The swelling of smectite clays in the interburden rock layers of coal seam gas wells results in spalling of fine particles that may negatively impact gas production through damage to the well's pump and/or the permeability of the coal layers. One of the causes of the clay swelling is the change in water chemistry at the wellbore location due to drilling fluids and the influx of produced water. The conventional technology to mitigate the swelling of smectite clays in oil and gas reservoirs is to stabilize the clay using a brine such as 4 % KCl, and although this technology is relatively low cost and initially effective the mitigation of clay swelling is temporary because K+ ions are easily washed from the clay when the well is brought into production. An alternative approach recently reported is to use nanoparticles and nanofluids to control clay swelling.
In this laboratory study we evaluated the effectiveness of five commercially available nanoparticles – SiO2, Al2O3, ZnO, Fe2O3, and ZrO2 – to prevent swelling of a natural bentonite clay that was rich in sodium montmorillonite. The effectiveness of the nanoparticles to prevent clay swelling was measured with a visual swelling index method based on ASTM D5890-11 and compared to the swelling of the clay in 4 % KCl brine. In the initial nanoparticle screening tests performed in distilled water all the nanoparticles except for the ZnO exhibited some potential to mitigate the swelling of bentonite. The next stage of screening experiments was performed in model formation water solutions containing 2500 mg /L and 9000 mg/L of Na ions at pHs of 5 and 9. In the model formation water tests, the SiO2 was the most effective nanoparticle to mitigate clay swelling across the range of conditions examined.
These experimental results suggest nanoparticles may be a potential solution to mitigate clay swelling and spalling in coal seam gas reservoirs as well as other types of reservoirs. Further research is required to elucidate the mechanism of swelling inhibition with SiO2 nanoparticles and to develop practical methods to deploy nanoparticles into a CSG well.