Abstract: Drift or residual oil saturation within a reservoir around a wellbore is determined by injection of a water-soluble tracer and then producing from the well. This injection is performed twice. The first injection is immediately followed by production in order to create a baseline. The second injection is followed by a soak period, and then production. Production of the tracers is compared to determine drift or residual oil saturation within the reservoir.

Abstract: A method is provided for troubleshooting gas-lift wells, to identify whether gas-lift valves on the production tubing are open or closed, without the use of wireline tools. The method may also be used to detect leaks in the production tubing or in the well casing. A quantity of a tracer gas is injected into the lift-gas at the wellhead, and its return in fluid produced from the well is monitored as a function of time. The tracer's return pattern may be correlated with the depth of entry points and volumes of lift-gas entering along the length of the production tubing.

Abstract: A method is provided for troubleshooting gas-lift wells, to identify whether gas-lift valves on the production tubing are open or closed, without the use of wireline tools. The method may also be used to detect leaks in the production tubing or in the well casing. A quantity of a tracer gas is injected into the lift-gas at the wellhead, and its return in fluid produced from the well is monitored as a function of time. The tracer's return pattern may be correlated with the depth of entry points and volumes of lift-gas entering along the length of the production tubing.

Abstract: A method is provided for troubleshooting gas-lift wells, to identify whether gas-lift valves on the production tubing are open or closed, without the use of wireline tools. The method may also be used to detect leaks in the production tubing or in the well casing. A quantity of a tracer gas is injected into the lift-gas at the wellhead, and its return in fluid produced from the well is monitored as a function of time. The tracer's return pattern may be correlated with the depth of entry points and volumes of lift-gas, entering along the length of the production tubing.

Abstract: The oil saturation within a subterranean reservoir is determined by injecting water containing dissolved reactants which are substantially oil-insoluble and which convert the injected solution into a tracer-containing solution in which there is at least one each of oil and water tracers, with the oil tracers being gaseous, and chromatographically analyzing the patterns of the concentrations of the tracers within fluid produced from the reservoir for determining the oil saturation.

Abstract: Residual oil saturation is determined by injecting an aqueous solution containing a carbonate salt, an acid-generating material and a radioactive material which are each selectively water soluble, displacing the solution with an aqueous solution devoid of the reactants and tracer, and, after CO.sub.2 has formed within the reservoir, producing aqueous fluid from the reservoir and utilizing radioactive analysis to measure the chromatographic separation between the radioactive material and the CO.sub.2.

Abstract: Residual oil saturation is determined by injecting water containing CO.sub.2, a base-generating material and at least one radioactively labeled material which is or becomes a selectively water-soluble tracer material mixed with the injected CO.sub.2, so that the arrival of the oil and water-partitioning tracer material is demarked by a decrease in CO.sub.2 concentration and the arrival of at least one of tracer material detected by a radioactivity analysis.

Abstract: Residual oil saturation is determined by injecting water containing or contacting dissolved halocarboxylic acid salt and carbonate salt into an oil and water containing reservoir and chromatographically analyzing the patterns of the concentrations of in situ generated CO.sub.2 and water soluble acid salt in fluid produced from the reservoir.

Abstract: Residual oil saturation is determined by injecting water containing dissolved CO.sub.2 and subsequently active base generating reactant into an oil and water containing reservoir and chromatographically analyzing the patterns of the concentrations of in situ reaction-depleted CO.sub.2 and reaction-increased bicarbonate salt in fluid produced from the reservoir.

Abstract: Materials in and around a well are acidized with chemically heated, hot acid by injecting a solution of both nitrogen and heat generating reactants and a mixture of weak acid and weak acid salt that both buffers the relation and provides a weak acid acidizing solution.

Abstract: A well which is producing slowly by artificial lift can be economically heated by first inflowing a nitrogen-generating solution, to form a pool of reacting liquid near the uppermost opening into the reservoir, then inflowing more solution while artificially-lifting liquid from near the lowermost opening into the reservoir at a rate substantially equalling the inflow rate.

Abstract: The volume change of a hydraulic cement slurry can be measured by measuring the amount of pressurized gas which flows into or out of the volume initially occupied by the slurry during the setting of the cement, for example, where the slurry is one formed by dissolving in the slurry mix water a correlated amount of gas-forming reactants having a delayed rate of reaction such that the gas production occurs mainly at the time the volume of the slurry mix water is being reduced to a low value during the setting and hardening of the cement.

Abstract: A testing apparatus is provided for measuring changes in the bulk volume and gas permeability of a cement slurry, such as one formed by dissolving in the slurry mix water a correlated amount of gas-forming reactants having a delayed rate of reaction such that the gas production occurs mainly at the time the volume of the slurry mix water is being reduced to a low value during the setting and hardening of the cement.

Abstract: Sand grains coated with a solid non-cured epoxy resin with a softening point above 35.degree. C. are placed in a well for gravel pack, well repair or fracturing purposes. The epoxy resin softens at formation temperature and reacts with a hardener (such as a tertiary amine) diluted in water present in the pore space of the mass of sand grains. A consolidated mass of sand grains is thus obtained. The coated sand grains can be transported to the well site and stored over long periods at relatively high temperatures without risk of quality decrease.

Abstract: A reservoir encountered by a drilling fluid-containing borehole can be sampled and/or a liquid can be removed from within a borehole by arranging conduits and a packer for isolating the reservoir or a selected fluid-removal location and then gas-lifting liquid by injecting an aqueous liquid solution which generates nitrogen gas within the borehole, with the depth of the injection and the rates of fluid inflow and outflow being adjusted to maintain a selected drawdown at the depth of the fluid-removal location.

Abstract: A recovery of attic oil, from a location within a subterranean reservoir between the top of the reservoir and the uppermost opening into a well encountering the reservoir, is improved by injecting fluid comprising or containing a nitrogen-gas-generating solution arranged to yield heat and gas within the reservoir, keeping the injected fluid static long enough for the reservoir to be heated and gas to migrate upward and then producing fluid in response to a gas cap drive.

Abstract: Fluid passageways between a well borehole and a subterranean reservoir which are both plugged and submerged within relatively dense brine can be contacted with heat and oil solvent by arranging a nitrogen gas generating aqueous solution to be both reactive at the reservoir temperature and denser than the brine in the borehole and flowing alternating slugs of it and a liquid oil solvent into the zone to be treated.

Abstract: The scaling of a production well in a clay-containing reservoir is inhibited by injecting a scale inhibitor dissolved in an aqueous solution having a pH and ratio of monovalent-to-multivalent cations such that multivalent cation salts of the inhibitor are precipitated as a result of a cation-exchange within the reservoir.

Abstract: The formation is consolidated by means of a silicon halide compound that reacts with water present on the walls of the formation pore space thereby forming silicon dioxide that bonds the formation grains together. The bonding strength is increased by a pretreatment of the formation grains with an acid in liquid or gaseous form.

Abstract: The scaling of a producing well is inhibited by injecting a self-reacting alkaline aqueous solution of a pH-lowering reactant, a compound containing scale-inhibiting anions and a compound containing multivalent cations, which solution subsequently precipitates a slightly soluble scale inhibitor within the reservoir.