GROUT DELIVERY

A grout delivery system (10) for delivery of a grout as a flowable substance comprising a mixture of two grout component materials at a downhole location. The grout delivery system (10) comprises an elongate body (31) comprises two reservoirs (41, 42) configured as cartridges (51, 52) for receiving respective charges of the two grout component materials. The two cartridges (51, 52) each comprise a piston (61). A selectively openable closure configured as a valve (62) is provided adjacent the bottom end (57) of each cylinder (53). Each piston (61) is operably to progressively advance towards the valve (62), thereby expelling grout component material from the respective cartridge (51, 52) through the valve. When the grout delivery system (10) is at the desired location downhole and a fluid seal established downhole, fluid such as water is pumped into the drill string and pressurised. Initially, fluid pressure is exerted on the two pistons (61) indirectly via an actuator (80) to initiate movement of the two pistons in concert. At a later stage, fluid under pressure is exerted directly on the pistons (61) to continue their movement in concert. Retrieval of the grout delivery system (10) may necessitate relief of the hydrostatic pressure differential across the fluid seal established downhole so that the grout delivery system (10) can be lifted relatively easily from the downhole drilling assembly. A selectively operable pressure relief system (150) is provided for this purpose. L'invention concerne un système de distribution de coulis de ciment (10) destiné à distribuer, au niveau d'un emplacement de fond de trou, un coulis de ciment sous la forme d'une substance fluide comprenant un mélange de deux matériaux de composant de coulis de ciment. Le système de distribution de coulis de ciment (10) comprend un corps allongé (31) qui comprend deux réservoirs (41, 42) configurés sous la forme de cartouches (51, 52) destinées à recevoir des charges respectives des deux matériaux de composant de coulis de ciment. Les deux cartouches (51, 52) comprennent chacune un piston (61). Une fermeture à ouverture sélective configurée sous la forme d'une soupape (62) est disposée adjacente à l'extrémité inférieure (57) de chaque cylindre (53). Chaque piston (61) est destiné à avancer progressivement vers la soupape (62), ce qui permet d'expulser le matériau de composant de coulis de ciment de la cartouche respective (51, 52) à travers la soupape. Lorsque le système de distribution