I cannot select my disk in Disk Utility

Sure you can. The disk is simply unmounted. Just select the grayed out entry, Macintosh HD which is the indented entry under Apple SSD SM025.... The click on the First Aid item in the Disk Utility toolbar. The volume should be mounted at the end.

Be sure you have booted from the Recovery HD for the above.

Repair the Drive for Sierra and El Capitan

1. Restart the computer and after the chime hold down the Command and R keys until the Utility Menu appears.
2. Select Disk Utility and press the Continue button.
3. Then select the indented (usually, Macintosh HD) volume entry from the side list.
4. Click on the First Aid tab in the toolbar and wait for the Done button to activate. Click on it, then quit Disk Utility.
5. Select Restart from the Apple menu.

Is your disk encrypted? If so, that's why it's grayed out. You might need to mount it and enter a passcode before you can repair it.