Geological Society of America

T10 CO2 Sequestration in Deep Saline Aquifers: Leakage Pathways, Risk Assessment, and Impact on Overlying Aquifers

Sunday, 31 October 2010
8:00 AM - 12:00 PM
Room 402

THE CHALLENGE OF PREDICTING GROUNDWATER QUALITY IMPACTS IN CO2 LEAKAGE SCENARIOS: RESULTS FROM FIELD, LABORATORY, AND MODELING STUDIES AT A NATURAL ANALOG SITE IN NEW MEXICO, USA

Paper number: T10-7
Program: Technical Sessions
Time: 9:25 AM – 9:45 AM

Authors

Elizabeth H. Keating Presenting Author
Earth and Environmental Sciences, Los Alamos, NM
J. Alexandra Hakala
National Energy Technology Lab; U.S. Department of Energy, Pittsburgh, PA
Hari Viswanathan
Los Alamos National Laboratory, Los Alamos, NM
Rosemary Capo
University of Pittsburgh, Pittsburgh, PA
Brian Stewart
University of Pittsburgh, Pittsburgh, PA
James B. Gardiner
University of Pittsburgh, Pittsburgh, PA
J. William Carey
Los Alamos National Laboratory, Los Alamos, NM
Julianna Fessenden
Los Alamos National Laboratory, Los Alamos, NM

Abstract

A vital aspect to public and regulatory acceptance of carbon sequestration is assurance that drinking water in overlying aquifers will be protected. Theoretical and laboratory studies can, to some extent, be used to predict the consequences of leakage. However, direct observations of CO₂ flowing through shallow drinking water aquifers are invaluable for informing credible risk assessments. To this end, we have sampled shallow wells in a natural analog site in New Mexico, USA, where CO₂ from natural sources is upwelling from depth. We collected major ion, trace element, and isotopic (³H, ¹⁸O, and Sr) data and, coupled with laboratory experiments and reactive transport modeling, have concluded that major controls on groundwater quality at this site include in-situ reactions driven by CO₂ and mixing with saline waters upwelling with the CO₂.

Using reactive transport modeling based upon field and laboratory data, we show the different reactivity of the CO₂ and CO₂/saline water source terms, particularly with respect to carbonate mineralogy. Sr isotopes can be used to understand whether particular waters are affected by carbonate mineral reaction with CO₂, or by saline water intrusion. Preliminary data suggest that Sr isotopes can successfully be used to discriminate between the two types of source terms at Chimayo; this technique shows promise for monitoring CCS sites.

Ultimately the information gained from field and laboratory measurements must be integrated into predictive models that can support risk assessment at future CCS sites. We are developing a 3-D reactive transport model for the New Mexico analog site that considers both CO₂impacts and CO₂/saline water impacts; constrained by water chemistry measurements at this site and specific reactions and mineral phases gleaned from our experiments. We demonstrate the utility of Sr isotopes data to further constrain mixing of source term(s) with background waters in the model, and redox controls on trace metal solubility in understanding influences of CO₂ and saline fluids on groundwater quality. The model is particularly useful in identifying the temporal and spatial scales of water quality changes and in developing possible mitigation strategies in the case of leaks at engineered CCS sites.