Abstract: The invention relates to a process for producing a highstrength a furan stone with high permeability and filtering effect mainly for protecting deep-drilled wells yielding mineral oil, natural gas and water against getting choked by sand. A mixture comprising an artificial resin as a binding material containing a catalyzer for controlling duration of binding and pumpability and an assorted granular material of high-strength forming the skeleton and salt filling and increasing pore spaces is homogenized and pumped into the corresponding producing section of the well into the area to be protected. After hardening of the mixture salt is dissolved from the obtained artificial stone and a filtering effect is achieved without binding the grains of the reservoir rock. Due to the mechanical characteristics and controlled porosity of the obtained artificial stone rock-parts, mainly sand delivered by the yielded fluidum into the well will be retained.

Abstract: A heat insulating tube, primarily for underground mining, is provided with an outer casing and an inner casing, separated from the other casing by a connecting element and a series of spacer rings. The distance between the connecting element and the spacer rings as well as between the spacer rings themselves is in the range of about 20 to 50 times the diameter of the inside casing.