Multi-slug staged method for plugging fractured formation
A multi-slug staged method for plugging a fractured formation includes: determining an average opening of fractures around a well as D, an average particle size of bridging particles for first-stage plugging as D 1 that is slightly less than D, and average particle sizes of plugging particles for second to last-stage plugging as D 2 -D n , where D n is small enough to form a tight plugging layer; and sequentially injecting a plugging slurry only containing the bridging particles having the average particle size of D 1 , plugging slurries containing the plugging particles having the average particle sizes of D 2 -D n-1 , and a plugging slurry containing the plugging particles having the average particle size of D n into the fractures to achieve the fractured formation plugging.
1. A multi-slug staged method for plugging a fractured formation, sequentially comprising steps of:
1) determining an average opening of fractures around a well as D according to logging data and a leakage amount of the fractures, determining a number of stages of a multi-stage plugging as n according to the average opening of the fractures, determining an average particle size D 1 of first plugging particles of first stage plugging of the multi-stage plugging, and respectively determining average particle sizes D 2 -D n of second to n th plugging particles of second to n th stage plugging of the multi-stage plugging, wherein the first plugging particles are bridging particles; D 1 is smaller than D; D 2 is larger than D 1 /4 and smaller than D 1 ; the n th plugging particles having the average particle size D n are configured to form a tight plugging layer; and one stage plugging of the multi-stage plugging corresponds to one slug;
2) injecting a plugging slurry only containing the bridging particles having the average particle size D 1 into the fractures through a first slug to form a bridging particle layer, wherein the bridging particles are rigid particles;
3) injecting plugging slurries respectively containing the second to (n−1) th plugging particles having the average particle sizes D 2 -D n-1 into the fractures in a plurality of times through respective second to (n−1) th slugs to form a particle filling layer; and
4) finally injecting a plugging slurry containing the n th plugging particles having the average particle size D n into the fractures through an n th slug to form the tight plugging layer.
2. The multi-slug staged method for plugging the fractured formation according to claim 1 , wherein in step 1), the average particle size D 2 of the second plugging particles used in the stage plugging approaches D 1 /4.
3. The multi-slug staged method for plugging the fractured formation according to claim 1 , wherein in step 1), the n th plugging particles used in the n th stage plugging are an ultrafine plugging agent having the average particle size D n being smaller than 0.1 mm.
4. The multi-slug staged method for plugging the fractured formation according to claim 1 , wherein the rigid particles are walnut shells or calcium carbonate.
5. The multi-slug staged method for plugging the fractured formation according to claim 1 , wherein in step 3), the second to n th plugging particles of the second to n th stage plugging are selected from the group consisting of fibers, flaky materials and elastic particles to improve plugging stability, wherein
a particle size of the fibers, a particle size of the flaky materials or a particle size of the elastic particles corresponds to the average particle sizes D 2 -D n .
6. The multi-slug staged method for plugging the fractured formation according to claim 5 , wherein the fibers are animal hairs or plant fibers, the flaky materials are mica flakes or rice husks, and the elastic particles are rubber particles or asphalt.
7. The multi-slug staged method for plugging the fractured formation according to claim 1 , wherein in step 4), bentonite or lime milk is added to the n th plugging particles used in the n th stage plugging to increase a compactness.