Chijioke, based on the review of subroutine oil_spill_2d, even if you set the # of soluble components to zero, the program will still allocate array size 1 for related variables. So it may not matter whether you set the number to zero or one (check result difference to confirm).
However, you can setup the Fraction Mass to zero for the soluble component. That way, no tracer should be present. Also check the total oil mass to confirm that none is lost into water.
Let me know whether this work,
Hailiang