PNNL-13501 - Pacific Northwest National Laboratory

Study Control Number: PN00053/1460
Impacts of CO2 Injection on Deep Geologic Formations
B. Peter McGrail, Paul F. Martin, K. Prasad Saripalli, Toni Owen
Sequestration in deep geologic formations is one option being considered by the Department of Energy to reduce the
global atmospheric concentration of the greenhouse gas CO2. This project addresses fundamental issues regarding the
effects of CO2 injection on the chemical and physical properties of these geologic formations.
Project Description
Injection of CO2 in deep geologic formations is one
option being considered by DOE (Office of Fossil
Energy) for managing man-made CO2 emissions. Costeffective
CO2 sequestration is being considered in
depleted oil or gas wells, coal seams, and deep
underground saline formations. However, the long-term
impacts of CO2 injection on the physical and chemical
properties of the host formation are not well understood.
The purpose of this project is to develop a better
understanding of the effects of carbonate mineral
precipitation during CO2 injection on the hydrogeologic
properties of porous rocks. A pressurized unsaturated
flow apparatus was developed and used to conduct alkaliflooding
experiments. Injection of CO2(g) caused pore
plugging near the injector and poor use of the available
sediment porosity for carbonate mineral trapping.
Therefore, a counter-flow, pulsed injection method was
developed that takes advantage of the properties of
precipitation waves to achieve much higher efficiency in
use of the sediment capacity for sequestering CO2.
Introduction
The three mechanisms of CO2 sequestration applicable to
deep geologic formations are hydrodynamic, dissolved,
and mineral phase trapping (DOE 1993; Hitchon 1996).
Reporting on the injection of supercritical CO2 into deep
geological formations, Gupta (1999) emphasized that
understanding the geochemical behavior of disposed CO2,
including the kinetics and equilibria of precipitationdissolution
reactions, is critical to the success of CO2
injection and storage. Lackner et al. (1997) recommend
the chemical binding of CO2 by chemical reactions with
oxides and hydroxides of calcium and magnesium to form
stable carbonates as an attractive and significant
sequestration mechanism. Based on batch experimental
studies, Lackner et al. (1997) found Mg(OH)2 to be
particularly suitable, because of faster reaction kinetics.
224 FY 2000 Laboratory Directed Research and Development Annual Report
A significant finding from their work was that several
geochemical processes may be suitable for mineral
trapping of CO2, but only a few may have sufficiently fast
kinetics to be of practical use. Similar observations were
made by Bachu et al. (1994). However, none of these
studies has been conducted in partially saturated
sediments. Because of the high solid-liquid ratio under
unsaturated conditions, significant increases in
precipitation kinetics may occur such that use of simpler
and cheaper Ca(OH)2 solutions is practicable.
Approach
Two sets of experiments were conducted to assess the
influence of injection of CO2 in porous media. The first
set of experiments was conducted with a modified
pressurized unsaturated flow apparatus (McGrail et al.
1999a), as shown in Figure 1. The sensor/effluent
collection package was pressurized with helium to
prevent modification of the effluent pore water pH.
Pressurized Sensor and
Effluent Collection Package
Pressure
Differential
Regulator
Computer Control and
Data Acquisition System
Figure 1. Picture of modified pressurized unsaturated flow
apparatus for CO 2 injection experiments. The pressurized
unsaturated flow system is patented.