US Patent 11643879 Nested drill bit assembly for drilling with casing

A nested drill bit assembly is disclosed for drilling a wellbore, comprising a parent bit and at least one child bit nested within the parent bit. Each bit in the nested drill bit assembly may be driven by a respective casing that gets cemented in place as part of a drilling with casing system. The parent bit and child bit(s) may be rotated together, with the parent bit and child bit collectively defining a contiguous cutting profile for drilling an initial segment of the wellbore. A driver is then lowered into the casing for connection to the child bit to drill beyond the parent bit. The driver may be configured as a drive bit for drilling through material leftover from a cementing operation prior to connecting to the child bit.