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Abstract
The most promising near term solution to reduce CO2 emissions is to capture
the CO2 produced from coal and gas fired power plants and inject it into deeply
buried saline aquifers. However a large amount of these plants are far away
from deep sedimentary basins and therefore alternative solutions have to be
sought. Detailed computer simulation, using compositional numerical model
software CMG-GEMGHG, was used to study the effects of aquifer anisotropy
(heterogeneity), well completion technique (perforation and well orientation),
brine production and injection rates on CO2 injectivity, and capability to
retain and store reasonably large amount of CO2 for an extended period of time.
The objective of this study is to find the optimal combination of operational
parameters (injection rates, well completion techniques and brine withdrawal
strategy), and how the interplay of these parameters with aquifer anisotropy
(heterogeneity) affects, and can be manipulated to optimally harness CO2
storage potential and leakage risk mitigation in shallow saline aquifers.
Injected CO2 exists in three main forms in the aquifer, supercritical,
dissolved and aqueous forms with amount depending largely on prevailing
formation pressure and the depth of well placement. Without brine withdrawal,
horizontal injector wells with the vertical sections closed have higher CO2
injectivity compared to vertical and deviated wells with bottom half
perforated. With brine withdrawal more CO2 was injected and anisotropy
(heterogeneity) (Kv/Kh ratio) has significant effect on CO2 injectivity, but
well perforation and orientation has negligible effect, except for an extended
(85 years) injection period when aquifer pressure has reached the maximum
allowable. The impact of anisotropy (heterogeneity) on CO2 injectivity was
observed to decrease with increase on injection rate for injection well placed
in uppermost layers. This study shows CO2 sequestration in shallow saline
aquifer has significant potential. Results from this study can potentially
provide guideline for well completion technique, injection rate and brine
withdrawal strategy, depending on aquifer properties, that can be applied in
CO2 sequestration in shallow saline aquifer.
Introduction
Global warming and its attendant consequences have become a major concern
to the world. The primary source of this phenomenon has long been attributed to
the burning of fossil fuel (automobile, gas and coal fired power plants), which
results in the emission of excessive amount of CO2 into the atmosphere. One of
the major sources of emission into the atmosphere is from the coal fired power
plants. A potential solution to this particular source of CO2 emission is to
capture the CO2 produced from these power plants and inject it into geological
formations, namely depleted oil, gas and coalbed methane (CBM) reservoirs, and
underground saline aquifer. The potential CO2 storage capacity of these
geological formations in the Southeast Carbon Sequestration Partnership alone
have been estimated to be 2,369.4 to 9,235.5 gigatonnes, with saline aquifers
accounting for 95% of this storage capacity (Petrusak et al. 2009). The SECARB
partnership comprises Alabama, Arkansas, Florida, Georgia, Louisiana,
Mississippi, North Carolina, South Carolina, Tennessee, Virginia and east
Texas. The Plains CO2 Reduction (PCOR) Partnership, comprising of regions in
Canada (Alberta, British Columbia, Manitoba, Saskatchewan,) and United States
(Iowa, Minnesota, Missouri, Montana, , Nebraska, North Dakota, South Dakota,
Wisconsin, Wyoming), have also been estimated to have geologic CO2 storage
potential of 242 billion tonnes; 91% of which is in the saline aquifers
(UND-EERC, 2009). However for many states, including the State of Missouri,
lies far away from the deep sedimentary basins and would likely be subject to
the highest transportation costs for CO2 disposal. Therefore for many utility
companies which are faced with the prospect of federal and state regulation of
CO2 emissions, need to develop an effective, economical means to capture and
sequester CO2 in the proximity of the power plants.
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