Abstract: A device for introducing high-pressure fluid through a well having a vertical passage with at least one valve and into a well having a well tubing into said vertical passage, has a lower part removably attachable to the well tubing, a hollow mandrel adapted to extend through the inner passage of the lower part and having a passage through which a high pressure fluid can be introduced, an upper part firmly connected with the mandrel to hold the mandrel and movable relative to the lower part between a distal position in which the upper part is spaced from the lower part and the mandrel is not introduced into the well tubing and a proximal position in which the upper part is located close to the lower part and the mandrel is introduced into the well tubing and passes through an area of the well tubing provided with the valve, so that when the high pressure fluid is introduced through the mandrel it can not affect the valve, the upper part having a port communicating the inner passage of the upper part with an ou