Thanks for the softball question. The number of new fields that must be found to maintain current production is some number 1 to n -- it depends on the size of the fields.
Actually the number may be zero, or even negative. The facts as we know them now, is that the amount of oil left is a fairly large multiple of present annual production. Fewer fields might actually produce more than the present, over some extended time period.
It seems unlikely that production could be increased for more than a short time period, but such an event does not violate logic, and is therefore within the realm of possibility. The future is bound by the present but it is not bound by our view of the present.