Fine-grained mixed rock pore pressure prediction method and system based on variable longitudinal wave velocity

The invention relates to a fine-grained mixed rock pore pressure prediction method and system based on variable longitudinal wave velocity, and belongs to the technical field of unconventional oil and gas reservoir pore pressure prediction.The method comprises the steps that rock longitudinal wave velocity tests under different effective stresses are carried out, a function form of the relation between sound wave velocity and the effective stresses is determined, parameters in the function are obtained through optimization fitting, and the effective stresses are obtained; and establishing an effective stress influence item evaluation model according to lithology. According to actually measured formation pressure data and the effective stress influence item model, reversely deducing a sound wave speed background value, preferably selecting a logging curve, and establishing a sound wave speed background value logging evaluation model; according to logging curves such as DT and DEN, a sound wave speed background