DETERMINING THRESHOLD HYDRAULIC GRADIENT FOR CAPROCKS ASSOCIATED WITH GEOLOGICAL CO2 AND H2 STORAGE

1 . A method comprising:

collecting a caprock core sample;

determining threshold hydraulic gradient for the caprock core sample using a testing apparatus, the testing apparatus comprising:

a core container comprising:

an upstream inlet in fluid communication with the core container;

a downstream inlet in fluid communication with the core container; and

a confining pressure pump in fluid communication with a bottom portion of the core container;

an upstream reservoir in fluid communication with the upstream inlet of the core container and comprising a first upstream valve for selectively permitting or ceasing fluid flow between the upstream reservoir and the core container;

an upstream pump in fluid communication with the upstream reservoir and comprising a second upstream valve for selectively permitting or ceasing fluid flow between the upstream pump and the upstream reservoir;

a downstream reservoir in fluid communication with the downstream inlet of the core container and comprising a first downstream valve for selectively permitting or ceasing fluid flow between the downstream reservoir and the core container; and

a downstream pump in fluid communication with the downstream reservoir and comprising a second downstream valve for selectively permitting or ceasing fluid flow between the downstream pump and the downstream reservoir,

wherein the determining comprises:

installing the caprock core sample in the core container, wherein the core container is pressurized using the confining pump to a predetermined confining pressure and the caprock core sample is saturated with water;

preparing the testing apparatus by closing the first upstream valve and the second downstream valve, pressurizing the upstream reservoir using the upstream pump, and closing the second upstream valve upon reaching a predetermined pressure in the upstream reservoir;

conducting a flow test by opening the first upstream valve and measuring the pressure difference between a measured pressure of the upstream inlet of the caprock core sample and a measured pressure of the downstream outlet of the caprock sample;

calculating a pressure differential as a function of time (ΔP t ) based on the measured pressure difference when the pressure difference does not change with time any longer; and

calculating a threshold hydraulic gradient (J t ), where

J

t

=

Δ

⁢

P

t

L

 and L is a length of the caprock core sample.

2 . The method of claim 1 , further comprising repeating the preparing and conducting steps if the measured pressure difference between the inlet and the outlet has not changed with time.

3 . The method of claim 1 , wherein installing the caprock core container comprises:

enclosing at least one sleeve about the caprock core sample.

4 . The method of claim 3 , wherein the core container is pressurized using the confining pump by pumping a confining fluid into core container outside of the at least one sleeve.

5 . The method of claim 1 , wherein the upstream pump in the testing apparatus pumps water or a saline solution into the upstream reservoir and the downstream pump in the testing apparatus pumps water or a saline solution into the downstream reservoir.

6 . The method of claim 1 , wherein the upstream pump in the testing apparatus pumps a liquid into the upstream reservoir and the downstream pump in the testing apparatus pumps a liquid into the downstream reservoir.

7 . The method of claim 1 , wherein the caprock core sample has a diameter in the range of 1 inch to 4 inches, and an axial length in the range of 1 inch to 2 inches.

8 . The method of claim 1 , wherein the caprock core sample has a diameter of 1 inch and an axial length of 1 inch.

9 . The method of claim 1 , wherein the predetermined confining pressure is in the range of 500 psi to 5,000 psi.

10 . The method of claim 1 , wherein the predetermined confining pressure is in the range of 500 psi to 2,500 psi.

11 . The method of claim 1 , wherein the caprock core sample is collected from a saline aquifer, the saline aquifer for sequestration of CO 2 or storage of H 2 .

12 . The method of claim 1 , wherein the caprock core sample is collected from a depleted oil and gas well, the oil and gas well for sequestration of CO 2 or storage of H 2 .

13 . A testing apparatus comprising:

a core container for receiving a core sample comprising:

an upstream inlet in fluid communication with the core container;

a downstream inlet in fluid communication with the core container; and

a confining pressure pump in fluid communication with a bottom portion of the core container;

an upstream reservoir in fluid communication with the upstream inlet of the core container and comprising a first upstream valve for selectively permitting or ceasing fluid flow between the upstream reservoir and the core container;

an upstream pump in fluid communication with the upstream reservoir and comprising a second upstream valve for selectively permitting or ceasing fluid flow between the upstream pump and the upstream reservoir;

a downstream reservoir in fluid communication with the downstream inlet of the core container and comprising a first downstream valve for selectively permitting or ceasing fluid flow between the downstream reservoir and the core container; and

a downstream pump in fluid communication with the downstream reservoir and comprising a second downstream valve for selectively permitting or ceasing fluid flow between the downstream pump and the downstream reservoir.

14 . The testing apparatus of claim 13 , further comprising a temperature sensor provided at each of the upstream pump, downstream pump, and confining pump.

15 . The testing apparatus of claim 13 , further comprising a pressure sensor provided at each of the upstream pump, downstream pump, and confining pump.

16 . The testing apparatus of claim 13 , further comprising a temperature sensor provided proximate to each of the upstream outlet and the downstream outlet.

17 . The testing apparatus of claim 13 , further comprising a pressure sensor provided proximate to each of the upstream outlet and the downstream outlet.

18 . The testing apparatus of claim 13 , further comprising a flow meter interposing the upstream reservoir and the core container.

19 . The testing apparatus of claim 13 , further comprising a flow meter interposing the downstream reservoir and the core container.