Abstract: A drilling mud comprising a base fluid in the form of a water-in-oil emulsion comprising droplets of a brine phase dispersed in a continuous oil phase wherein the brine phase has a dissolved salt concentration of at least 2.5 weight % and the emulsion is stabilized with (i) a first polymeric emulsifier that is a block or graft copolymer of the general formula (A-COO)mB, wherein m is an integer of at least 2, A is a polymeric component having a molecular weight of at least 500 and is the residue of an oil-soluble complex mono-carboxylic acid and (ii) a second polymeric emulsifier that is a graft copolymer of a polyvinylpyrrolidone polymer and an alpha olefin selected from the group consisting of C14 to C20 alphaolefins and mixtures thereof and wherein structural units derived from vinylpyrrolidone are present in the graft copolymer in an amount in the range of 40 to 50 mole %.

Abstract: Oil-based wellbore fluid in the form of an emulsion having a continuous phase containing an oil and, dispersed therein, a first dispersed liquid phase and a second separate dispersed liquid phase. The first dispersed liquid phase is a brine phase containing at least 5% by weight of a dissolved salt or a mixture of salts, and the second dispersed liquid phase is a polar organic liquid which is insoluble or sparingly soluble in the brine and contains the first dispersed liquid phase, but is soluble in pure water. The second dispersed liquid phase is in the form of droplets having an average diameter of not less than 5 microns.

Abstract: The invention relates to the use of one or more water-soluble reactive liquid component capable of subsequent polymerization or cross-linking to form a solid to improve the zonal isolation and alleviate the impacts of cracks and fissures in the cement sheath around a completed subterranean well. It includes the steps of injecting a wellbore fluid carrying the reactive component or additive into the wellbore, injecting a cementitious composition as slurry into the wellbore and letting said reactive liquid component pass through at least one of the interfaces between cement and formation, cement and filter cake, and filter cake and formation before forming a solid of said reactive liquid component that traverses said at least one of the interfaces.

Abstract: A wellbore fluid comprising a base fluid and a particulate bridging agent comprised of a sparingly water-soluble material selected from the group consisting of melamine (2,4,5-triamino-1,3,5-triazine), lithium carbonate, lithium phosphate (Li3PO4), and magnesium sulfite.

Abstract: The invention relates to a wellbore operation, which includes the steps of: (a) introducing into a wellbore a wellbore fluid in the form of a water-in-oil emulsion comprising a dispersed brine phase and comprising as an emulsifier at least one polymer which contains both hydrophilic units and hydrophobic units, at least some of said hydrophilic units containing sulfonate groups, and at least some of said hydrophobic units containing pendant alkyl groups having at least 8 carbon atoms, wherein the sulfonate groups have been introduced into said polymer by first preparing a precursor polymer containing units derived from at least one unsaturated carboxylic acid and/or unsaturated anhydride and then reacting at least a portion of the carboxylic acid and/or anhydride groups of the precursor polymer with a compound of general formula R12N(CH2)nSO3X (I) and/or a compound of general formula HO(CH2)nSO3X (II) wherein each R1 is independently selected from hydrogen, methyl or ethyl, X is H, ammonium, or a Group IA met

Abstract: Wellbore fluid having a continuous aqueous phase, and containing at least one polymer which (a) has a number average molecular weight in the range of from 10,000 to less than 100,000; (b) contains hydrophilic units such that the polymer is at least 2% soluble in water at a temperature of 20° C. wherein none of said hydrophilic units comprise —CH2.CH2.O— units; and (c) contains pendant alkyl groups having at least 10 carbon atoms. The combined molecular weight of the pendant alkyl groups is in the range of from 15 to 70% by weight based on the weight of the polymer.

Abstract: Wellbore fluid having a continuous aqueous phase, and comprising at least one polymer which has a number average molecular weight in the range of from 10,000 to less than 100,000, wherein the polymer is selected from a copolymer of at least one hydrophilic monomer and at least one hydrophobic monomer containing an alkyl group having at least 8 carbon atoms. The hydrophilic monomer is selected from acrylic acid, methacrylic acid, maleic acid, maleic anhydride, fumaric acid and itaconic acid, and sulfonate groups have been introduced into the copolymer by reaction of at least a portion of the carboxylic acid and/or anhydride groups with a compound of general formula R12N(CH2)nSO3X (I) or a compound of general formula HO(CH2)nSO3X (II). Each R1 is independently selected from hydrogen, methyl or ethyl, X is either H or a Group IA metal, and n is an integer of from 1 to 6.

Abstract: A wellbore fluid comprising a base fluid and a particulate bridging agent comprised of a sparingly water-soluble material selected from the group consisting of melamine (2,4,5-triamino-1,3,5-triazine), lithium carbonate, lithium phosphate (Li3PO4), and magnesium sulfite.

Abstract: Wellbore fluid containing a base fluid and a particulate bridging agent comprised of melamine. A method is also described of forming a removable filter cake on the walls of a wellbore that penetrates a porous and permeable rock formation by placing in the wellbore a wellbore fluid containing a base fluid and melamine, and permitting the melamine to deposit from the wellbore fluid onto or into the walls of the wellbore to form the filter cake, whereby fluid loss to the formation through the removable filter cake is reduced.

Abstract: The invention provides an oil-based wellbore fluid in the form of an emulsion which comprises a continuous phase comprising an oil and, dispersed therein, a first dispersed liquid phase and a second separate dispersed liquid phase, the first dispersed liquid phase being a brine phase, and the second dispersed liquid phase comprising a polar organic liquid, said polar organic liquid being insoluble or sparingly soluble in the brine comprising said first dispersed liquid phase, but being soluble in pure water. There is also provided a method of carrying out a wellbore operation, which includes the steps of (a) introducing into a wellbore a wellbore fluid of the invention; (b) allowing a filter-cake to form; and subsequently (c) allowing a further fluid to come into contact with the filter-cake, said further fluid having a level of salinity which is lower than the level of salinity of said first dispersed liquid phase, and being such that said polar organic liquid is soluble therein.

Abstract: The invention relates to the use of one or more water-soluble reactive liquid component capable of subsequent polymerization or cross-linking to form a solid to improve the zonal isolation and alleviate the impacts of cracks and fissures in the cement sheath around a completed subterranean well. It includes the steps of injecting a wellbore fluid carrying the reactive component or additive into the wellbore, injecting a cementitious composition as slurry into the wellbore and letting said reactive liquid component pass through at least one of the interfaces between cement and formation, cement and filter cake, and filter cake and formation before forming a solid of said reactive liquid component that traverses said at least one of the interfaces.

Abstract: There is provided a wellbore fluid comprising a polymeric saccharide having a number average molecular weight of not more than 50,000 which is a fructan or a partially-hydrolysed fructan or partially-hydrolysed starch, said fructan of partially-hydrolysed fructan or partially-hydrolysed starch having been modified by the introduction of one or more groups having the formula R—NH—CO— and/or R—CO—, wherein R represents a group having 4 to 32 carbon atoms.

Abstract: There is provided a wellbore fluid having a continuous aqueous phase, and comprising at least one polymer which contains both hydrophilic units and hydrophobic units, at least some of said hydrophilic units containing sulfonate groups, and less than 50% by weight of said hydrophilic units comprising —CH2.CH2.O— units; and at least some of said hydrophobic units containing pendant alkyl groups having at least 8 carbon atoms. Such aqueous based wellbore fluids exhibit significantly improved fluid loss properties when used in wellbore operations, such as drilling, completion or workover.

Abstract: A wellbore fluid comprising a base fluid and a particulate bridging agent comprised of a sparingly water-soluble material selected from the group consisting of melamine(2,4,5-triamino-1,3,5-triazine), lithium carbonate, lithium phosphate (Li3PO4), and magnesium sulfite.

Abstract: The present invention relates to a wellbore fluid comprising a particulate material composed of the reaction product of A) one or more water soluble organic compound having possessing a molecular weight of less than 30,000 and possessing at least two hydroxyl groups and B) any other organic compound(s) capable of forming acetal or hemiacetal cross-links with the hydroxyl groups of compound A. The invention relates also to the specific particulate material itself and to applications of the wellbore fluid of the invention for well processes such as drilling, under-reaming, completing, working over, sealing loss zones, sealing fractures, sealing cavities or other very high permeability conduits in a rock formation, or hydraulic fracturing to stimulate a hydrocarbon-producing zone.

Abstract: Wellbore fluids are disclosed which comprise liquid dispersions of particulate mixed divalent metal carbonates having a generally platy crystal form. Mixed alkaline earth metal carbonates are preferred. The invention further relates to a method of well construction, well remediation, or stimulation utilizing such wellbore fluids.

Abstract: The invention concerns wellbore fluids suitable for use in the oil and gas exploration and production industries and embraces fluids used for drilling, completion, workover or packing of wellbores. The invention is especially concerned with biodegradable wellbore fluids the liquid phase of which consists of an oil, or of water-in-oil "invert" emulsions, where the oil phase comprises n-alkanes.