The invention relates to a composition C which comprises, in an aqueous medium M: surfactants suitable for creating a foam in the presence of a gas; and polymers P based on acrylamide or acrylamido units, having a molecular mass of 1,000,000 to 20,000,000 g/mol;
or: composition C has a viscosity of less than 6 mPa.Math.s; and the content of polymer P is greater than the concentration limit beyond which the apparent viscosity of a foam obtained from composition C is greater by at least 10% than the apparent viscosity of a foam obtained from the same composition but deprived of polymers. The invention further relates to the use of these compositions as foaming compositions for EOR.

An aqueous wellbore fluid may include a surface active agent package in an amount ranging from 1 to 20 gpt, a thickener in an amount ranging from 0.01 to 0.3 wt. %, and an aqueous base fluid. The surface active agent package may include an α-olefin sulfonate, a terpenoid, and isopropyl alcohol. The thickener may include a biopolymer.

A method for pumping a liquid-gas mixture into a subsurface well includes introducing gas into a liquid at a first pressure to generate a mixture. The mixture is pumped through a first positive displacement pump to a second pressure greater than the first pressure. The mixture at the second pressure is pumped through at least a second positive displacement pump to a third pressure greater than the second pressure. The mixture is moved into the subsurface well at at least the third pressure.

Disclosed are compositions and methods for the pressure protection of existing wells during infill drilling operations.

A method for pumping a liquid-gas mixture into a subsurface well includes introducing gas into a liquid at a first pressure to generate a mixture. The mixture is pumped through a first positive displacement pump to a second pressure greater than the first pressure. The mixture at the second pressure is pumped through at least a second positive displacement pump to a third pressure greater than the second pressure. The mixture is moved into the subsurface well at at least the third pressure.

A method and system enable injection of gas into an underground formation, enhanced by the simultaneous injection of liquid. Mixing of the gas and the liquid that have been separately injected into a well comprising two coaxial cylinders can occur at different levels in the well in order to facilitate the flow and to limit the gas pressure necessary for reinjection at the wellhead. Thus, the system and the method require less energy and the associated gas compression equipment is less expensive. The method and system can be applied to geothermal energy applications, underground gas storage, notably CO.sub.2, or to enhanced recovery in petroleum reservoirs.

Disclosed are compositions and methods for the pressure protection of existing wells during infill drilling operations. The methods can include injecting a gas into the existing wellbore in fluid communication with an unconventional subterranean formation prior to and/or during fracturing of the new wellbore in fluid communication with the unconventional subterranean formation.

Disclosed are compositions and methods for the pressure protection of existing wells during infill drilling operations. The methods can include injecting a foamed pressure protection composition into the existing wellbore in fluid communication with an unconventional subterranean formation prior to and/or during fracturing of the new wellbore in fluid communication with the unconventional subterranean formation.

The invention discloses an integrated method for nitrogen-assisted carbon dioxide fracturing and development of shale oil reservoirs, comprising the following steps: fracture the target shale reservoir with nitrogen-assisted carbon dioxide; after fracturing, firstly inject carbon dioxide gas into the target shale oil reservoir, and then inject nitrogen gas to push the carbon dioxide gas into the further location of the oil reservoir; shut in the well in the target shale oil reservoir; after shut-in, open the well to implement depletion production; after the first cycle of production, the slug volume of the injected gas and the shut-in time are 1.5 times of those in the previous cycle in the subsequent production, and Steps 5 to 7 are repeated for each cycle. The present invention maximizes the recovery efficiency of shale oil reservoirs; in this way, carbon dioxide gas can be used most efficiently, making the development of shale reservoir more economical and efficient; the integrated fracturing and development design enables the field operation to be streamlined and standardized, and thus different departments to cooperate each other closer.

A dispersion of capsules in critical or supercritical carbon dioxide is provided. The capsules include an aqueous solution encapsulated by zeolite-templated carbon particles. Also provided is a method of making a dispersion of aqueous solution capsules. The method includes providing a medium of critical or supercritical carbon dioxide, introducing the aqueous solution into the critical or supercritical carbon dioxide medium, and introducing a zeolite-templated carbon particle into the critical or supercritical carbon dioxide medium. Associated methods of using the disclosed dispersions in hydrocarbon-bearing formations are also provided.