Understanding the initial wettability of reservoirs

Panagiotis Aslanidis defended his thesis on wettability for core analysis. The purpose of his research was to link reservoir wettability to the properties of the crude oil, rock mineralogy and formation water composition.

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Portrett av Panagiotis Aslanidis
Panagiotis Aslanidis

Panagiotis Aslanidis defended his thesis November 8th. He did his PhD project for The National IOR Centre of Norway.

See his thesis here: Experimental Reproduction of Wettability for Core Analysis

About the PhD project: Any EOR (enhanced oil recovery) method aiming at improving the water-wet-ness of the reservoir rock is dependent on the state of the initial rock wettability. The initial reservoir wettability is generated through chemical interactions between reservoir rock, formation water and crude oil components, influenced by reservoir temperature over geological time. The importance of reservoir chemistry is often overlooked in oil production processes. However, the chemistry affects the initial wettability of the reservoir, and thereby also the fluid location and flow during oil production.

Aslanidis' study focused on improving the understanding of the initial wettability of the reservoir rock, by investigating chemical interactions between the different reservoir phases; crude oil, brine and rock.

The ideal scenario when core samples are retrieved from the field to the lab is to start the experiment immediately without any treatment. Due to a decrease in pressure and temperature from reservoir to standard conditions, fluid expansion occurs. The depressurized cores will not have a correct fluid saturation and need to be restored prior to laboratory core experiments. To achieve representative reservoir data from these tests, the restored core wettability needs to be close to reservoir conditions.

Wettability dictates the fluid flow in porous media, and the restored wettability will dramatically influence the results on capillary pressure, relative permeability, and oil recovery tests in laboratory experiments. Therefore, wettability should be preserved in-between restoration processes.

The wettability of a core retrieved in the lab can be affected during cleaning and restoration procedures. A wide range of cleaning techniques are followed in laboratories. The same applies in core restoration, where the restoring protocol differs from one lab to another.

In this project, several reservoir sandstone and outcrop carbonate cores, underwent a series of experiments in regard to wettability. The solvents utilized during core cleaning and the amount of crude oil exposed to the core during core restoration were the study's major emphasis.

The findings indicated that mild cleaning followed by an uncontrolled quantity of crude oil exposure might have a substantial influence on the wettability of the system, causing it to become less water-wet. A more comprehensive adsorption test on the reservoir sandstone core demonstrated that polar organic components (POC) continue to adsorb on the mineral surface. However, the use of more rigorous solvents resulted in the reverse situation, resulting in more water-wet conditions. Finally, the use of mild solvents had no effect on the wettability of the systems between restorations.

In conclusion, this doctoral thesis proposes an efficient core cleaning and restoration process in which the wettability of the cores is replicated from one restoration to the next.