Composite foaming agent, foam drilling fluid as well as preparation method and application of foam drilling fluid

The invention provides a composite foaming agent, a foam drilling fluid as well as a preparation method and application of the foam drilling fluid. The composite foaming agent comprises a first foaming agent of zinc dialkyl thiophosphate (ZDDP), a second foaming agent of alkyl sulfate and water, the foam drilling fluid provided by the invention comprises 0.3 wt%-0.8 wt% of a composite foaming agent, 0.2 wt%-0.5 wt% of a foam stabilizer, 1.5 wt%-3.0 wt% of a filtrate reducer and the balance of water, the foam half-life period of the foam drilling fluid can reach 240 min at most, the temperature resistance can reach 150 DEG C, the API filter loss is smaller than or equal to 12 mL, and the performance of the foam drilling fluid is obviously higher than that of a foam drilling fluid prepared from a conventional foaming agent. 本发明提出了一种复合起泡剂、泡沫钻井液及其制备方法和应用；本发明的复合起泡剂包括二烷基硫代磷酸锌(ZDDP)的第一起泡剂和烷基硫酸盐的第二起泡剂、水；本发明的泡沫钻井液，复合起泡剂0.3wt％～0.8wt％、稳泡剂0.2wt％～0.5wt％、降滤失剂为1.5wt％～3.0wt％，余量为水；该泡沫钻井液的泡沫半衰期最长可达240min，抗温可达150℃，API滤失量≤12mL，明