Del. Code tit. 7, § 6121

Subject to the lessee’s right to surrender, the lessee shall commence operations for the drilling of a well within 5 years from date of the lease and commence production within 3 years of discovery of oil, gas, sulphur or other minerals in paying quantities, unless the Secretary shall have, for cause, granted an extension of time for such act. In addition, the lease shall have such exploratory, drilling and producing requirements as the Secretary deems necessary to encourage the exercise of due diligence on the part of the lessee.