# A Novel Application of New High-Strength Plugging Agent in Baikouquan Oilfield
## 3 Performance Evaluation by Laboratory Tests
These results show that in a high-temperature environment, the plugging strength does not decay but tends to be stable. It shows that the plugging agent has a superior plugging effect and improved the period of validity for field application. Based on the above analysis and discussion, the experimental data shows that with the increase in plugging density, the plugging strength is stronger, and the plugging agent presents favorable temperature resistance. Combined with the actual situation, it can be confirmed that the plugging agent has high plugging strength in high salinity formations, which can effectively plug the leakage formation and casing damage, improving its pressure-bearing capacity. In the research by [PERSON] [40] and [PERSON] [41] on a gel plugging agent, the pressure-bearing capacity of the plugging agent was less than 10 MPa. [PERSON], \(S\)'s [42] research on resin plugging agents shows that the plugging strength can reach 40.65 MPa, but it easily solidifies instantaneously during construction and has poor drillability. Mechanism of plugging agent. On the one hand, the plugging agent slurry is squeezed into the leakage formations under pump pressure during the repair process of casing damage in wells. The components of the plugging agent slurry are condensed together to extrude part of the free water in the case that the structure promoter is subjected to differential pressure. The different lengths of flexible fibers, rigid fibers, hydration product gels and crystals produced by chemical reactions in the plugging slurry play the role of stretching, winding and so on, which can increase the flow resistance of the plugging slurry in the leakage formation and rapidly form a bonding between the plugging agent slurry and the action layer, limiting its flow to the far formation. It can be concentrated in the leakage layer to play a role in plugging. After the slurry flows into the leakage formation, it preferentially flows into the large channel with little resistance. With the increase in the plugging slurry injection rate, the resistance flowing into the large channel increases, forcing the plugging slurry to flow into the small channel, which plays an effective role in plugging the leakage formation channel. On the other hand, the dense spatial network structure is formed by winding and bridging of active filler, crystal formed by reactions, hydration products, etc., which enhances the plugging effect [43; 44]. With the increase in injection pressure, the downhole solidified body has high strength and interfacial bonding strength because of the synergistic effect generated by various materials such as interface strength enhancer, toughening agent, structure promoter and nano-active filler. Moreover, under the further action of sealing internal pressure, the close contact of the plugging agent particles makes the hydration reaction more complete and the structure of the hydration product more compact, so as to promote the improvement in the strength of the solidified body and interface bonding strength. The expansion active components of the plugging agent further enhance the tightness of the interface cementation through its own micro-expansion [45; 46; 47]. Therefore, the solidified body after plugging has favorable toughness and flushing resistance, which ensures the reliability and success rate of the plugging operation. Expansion performance of plugging agent. Figure 7 shows the curve for the expansion rate of the plugging agent over time. It can be found that the expansion rate of the plugging agent increases with the increase in time. The expansion rate increases rapidly from 0 to 6 days, and the rate slows down from 6 to 9 days. The expansion rate of the plugging agent tends to be stable from 9 to 10 days, and the final recorded value is stable at about 4.3%. The experimental results show that the expansion rate of the plugging agent is due to the micro-expansion system.