Abstract
AbstractTemperature changes and variations in pore fluid salinity may negatively affect the permeability of clay‐bearing sandstones with implications for natural fluid flow and geotechnical applications alike. In this study these factors are investigated for a sandstone dominated by illite as the clay phase. Systematic long‐term flow‐through experiments were conducted and complemented with comprehensive microstructural investigations and the application of Derjaguin‐Landau‐Verwey‐Overbeek (DLVO) theory to explain mechanistically the observed permeability changes. Initially, sample permeability was not affected by low pore fluid salinity indicating strong attraction of the illite particles to the pore walls as supported by electron microprobe analysis (EMPA). Increasing temperature up to 145°C resulted in an irreversible permeability decrease by 1.5 orders of magnitude regardless of the pore fluid composition (i.e., deionized water and 2 M NaCl solution). Subsequently diluting the high salinity pore fluid to below 0.5 M yielded an additional permeability decline by 1.5 orders of magnitude, both at 145°C and after cooling to room temperature. By applying scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) thermo‐mechanical pore throat closure and illite particle migration were identified as independently operating mechanisms responsible for observed permeability changes during heating and dilution, respectively. These observations indicate that permeability of illite‐bearing sandstones will be impaired by heating and exposure to low salinity pore fluids. In addition, chemically induced permeability variations proved to be path dependent with respect to the applied succession of fluid salinity changes.
Highlights
When the thermal and/or chemical equilibrium in geological formations is disturbed by variations in environmental conditions, permeability changes may occur
Sample permeability was not affected by low pore fluid salinity indicating strong attraction of the illite particles to the pore walls as supported by electron microprobe analysis (EMPA)
The application of DLVO theory for deionized water pore fluid conditions to our results suggests that repulsions between illite particles and between illite and the grain walls are strong
Summary
When the thermal and/or chemical equilibrium in geological formations is disturbed by variations in environmental conditions, permeability changes may occur. A number of experimental studies performed on Berea, Vosges, Upper Coal, and Fontainebleau sandstones indicate that increasing temperature causes a permeability decrease that in most cases is fully or at least partially recovered after cooling (e.g., Jing, 1990; McKay & Brigham, 1984; Rosenbrand et al, 2015; Sun et al, 2016). The permeability of some low‐permeable sandstones was observed to be independent of temperature (Gobran et al, 1987; Potter et al, 1980; Wei et al, 1986).
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
