Owners or operators of oil, gas or disposal wells heretofore drilled and completed within the city shall not be required to procure the initial municipal drilling permit hereinabove provided; however, it shall be incumbent upon such owners and operators to furnish evidence of liability insurance coverage and post the bond for the restoration of the land and plugging of the well upon its abandonment in the form and amount above required for issuance of a municipal drilling permit at the time of application for the annual renewal permit as hereinafter provided, or within 60 days after the effective date hereof, whichever shall first occur, as a condition of continuing the operation and maintenance of any well heretofore drilled and prior to commencing any swabbing, cleaning or reworking operations of all oil, gas and disposal wells heretofore or hereinafter drilled within the city. All existing wells shall also comply with all of the following provisions of this chapter.