Anti lost-circulation performance evaluation and function mechanism of fiber slurry system

Key words:  cementing  oil-well cement  fiber  slurry lost circulation  anti -lost-circulation performance

Abstract:

The lost circulation of slurry appears frequently when the vuggy formation and crack formation are encountered during cementing. Lost circulation of slurry will decrease the annular velocity，the displacement efficiency, performance of interface bonding and oil well productivity. The performances of several kinds of anti-lost-circulation slurry systems were evaluated by self-made equipment，and the anti-lost-circulation mechanisms of S90 slurry were analyzed. The results show that the S90 fiber slurry system could plug 3 mm hole and crack plate, and it can bear the pressure of 5 MPa for 10 minutes. The S90 slurry system added special bonding element KE50 could plug 4 mm hole and crack plate, and it can bear the pressure of 7 MPa for 10 minutes. During the process of lost circulation of slurry, the long fibers，short fibers and cement could form tight and fast fiber net, which can slow and prevent slurry passing. A tight filter cake is formed around fractures, so the anti-lost-circulation effect is good. While the clean slurry, latex slurry and low-density slurry have no anti -lost-circulation effect.