A method for fracturing a formation in a reservoir uses a fracturing fluid mixture comprising natural gas and a base fluid. The method comprises: determining certain reservoir conditions of the reservoir comprising the formation; selecting at least one desired behavior of the fracturing fluid mixture during a fracturing operation in the formation under the determined reservoir conditions; determining properties of the fracturing fluid mixture required to achieve the selected at least one behavior, preparing the fracturing fluid mixture having the determined properties; and injecting the fracturing fluid mixture into the reservoir under the determined reservoir conditions, such that the mixture exhibits the desired behavior during the fracturing operation. The determined properties include a mole fraction of natural gas in the mixture.