Nano-encapsulated triggered-release viscosity breakers

Abstract

A method for the encapsulation and triggered-release of water-soluble or water-dispersible materials. The method comprises a) providing an amount of electrolyte having a charge, b) providing an amount of counterion having a valence of at least 2, c) combining the polyelectrolyte and the counterion in a solution such that the polyelectrolyte self-assembles to form aggregates, d) adding a compound to be encapsulated, and e) adding nanoparticles to the solution such that nanoparticles arrange themselves around the aggregates. Release of the encapsulated species is triggered by disassembly or deformation of the microcapsules though disruption of the charge interactions. This method is specifically useful for the controlled viscosity reduction of the fracturing fluids commonly utilized in the oil field.

Description

FIELD OF THE INVENTION[0001]The present invention relates to methods and compositions for controlled viscosity reduction of fracturing fluids used in subterranean formations. The method involves both encapsulation and release of viscosity breakers by using microcapsules assembled from charged nanoparticles and polyelectrolytes. During the microcapsule assembly process, breakers such as enzymes, persulphate, aminocarboxylates, etc., are encapsulated into the shell. The encapsulated species are released during the disassembly or deformation of the microcapsules induced by the addition of salt (NaCl, brine, sea water, etc.). The methods and compositions are designed in such a way that the reduction of viscosity is initiated by contacting fracturing fluids with brine solution.[0002]This method can more generally be utilized for encapsulating water-soluble or water-dispersible materials in microcapsules assembled from nanoparticles and, as such, is useful for the encapsulation and releas...

AI Technical Summary

Benefits of technology

[0012]The present invention provides a simple method for encapsulating and releasing various species using nanoparticle-assembled capsules (NACs) having spherical and non-spherical shapes. In preferred embodiments, the present methods for the encapsulation comprise providing a polyelectrolyte having a positive or negative charge, providing an oppositely charged counterion having a valence of at least 2, combining the polyelectrolyte and the counterion in a solution such that the polyelectrolyte self-assembles to form aggregates, adding the compound to be encapsulated, allowing the compound to enter the aggregates, and adding nanoparticles to the solution such that nanoparticles arrange themselves around the aggregates and encapsulate the compound.

[0016]The herein presented method to encapsulate and release breakers and various other species using hybrid microcapsules offers several advantages. The method is extremely simple to carry out, allows huge flexibility in materials composition, and can be made environmentally and economically favorable. The ease of encapsulating a wide variety of compounds makes it viable for a broad spectrum of applications. The one-step method of encapsulation during the assembly of NACs occurs in one pot, and thus there is no need for a large synthesis set-up. NACs can be used to encapsulate both enzymatic and oxidative viscosity breakers. The one-step method of releasing the encapsulate by salt-induced disruption of NACs is simple and does not require any harsh conditions, as opposed to the extreme pH and / or temperature treatments generally employed in other methods. These mild synthesis conditions, which cover a wide pH range, allow the encapsulation of sensitive organic compounds that would otherwise be degraded. And, finally, the present composition and processes can easily be adapted to the procedures for using breaker-containing fracturing fluids currently employed in the stimulation of subterranean formations.

Problems solved by technology

When a fracturing fluid containing such beads passes or leaks off into the formation or the fluid is removed by back flowing, any resulting fractures in the subterranean formation close and crush the beads.

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