In the [i]minesweeper[/i] game below, each unopened square (for example, the one in the top left corner) is either empty or contains a mine. The other squares are empty and display the number of mines in the neighboring 8 squares (if this is 0, the square is unmarked). What is the minimum possible number of mines present on the field?

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[i]2016 CCA Math Bonanza Team #4[/i]
1. **Label the grid**: Let's label the rows from top to bottom as A through K and the columns from left to right as 1 through 13. This will help us refer to specific squares easily.

2. **Identify forced mines**: 
   - The square D5 has a 1, and the only available square for a mine is C6. Therefore, C6 must contain a mine.
   - Similarly, E7 has a 1, and the only available square for a mine is D7. Therefore, D7 must contain a mine.
   - E11 has a 1, and the only available square for a mine is D11. Therefore, D11 must contain a mine.
   - I8 has a 1, and the only available square for a mine is H8. Therefore, H8 must contain a mine.
   - The 4 in B3 implies that A2, A3, A4, and B2 all have mines.

3. **Eliminate possibilities**:
   - Since B3 is surrounded by 4 mines, B4 cannot have a mine.
   - The 1 in C5 is satisfied by the mine in C6, so B6 cannot have a mine.
   - Therefore, A6 must contain a mine.

4. **Continue with forced mines**:
   - The 1 in F7 is satisfied by the mine in E7, so E6 is satisfied, and D7 cannot have a mine.
   - The 3 in D6 requires three mines around it, and since D7 cannot have a mine, C7 must have a mine.

5. **Move to another section**:
   - The 1 in F10 is satisfied by the mine in E11, so E10 and F11 cannot have mines.
   - The 3 in D8 requires three mines around it, and since D9 is satisfied by the mine in D11, C8 or C9 must have a mine. But since D9 is satisfied, C10 cannot have a mine.
   - Therefore, C11 must have a mine, eliminating C9 from having a mine, so C8 must have a mine.

6. **Analyze the bottom section**:
   - The 1 in J12 is satisfied by the mine in J12, so I12, J13, I13, and H13 cannot have mines.
   - The 1 in H13 requires a mine in G13.
   - The 2 in F12 is satisfied by the mines in G13 and H12, so all neighboring squares in this area have no mines.

7. **Continue with forced mines**:
   - The 1 in I9 is satisfied by the mine in I8, so J8 cannot have a mine.
   - Therefore, K8, K9, K10, and K11 must contain mines.
   - The 1 in J12 is satisfied, so K12 does not have a mine.

8. **Analyze the remaining squares**:
   - The 2 in H8 requires a mine in I7.
   - The 1 in H7 is satisfied, so I6 cannot have a mine, forcing I5 to contain a mine.
   - The 1 in H5 is satisfied, so I4 does not contain a mine.
   - The 2 in H4 requires mines in I3 and H3.
   - The 2 in G4 is satisfied, so G3 cannot contain a mine.

9. **Final analysis**:
   - The squares C1, D1, and E1 are not uniquely determined, but placing a mine in D1 satisfies the conditions for C2, D2, and E2.

10. **Count the mines**: Pooling everything together, we count the number of mines marked on the diagram.

The final answer is $\boxed{23}$