Abstract
Water hammer shock pulses are generated when the flow in a length of tubing is interrupted in a time that is much shorter than the pulse duration. Water hammer tools used for well intervention incorporate a poppet valve that closes very quickly and a pilot valve that then causes the valve to open so that the flow is stopped periodically. The upstream water hammer shock generates an impulsive mechanical load on the bottom hole assembly (BHA) that can be used for milling or other applications. The intense axial vibration also extends the reach of tubing in long tortuous completions. These tools also generate a significant rarefaction shock downstream of the tool, comprising a sudden drop in pressure that can extend over 100's of meters of wellbore. The rarefaction pulse propagates into the dead volume beneath the tool and upstream into the annulus. The rarefaction shock causes flow to surge into and out of the formation. The extent and duration of these pulses has been observed in surface tests. Case histories of well cleaning and stimulation applications are described. Best practices for operation include squeezing treatment fluids into the formation followed by flow circulation to shock surge the completions.
