Abstract: This invention relates to methods and apparatus for determination of ion concentrations, particularly in downhole water from hydrocarbon wells, aquifers etc. It is useful in a wide range of applications, including predicting the formation of scale and fingerprinting waters from different sources. More particularly, the invention relates to the use of ligands whose electronic configuration is altered by the binding of the scaling ions within a water sample. These alterations are detected, for example by electrochemical means, and are indicative of the concentration of scaling ions in the sample.

Abstract: An electrochemical sensor for measuring the amount of hydrogen sulphide or thiols in a fluid in a wellbore comprises a temperature- and pressure-resistant housing containing a flow path for the fluids. The fluids flow over one side of a gas permeable membrane made of zeolite or a suitable ceramic material, the other side of the membrane being exposed to a chamber containing a reaction solution which together with the hydrogen sulphide or thiols create a redox reaction resulting in an electrical current dependent upon the amount of hydrogen sulphide or thiols in the fluid.

Abstract: A treatment of a subterranean formation which contains a hydrocarbon-bearing zone, is carried out using a hydrocarbon-responsive fluid thickened with an oligomeric surfactant consisting of from 2 to 8_linked surfactant monomer subunits. The process of treatment comprises (i) mixing a thickening amount of oligomeric surfactant with an aqueous liquid to make a viscoelastic treatment fluid, (ii) pumping said viscoelastic treatment fluid through a wellbore and into the subterranean formation, where (iii) contact with hydrocarbons within the formation dissipates the viscosity of the treatment fluid.

Abstract: A water-based wellbore treatment fluid contains: one or more viscoelastic-gelling carboxylic acids and/or alkali metal salts thereof; and one or more solubilising alkylolamines. The carboxylic acids and/or alkali metal salts and the alkylolamines are present in the fluid in respective amounts such that, at 25° C., the alkylolamines solubilise a sufficient portion of the carboxylic acids and/or alkali metal salts to render the fluid viscoelastic. A remaining portion of the carboxylic acids and/or alkali metal salts forms a suspension of solid particulates in the fluid.

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 viscoelastic wellbore treatment fluid comprises an effective amount of an oligomeric surfactant for controlling the viscoelasticity of the fluid.

Abstract: Hydraulic fracturing of a subterranean hydrocarbon reservoir is carried out using an aqueous wellbore fluid which is an aqueous solution of a surfactant which has the formula (R1—X)nZ, where R1 is an aliphatic group comprising a C10-C25 principal straight chain bonded at a terminal carbon atom thereof to X, and comprising at least one C1-C6 side chain. X is a charged head group, Z is a counterion, and n is an integer which ensures that the surfactant is charge neutral. The surfactant reversibly thickens the aqueous solution such that the wellbore fluid is a viscoelastic gel. The viscoelastic gel breaks and undergoes a reduction in viscosity within the reservoir and surfactant from the broken gel mixes with hydrocarbon in the reservoir.

Abstract: The present invention provides aqueous viscoelastic compositions comprising a cleavable anionic surfactant which is a sulphonate and possibly also an electrolyte. The cleavable surfactants useful in the present invention comprise a chemical bond, which is capable of being broken under appropriate conditions, to produce oil soluble and water soluble products typically having no interfacial properties and surface activity compared with the original surfactant molecule. Further, the rheological properties of the aqueous viscoelastic composition are usually altered upon cleavage of the cleavable surfactant generally resulting in the elimination of the viscosifying, viscoelastic and surfactant properties of the composition. Aqueous viscoelastic compositions in accordance with the present invention are suitable for use in oil-field applications, particularly for hydraulic fracturing of subterranean formations.

Abstract: Hydraulic fracturing of a subterranean hydrocarbon reservoir is carried out using an aqueous wellbore fluid which is an aqueous solution of a surfactant which has the formula(R1?X)nZ, where R1 is an aliphatic group comprising a C10-C25 principal straight chain bonded at a terminal carbon atom thereof to X, and comprising at least one C1-C6 side chain. X is a charged head group, Z is a counterion, and n is an integer which ensures that the surfactant is charge neutral. The surfactant reversibly thickens the aqueous solution such that the wellbore fluid is a viscoelastic gel. The viscoelastic gel breaks and undergoes a reduction in viscosity within the reservoir and surfactant from the broken gel mixes with hydrocarbon in the reservoir.

Abstract: A wellbore fluid comprising a surfactant, the surfactant having the formula (R1—X)nZ, wherein R1 is an aliphatic group—comprising a C18-C22 principal straight chain bonded at a terminal carbon atom thereof to X, and comprising at least one C1-C2 side chain—X is a charged head group, Z is a counterion, and n is an integer which ensures that the surfactant is charge neutral, and wherein the charged head group X is selected to provide that the surfactant is soluble in oil and at least one part of the charged head group is anionic.

Abstract: This invention relates to the synthesis and use in oilfield applications of copolymers which can undergo the Diels-Alder reaction to form a gel. Under appropriate conditions, the retro Diels-Alder reaction can take place to provide for decreasing the viscosity of the aforementioned gel.

Abstract: A well bore treatment fluid and methods for selectively reducing the outflow of water during recovery of hydrocarbons from a hydrocarbon reservoir in a formation are described, wherein fluid contains 5 to 40 weight per cent of a dissolved compound based on ?-branched carboxylic acid, derivatives or co-polymers thereof, and capable of forming a precipitate that is substantially soluble in hydrocarbons and substantially insoluble in water.

Abstract: Methods and related apparatuses and mixtures are described for detecting hydrogen sulfide in a formation fluid downhole. A detection mixture is combined with the formation fluid downhole. The detection mixture includes metal ions for reacting with hydrogen sulfide forming a metal sulfide, and charged nanoparticles sized so as to inhibit significant aggregation of the metal sulfide so as to enable spectroscopic detection of the metal sulfide downhole. The combined mixture and formation fluid is then spectroscopically interrogated so as to detect the presence of the metal sulfide thereby indicating the presence of hydrogen sulfide in the formation fluid. The mixture also includes chelating ligands for sustaining thermal endurance of the mixture under downhole conditions.

Abstract: An electro-chemical sensor for methane is described having a catalyst to react methane or other low molecular weight hydrocarbons and a detector to detect the turnover or reaction rate and using such information to determine the concentration of the methane or other low molecular weight species. The sensor is preferably used for measurements in a wellbore.

Abstract: An optical sensor for pH is described using a cross-linked network of bisilanes to immobilize a pH sensitive chromophore to a surface potentially exposed to a high pressure, high temperature environment such as wellbore effluents at a downhole location.

Abstract: A method and system is disclosed for monitoring one or more characteristics associated with a fluid. An insulating layer comprising non-conducting diamond is positioned within a housing and has a surface exposed directly or indirectly to the fluid. A plurality of microelectrodes made of electrically conducting diamond each have a surface exposed directly or indirectly to the fluid. An electrical circuit in electrical communication with each of the microelectrodes is adapted to convert electrical signals from the microelectrodes into at least one signal associated with a characteristic being monitored. The sensing system is well suited to hydrocarbon wellbore related applications, but can also be used in other applications.

Abstract: The invention concerns an aqueous viscoelastic fluid for use in the recovery of hydrocarbons. According to the invention, the aqueous viscoelastic fluid comprises a monomer, a dimer or an oligomer of a viscoelastic surfactant able to form a viscoelastic gel under downhole conditions, said surfactant comprising a hydrophobic tail and a hydrophilic head, and being of the following formulae: R—X—Y-Z where R is the hydrophobic tail of the surfactant, Z is the hydrophilic head of the surfactant, said hydrophilic head being charged, X is a stabilising group and Y chain is a linear, saturated or unsaturated, hydrocarbon chain of 1, 2 or 3 carbon atoms or a branched, saturated or unsaturated hydrocarbon chain wherein the main chain is of 1, 2 or 3 carbon atoms, possibly incorporating an aromatic ring.

Abstract: A method and system is disclosed for monitoring one or more characteristics associated with a fluid. An insulating layer comprising non-conducting diamond is positioned within a housing and has a surface exposed directly or indirectly to the fluid. A plurality of microelectrodes made of electrically conducting diamond each have a surface exposed directly or indirectly to the fluid. An electrical circuit in electrical communication with each of the microelectrodes is adapted to convert electrical signals from the microelectrodes into at least one signal associated with a characteristic being monitored. The sensing system is well suited to hydrocarbon wellbore related applications, but can also be used in other applications.

Abstract: A non-aqueous wellbore fluid comprises a non-aqueous continuous phase with one or more organic salts having the formula ((R1-Q)pX)mZn, one or more oligomeric organic salts based on linked ((R1-Q)pX)mZn subunits, or a combination thereof dissolved therein. X is a negatively charged functional group. R1 is an organic group comprising a principal straight chain and one or more side chains which branch from and are shorter than said principal straight chain. Q is a covalent bond or a polar linkage group which connects a terminal atom of the principal straight chain of the organic group R1 to the functional group X. p is a positive integer which is the number of organic groups R1 which are connected to the functional group X. Z is a cation. m and n are positive integers which ensure that the organic salts are charge neutral. The one or more organic salts increase the electrical conductivity of the wellbore fluid.

Abstract: A scale dissolver fluid for dissolving scale in a subterranean hydrocarbon-bearing formation comprises an effective amount of a scale dissolver formulation and an effective amount of a surfactant for controlling the viscosity of the fluid. In use, formation hydrocarbons act on the surfactant to reduce the viscosity of the fluid so that the fluid selectively invades a hydrocarbon-bearing zone of the formation.