Abstract: The invention provides a system comprising a encapsulating material (B) and a component (A), wherein said component (A) is trapped within said encapsulating material (B) and said encapsulating material (B) being able to break and release said component (A) under pressure drop higher than 10 bars.

Abstract: A method of providing thixotropy to a fluid downhole comprising: adding an encapsulated thixotropic agent to a fluid at the surface; introducing the fluid into a borehole; and subjecting the fluid to a shearing action so as to release the thixotropic agent into the fluid.

Abstract: A cement slurry having a density between 750 kg/m3 and 1,000 kg/m3, comprising a solid fraction comprising: either 75%-90% (by volume) of lightweight particles having a mean particle size between 10 and 60 &mgr;m; 10%-25% (by volume) of Portland cement having a mean particle size of between 10 and 50 &mgr;m, or micro-cement having a mean particle size between 0.5 and 5 &mgr;m; or: 20%-50% (by volume) of lightweight particles having a mean particle size between 10 and 60 &mgr;m; 10%-25% (by volume) of Portland cement having a mean particle size of between 10 and 50 &mgr;m, or micro-cement having a mean particle size between 0.5 and 5 &mgr;m; 35%-65% (by volume) of lightweight particles having a mean particle size between 100 and 200 &mgr;m; and a liquid fraction present in an amount of 37%-50% (by volume) of the total volume. Such cements have remarkable mechanical properties due to their very low porosity in spite of having very low density.