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E4D User Guide

E4D User Guide

### Time-lapse Inverse Modeling

In time lapse inverse modeling, the starting model in most cases is the inverse solution from a baseline dataset. The reference model can be either the baseline inverse solution (i.e., the first solution in the time-lapse sequence), or the previous solution in the sequence.

All of the constraint options available in inverse modeling are also available in time-lapse inverse modeling, however space-time smoothness contraints are given by structural metrics 7 and 8. These compute the difference between the temporal change in log conductivity among spatially adjacent elements, where the temporal change for a given element is the log conductivity of that element minus the log conductivity of the same element at some reference time.

The functionality enabled by run mode ERT4 can be duplicated using repeated executions of mode ERT3. Run mode ERT4 automates the process for a list of surveys and reduces computation time. Users are encouraged to review the workflow for an inverse solution before beginning the time-lapse inversion workflow.

**Workflow for Time-lapse Inverse Modeling**

**Step 1: Mesh Selection**

- If mesh exists, go to step 2
- If mesh does not exist, create mesh using
**E4D Mesh Generation**

**Step 2: Inverse Modeling Input**

- starting conductivity model
- specify homogeneous distribution (eg. 0.01) in
**<e4d.inp> file** create*OR***conductivity file**

- specify homogeneous distribution (eg. 0.01) in
**survey file****output options file****inversion options file**- reference model
**conductivity file**

**Step 3: E4D Execution**

- Create
**<e4d.inp> file** **Run E4D**

**Output Files**

**conductivity files**- Named <tl_sig#.000> where # is the time-step as defined in the
**time lapse survey file list**. - Named <si.#> where # is the current iteration number for the current inversion time, and # restarts at zero with each new time-lapse survey.

- Named <tl_sig#.000> where # is the time-step as defined in the
**<run_time.txt> file****simulated data file****<e4d.log>**