Gaps tend to be closed before major moves. Expect it to reach 12eu again before closing upside gaps.
If it doesn't close it now there will be a major move on the downside this year to still close it. Just like the Jan '19 gap that got closed in Aug that same year.
First fib to cross is the 0.3 at 18,5eu. After that 22eu. Shell is lacking momentum compared to the AEX.