Disclosed here compositions and methods suitable for injection of a nanosurfactant-containing fluid into a hydrocarbon-bearing formation for enhanced recovery operations. Embodiments of the composition contain a petroleum sulfonate surfactant, mineral oil, and a zwitterionic co-surfactant.

A Janus graphene nanosheet (JGN) surfactant formed from a two-dimensional graphene oxide sheet and functionalized to produce an amphiphilic graphene nanosheet. The JGN may be a component of a nanofluid utilized in nanofluid flooding for oil recovery. The JGN may also be used as solid surfactants to form emulsions for oil recovery.

A method of removing calcium-containing water-based filter cake from a wellbore involving contacting the calcium-containing filter cake with a biodegradable acid solution of water, hydrochloric acid, formic acid, citric acid, and a surfactant. The method is performed at a pressure of 200 to 400 psi and a temperature of 50 to 125 C. The method removes calcium-containing filter cake made of water, calcium carbonate, a polymer or starch and a clay. The method meets industry standard steel corrosion rates of less than 0.049 lb/ft.sup.2 per day. Also disclosed is a biodegradable acid solution of water, hydrochloric acid, formic acid, citric acid, and a surfactant that meets OECD 301B thresholds for ready biodegradability.

Surfactants are imbibed into Halloysite nanotubes (HNT) and the imbibed nanotubes are coated with wax on the nanotube outer surface. The wax layer prevents the surfactant from being disgorged from the HNT lumen until a triggering condition exists. Triggering conditions include contact with oil, which dissolves the wax; or exposure to temperatures above a melt transition of the wax, which causes the wax to melt. Upon exposure to a triggering condition, at least some of the imbibed surfactants are disgorged from the HNT and into the surrounding environment. The disgorged surfactants provide a conventional effect of reducing interfacial tension and changing reservoir rock wettability to enhance oil recovery. A range of surfactants and waxes are usefully employed in the compositions and methods described herein.

Ecofriendly emulsifier synthesis from esterified waste vegetable oil for wellbore drilling fluids is described. A raw material waste vegetable oil is esterified to produce a methyl ester of the raw material waste vegetable oil. A caustic soda solution is added to the methyl ester resulting in a mixture. The mixture is thermally treated. A pH of the mixture is adjusted resulting in formation of an aqueous phase and a non-aqueous phase. The aqueous phase is separated from the non-aqueous phase.

A method for suspending lightweight beads in a fluid includes combining lightweight beads, a fluid, and a surfactant to form a liquid additive. The liquid additive may be used to reduce the density of a wellbore fluid. The liquid additive or wellbore fluid can be combined with a cementitious material to form a lightweight cement composition.

The invention discloses a nonionic Gemini surfactant, (octylphenol polyoxyethylene ether disubstituted) dicarboxylic acid diphenyl ether and its synthesis method, which nonionic Gemini surfactant has a structural formula of:

##STR00001##

and is prepared by a two-step reaction: S1, diphenyl ether 4,4-dicarboxylic acid is subjected to an acyl chlorination reaction to obtain diphenyl ether 4,4-dicarbonyl dichloride; S2, diphenyl ether 4,4-dicarbonyl dichloride is subjected to an esterification reaction with octylphenol polyoxyethylene ether (OP-10) to obtain the target product (octylphenol polyoxyethylene ether disubstituted) dicarboxylic acid diphenyl ether. The surfactant of the present invention is expected to be applied in tertiary oil recovery as an alkali/surfactant, in polymer/surfactant binary composite flooding, in alkali/surfactant/polymer ternary composite flooding, as a microemulsion emulsifier and the like, and it can also be compounded with a common surfactant to reduce the use cost, and thus create conditions for its large-scale application.

The invention discloses a core-shell structured non-ionic nanoemulsion system and the preparation and use thereof. The system comprises a non-ionic gemini surfactant, an oil phase material, a solubilizer, and water; wherein the microemulsion has a core-shell structure, with the outer shell being the non-ionic Gemini surfactant, and the inner core being the oil phase material. The non-ionic Gemini surfactant is di(octylphenol polyoxyethylene ether)-substituted dicarboxylic acid diphenyl ether having the structural formula:

##STR00001##

The non-ionic nanoemulsion system of the present invention is homogeneous and transparent, and has a spherical core-shell structure with nanometer-sized (3-40 nm) droplets, narrow particle size distribution, low tendency to agglomerate, good stability, and both an ultra-low interfacial tension and the ability to reduce viscosity of crude oil.

The invention discloses a core-shell structured anionic nano microemulsion system, and preparation and application thereof. The system comprises an anionic Gemini surfactant, an oil phase material, a solubilizer and water; wherein the microemulsion has a core-shell structure, with the outer shell being an anionic Gemini surfactant, and the inner core being an oil phase material. The anionic Gemini surfactant is N,N,N,N-dodecyl tetrasubstituted diphenyl ether sulfonate having the structural formula:

##STR00001##

The anionic nano-microemulsion system of the present invention is homogeneous and transparent, has a spherical core-shell structure, has a nanometer size (3 to 40 nm) as droplets, has a narrow particle size distribution, is not easy to agglomerate, has good stability, and has an ultra-low interfacial tension and a capability of reducing viscosity of crude oil.

The present invention discloses a N,N,N,N-tetradodecyl-substituted diphenyl ether sulfonate anionic Gemini surfactant and the synthesis method thereof. It has a structural formula of:

##STR00001## and is prepared in a two-step reaction comprising: S1. subjecting 4,4-diaminodiphenyl ether and bromododecane to an amine alkylation reaction to obtain N,N,N,N-tetradodecyl-substituted diphenyl ether; and S2. sulfonating the N,N,N,N-tetradodecyl-substituted diphenyl ether with concentrated sulfuric acid to produce the target product, N,N,N,N-tetradodecyl-substituted diphenyl ether sulfonate. The surfactant of the present invention has a high surface activity and can be synthesized with a simple procedure under mild reaction conditions, and can be easily separated and purified. The surfactant of the present invention is promising in applications for alkaline/surfactant in tertiary oil recovery, for polymer/surfactant binary compound flooding, alkaline/surfactant/polymer tertiary compound flooding, microemulsion emulsifier, and the like, and may also be compounded with common surfactants to lower the cost, thereby enabling its application in a large scale.