Multi-slug staged plugging method applicable to fractured formation

A multi-slug staged plugging method applicable to a fractured formation, sequentially comprising the following steps:

• 1) determining an average opening of fractures around a well as D according to logging data and a leakage amount, determining a number of stages of a multi-stage plugging according to the average opening of the fractures, and a particle size of each of a plurality of plugging particles in each stage, one stage of the multi-stage plugging corresponding to one slug, wherein a process is as follows:
• a first-stage plugging is performed by using bridging particles, the bridging particles have a particle size being slightly smaller than D, and an average particle size of the bridging particles is represented as D1;
• a second-stage plugging is performed by using a first plurality of plugging particles of the plurality of plugging particles, wherein the first plurality of plugging particles have an average particle size D2 being larger than D1/4 and smaller than D1;
• and a particle size of each of the following stages of the plurality of plugging particles is determined sequentially in a same way until an average particle size Dn of a second plurality of plugging particles in a last-stage plugging of the plurality of plugging particles is small enough to form a tight plugging layer;
• 2) injecting a first plugging slurry only containing the bridging particles having the average particle size of D1 through a first slug first to form a bridging particle layer;
• 3) injecting a second plugging slurry containing a third plurality of plugging particles of the plurality of plugging particles in several times through a plurality of slugs to form a particle filling layer, wherein the third plurality of plugging particles have an average particle size of D2˜Dn-1;
• and
• 4) finally injecting a third plugging slurry containing the second plurality of plugging particles having an average particle size being Dn through a second slug to form the tight plugging layer.