Isobaric expansion casing leakage stopping method

The invention relates to the technical field of leakage stopping operation for multi-pressure-system strata and malignant leaking strata, in particular to an isobaric expansion casing leakage stoppingmethod. The method comprises the following steps that 1, when an upper-layer casing body is put down into a designed position, casing shoes of a horn-mouth structure follow the upper-layer casing body to be put down into the design position in advance, and after well cementation is conducted according to construction design, a lower drill drills the casing shoes to form a first lap-joint horn mouth, wherein the inner diameter of the horn-mouth structure of the lower ends of the casing shoes is larger than the inner diameter of the upper-layer casing body; 2, after a complex stratum has well leaking during drilling, a reaming tool is put down into a well for fixed-diameter reaming on a to-be-drilled section. According to the method, the borehole size is not damaged, the well depth structure is not changed, the int