The reaction forces in wellhead equipment due to the flow-back of nitrogen foam fracture fluids are analyzed. The forces in the flow-back lines are analyzed for both unchoked and choked lines. The reaction forces are found to be excessive and uncontrollable for unchoked lines with normal field equipment and procedures. The reaction forces in choked flow-back lines are controllable and a safe choke size can be determined for the anticipated wellhead pressure. A new technique for controlling blowdown operations is discussed and preliminary designs for equipment to be used in applying such a technique are given.