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 and subsequently recovering hydrogen gas in a kerogen-rich, hydraulically-fractured unconventional gas reservoir, the method comprising:
a. sampling, at a plurality of times, a methane-containing gas recovered from the geological formation through a horizontal wellbore;
b. determining, from each sampling, an isotopic signature of a molecular component in the sampled methane-containing gas, the isotopic signature being based upon an isotope ratio;
c. responsively to and contingent upon detecting an increase in the isotopic signature of at least two successive samplings, injecting hydrogen gas through the wellbore into the geological formation at a pressure higher than a shut-in gas pressure; and
d. recovering, through the wellbore, a hydrogen-containing gas having an H 2 molar fraction of at least 85%.
2 . The method of claim 1 , wherein the isotope ratio is δ( 13 C).
3 . The method of claim 1 , wherein the isotope ratio is of the form δ(C X H Y-1 D/C X H Y ).
4 . The method of claim 1 , wherein the molecular component comprises at least one hydrocarbon selected from a hydrocarbon group consisting of methane, ethane, propane, butane, and pentane.
5 . The method of claim 1 , wherein (i) the isotopic signature is based upon an isotope ratio, and the isotopic ratio is of the form δ(C X H Y-1 D/C A H B ), (ii) C X H Y-1 D is a monodeuterated molecule of a first hydrocarbon selected from a hydrocarbon group consisting of: methane, ethane, propane, butane and pentane hydrocarbon, and (iii) C A H B is a non-deuterated molecule of a second hydrocarbon that is not the first hydrocarbon, selected from the hydrocarbon group.
6 . The method of claim 1 , wherein (i) the isotopic signature has the form δ(EXP 1 /EXP 2 ), (ii) EXP 1 is an expression representing a monodeuterated multi-alkane sum of respective concentrations of one or more of: monodeuterated ethane, monodeuterated propane, monodeuterated butane, and monodeuterated pentane, and (iii) EXP 2 is an expression representing a concentration of monodeuterated methane.
7 . The method of claim 1 , wherein (i) the isotopic signature has the form δ(EXP 1 /EXP 2 ), (ii) EXP 1 is an expression representing a monodeuterated-methane concentration, and (iii) EXP 2 is an expression representing a respective concentration of any one of: monodeuterated ethane, monodeuterated propane, monodeuterated butane, and monodeuterated pentane.
8 . The method of claim 1 , wherein (i) the isotopic signature has the form δ(EXP 1 /EXP 2 ), (ii) EXP 1 is an expression representing respective concentrations of one or more members of the monodeuterated C1-C5 alkane group consisting of monodeuterated methane, monodeuterated ethane, monodeuterated propane, monodeuterated butane, and monodeuterated pentane, and (iii) EXP 2 is an expression representing respective concentrations of one or more members of said monodeuterated C1-C5 alkane group with the exception of the one or more members represented in EXP 1 .
9 . The method of claim 1 , wherein (i) the isotopic signature has the form δ(EXP 1 /EXP 2 ), (ii) EXP 1 is an expression representing any member of the monodeuterated C1-C5 alkane group consisting of monodeuterated methane, monodeuterated ethane, monodeuterated propane, monodeuterated butane, and monodeuterated pentane, and EXP 2 is an expression representing any other member of said monodeuterated C1-C5 alkane group.
10 . The method of claim 1 , wherein the isotopic signature is based upon a ratio of isotope ratios and has the form δ( 13 C) ALKANE1 /δ( 13 C) ALKANE2 , where each of ALKANE1 and ALKANE2 includes an alkane selected from an alkane group consisting of: methane, ethane, propane, butane and pentane.
11 . A method of storing and subsequently recovering hydrogen gas in a kerogen-rich unconventional gas reservoir, the method comprising:
a. injecting a fracturing fluid through a horizontal wellbore into the geological formation to cause fracturing within the gas reservoir;
b. recovering a methane-containing gas through the wellbore;
c. monitoring an isotopic signature respective of at least one molecular component of the recovered methane-containing gas;
d. determining an isotopic-signature trigger criterion at or above 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 reaching an isotopic-signature trigger criterion based upon the monitored isotopic signature, injecting hydrogen gas through the wellbore into the geological formation at a pressure higher than a shut-in gas pressure at a wellhead; and
f. recovering, through the wellbore, a hydrogen-containing gas having an H 2 molar fraction of at least 85%.
12 . The method of claim 11 , wherein the isotopic signature is based upon an isotope ratio, and the isotopic ratio is δ( 13 C).
13 . The method of claim 11 , wherein the isotopic signature is based upon an isotope ratio having the form δ(C X H Y-1 D/C X H Y ).
14 . The method of claim 11 , wherein the at least one molecular component comprises at least one hydrocarbon selected from a hydrocarbon group consisting of methane, ethane, propane, butane, and pentane.
15 . The method of claim 11 , wherein (i) the isotopic signature is based upon an isotope ratio, and the isotopic ratio is of the form δ(C X H Y-1 D/C A H B ), (ii) C X H Y-1 D is a monodeuterated molecule of a first hydrocarbon selected from a hydrocarbon group consisting of: methane, ethane, propane, butane and pentane hydrocarbon, and (iii) C A H B is a non-deuterated molecule of a second hydrocarbon that is not the first hydrocarbon, selected from the hydrocarbon group.
16 . The method of claim 11 , wherein (i) the isotopic signature has the form δ(EXP 1 /EXP 2 ), (ii) EXP 1 is an expression representing a monodeuterated multi-alkane sum of respective concentrations of one or more of: monodeuterated ethane, monodeuterated propane, monodeuterated butane, and monodeuterated pentane, and (iii) EXP 2 is an expression representing a concentration of monodeuterated methane.
17 . The method of claim 11 , wherein (i) the isotopic signature has the form δ(EXP 1 /EXP 2 ), (ii) EXP 1 is an expression representing a monodeuterated-methane concentration, and (iii) EXP 2 is an expression representing a respective concentration of any one of: monodeuterated ethane, monodeuterated propane, monodeuterated butane, and monodeuterated pentane.
18 . The method of claim 11 , wherein (i) the isotopic signature has the form δ(EXP 1 /EXP 2 ), (ii) EXP 1 is an expression representing respective concentrations of one or more members of the monodeuterated C1-C5 alkane group consisting of monodeuterated methane, monodeuterated ethane, monodeuterated propane, monodeuterated butane, and monodeuterated pentane, and (iii) EXP 2 is an expression representing respective concentrations of one or more members of said monodeuterated C1-C5 alkane group with the exception of the one or more members represented in EXP 1 .
19 . The method of claim 11 , wherein (i) the isotopic signature has the form δ(EXP 1 /EXP 2 ), (ii) EXP 1 is an expression representing any member of the monodeuterated C1-C5 alkane group consisting of monodeuterated methane, monodeuterated ethane, monodeuterated propane, monodeuterated butane, and monodeuterated pentane, and (iii) EXP 2 is an expression representing any other member of said monodeuterated C1-C5 alkane group.
20 . The method of claim 11 , wherein monitoring the isotopic signature includes detecting a decrease in the isotope ratio from an initial value to a minimum value and, subsequently thereto, detecting an increase in the isotope ratio.