Self activating seal assembly backup

A seal assembly, comprising:

• a first member, the first member formed of a first material;
• a second member overlapping with the first member, the second member formed of a second material, the first and second members defining an overlapping fluid leakage path;
• an unintentionally breached primary seal positioned in the overlapping fluid leakage path, the primary seal originally configured to prevent fluid from passing from a first side of the overlapping fluid leakage path to a second side of the overlapping fluid leakage path but over time failed;
• and
• a backup seal structure positioned in the overlapping fluid leakage path downstream of the fluid from the unintentionally breached primary seal, the backup seal structure including an expanded metal backup seal comprising a cement like material that resulted from a metal that has expanded in response to hydrolysis.

A well system, comprising:

• a wellbore located in a subterranean formation;
• and
• a seal assembly positioned within the wellbore, the seal assembly including:
• a first member, the first member formed of a first material;
• a second member overlapping with the first member, the second member formed of a second material, the first and second members defining an overlapping fluid leakage path;
• a primary seal positioned in the overlapping fluid leakage path, the primary seal configured to prevent fluid from passing from a first side of the overlapping fluid leakage path to a second side of the overlapping fluid leakage path;
• and
• a backup seal structure positioned in the overlapping fluid leakage path downstream of the fluid from the primary seal, the backup seal structure including an expandable metal body configured to expand in response to hydrolysis, wherein the expandable metal body:
• is configured to be isolated from the fluid until such time as the primary seal unintentionally breaches;
• and
• only after the primary seal unintentional breaches is the fluid allowed to contact the expandable metal body to form a permanent backup seal.