Abstract: A process for disrupting filter cake in an underground formation, which process comprises: (i) incorporating into a treatment fluid a solid polymer capable of being converted by hydrolysis into one or more organic acids; (ii) introducing the treatment fluid into the underground formation; and (iii) allowing the solid polymer to hydrolyse in the presence of water to produce organic acid such that acid soluble material within the filter cake or adjacent formation is dissolved.

Abstract: An underground formation is consolidated by (a) incorporating into a treatment fluid (i) at least one chemical substance which is capable of undergoing a chemical change that alters the physico-chemical environment of the treatment fluid and which is a bicarbonate or a compound that generates a phosphate, phosphoric acid, sulphate, sulphuric acid, hydrogen sulphide, S2?, carbon dioxide, bicarbonate, base or acid; and, optionally, (ii) at least one additional chemical substance selected from salts and complexes of metals having a valency of 2 or higher; introducing the treatment fluid into the formation; and allowing the chemical substance (i), alone or in combination with the optional chemical substance (ii), to undergo a chemical change that alters the physico-chemical environment of the treatment fluid such that a consolidating mineral is deposited in the underground formation.

Abstract: A process for producing a self-disrupting filter cake in an underground formation, which process comprises: (a) incorporating into a drilling fluid a solid polymer capable of being converted by hydrolysis into one or more organic acids; (b) using the drilling fluid to drill a wellbore into the underground formation such that the solid polymer in the drilling fluid contributes to the formation of a filter cake; and (c) allowing the solid polymer to hydrolyse in the presence of water and to disrupt the integrity of the filter cake. A drilling fluid which contains as a bridging agent one or more solid polymers capable of being converted by hydrolysis into one or more organic acids is also provided.

Abstract: A process for forming a gel, which process comprises mixing an alkaline silicate solution with a polymer in solid form, the polymer being capable of being converted by hydrolysis into one or more organic acids; and allowing the polymer to release sufficient acid to cause formation of a silicate gel.

Abstract: A process for treating an underground formation, which process comprises: (a) introducing into the underground formation a treatment fluid comprising an organic acid precursor; (b) heating a zone within the formation, which zone contains at least a portion of the organic acid precursor, to a temperature which is above the natural formation temperature and sufficient to increase the rate of hydrolysis of the organic acid precursor; and (c) allowing the organic acid precursor to hydrolyse to produce an organic acid in an amount effective to acidize the underground formation.

Abstract: A process for forming a gel, which process comprises mixing an alkaline silicate solution with a polymer in solid form, the polymer being capable of being converted by hydrolysis into one or more organic acids; and allowing the polymer to release sufficient acid to cause formation of a silicate gel.

Abstract: A process for disrupting filter cake in an underground formation, which includes (i) incorporating into a treatment fluid a solid polymer capable of being converted by hydrolysis into one or more organic acids; (ii) introducing the treatment fluid into the underground formation; and (iii) allowing the solid polymer to hydrolyze in the presence of water to produce organic acid such that acid soluble material within the filter cake or adjacent formation is dissolved.

Abstract: An underground formation is consolidated by (a) incorporating into a treatment fluid (i) at least one chemical substance which is capable of undergoing a chemical change that alters the physico-chemical environment of the treatment fluid and which is a bicarbonate or a compound that generates a phosphate, phosphoric acid, sulphate, sulphuric acid, hydrogen sulphide, S2?, carbon dioxide, bicarbonate, base or acid; and, optionally, (ii) at least one additional chemical substance selected from salts and complexes of metals having a valency of 2 or higher; introducing the treatment fluid into the formation; and allowing the chemical substance (i), alone or in combination with the optional chemical substance (ii), to undergo a chemical change that alters the physico-chemical environment of the treatment fluid such that a consolidating mineral is deposited in the underground formation.

Abstract: A method for treating an underground reservoir, which method comprises introducing into the reservoir a treatment fluid comprising, dissolved or dispersed in water, an ester and a polymer breaker, such that the ester hydrolyses to produce an organic acid to dissolve acid soluble material present within the reservoir and the polymer breaker degrades polymeric material present within the reservoir.

Abstract: A method for treating an underground reservoir, which method comprises introducing into the reservoir a treatment fluid comprising, dissolved or dispersed in water, an ester and a non-enzyme catalyst capable of increasing the rate of hydrolysis of the ester, such that the ester hydrolyses to produce an organic acid to dissolve acid soluble material present within the reservoir.

Abstract: A method of precipitating or depositing material within an underground reservoir which comprises introducing into the reservoir in aqueous solution (i) an isolated enzyme and (ii) a substrate for the enzyme, such that the action of the enzyme on the substrate leads to the precipitation or deposition of material within the underground reservoir.