Fracturing a reservoir includes providing a pad fluid to the reservoir via a wellbore in a well to create fractures in the reservoir, providing a fracturing fluid to the fractures via the wellbore, providing a geopolymer precursor fluid to the fractures via the wellbore, shutting in the wellbore at a wellbore pressure, thereby allowing the geopolymer precursor fluid to harden and form geopolymer proppant pillars in the fractures. Providing the geopolymer precursor fluid to the fractures includes pulsing quantities of the geopolymer precursor fluid into a continuous flow of the fracturing fluid or alternately pulsing quantities of the geopolymer precursor fluid and the fracturing fluid. An elapsed time between pulsing the quantities of the geopolymer precursor fluid is between 2 seconds and 20 minutes.