Pore-Scale Study of Transverse Mixing Induced CaCO ₃ Precipitation and Permeability Reduction in a Model Subsurface Sedimentary System

Journal Article · Fri Oct 15 04:00:00 EDT 2010 · Environmental Science and Technology

DOI:https://doi.org/10.1021/es1019788· OSTI ID:1000625

Zhang, Changyong; Dehoff, Karl; Hess, Nancy; Oostrom, Mart; Wietsma, Thomas W.; Valocchi, Albert J.; Fouke, Bruce W.; Werth, Charles J.

A microfluidic pore structure etched into a silicon wafer was used as a two-dimensional model subsurface sedimentary system (i.e., a micromodel) to study mineral precipitation and permeability reduction relevant to groundwater remediation and geological carbon sequestration. Solutions containing CaCl₂ and Na₂CO₃ at four different saturation states (Ω = [Ca²⁺] [CO^32-] / KspCaCO₃) were introduced through two separate inlets and they mixed by diffusion transverse to the main flow direction along the center of the micromodel resulting in CaCO₃ precipitation. Precipitation rates increased and the total amount of precipitates decreased with increasing saturation state, and only vaterite and calcite crystals were formed (no aragonite). The relative amount of vaterite increased from 80% at the lowest saturation (Ω_v = 2.8 for vaterite) state to 95% at the highest saturation state (Ω_v = 4.5). Fluorescent tracer tests conducted before and after CaCO₃ precipitation indicate that pore spaces were completely occluded by CaCO₃ precipitates along the transverse mixing zone, thus significantly reducing porosity and permeability, and potentially limiting transformation from vaterite to the more stable calcite. The results suggest that mineral precipitation along plume margins can decrease both reactant mixing during groundwater remediation, and injection and storage efficiency during CO₂ sequestration.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 1000625
• Report Number(s): PNNL-SA-73959; 38008
• Journal Information: Environmental Science and Technology, Journal Name: Environmental Science and Technology Journal Issue: 20 Vol. 44; ISSN 0013-936X
• Publisher: American Chemical Society (ACS)
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
ARAGONITE
CALCITE
CARBON SEQUESTRATION
DIFFUSION
EFFICIENCY
Environmental Molecular Sciences Laboratory
FORMATION DAMAGE
PERMEABILITY
PLUMES
PORE STRUCTURE
POROSITY
PRECIPITATION
SATURATION
SILICON
STORAGE
TRANSFORMATIONS
carbon sequestion
groundwater
micromodel
mineral precipititation
transverse mixing