An additive for a cement slurry for a well that is capable of suppressing the generation of free water and preventing flotation/separation of low-specific-gravity aggregate while securing sufficient cement strength even at a high temperature and a method for producing this additive are disclosed. The additive contains an aqueous dispersion of silica and a layered silicate.

An additive capable of suppressing generation of free water from a cement slurry even under a high temperature environment of 150° C. or more and a silica-based additive that suppresses, in a cement slurry for cementing in oil fields and gas oil fields, free water under high temperature and high pressure environments of 100° C. or more, the silica-based additive containing an aqueous silica sol containing nanosilica particles with a true density of 2.15 g/cm.sup.3 or more and less than 2.30 g/cm.sup.3, and a cement slurry for cementing that contains the silica-based additive.

Provided is an additive for a cement slurry for a well that is capable of suppressing the generation of free water and preventing flotation/separation of low-specific-gravity aggregate while securing sufficient cement strength even at a high temperature. Also provided is a method for producing this additive. This additive for a cement slurry for a well contains an aqueous dispersion of silica and a layered silicate.

A method of incorporating a compressible cementitious composition into a subterranean structure having a tunnel including: (a) incorporating a compressible cementitious composition into annular gaps formed around the tunnel of the subterranean structure, and (b) allowing the compressible cementitious composition to cure to a hardened cementitious material within the annular gaps. Further, the compressible cementitious composition includes: (i) water; (ii) a cementitious material; and (iii) a rubber material, in which the rubber material comprises at least 15 weight % of the composition based on the total weight of the composition. A subterranean system and compressible cementitious composition is also included.

An expandable porous framework, the framework containing a dry cementitious powder fill that when exposed to an aqueous media, will expand against the constraint of the framework and set to form a solid, hard and coherent material, the formwork being porous to liquids but substantially impermeable to the powder fill.

Provided are solvent cement formulations that include cyclopentanone, one or more additional solvents, and at least one resin. The formulations can contain a high concentration of dissolved resin, which confers beneficial properties and enables the use of the formulations for bonding large diameter piping components.

A method for encasing underground electrical cables, includes (a) providing a fresh concrete composition including a paste that includes a hydraulic binder, a mineral addition and water, the paste being present in a mixture with sand and aggregates, whereby the paste is present in the concrete composition in a volume of <320 L/m.sup.3 and/or the solid volume fraction of said paste is >50 vol.-% and (b) placing the fresh concrete composition so as to encase the underground cables therewith.

A low strength backfill material having a 28 days compressive strength less than approximately 2.0 MPa is provided. The backfill is suitable for use in areas with dense underground utilities due to its high excavatability and good thermal conductivity. The backfill includes a cementitious binder of approximately 1 weight percent to approximately 10 weight percent and fine aggregates in an amount of approximately 40 to approximately 75 weight percent. Filler is provided at 20 microns to approximately 100 microns for high flowability. A density-controlling agent of 0.0001-5 weight percent is used such that the density of a cured backfill material is approximately 1600 kg/m.sup.3 to 2000 kg/m.sup.3. Thermally conductive particles having a size range of approximately 0.01 microns to 500 microns in an amount of approximately 0.1 to 10 weight percent are evenly dispersed throughout the backfill.

Methods of the present disclosure relate to tailoring cement compositions to withstand carbon dioxide injection. A method comprises predicting a depth of carbonation in a cement sheath; predicting spatially varying mechanical properties of the cement composition due to the carbonation; and determining a mechanical response of the cement sheath based on the spatially varying mechanical properties of the cement composition.

A multiphase particle has a multiphase structure comprising a first phase and a second phase and has an average particle size of 0.1-100 mm. The multiphase particle has a high bulk strength and a good interface binding power with the hardened cement and is particularly suitable for the toughening application of the hardened cement.