in the effective permeability and relative permeability both u03b4k ew k ew and u03b4k rw k rw decreased with increasing comparative compound a concentration but compound a had an optimum concentration at 3 wt among all the chemicals compound d had the best performance in increasing the water effective permeability in berea followed by compound a compound d was the only chemical containing siloxane which was perhaps contributing to its superior performance to repel water however for the reservoir core comparative compound a was more effective than compound a between compound e and compound f compound e 1 05 wt polymer with the largest u03b4k ew k ew and u03b4k rw k rw performed the best in water injection test all the results for k rw in table 7 and table 8 provided a strong indication that the chemical treatment changed the core surface from hydrophilic to hydrophobic resulting in an increase in water mobility in summary the examples demonstrated the wettability modification of various rock samples from liquid wetting to intermediate gas wetting by the method of the present invention wherein the rock samples are contacted with a composition comprising a low molecular weight fluorinated copolymer in accordance with the invention the wettability modification increased the contact angle of liquid drops on the core and decreased the spontaneous imbibition the effect of wettability modification on liquid mobility was pronounced in the gas water system the adsorption of the fluorochemical onto the core surface has negligible effect on the absolute permeability for the chemicals with small molecular weight thus while there have been described what are presently believed to be the preferred embodiments of the present invention those skilled.