Systems and methods for enhancing carbon dioxide injectivity into a subterranean formation
A method includes identifying a wellbore that extends from a terranean surface and to a subterranean formation that includes a saline aquifer; injecting, through the wellbore, a predetermined volume of freshwater into a portion of the saline aquifer adjacent the wellbore to create a freshwater ring about the wellbore in the subterranean formation; and subsequent to injecting the predetermined volume of freshwater, injecting a carbon dioxide fluid, through the wellbore, and into the subterranean formation for sequestration.
1 . A method, comprising:
identifying a wellbore that extends from a terranean surface and to a subterranean formation that comprises a saline aquifer;
injecting, through the wellbore, a predetermined volume of freshwater into a portion of the saline aquifer adjacent the wellbore to create a freshwater ring about the wellbore in the subterranean formation; and
subsequent to injecting the predetermined volume of freshwater, injecting a carbon dioxide (CO 2 ) fluid, through the wellbore, and into the subterranean formation into which the predetermined volume of freshwater was injected for sequestration.
2 . The method of claim 1 , further comprising drilling the wellbore from the terranean surface to the subterranean formation.
3 . The method of claim 1 , wherein injecting the CO 2 fluid occurs prior to substantial mixing of the predetermined volume of freshwater with a brine fluid in the saline aquifer.
4 . The method of claim 3 , further comprising deriving the volume of freshwater by desalting at least a portion of the brine fluid that is pumped from the saline aquifer.
5 . The method of claim 1 , further comprising determining the volume of freshwater based on a plurality of geometric characteristics of the wellbore and the subterranean formation.
6 . The method of claim 5 , wherein the plurality of geometric characteristics of the wellbore and the subterranean formation comprise a geometric characteristic of the wellbore, a first geometric characteristic of the subterranean formation, and a second geometric characteristic of the subterranean formation.
7 . The method of claim 6 , wherein the geometric characteristic of the wellbore comprises a radius of the wellbore, a first geometric characteristic of the subterranean formation comprises a radius of the freshwater ring, and the second geometric characteristic of the subterranean formation comprises a thickness of the subterranean formation.
8 . The method of claim 7 , wherein determining the volume of freshwater comprises solving:
V
f
=
π
r
w
2
H
(
n
2
-
1
)
,
where V f is the volume of freshwater, r w is the radius of the wellbore, H is the thickness of the subterranean formation, and n is a ratio of the radius of the wellbore to the radius of the freshwater ring.
9 . The method of claim 8 , wherein n is a dimensionless number between 3 and 7.
10 . The method of claim 8 , further comprising calculating an injectivity ratio as a function of n, where the injectivity ratio is a measure of an ease of injection of the CO 2 fluid into the subterranean formation subsequent to injecting the predetermined volume of freshwater to an ease of injection of a CO 2 fluid into the subterranean formation exclusive of injecting the predetermined volume of freshwater.
11 . The method of claim 10 , wherein calculating the injectivity ratio comprises solving:
injectivity
ratio
=
I
*
I
=
K
K
f
ln
(
r
f
r
w
)
+
ln
(
r
p
r
f
)
ln
(
r
p
r
w
)
,
where I* is the ease of injection of the CO 2 fluid into the subterranean formation subsequent to injecting the predetermined volume of freshwater, I is the ease of injection of a CO 2 fluid into the subterranean formation exclusive of injecting the predetermined volume of freshwater, K is a conductivity of the subterranean formation adjusted for a CO 2 -dryout effect, K f is a conductivity of the subterranean formation, and r p is a radial distance from a radial center of the wellbore to a point in the subterranean formation.
12 . The method of claim 11 , wherein K f /K is a dimensionless number between 2 and 10, and r p /r w is a dimensionless number of 10.
13 . The method of claim 1 , wherein the CO 2 fluid is supercritical CO 2 .
14 . A system, comprising:
a freshwater circulation system configured to circulate freshwater into a wellbore formed from a terranean surface and to a subterranean formation that comprises a saline aquifer;
a carbon dioxide (CO 2 ) circulation system configured to circulate a CO 2 fluid into the wellbore and to the subterranean formation; and
a control system configured to perform operations comprising:
determining a volume of freshwater sufficient to create a freshwater ring about the wellbore in the subterranean formation;
causing the freshwater circulation system to circulate the determined volume of freshwater into the subterranean formation; and
causing the CO 2 circulation system to circulate, subsequent to circulation of the determined volume of freshwater, an amount of the CO 2 fluid into the subterranean formation into which the predetermined volume of freshwater was injected for sequestration.
15 . The system of claim 14 , wherein the control system causes the CO 2 circulation system to circulate the amount of CO 2 fluid into the subterranean formation prior to substantial mixing of the determined volume of freshwater with a brine fluid in the saline aquifer.
16 . The system of claim 15 , wherein the volume of freshwater is derived by desalting at least a portion of the brine fluid that is pumped from the saline aquifer.
17 . The system of claim 15 , wherein the operation of determining the volume of freshwater comprises determining the volume of freshwater based on a plurality of geometric characteristics of the wellbore and the subterranean formation.
18 . The system of claim 17 , wherein the plurality of geometric characteristics of the wellbore and the subterranean formation comprise a geometric characteristic of the wellbore, a first geometric characteristic of the subterranean formation, and a second geometric characteristic of the subterranean formation.
19 . The system of claim 18 , wherein the geometric characteristic of the wellbore comprises a radius of the wellbore, a first geometric characteristic of the subterranean formation comprises a radius of the freshwater ring, and the second geometric characteristic of the subterranean formation comprises a thickness of the subterranean formation.
20 . The system of claim 19 , wherein the operation of determining the volume of freshwater comprises solving:
V
f
=
π
r
w
2
H
(
n
2
-
1
)
,
where V f is the volume of freshwater, r w is the radius of the wellbore, H is the thickness of the subterranean formation, and n is a ratio of the radius of the wellbore to the radius of the freshwater ring.
21 . The system of claim 20 , wherein n is a dimensionless number between 3 and 7.
22 . The system of claim 20 , wherein the operations further comprise calculating an injectivity ratio as a function of n, where the injectivity ratio is a measure of an ease of injection of the CO 2 fluid into the subterranean formation subsequent to injecting the predetermined volume of freshwater to an ease of injection of a CO 2 fluid into the subterranean formation exclusive of injecting the predetermined volume of freshwater.
23 . The system of claim 22 , wherein calculating the injectivity ratio comprises solving:
injectivity
ratio
=
I
*
I
=
K
K
f
ln
(
r
f
r
w
)
+
ln
(
r
p
r
f
)
ln
(
r
p
r
w
)
,
where I* is the ease of injection of the CO 2 fluid into the subterranean formation subsequent to injecting the predetermined volume of freshwater, I is the ease of injection of a CO 2 fluid into the subterranean formation exclusive of injecting the predetermined volume of freshwater, K is a conductivity of the subterranean formation adjusted for a CO 2 -dryout effect, K f is a conductivity of the subterranean formation, and r p is a radial distance from a radial center of the wellbore to a point in the subterranean formation.
24 . The system of claim 23 , wherein K f /K is a dimensionless number between 2 and 10, and r p /r w is a dimensionless number of 10.
25 . The system of claim 14 , wherein the CO 2 fluid is supercritical CO 2 .
26 . A method, comprising:
identifying a wellbore that extends from a terranean surface and to a subterranean formation that comprises a saline aquifer;
determining a volume of freshwater based on a plurality of geometric characteristics of the wellbore and the subterranean formation, wherein the plurality of geometric characteristics of the wellbore and the subterranean formation comprise a geometric characteristic of the wellbore, a first geometric characteristic of the subterranean formation, and a second geometric characteristic of the subterranean formation;
injecting, through the wellbore, the predetermined volume of freshwater into a portion of the saline aquifer adjacent the wellbore to create a freshwater ring about the wellbore in the subterranean formation, the geometric characteristic of the wellbore comprising a radius of the wellbore, the first geometric characteristic of the subterranean formation comprising a radius of the freshwater ring, and the second geometric characteristic of the subterranean formation comprising a thickness of the subterranean formation; and
subsequent to injecting the predetermined volume of freshwater, injecting a carbon dioxide (CO 2 ) fluid, through the wellbore, and into the subterranean formation for sequestration.