Large-Scale Geological Carbon Sequestration - Introduction to Carbon Capture and Sequestration - page 482

considers it separately. The bigger difference between the DOE and
CSLF approaches is that the CSLF approach makes a conservative
assumption that only the volume of the formation with structurally closed
traps is available for storage. In contrast, the DOE approach includes the
entire formation thickness as potential storage volume in acknowledg-
ment of the potential importance of residual-phase trapping. This differ-
ence can be large, as sketched in Figure 10.3.3 , and this points out an
unresolved source of uncertainty and variability that must be considered
when evaluating various published capacity estimates.
Also listed in Table 10.3.1 for completeness is the USGS approach
which is based on principles used in the National Oil and Gas Assessment
[10.32]. Briefl y, the USGS approach considers the uncertainty in proper-
ties of the storage formations and performs Monte Carlo analyses to
arrive at probabilistic estimates of capacity [10.33,10.34]. Although a

Table 10.3.1 Approaches used for estimating reserve capacity

Group Approach Notes

US DOE C = A h g φ tot ρ E Applies to entire area being

assessed, and includes entire
gross thickness of formation.
Effi ciency factor accounts for all
of the effects that limit CO 2
pore-fi lling.

CSLF C = A trap h trap φ trap ρ (1- S lr ) C c Applies only to the closed

structure parts of the reservoir
(trap). Separates out effect of
residual aqueous phase ( S w )
from the effi ciency factor ( C c ).

USGS Probabilistic assessment carried out

by categorizing trapping as either
primarily structural or primarily
residual-phase. Based on
geological model uncertainty,
uses Monte Carlo simulation to
determine likely storage capacity.

Requires expert judgment about
trapping style, knowledge of
structure, and other critical
factors. Well-established
precedent in the National Oil
and Gas Assessment.

Definitions: A = area of region being assessed for CO 2 storage capacity; h g = gross thickness of
formation being assessed; φ tot = average porosity over thickness h g ; ρ = density of CO 2 averaged
over h g ; E = efficiency factor reflecting fraction of total pore volume filled by CO 2 .