Methods, apparatus and systems for creating wellbore plugs for abandoned wells

A formation plug formed in situ in a wellbore traversing a formation, comprising:

• solid bismuth alloy material having a solid first cylindrical body portion, a dendritic web extending outwardly from and around at least a portion of said solid first cylindrical body portion, and a solid second cylindrical body portion of smaller diameter than the first
• cylindrical body portion, a shoulder being defined at a transition from said first cylindrical body portion to said second cylindrical body portion.

A system for plugging a wellbore traversing a formation, comprising:

• a barrier deployed in the wellbore at or below a relatively permeable layer of the formation;
• and
• a wellbore tool assembly including a packer deployed at a relatively impermeable layer of the formation, a tool body extending through the packer in the wellbore and comprising a fluid passageway having a fluid inlet located above the packer, a fluid outlet located below the packer, and a pump between said fluid inlet and fluid outlet for pumping fluid from above the packer to below the packer in the wellbore, said tool body including a bismuth alloy storage chamber storing bismuth alloy and adapted to release the bismuth alloy into the wellbore towards the barrier.