since the faults are sealing you might assume the closure to be the drainage area
but usually the drainage area of a well can be calculated by finding you EUR then that will by the well OIIP
then use the equation of OIIP to estimate your drainage area

N = A*h*NTG*por*(1-Swi)/Bo

hope this gives some insight
good luck
you can ask your mentor
or any sr. res engineer there