Reservoir condition pore-scale imaging of reaction

This thesis presents the first dynamic imaging of fluid/rock reaction using x- ray microtomography (μ-CT) and focuses on three series of experiments: (1) imaging a homogenous carbonate during dissolution using a laboratory scanner; (2) imaging heterogeneous carbonates at multiple flow rates using a synchrotron pink beam; (3) imaging the same rocks using a laboratory scanner at multiple reactive conditions incorporating effluent analysis. First the in situ reservoir condition imaging apparatus was adapted to image Ketton carbonate dynamically using a laboratory μ-CT scanner. 10 images were acquired over 2 1⁄2 hours. Porosity and surface area were measured from the images and permeability and connectivity were calculated using flow models. Ketton dissolved uniformly at these conditions although the effective reaction rate (reff) was 16 times lower than those measured in batch reactor experiments with no transport limitations. Second the experimental apparatus was used with fast synchrotron-based μ- CT to image two more complex carbonates, Estaillades and Portland Basebed at two different flow conditions. ~100 images were taken over 2 hours, which captured the complexity of dissolution. It was found that the type of dissolution is both pore structure and flow rate dependent. A new type of dissolution, channelling, is observed which has a reff up to 100 times lower than batch rates. Third, effluent analysis was incorporated into the experimental apparatus. All three rocks were imaged again at two separate reactive conditions. The reff was between 10 and 100 times lower than the batch rates, with the lowest rates in samples with the most channelized flow, confirming that transport limitations are the dominant mechanism in determining reff at the fluid/solid boundary. Effluent analysis confirmed that using the in situ, rather than the injected pH, to determine reff is valid in the uniform regime, but overestimates reff with channelling by an order of magnitude.Open Acces