Downhole apparatus and method

摘要

This invention relates to apparatus for generating a fluid pressure pulse downhole. One such apparatus (12) is disclosed which comprises an elongate, generally tubular housing (46) defining an internal fluid flow passage (48); a first device (50) for controlling the flow of fluid along a first flow path (52) which communicates with the internal fluid flow passage, to generate a first fluid pressure pulse; and a second device (54) for controlling the flow of fluid along a second flow path (56) which communicates with the internal fluid flow passage, to generate a second fluid pressure pulse. The first and second devices are both provided in the housing, take the form of a cartridge which can be releasably mounted in a space (80, 82) provided in a wall (60) of the housing, and house a valve (74) having a valve element (76) and a valve seat (78), the valve being actuable to control the flow of fluid along the respective flow path.