Mixed gas foam fracturing fluid and preparation method thereof

According to the mixed gas foam fracturing fluid and the preparation method thereof provided by the invention, the foaming speed of a mixed gas foam fracturing fluid system can be controlled, and the mixed gas foam fracturing fluid has the characteristics of good foamability, high foam stability, strong sand-carrying capacity and low filter loss, and is simple to prepare and strong in operability. The mixed gas foam fracturing fluid is prepared from the following components in percentage by volume: 65 to 80 percent of gas phase and 20 to 35 percent of liquid phase, wherein the gas phase is mixed gas formed by mixing carbon dioxide and nitrogen according to the volume ratio of 3: 2; the liquid phase is prepared from, by mass, 12-18 parts of liquid carbon dioxide, 1-2 parts of zwitterionic surfactant, 2-3 parts of acrylamide, 2-3 parts of foaming agent, 2-3 parts of foam stabilizer, 1-3 parts of nano particles, 2-4 parts of clay stabilizer, 1-2 parts of thickening agent, 1-3 parts of acid catalyst and 10-20 par