Repair of shallow casing leaks in oil wells

In a production oil or well installation the method of repairing damage, such as a leak, in an outermost damaged string of casing or production string positioned concentrically within a well conductor or drive pipe of larger diameter forming an annular space therebetween, said method comprising,

• determining the depth in the damaged casing string at which the damage exists,
• closing the bore of the damaged casing string at a selected distance below the damage therein,
• closing the upper end of the damaged casing string during the repair operation,
• providing access to the upper end of the annular space between the well conductor and the damaged casing string,
• providing a section of a protective casing string with a milling shoe at the lower end thereof, said protective string and said milling shoe being of a size to fit within the annular space formed between the damaged casing string and the well conductor,
• vertically positioning the milling shoe at the lower end of said section of protective casing string in the top of the annular space between said damaged casing string and the well conductor,
• drilling the section of protective casing string into the earth formation while removing the earth formation outside the damaged casing string,
• repeatedly connecting additional sections of protective casing string in end-to-end relationship to the first section milled into the earth formation and continuing to mill the protective string into the earth formation until the milling shoe at the lower end of the protective string is a selected depth below the damage in said damaged casing string,
• pumping cement into annular spaces formed on both sides of the protective string to cement the protective string to the earth formation on one side thereof and to the damaged casing string on the other side thereof to a selected distance below the damage therein,
• allowing cement to harden, and
• opening the previously-closed upper end of the damaged casing string and the bore throughout said string.