Lost circulation plug

Lost circulation. A cement plug can be placed adjacent to a zone of lost circulation in the hope that the cement slurry will penetrate and seal fractures (see Figure 4-406). 

Other methods propose to use materials that interact in the fissures of the formation to form a plug of increased strength. Lost circulation additives are sunamarized in Table 1-12. 

Fiber-containing cement was initially developed as a high-strength material that could be used to line a borehole [1789]. Several relatively simple and cheap spin-off applications of fiber cement were identified, such as the use of fiber cement in cement plugs for borehole stabilization and as a lost circulation material. Several companies are already applying or offering fiber cement for these purposes in the field, in both organic fibers and metal fibers [372,1077, 1682-1684]. 

Vinyl monomers are used as such and are allowed to polymerize in place to form a gel. This technique is used to enable a solution to gel slowly, even at high temperatures. An aqueous solution of a vinyl monomer is mixed with a radicalforming initiator and optionally with a dispersant. The initiator decomposes at elevated temperatures and initiates the polymerization process. In this way, a gel is formed in place. Radical polymerization is sensitive to molecular oxygen. For a more pronounced delay, polymerization inhibitors may be added to the solution in small amounts. The technique is used in the treatment of subterranean formations, especially for plugging lost circulation in drilling operations, particularly at elevated temperatures. 

Two other types of operations involve cement slurries. They are used to plug back a well from a deeper to a shallower depth for a number of reasons abandonment, whip stocking, lost circulation, or shutting olf water. Squeeze cementing consists of forcing a column of cement slurry... 

To remove the blockage, the line was depressured on both sides of the plug. Then methanol was circulated into the line to accelerate the hydrate dissociation rate. After complete removal of the hydrates, the dehydrator was cleaned, inspected and restarted properly. The entire remedial operation required 36 h to complete. The major cost was the lost production time. 

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