Summary
We present the results of compositional reservoir simulation of a
prototypical CO2 sequestration project in a deep saline aquifer. The objective
was to better understand and quantify estimates of the most important CO2
storage mechanisms under realistic physical conditions. Simulations of a few
decades of CO2 injection followed by 103 to 105 years of natural gradient flow
were performed. The impact of several parameters was studied, including average
permeability, the ratio of vertical to horizontal permeability, residual gas
saturation, salinity, temperature, aquifer dip angle, and permeability
heterogeneity. The storage of CO2 in residual gas emerges as a potentially very
significant issue meriting further study. Under some circumstances this form of
immobile storage can be larger than storage in brine and minerals. Most
importantly, we find that permanent storage is feasible. That is, the storage
process can be designed to place large volumes of CO2 in forms that will not
escape the aquifer any faster than fluids originally present in the
aquifer.
Introduction
Geological Storage. Geological sequestration of CO2 is one of the few
ways to remove combustion emissions in sufficient volumes1 to mitigate the
greenhouse effect. Several groups have reported aquifer-scale simulations of
the storage process, usually in order to estimate the volume that can be
stored.1–14 Most schemes that have been put forward depend on storing CO2 in
the supercritical state. In these schemes, buoyancy forces will drive the
injected CO2 upward in the aquifer until a geological seal is reached. The
permanence of this type of sequestration depends entirely on the integrity of
the seal over very long periods of time. Assuring such integrity in advance is
difficult, and long-term monitoring for integrity will be costly.
Our study focuses on three modes of CO2 sequestration that avoid this
concern: 1) pore-level trapping of the CO2-rich gas phase within the geologic
formation; 2) dissolution into brine in the aquifer; and 3) precipitation of
dissolved CO2 as a mineral (e.g., calcite). All three modes are well known
phenomena among reservoir engineers and others familiar with flow in permeable
media. To date, however, little attention has been paid to the practical
implications of the first mode for storage in aquifers.
© 2005. Society of Petroleum Engineers
View full textPDF
(
1,391 KB
)
History
- Original manuscript received:
17 January 2004
- Revised manuscript received:
12 April 2005
- Manuscript approved:
9 May 2005
- Version of record:
15 September 2005
View Cart
