American Oil and Gas Reporter - September 2023 - 80

SpecialReport: CCS Feasibility Studies
density. It also incorporates a swelling
or shrinking factor to account for the
reality that a mixture of CO2, hydrocarbons
and water will have a different
volume at reservoir conditions than each
phase by itself.
Another factor is reservoir heterogeneity.
The more homogenous the reservoir,
the higher its storage capacity/efficiency
is likely to be.
This equation can be applied at the
regional scale or to individual wells. In
general, a well that produces high volumes
of oil, gas and water will be a good candidate
for CO2 injection and storage.
Basins' Storage Capacity
By plugging production data from unconventional
basins into the equation, we
can estimate those areas' potential CO2
storage capacity.
The production data came from IHS
Enerdeq. Using an imported geographic
polygon of each basin outline, all horizontal
wells located within the boundary
were selected and exported. This list then
was filtered by stratigraphic formation,
when necessary, and used to build a production
allocated query, generating proTABLE
1
Cumulative Production and Estimated Storage Capacity For Various Plays
Produced Volumes
Basin
Marcellus
Delaware
Eagle Ford
Barnett
Haynesville
Anadarko
Midland
Fayetteville
Bakken
Niobrara
Utica
Piceance
Total
Oil (MMbbl)
164
5,009
4,697
62.9
16.0
1,478
3,557
3,207
1,038
2.35
1.74
19,232
Gas (Bcf) Water (MMbbl)
73,319
580
21,123
22,334
33,853
19,067
10,447
10,021
5,347
5,584
1,087
207
225,652
80 THE AMERICAN OIL & GAS REPORTER
17,898
4,667
2,131
970
6,273
2.99
2,751
455
27.1
7.96
39,019
619
188
0.34
0.32
3,681
648
94.5
15.7
16,057
296
679
1,250
From Oil
27.7
973
23,262 3,254 887 1,772
11.3
1,889
1,888
1,460
7,039
63.8
2,307
410
552
286
131
788
0.25
354
59.4
2.56
0.98
4,955
CO2 Storage Capacity (MT)
From Gas
duced volumes for oil, gas and water.
For these estimates, we calculated average
temperatures and pressures across
the basin. Table 1 summarizes the produced
volumes and calculated storage
capacities. The total storage capacity approaches
25 GT of CO2.
Figure 2 presents the storage capacity
estimates using a bubble map. The larger
the bubble, the higher the capacity. The
pie slices indicate the contribution from
different liquids (red for gas, green for
oil and blue for water). For basins with
no gas contribution indicated, gas was
treated as entirely solution gas, rather
than free gas at reservoir conditions.
Today, gas plays contribute more storage
capacity. For instance, the Marcellus
has a potential capacity of 7.1 GT, more
than twice that of the Delaware (3.3 GT).
This result reflects the fact that gas plays
have produced more than oil plays on a
barrel-of-oil-equivalent basis (37.6 billion
barrels of oil equivalent gas to 19.2 billion
barrels of oil).
At the same time, there is more storage
capacity from produced water than from
produced oil. The dominance of water
comes primarily from the Delaware
Basin. At around 18 billion barrels, the
basin's water production is almost equal
to total oil production from all these
plays combined.
There are several uncertainties associated
with the basin-scale capacity estimation.
First, some of the produced
water may have originated from outer
reservoirs and reached the well through
fractures or faults, meaning it should
not be considered part of the pressure
cavity in the unconventional reservoir.
Second, in gas reservoirs, preferential
adsorption of CO2 to methane can increase
the overall capacity, although the
increase may be minor.
Third, there is uncertainty in calculating
the formation volume factors and scCO2
density using the basin-scale average
pressure and temperature. The estimates
also could benefit from more specific information
on other parameters, such as
shrinkage or swelling factors.
Other sources of uncertainty include
the presence of free gas or oil in primary
oil or gas producing plays.
Taking these uncertainties into account,
storage capacity in the United
States' unconventional reservoirs likely
From Water
Total
7,130
3,280
3,069
2,453
2,174
1,888
1,467
1,250
973
916
97.4
17.0
24,714
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