Mixed inversion using a coarse layer model

A system for creating an inverted deep-resistivity formation model comprising:

• a transmitter;
• a first receiver antenna at a first axial distance from the transmitter, wherein the first receiver antenna collects real shallow-resistivity measurements;
• a second receiver antenna at a second axial distance from the transmitter, wherein the second receiver antenna collects real deep-resistivity measurements and wherein the second axial distance is greater than the first axial distance;
• and
• one or more processors coupled to the first and second receiver antennas, wherein the one or more processors:
• obtain an initial resistivity log;
• derive an initial formation model based at least in part on the initial resistivity log;
• estimate deep resistivity measurements from the initial formation model, the deep resistivity measurements associated with a measurement range greater than that of the initial resistivity log;
• derive a reduced-complexity formation model from the estimated deep resistivity measurements, wherein the reduced-complexity formation model includes a lower number of coarser formation layers compared to the a higher number of finer formation layers included in the initial formation model;
• collect actual resistivity measurements with a range greater than that of the initial resistivity log;
• and
• invert the actual resistivity measurements to obtain look-ahead or look-around parameter values, said inverting using the reduced-complexity formation model.

A method of creating an inverted deep-resistivity formation model comprising:

• synthesizing deep-resistivity measurements based on a shallow-resistivity model created from real shallow-resistivity measurements;
• creating an equivalent deep-resistivity formation model based on the synthesized deep-resistivity measurements;
• creating an augmented deep-resistivity formation model by adding unknown formation layers to the equivalent deep-resistivity model;
• creating an inverted deep-resistivity formation model by performing an inversion on the augmented deep-resistivity formation model;
• and
• displaying at least a portion of the inverted deep-resistivity formation model.