysical" and "structural" couplings. The former assumes that there exists a relationship between different physical parameters and correlates them via a theoretical, empirical, or statistical petrophysical relationship (e.g. Sun and Li, 2015); the latter enforces the models of different physical properties to have similar spatial structures (e.g. Gallardo and Meju, 2004).
Most joint inversion studies focus on utilizing either "petrophysical" or "structural" couplings in a specific study area. However, in situations where prior petrophysical reference relationships exist, relying solely on "structural" coupling is insufficient to enforce relationships between different geophysical parameters. Meanwhile, "petrophysical" coupling usually heavily depends on the accuracy of empirical relationships, and using only "petrophysical" coupling in the whole model space can lead to biased results caused by inaccurate relationships. Therefore, to comprehensively leverage multi-geophysical, petrophysical, and geological information in joint inversion, we propose a 3D joint inversion framework that incorporates both structural and petrophysical couplings. This framework provides a chance to use hybrid "petrophysical" and "structural" couplings simultaneously. This is important in the case of complex geology.
In this newly developed joint inversion framework, the following options are available:
1) MT (Usui, 2015; Usui et al., 2017; Usui et al., 2021), seismic (Rawlinson and Sambridge, 2003; 2004; 2005) stand-alone inversion;
2) MT, seismic constraint inversion guided by geological information or other geophysical models using (a) structural information; (b) petro-physical information; (c) hybrid structural and petrophysical information:
3) Joint inversion of MT and seismic using (a) structural information; (b) petrophysical information; (c) hybrid structural and petrophysical information in each iteration, or using specified iteration ratios considering different convergence speeds of different geophysical methods.
This framework is suitable for almost all situations in which we can obtain the corresponding data and prior information. The effectiveness of the framework is validated through synthetic model verification and field data applications. Of course, joint inversion is not simply "1+1". Beyond methodology and this framework, if we want to unlock the merits of joint inversion, it is necessary to master different geophysical methods (not necessary for constraint inversion) and have a deep understanding of the geophysical, geochemical, petrophysical, and geological information of the study area, as well as extract key prior information that can provide help to our inversion and interpretation.
Most joint inversion studies focus on utilizing either "petrophysical" or "structural" couplings in a specific study area. However, in situations where prior petrophysical reference relationships exist, relying solely on "structural" coupling is insufficient to enforce relationships between different geophysical parameters. Meanwhile, "petrophysical" coupling usually heavily depends on the accuracy of empirical relationships, and using only "petrophysical" coupling in the whole model space can lead to biased results caused by inaccurate relationships. Therefore, to comprehensively leverage multi-geophysical, petrophysical, and geological information in joint inversion, we propose a 3D joint inversion framework that incorporates both structural and petrophysical couplings. This framework provides a chance to use hybrid "petrophysical" and "structural" couplings simultaneously. This is important in the case of complex geology.
In this newly developed joint inversion framework, the following options are available:
1) MT (Usui, 2015; Usui et al., 2017; Usui et al., 2021), seismic (Rawlinson and Sambridge, 2003; 2004; 2005) stand-alone inversion;
2) MT, seismic constraint inversion guided by geological information or other geophysical models using (a) structural information; (b) petro-physical information; (c) hybrid structural and petrophysical information:
3) Joint inversion of MT and seismic using (a) structural information; (b) petrophysical information; (c) hybrid structural and petrophysical information in each iteration, or using specified iteration ratios considering different convergence speeds of different geophysical methods.
This framework is suitable for almost all situations in which we can obtain the corresponding data and prior information. The effectiveness of the framework is validated through synthetic model verification and field data applications. Of course, joint inversion is not simply "1+1". Beyond methodology and this framework, if we want to unlock the merits of joint inversion, it is necessary to master different geophysical methods (not necessary for constraint inversion) and have a deep understanding of the geophysical, geochemical, petrophysical, and geological information of the study area, as well as extract key prior information that can provide help to our inversion and interpretation.