THE IMPORTANCE OF WETTABILITY AND WETTABILITY TESTING METHODS USED IN THE OIL INDUSTRY

Abstract

The wettability of a petroleum reservoir governs the location of fluids within its pore space and hence the movement of fluids through it during production. Properties that may be affected by wettability include resistivity, capillary pressure, relative permeability and rock strength as well as behaviour during waterflood and enhanced oil recovery. Generally every reservoir is initially assumed to be water wet. When production problems arise, the wettability of a reservoir will only be questioned when all other possibilities have been accounted for. By correctly determining the wettability of a reservoir more accurate models can be provided for reservoir simulation, which in turn will improve the prediction of future field performance.

Many methods of varying difficulty and accuracy can be used to measure wettability. However, they can only be as good as the quality of the fluid samples used. It is important to understand that reliable results are only obtained when sample contamination is minimised and experimental control is maximised. Some wettability experiments can be carried out at reservoir conditions, which may be more representative, but also more susceptible to contamination.

In an oil reservoir either oil or brine can be the most wetting phase and gas is normally the least wetting phase. From a thorough investigation of downhole logs and production data it may be possible to identify wetting anomalies. Examining formation pressure data is the most recent method proposed for determining wettability.