X-ray CT and multiphase flow characterization of a ‘bio-grouted’ sandstone core: The effect of dissolution on seal longevity

James M Minto,Ferdinand F Hingerl,Sally M Benson,Rebecca J Lunn

doi:10.1016/j.ijggc.2017.07.007

Abstract

Microbially induced carbonate precipitation (MICP) is a novel method for controlling permeability in the subsurface with potential for sealing or reducing leakage from subsurface engineering works such as carbon sequestration reservoirs. The purpose of this research was to measure, at core scale, the change in reservoir permeability and capillary pressure due to MICP during seal formation, then to monitor the integrity of the seal when exposed to acidic groundwater capable of causing dissolution. The experiment was carried out with a Berea sandstone core mounted in a high pressure core holder within a medical X-ray CT scanner.Multiple full volume CT scans gave spatially resolved maps of the changing porosity and saturation states throughout the experiment. Porosity and permeability decreased with MICP whilst capillary pressure was increased. Dissolution restored much of the original porosity, but not permeability nor capillary pressure. This lead to the conclusion that injection pathways were coupled with carbonate precipitation hence preferential flow paths sealed first and transport of the dissolution fluid was limited. Provided a high enough reduction in permeability can be achieved over a substantial volume, MICP may prove to be a durable bio-grout, even in acidic environments such as a carbon sequestration reservoir.

Highlights

IntroductionInduced carbonate precipitation (MICP) is a process in which bacteria (e.g. the soil bacteria Sporosarcina pasteurii) mediate a biochemical reaction that can result in the precipitation of calcium carbonate
Induced carbonate precipitation (MICP) is a process in which bacteria mediate a biochemical reaction that can result in the precipitation of calcium carbonate
Results are interpreted with respect to: change in permeability and capillary pressure at the core scale; average values of porosity and variation in X-ray attenuation from inlet to outlet; and fully 3D representations of porosity (Fig. 3) at each stage of CaCO3 precipitation and dissolution

Summary

Introduction

Induced carbonate precipitation (MICP) is a process in which bacteria (e.g. the soil bacteria Sporosarcina pasteurii) mediate a biochemical reaction that can result in the precipitation of calcium carbonate. When urea hydrolysis takes place in the presence of a calcium source such as calcium chloride (CaCl2), the pH increase and the production of carbonate lead to CaCO3 precipitation with the bacteria acting as nucleation points for crystal growth (Ferris et al, 2003) This MICP process has been investigated for several purposes including: improving strength and stiffness of porous media whilst maintaining permeability (DeJong et al, 2010; van Paassen, 2009; Whiffin et al, 2007); permeability reduction in porous media (Handley-Sidhu et al, 2013; Mitchell et al, 2013; Tobler et al, 2012); immobilising pollutants (Fujita et al, 2008; Mitchell and Ferris, 2005) and producing selfhealing concrete (Jonkers et al, 2010). MICP is both less expensive (Gallagher et al, 2013; Ivanov and Chu, 2008; Suer et al, 2009) and less toxic than many chemical grouts

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