Silica-encapsulated tracers for use in fracturing fluids and methods of preparation and etching thereof
AssigneeNCS Multistage Inc.
InventorsKha Quan TRAM, Hongbin YAN, Frank MONTOYA BETANCOURT
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Abstract
Silica-encapsulated tracers suitable for use in tracing fracturing fluid in subsurface formations are described herein. More specifically. described herein is an improved method of encapsulating tracers for reduced adsorption on a rock material, as well as less caustic methods for releasing the encapsulated tracers using ammonium hydroxide or other weak base as an etching agent. as an alternative to using highly corrosive reagents such as hydrofluoric acid.
Claims34
Use of concentrated ammonium hydroxide or other weak base as an etching agent for the release of a tracer encapsulated in a silica outer shell.
9, or 9;
- or between 7.2 and 9).
A method for recovering a tracer encapsulated in a silica outer shell, said method comprising:
- (a) contacting the silica outer shell with an etching solution comprising ammonium hydroxide or other weak base as an etching agent at a sufficient concentration and for a sufficient time to enable release of the tracer into solution:
- and
- (b) isolating and/or detecting the released tracer.
A method of tracing fluids in subsurface formations (e.g., fracturing fluids in oil-or gas-containing subsurface formations), the method comprising:
- (a) providing a plurality of unique encapsulated tracers, each tracer encapsulated in a silica outer shell:
- (b) pumping a plurality of fracturing fluid volumes into the subsurface formation, each volume comprising a unique encapsulated tracer, thereby defining a plurality of fracture zones;
- (c) pumping fluids out of the formation while taking well fluid samples:
- (d) collecting the unique encapsulated tracers from each well fluid sample and releasing the unique encapsulated tracers by contacting the silica outer shell with an etching solution comprising ammonium hydroxide or other weak base as an etching agent at a sufficient concentration and for a sufficient time to enable release of the tracer into solution;
- and
- (e) identifying and/or detecting the unique tracer within each well fluid sample.
A method of encapsulating a tracer prone to adsorption on a rock material (e.g., shale or sandstone), the method comprising:
- (a) providing a silica nanoparticle (SNP) that is functionalized to facilitate complexing to the tracer prone to adsorption on the rock material:
- (b) complexing the tracer to the silica nanoparticle in the presence of a buffer that facilitates tracer loading or deposition on the SNP to form a tracer-nanoparticle core:
- and
- (c) encapsulating the tracer-nanoparticle core in a silica shell by treating the tracer-nanoparticle core particles with a silica shell-forming solution in the presence of a low concentration of ammonium hydroxide for a sufficient time to fully encapsulate the tracer-nanoparticle core, optimally said low concentration of ammonium hydroxide being 0.01 to 0.2 M, 0.015 to 0.15 M, 0.02 to 0.1 M, 0.025 to 0.075 M:
- or being at about 0.01, 0.02, 0.03, 0.04, 0.05, 0.06,0.07, 0.08, 0.09, 0.1, 0.125, 0.15, or 0.175 M.
A method of tracing a fluid recovered from a subsurface reservoir, the method comprising:
- providing the encapsulated tracer as defined above/herein comprising an outer shell and a tracer compound, in a formation to mix with a reservoir fluid:
- recovering a portion of the reservoir fluid to surface, the reservoir fluid comprising the encapsulated tracer;
- and
- detecting the tracer compound in the sample.
Dependencies are inferred from the claim text.