Toolstring and method for inner casing perforating, shattering annulus cement, and washing the first annulus in a second casing

A casing annulus cleaning tool string comprising:

• a drill pipe string with:
• a conveyed perforation gun;
• and
• a cement shattering device,
• wherein both the perforation gun and the cement shattering device are arranged near said drill pipe string's lower end, for being lowered into a casing with an annulus cemented casing portion about said casing in a petroleum well,
• wherein said perforating gun is arranged with:
• first, shallow-perforating charges for shooting first, shallow perforations through said casing portion into a first annulus, said shallow-perforating charges arranged for leaving a surrounding second casing intact;
• wherein said shattering device is arranged for being activated after said shallow-perforating charges to provide combustion energy through said shallow perforations to disintegrate all or part of said cement within said first perforated annulus, and
• wherein a washing tool is arranged above said perforation gun and cement shattering device on said drill pipe string, said washing tool for washing out said shattered cement from said annulus.