A method for plugging and sealing subsurface formations using alkaline nanosilica dispersion and a delayed activation chemistry includes introducing a mixture with a first pH into the subsurface formation. The mixture comprises an aqueous solution, an alkaline nanosilica dispersion and a water-insoluble hydrolyzable compound. The method further includes allowing the water-insoluble hydrolyzable compound to hydrolyze in the subsurface formation to form an acid at 70 C. or greater, thereby acidizing the mixture to a reduced second pH and causing the alkaline nanosilica dispersion to gel into a solid and seal the subsurface formation. A composition for sealing a subsurface formation includes an aqueous mixture including water, an alkaline nanosilica dispersion, and a water-insoluble hydrolyzable compound.

The strength of a proppant or sand control particulate may be improved by coating the proppant to form a composite. The composite has enhanced compressive strength between about 34 to about 130 MPa and minimizes the spelling of fines at closure stresses in excess of 5,000 psi. Conductivity of fractures is further enhanced by forming a pack of the composites in the fracture.

A method including providing a drilling fluid that comprises a base fluid, a weighting agent, and a sag stability enhancer, wherein the sag stability enhancer comprises polyethylene glycol (PEG) having a molecular weight of greater than or equal to about 200 g/mol; and placing the drilling fluid in a subterranean formation via a wellbore penetrating the subterranean formation. A method including forming a fluid comprising a base fluid, a weighting agent, and from about 0.5 ppb (1.4 kg/m.sup.3) to about 30 ppb (85.5 kg/m.sup.3) of a sag stability enhancer, wherein the sag stability enhancer comprises a glycol; and introducing the fluid into at least a portion of a well. A drilling fluid containing a base fluid, a weighting agent, and a sag stability enhancer comprising polyethylene glycol (PEG) having a molecular weight of greater than or equal to about 200 g/mol.

A composition of matter includes a liquid and nanoparticles suspended in the liquid. The nanoparticles each include silica, alumina, and an organosilicon functional group having a molecular weight of at least 200. A method includes functionalizing a surface of nanoparticles with an organosilicon functional group and dispersing the nanoparticles in a liquid to form a suspension. The functional group has a molecular weight of at least 200. The nanoparticles each include silica and alumina at a surface thereof.

Disclosed are methods for using a composition comprising HCl, urea, complex substituted keto-amine-hydrochloride, at least one alcohol selected from the group consisting of isopropyl alcohol and propargyl alcohol, an ethoxylate, and at least one ketone selected from the group consisting of methyl vinyl ketone, acetone, and acetophenone.

Methods including preparing a treatment fluid comprising a bulk amount of anhydrous ammonia, wherein the anhydrous ammonia is present in an amount greater than about 10% by weight of a liquid portion of the treatment fluid, and wherein the anhydrous ammonia is in a phase selected from the group consisting of a liquid phase, a gaseous phase, supercritical phase, and any combination thereof; and introducing the treatment fluid into a subterranean formation.

A well treatment composition for use in a hydrocarbon-bearing reservoir, optionally as a kill pill, and comprising a reversible aminal gel composition. The reversible aminal gel composition includes a liquid precursor composition. The liquid precursor composition is operable to remain in a liquid state at about room temperature. The liquid precursor composition comprises an organic amine composition; an aldehyde composition; a polar aprotic organic solvent; and a metal salt composition. The liquid precursor composition transitions from the liquid state to a gel state responsive to an increase in temperature in the hydrocarbon-bearing reservoir. The gel state is stable in the hydrocarbon-bearing reservoir at a temperature similar to a temperature of the hydrocarbon-bearing reservoir, and the gel state is operable to return to the liquid state responsive to a change in the hydrocarbon-bearing reservoir selected from the group consisting of: a decrease in pH in the hydrocarbon-bearing reservoir and an addition of excess metal salt composition in the hydrocarbon-bearing reservoir.

A well treatment composition for use in a hydrocarbon-bearing reservoir comprising a reversible aminal gel composition. The reversible aminal gel composition includes a liquid precursor composition. The liquid precursor composition is operable to remain in a liquid state at about room temperature. The liquid precursor composition comprises an organic amine composition; an aldehyde composition; a polar aprotic organic solvent; and a metal salt composition. The liquid precursor composition transitions from the liquid state to a gel state responsive to an increase in temperature in the hydrocarbon-bearing reservoir. The gel state is stable in the hydrocarbon-bearing reservoir at a temperature similar to a temperature of the hydrocarbon-bearing reservoir, and the gel state is operable to return to the liquid state responsive to a change in the hydrocarbon-bearing reservoir selected from the group consisting of: a decrease in pH in the hydrocarbon-bearing reservoir and an addition of excess metal salt composition in the hydrocarbon-bearing reservoir.

A well treatment composition for use in a hydrocarbon-bearing reservoir, optionally as a kill pill, and comprising a reversible aminal gel composition. The reversible aminal gel composition includes a liquid precursor composition. The liquid precursor composition is operable to remain in a liquid state at about room temperature. The liquid precursor composition comprises an organic amine composition; an aldehyde composition; a polar aprotic organic solvent; and a metal salt composition. The liquid precursor composition transitions from the liquid state to a gel state responsive to an increase in temperature in the hydrocarbon-bearing reservoir. The gel state is stable in the hydrocarbon-bearing reservoir at a temperature similar to a temperature of the hydrocarbon-bearing reservoir, and the gel state is operable to return to the liquid state responsive to a change in the hydrocarbon-bearing reservoir selected from the group consisting of: a decrease in pH in the hydrocarbon-bearing reservoir and an addition of excess metal salt composition in the hydrocarbon-bearing reservoir.

A system for slowly releasing an oil-soluble well treatment agent into a well or a subterranean formation includes a composite of the oil-soluble well treatment agent associated with a second component. The amount of the oil-soluble well treatment agent in the composite is from 20 to 35 weight percent and the average particle size of the oil-soluble well treatment agent in the composite is less than or equal to 1 micrometer. The composite may further contain a water-soluble well treatment agent.