Dear reginto,
What you are really questioning is something called a Habendum Clause, which is an essential part of the oil and gas lease.
Although there are numerous variations of habendum clauses, a typical habendum clause will read substantially as follows:
This lease shall remain in force for a term of ___ years from this date, and as long thereafter as oil or gas or either of them is produced from said lands, or on lands pooled or unitized therewith.
Find that specific clause in the existing lease and you will see that the lease has likely moved from the Primary Term of the lease into the Secondary Term of the lease.
Congratulations on having production and getting royalty checks.
Best,
Buddy Cotten