Microbially Induced Carbonate Precipitation: a Novel Grout for Permeability Control in Subsurface Engineering Works
Abstract
ContextWe utilise the urea hydrolysing capability of soil bacteria Sporosarcina pasteurii to precipitate CaCO3 in a process termed Microbially Induced Carbonate Precipitation (MICP). MICP injection fluid properties are low particle size and low viscosity giving excellent grout penetrability. The CaCO3 grout has been shown to be effective at reducing permeability in porous and fractured media. MICP has consequently been proposed as an alternative to more traditional cement and chemical grouts, particularly in the fields of radioactive waste disposal and geological sequestration of CO2. This study investigates the role of fluid flow/CaCO3 feedback during precipitation and accelerated dissolution to better understand the longevity of an MICP grout under low pH environmental conditions such as found in a carbon sequestration reservoir. MethodsExperiments were conducted on a single Berea sandstone core in a high pressure core holder to characterise permeability, porosity and multiphase flow behaviour at sequestration reservoir temperature and pressure. Characterisation was carried out before MICP, after MICP, and after accelerated dissolution with hydrochloric acid. At each step the entire core was scanned in a medical x-ray CT scanner to spatially resolve (with a resolution of 0.5x0.5x1mm) the changes in porosity and saturation with CaCO3 precipitation and dissolution. Finally, the dried core was scanned with μ-CT at 30μm (full core) and 10μm (sub-volume) resolutions to investigate structural changes to the Berea at near pore scale. ResultsSix MICP treatment cycles over two days reduced core permeability from 886 mDarcy to 40 mDarcy with a greater reduction in porosity at the inlet. Dissolution with acid restored much of the porosity, but did not restore permeability to the same extent. Preferential flow paths formed during the dissolution step were visible in the first 4mm of the 100mm core, but did not extend further into the core. DiscussionThis study provides evidence that MICP can potentially produce a long lasting seal, even in challenging subsurface environments, provided that a thick enough layer of CaCO3 can be precipitated with a low initial permeability. Challenges remain for ensuring that such a barrier can be created in the subsurface and are the subject of further investigation.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFM.H12C..04M
- Keywords:
-
- 1055 Organic and biogenic geochemistry;
- GEOCHEMISTRYDE: 1829 Groundwater hydrology;
- HYDROLOGYDE: 1847 Modeling;
- HYDROLOGYDE: 5114 Permeability and porosity;
- PHYSICAL PROPERTIES OF ROCKS