H41C-1313
Modification of Fracture Apertures by Reactive Multiphase Flow

Thursday, 17 December 2015
Poster Hall (Moscone South)
Zhenyu Xu, Purdue University, West Lafayette, IN, United States, Julie Sheets, The Ohio State University, Columbus, OH, United States, Qingyun Li, Washington University in St Louis, St. Louis, MO, United States, Timothy J Kneafsey, Lawrence Berkeley National Laboratory, Berkeley, CA, United States, David R Cole, Ohio State University Main Campus, Columbus, OH, United States, Young-Shin Jun, Washington University, St. Louis, MO, United States and Laura J Pyrak-Nolte, Purdue Univ, Department of Physics, West Lafayette, IN, United States
Abstract:
Geochemical interactions during the withdrawal/injection of fluids into the subsurface can modify fracture apertures through dissolution and/or precipitation of minerals. Modification of fracture apertures during reactive flow is strongly affected by non-reactive, non-wetting fluids that limit the fracture surface area and void volume that can be affected by reactive phases. We present results on the effect of a non-reactive, non-wetting phase during reactive flow on the distribution of precipitates and channelization caused by dissolution in fractures.

Transparent acrylic casts of a fracture in Austin chalk were used to image mineral precipitation during reactive flow. Initially, the fracture was saturated with a solution of 0.6mol/L NaHCO3 and 0.00085mol/L NaCl. Then, both the aqueous NaHCO3 - NaCl and a solution containing 3mol/L CaCl2 were pumped into the sample (0.5 ml/min) for 2 hrs. When the two solutions mix inside the fracture, CaCO3 precipitates form and CO2 bubbles are generated. CO2 bubbles affect the amount of precipitation. X-ray CT data show that precipitate thickness varies within the fracture, occurs on both fracture surfaces and also bridges the surfaces. In the test, where a CO2 bubble filled a void, precipitation did not occur. If the CO2 bubble was smaller than the pore, thin films of precipitates occurred on the fracture surfaces above and below the bubble. While fracture apertures controlled the mixing of the fluids, CO2 bubbles affected the thickness and distribution of the precipitates.

From our numerical study, channelization in a fracture is affected by the presence of a non-wetting non-reactive phase (e.g. gas) during dissolution. A modified Navier-Stokes approach was used to calculate fluxes through spatially correlated aperture distributions as a function of gas saturation. Dissolution was taken to be proportional to flux. For gas saturations < 15%, channelization occurred along the dominant flow path. However, for gas saturations >25%, dissolution along the dominant flow path was prevented, a new dominant channel was formed and single phase flow rates decreased by a factor of 10.

This work was supported by Center for Nanoscale Control of Geologic CO₂ (NCGC) an Energy Frontier Research Center funded by DOE, Office of Science, BES under Award # DE-AC02-05CH11231

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