Oil Removal in Prewet Calcite: Active Versus Inactive Ions Investigated by a Fourier Transform Infrared and X-ray...

Area of Science:

• Geochemistry
• Petroleum Engineering
• Surface Science

Background:

• Presalt reservoirs contain calcite rocks interacting with formation water (FW) and mineral oil.
• Understanding oil adsorption and removal on calcite surfaces is crucial for enhanced oil recovery (EOR).

Purpose of the Study:

• To investigate the effect of prehydration with different water types (FW, demineralized water (DW), low salinity (LS) water) on calcite surface properties.
• To analyze how these surface alterations influence subsequent oil adsorption and removal.

Main Methods:

• Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) were used to characterize calcite surfaces.
• Experiments involved prehydrating calcite with FW, DW, and LS waters, followed by conditioning with Nujol (oil) and subsequent treatment with LS water.

Main Results:

• Calcite dissolution and surface modification (Mg incorporation, water anchoring, salt deposition) occurred upon contact with DW and diluted LS water.
• Oil adsorption was higher on FW-prehydrated calcite compared to DW-prehydrated or pristine calcite.
• Enhanced oil removal was observed with LS water treatment, particularly at 0.2 mol/L ion strength, irrespective of prior surface prehydration.

Conclusions:

• Calcite's chemical composition and dissolution state significantly influence oil adsorption and removal.
• Brine ion strength, oil composition, and altered surface properties competitively affect EOR processes using LS water.