Circulation System for Retrieval of Bottom Hole Assembly During Casing While Drilling Operations

In a casing-while-drilling operation wherein a casing string gripper is suspended by a top drive of a drilling rig, the casing string gripper having slips that engage the upper end of the casing string to support and rotate the casing string, a circulation system that pumps a fluid through a conduit leading to a flow passage in the casing string gripper and down the casing string, and a bottom hole assembly releasably mounted at a lower end of the casing string for drilling a wellbore, a method of retrieving the bottom hole assembly, comprising:

• (a) mounting a circulation sub to the casing string below the casing string gripper, the circulation sub having a lateral outlet;
• (b) connecting a return flow line from the outlet to the circulation system;
• (c) placing a retrieval tool in the casing string and pumping fluid from the circulation system downward through the flow passage in the casing string gripper, thereby assisting in moving the retrieval tool down the casing string;
• (d) engaging the retrieval tool with the bottom hole assembly, defining a retrievable unit;
• then
• (e) ceasing to pump fluid down the casing string and beginning to flow fluid downward in an annulus of the casing string and back up the casing string, causing the retrievable unit to move upward;
• and
• (g) while the casing string is still suspended by the casing string gripper, diverting the fluid flowing up the casing string through the outlet in the circulation sub and through the return flow line to the circulation system without passing through the flow passage in the casing string gripper.

A casing-while-drilling system, comprising:

• a casing string gripper adapted to be suspended by a top drive of a drilling rig, the casing string gripper having a set of slips that move between a retracted and a gripping position in engagement with an upper end of a casing string to suspend and impart torque to the casing string;
• a circulation sub mounted to and forming part of the casing string for rotation therewith, the sub having a sidewall containing a circulation sub port;
• a housing mounted around the sub, the sub being rotatable relative to the housing;
• seals between an exterior surface of the housing and an interior surface of the sub above and below the circulation sub port;
• a housing port through a sidewall of the housing;
• and
• a flowline connected to the housing port and to a fluid circulation system for discharging fluid flowing up the casing string to the fluid circulation system