Salt Precipitation in Ultratight Porous Media and Its Impact on Pore Connectivity and Hydraulic Conductivity

• Published in: Water resources research Vol. 54; no. 4; pp. 2768 - 2780
• Main Authors: Alizadeh, A. H., Akbarabadi, M., Barsotti, E., Piri, M., Fishman, N., Nagarajan, N.
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 01-04-2018
• Subjects: Chemical precipitation; Cleaning; Cleaning process; Effluents; FIB‐SEM; Fluid dynamics; Fluid flow; Hydraulic conductivity; Ion beams; Laboratory experiments; Methanol; Oil reservoirs; Permeability; Plugs; pore connectivity; Porous media; Precipitation; Pressure drop; Removal; salt extraction; salt precipitation; Salts; Scanning electron microscopy; Sediment samples; Silver; Silver nitrate; Workflow
• ISSN: 0043-1397; 1944-7973
• DOI: 10.1002/2017WR021194

The degree of salt precipitation and its impact on fluid flow in ultratight porous media are investigated in three preserved core plugs selected from two different wells in an unconventional hydrocarbon reservoir. Small specimens are cut from the core plugs and then imaged using a focused ion beam scanning electron microscope (FIB‐SEM) to detect any salt precipitation in the pore space. The SEM results show that salt covers the pore walls and either partially or fully blocks pore elements, making some parts of the pore space inaccessible to flow. To examine the effect of salt removal on fluid flow, one of the core plugs is subjected to a cleaning process. The plug is initially saturated with methanol, and then methanol is continuously injected into the sample while the effluent is periodically titrated using silver nitrate to monitor salt removal. The variation of the salinity of the methanol effluent with time, the decrease in the pressure drop across the core, and the increased permeability to methanol indicated the effectiveness of the cleaning process. The successful removal of salt from the sample prompts the adoption of a new workflow for preparing tight rock samples for laboratory experiments.
Key Points
Precipitation of salt in the pore space may adversely affect the hydraulic conductivity of ultratight rocks
Salt crystals can partially or fully occupy pore elements, leading to unrealistic measurements of transport properties of the medium
Solid salt must be extracted from the pore space by injecting a solvent before conducting any laboratory core analyses