Water accumulation around wellbore can block flammable hydrocarbon gas and liquid flow into the oil and gas well. The water builds high capillary pressure. High drawdown pressure is required to break the water blocking. Sometimes, even with zero flowing well pressure, the blocking still remains. In well performance analysis, the blocking is included in skin factor.
Thorough fluid and core analysis are important to establish reservoir delivery problems. Whether the reservoir is water wet or oil wet must be answered and then the most suitable way to increase the well delivery is chosen.
Altering wettability around wellbore is one way among many other ways to break water blocking. By converting the pore surfaces to oil wet condition, the capillary pressure to water is reduced or eliminated.
Before altering wettability around a wellbore, blocking water must be released or solved. Co-solvent such as surfactants, ketones, and alcohols can solve water blocking. The co-solvent volume is determined to solve water between 2 and 10 ft from the wellbore. Surfactants and ketones are usually applied for oil reservoirs while alcohols are for gas reservoirs.
Pore surfaces will return to the water-wet state after unloading the co-solvent thereby it is required to alter the wettability. Crude oil or mineral oil can be used to alter the wettability. A suitable crude oil or mineral oil is chosen in the lab by doing core flooding. The wettability alteration fluid is selected by asphaltene content, surface adsorption, and precipitation characteristics. Asphaltene content is important to maintain wettability changes.
The following figures illustrate the procedures:
Recommended reading, and an example of mineral oil: