BIOMINERALIZATION: A STRATEGY TO MODIFY PERMEABILITY IN THE SUBSURFACE

Strategies to mitigate leakage pathways or seal fractures in the subsurface are important to seal leaking wells or control fluid transport. Biomineralization is a proposed technology for sealing unwanted leakage pathways in the near wellbore environment and modifying permeability in the subsurface. The biomineralization sealing technology developed at Montana State University utilizes microbes to promote biomineral formation in fractures (for example fractured shale, sandstone, or between cement/steel interfaces) and in the pore spaces of rocks (for example sandstone).

Reactor systems have been designed in the laboratory to study the permeability reduction achievable by biomineralization under ambient and subsurface pressure conditions. These reactor systems are being used to develop injection strategies which have resulted in 3-6 orders of magnitude permeability reduction in 100 µm- 4mm gaps between shale, sandstone and cement/steel interfaces. The laboratory reactor systems were used to scale up and develop injection strategies applicable to the field.

Two field demonstrations of the biomineralization sealing technology have been completed. The first demonstration showed fracture sealing was possible in a sandstone formation 1120’ below ground surface and that the fracture had increased resistance to re-fracturing after biomineralization treatment. The second field demonstration was performed in a well with an identified channel 1017’ below ground surface in cement near the wellbore. Biomineralization treatment resulted in reduced pressure decay during shut in periods and reduced injectivity. In addition, a noticeable difference was observed in the solids percentage in the ultrasonic imaging logs before and after biomineralization treatment. These successful experiments suggest biomineralization is a promising technology for modifying permeability in the subsurface. Work continues to develop strategies to promote mineralization in CO₂-affected brine environments as well as in high temperature environments.