Abstract
Novel strategies aimed at increasing underground storage security by sealing unwanted leakage pathways near wellbores are currently under development. One such strategy is to engineer the process known as microbially-induced calcite precipitation (MICP) to achieve mineral-based sealing of fractures and reduction of permeability. Laboratory-based MICP research reported herein has demonstrated the ability to effectively reduce permeability in multiple 2.54 cm (1 inch) diameter Berea sandstone cores, seal fractures in shale cores, and seal a hydraulically fractured, 74 cm (29 inch) diameter sandstone core. This research involves integration of experimental testing and simulation modeling. In all experiments reported, Sporosarcina pasteurii biofilms were established and an injection strategy developed to optimize CaCO3 precipitation induced via enzymatic urea hydrolysis. Permeability reductions of 3-5 orders of magnitude were demonstrated. A field demonstration project successfully sealed a fractured sandstone formation located 341 m (1118 feet) below ground surface with MICP using conventional field delivery technology. MICP is a developing novel technology with the potential to seal fractures to reduce the risk of leakage from the subsurface.
1. INTRODUCTION
To manage the environmental risk of storing carbon dioxide in geologic formations, unconventional oil & gas resource development and nuclear waste disposal, novel methods are needed to prevent leakage of subsurface fluids to functional overlying drinking water aquifers or the ground surface. One method currently being explored on multiple scales (from laboratory to field) is the use of microbially-induced calcite precipitation (MICP) [1-8]. This method utilizes microbes that have the capability to alter the chemical environments in host rock pore spaces. One example is the use of ureolytic microorganisms that produce enzymes to create saturation conditions favorable for promoting MICP [9- 11]. MICP has been proposed for a number of subsurface engineering applications including preventing gas leakage by sealing fractures to secure geologic storage of CO2 or other fluids, improving wellbore integrity, and stabilizing fractured and unstable porous media [3, 6, 12-16].
