Surface characterization of reservoir rocks by inverse gas chromatography: Effect of a surfactant

• Four reservoir rocks were characterized by inverse gas chromatography.
• The studied rocks are quartz with a high purity.
• The surface heterogeneity was determined by inverse gas chromatography at finite concentration.
• The heterogeneity indexes, reflecting the high energy sites, are higher than 30%.
• The progressive impregnation with a surfactant hides chemical function.

The description of the surface chemistry of reservoir rock is essential in understanding the physico-chemical interaction between the rock surface and its environment. In this study, inverse gas chromatography (IGC) is used to characterize the surface chemistry of rocks extracted from four petroleum reservoirs in Algeria. By means of IGC at infinite dilution (IGC-ID), the dispersive component of the surface energy (γ_s^d), the nanomorphological index I_M (χ_t) and the specific component of the surface energy were determined at 100 °C. IGC at finite concentration (IGC-FC) was implemented using n-octane and isopropanol probes, allowing the irreversibility indexes and the adsorption isotherms to be obtained. From the latter, the BET specific surface area and BET constant of the injected probes were determined. Energy distribution functions and indexes of heterogeneity were also computed for the n-octane and isopropanol probes. The results showed that the polar probe, isopropanol, interacts more strongly with the rock surface than the apolar probe. In the second part of this study, the influence of a surfactant used in drilling mud on the heterogeneity of the surface energy was investigated. Different surfactant impregnation ratios were examined by means of IGC-FC. The results indicated that the progressive covering of the solid surface by the surfactant hid chemical functions likely to interact with the injected probes and made the surface smooth by covering the roughness of the surface, which led to the decrease in all parameters obtained by IGC-CF.

Figure optionsDownload as PowerPoint slideThe asymmetric distribution function obtained by Inverse gas chromatography at finite concentration on a reservoir rock becomes symmetric after the surface covering by the surfactant. This latter hid chemical functions likely to interact with the injected isopropanol probe.