Self-powered microsensors for in-situ spatial and temporal measurements and methods of using same in hydraulic fracturing

1. A delayed-activation sensor system comprising:

a plurality of microsensors, each of said plurality of microsensors comprising at least one sensor module for sensing a condition in an environment; and

a group coating encapsulating the plurality of microsensors, the group coating configured to dissolve based on a first condition to expose said plurality of microsensors;

wherein at least a first one of said plurality of microsensors further comprises a first individual dissolvable coating encapsulating at least a portion of the at least one sensor module, the first individual dissolvable coating configured to dissolve after the group coating and based on a second condition different than the first condition to expose the at least one sensor module to the environment;

wherein at least a second one of the plurality of microsensors comprises a second individual dissolvable coating encapsulating the second one of the plurality of microsensors, the first and the second individual dissolvable coatings configured to cause said plurality of microsensors to cluster together through electrostatic surface charge, van der Waal forces, electrostatic force, or surface polarity; and

at least one of a fracking mixture or proppants, wherein the plurality of the microsensors are mixed therein.

2. A method of in-situ monitoring a hydraulic fracturing operation, the method comprising:

injecting a plurality of self-powered microsensors with a fracking mixture, proppants, or a combination thereof into a well bore, each of said plurality of microsensors comprising at least one sensor module for sensing a condition in an environment,

wherein a group coating encapsulates the plurality of microsensors, the group coating configured to dissolve based on a first condition to expose said plurality of microsensors;

wherein at least a first one of said plurality of microsensors comprises a first individual dissolvable coating encapsulating at least a portion of the at least one sensor module, the first individual dissolvable coating configured to dissolve after the group coating and based on a second condition different than the first condition to expose the at least one sensor module to the environment;

wherein at least a second one of the plurality of microsensors comprises a second individual dissolvable coating encapsulating the second one of the plurality of microsensors, the first and the second individual dissolvable coatings configured to cause said plurality of microsensors to cluster together through electrostatic surface charge, van der Waal forces, electrostatic force, or surface polarity;

dissolving at least the group coating on the self-powered microsensors in the well bore;

activating the self-powered microsensors; and

obtaining measurements from each of the self-powered microsensors.

3. The method of claim 2 , wherein the group coating includes a thermal dissolvable coating, the thermal dissolvable coating being selected from a group consisting of a polyamide, polyglycolide or polyglycolic acid, polyvinyl alcohol, polyvinyl pyrrolidone, polyethylene glycol, polystyrenesulfonate, quaternized amine polymers, alkoxomers, and mixtures thereof.

4. The method of claim 2 , wherein the group coating includes a water dissolvable coating, the water dissolvable coating being selected from a group consisting of a polymer, PC polymer, cellulose, hydroxyethylcellulose, ethylcellulose, cellulose esthers, resins, and mixtures thereof.

5. The method of claim 2 , wherein the group coating includes a pH dissolvable coating, the pH dissolvable coating being selected from a group consisting of a cationic polyacrylamide, acrylate, aminoacrylate, alkyl PEG-20, and mixtures thereof.

6. The method of claim 2 , wherein the plurality of microsensors each have dimensions from 1 mm to 20 mm.

7. The method of claim 2 , wherein at least one of the plurality of microsensors further comprises a support body for supporting the at least one sensor module, and wherein the first individual dissolvable coating encapsulates the support module.

8. The method of claim 7 , wherein the support body has a cuboid shape, and wherein the first individual dissolvable coating forms a spheroid shape.

9. The method of claim 2 , wherein at least one of the plurality of microsensors further comprises at least one energy harvester module to generate electrical power for the microsensor from the environment, wherein the at least one energy harvester module is selected from a mechanical energy harvester module, a thermal energy harvester module, or an electrochemical energy harvester module including two dissimilar metals that form an electrochemical cell with a fluid in the environment.

10. The method of claim 2 , wherein the first individual dissolvable coating of the first microsensor dissolves slower than the second individual dissolvable coating of the second microsensor such that the first and the second microsensors provide staggered sensor activation at different times.

11. The method of claim 2 , further comprising receiving, at one or more supersensors, sensor data from the plurality of microsensors and retransmitting the sensor data to a receiving point outside the environment.

12. The method of claim 2 , wherein the measurements are obtained during the hydraulic fracturing.

13. The method of claim 2 , wherein the measurements are obtained from within fractures created by the hydraulic fracturing.

14. The method of claim 2 , further comprising creating a map during and/or after hydraulic fracturing based on data from the self-powered microsensors.

15. The method of claim 2 , further comprising transmitting wireless signals between the microsensors to form a sensor network of microsensor nodes.

16. The method of claim 2 , further comprising transmitting signals from the microsensors to a collection point for telemetry.

17. The method of claim 2 , further comprising transmitting signals to and/or from the microsensors for determining locations of the microsensors using triangulation.

18. The method of claim 2 , wherein the first and the second individual dissolvable coatings are configured to dissolve based on different environmental conditions.