Hydrogen production, storage and recovery
A method for operating a kerogen-rich unconventional gas reservoir characterized by there being multiple hydraulically-fractured wells drilled thereinto comprises: recovering a methane-containing gas from a first hydraulically-fractured well drilled into the gas reservoir, steam-methane reforming the recovered methane-containing gas to yield a hydrogen gas and an inorganic carbon-containing gas, injecting at least a portion of the hydrogen gas into a second hydraulically-fractured well drilled into the gas reservoir, and injecting at least a portion of the inorganic carbon-containing gas into a third hydraulically-fractured well drilled into the gas reservoir.
1. A method of storing hydrogen gas in a kerogen-rich geological formation, the method comprising:
a. injecting a fracturing fluid through a horizontal wellbore into the geological formation to cause fracturing within the geological formation;
b. recovering a methane-containing gas through the wellbore, the recovering characterized by a maximum flow rate FLOW MAX ;
c. monitoring a current flow rate FLOW CURRENT of the recovered methane-containing gas over time;
d. determining a flow-rate trigger criterion FLOW TRIGGER at or below which hydrogen injected into the geological formation is subsequently recoverable in a hydrogen-containing gas having an H 2 molar fraction of at least 85%;
e. responsively to and contingent upon the monitored FLOW CURRENT being equal to or below FLOW TRIGGER , ceasing the recovering of the methane-containing gas and injecting a hydrogen gas through the wellbore into the geological formation at a pressure higher than a current shut-in gas pressure at the wellbore; and
f. subsequent to the injecting, recovering, through the wellbore, the hydrogen-containing gas having the H 2 molar fraction of at least 85%.
2. The method of claim 1 , wherein FLOW TRIGGER is equal to at least 10% of FLOW MAX and not more than 20% of FLOW MAX .
3. The method of claim 1 , wherein FLOW TRIGGER is determined based at least in part on a kerogen concentration in the geological formation.
4. The method of claim 1 , wherein FLOW TRIGGER is determined based at least in part on a fluid flow regime of the geological formation.
5. The method of claim 1 , wherein the injecting of the hydrogen gas is at a pressure that is less than a calculated hydrogen fracture extension pressure H2FRAC EXT within the geological formation.
6. The method of claim 1 , wherein the monitoring of the current flow rate FLOW CURRENT includes determining the flow regime in the geological formation.
7. The method of claim 1 , wherein (i) the determining includes determining the flow-rate trigger criterion FLOW TRIGGER at or below which hydrogen injected into the geological formation is subsequently recoverable in a hydrogen-containing gas having an H 2 molar fraction of at least 90%, and (ii) the recovered hydrogen-containing gas has an H 2 molar fraction of at least 90%.
8. The method of claim 1 , wherein the kerogen concentration of the kerogen-rich geological formation is at least 2% by volume.
9. A method of storing and subsequently recovering a hydrogen gas, the method comprising:
a. injecting the hydrogen gas through a horizontal wellbore into a hydraulically-fractured, kerogen-rich, and partially-depleted reservoir of a methane-containing gas, at a pressure higher than a current shut-in gas pressure at the wellbore, the partial depletion of the reservoir being by a methane-containing-gas recovery process characterized by a maximum flow rate of FLOW MAX ,
b. determining a flow-rate trigger criterion FLOW TRIGGER below which hydrogen injected into the reservoir is subsequently recoverable in a hydrogen-containing gas having an H 2 molar fraction of at least 85%; and
c. recovering a portion of the hydrogen gas through the wellbore, the recovered portion of the hydrogen gas having an H 2 molar fraction of at least 85%,
wherein FLOW TRIGGER is equal to at least 10% of FLOW MAX and not more than 20% of FLOW MAX .
10. The method of claim 9 , additionally comprising a step, performed before the injecting of the hydrogen gas, of selecting the reservoir based on a kerogen concentration in the reservoir.
11. The method of claim 9 , additionally comprising a step, performed before the injecting of the hydrogen gas, of selecting the reservoir based on a fluid flow regime of the reservoir.
12. The method of claim 9 , wherein (i) the determining includes determining the flow-rate trigger criterion FLOW TRIGGER at or below which hydrogen injected into the reservoir is subsequently recoverable in a hydrogen-containing gas having an H 2 molar fraction of at least 90%, and (ii) the recovered hydrogen-containing gas has an H 2 molar fraction of at least 90%.
13. The method of claim 9 , wherein the kerogen concentration in the reservoir is at least 2% by volume.
14. A system configured for storing and subsequently recovering a hydrogen-containing gas by performing the method of claim 9 , the system comprising:
a. pumping arrangements for injecting hydrogen-containing gas, disposed in fluid communication with the hydraulically-fractured, kerogen-rich and partially-depleted reservoir of a methane-containing gas and operative to inject the hydrogen gas through a horizontal wellbore into the reservoir at a pressure higher than a shut-in gas pressure at the wellbore; and
b. gas-recovery equipment disposed in fluid communication with the reservoir and operative to recover the portion of the hydrogen-containing gas through the wellbore.
15. The system of claim 14 , wherein the fluid flow regime of the reservoir is substantially characterized by diffusional processes.
16. The system of claim 14 , wherein the fluid flow regime of the reservoir is substantially Knudsen diffusion.
17. The system of claim 14 , additionally comprising equipment for monitored by a delta (C13) isotope ratio in the recovered methane to determine a fluid flow regime in the reservoir.