Apparatus and method are provided for storing selected quantities of granular materials, for programmable extraction in selected proportions and at selected rates, for delivery to a changeable location through a flexible auger-driven common delivery conduit. Individual containers containing specific granular products are mounted so that they are continually weighed by load cells communicating with a central control system including a microprocessor. Each of the containers is provided with an individual valve which is controllable by the microprocessor pursuant to a user-provided program, so that precisely determined and timed gravity-assisted extraction of the granular materials is effected. Auger mounted immediately below each container to positively transfer the extracted granular material along the delivery conduit. By the addition of a liquid carrier, either from one of the cooperating containers or after delivery of the granular material to the selected location, slurries, e.g., drilling mud, can be formed to selected, time-varying compositions. The individual containers may have their contents replenished in place or, at the user's option, the containers may be physically removed and replaced by other loaded containers containing the same or different granular materials to suit the user's specific needs. Agitators to facilitate gravity-assisted flow of the granular materials may be provided in the individual containers.