# A Novel Application of New High-Strength Plugging Agent in Baikouquan Oilfield
## 3 Performance Evaluation by Laboratory Tests  
Plugging Strength. The strength of the plugging agent in a leakage environment is a key parameter of new micro-expansion plugging agents. In order to evaluate the plugging capacity, the laboratory test was carried out by simulating the lost formation with the bearing-capacity test apparatus, which can simulate a complex downhole environment. The plugging agent pressure-bearing capacity test apparatus and test process are shown in Figures 3 and 4. The specific experimental method for pressure-bearing capacity of the plugging agent experiment and performance evaluation of plugging agent were as follows:  
1. The electronic balance YP3002 from Shanghai Youke Instrument Co., LTD. was used to weigh the appropriate amount of plugging agent powder, and the plugging agent was stirred evenly by electric mixer D90-A from Qingdao Haitongda Special Instrument Company Ltd. According to different water-cement ratios, the plugging agent slurries with different densities of 1.55 g/cm\({}^{3}\), 1.65 g/cm\({}^{3}\), 1.70 g/cm\({}^{3}\) and 1.75 g/cm\({}^{3}\) were prepared, respectively. 2. The steel pipe was fixed with a core holder, and a sand control net was placed at the bottom of the steel pipe. Subsequently, on-site formation water with a salinity of 1.5 \(\times\) 10\({}^{5}\) mg/L was used to saturate the quartz sand. A certain mesh and particle size of quartz sand were filled into the steel tube uniformly to simulate the Baikouquan Formation with a porosity of 12% [38], and the prepared plugging agent slurry was filled into the steel tube. 3. The booster pumper and the pressure valve were opened in turn. The pump pressure was adjusted and maintained at a certain pressure to simulate the wellbore conditions at the construction site. At the same time, the temperature simulator was turned on to select different temperatures to simulate the formation environment. The solidified body of plugging agent was maintained under pressure for 48 h under this condition. 4. The experimental temperatures were selected as 40 \({}^{\circ}\)C, 60 \({}^{\circ}\)C, 80 \({}^{\circ}\)C, 100 \({}^{\circ}\)C and 120 \({}^{\circ}\)C, respectively. The booster pumper and the pressure valve were opened in turn to adjust the pump pressure. Water with different salinities was passed through the solidified body and the simulated formation under water pressure. 5. When the first drop of water drops out, the pressure displayed by the pressure meter is the breakthrough pressure, which is also called plugging strength. As water pressure increases, breakthrough phenomena become more obvious. When the pressure suddenly displays zero, this is the maximum pressure, and it is called the breakdown pressure. 6. In this step, the plugging agent with a density of 1.70 g/cm\({}^{3}\) was used. In order to study the effect of time on plugging effect, the plugging strength corresponding to the curing time of 0.5 weeks, 1 week, 5 weeks, 10 weeks, 15 weeks, 20 weeks and 25 weeks was measured under the conditions that the curing temperatures were 80 \({}^{\circ}\)C and 100 \({}^{\circ}\)C, respectively, referring to the above procedure. Figure 3: Apparatus for plugging strength simulation experiment. Expansion performance of plugging agent. The expansion rate was measured by an HTP-3 high-temperature and high-pressure intelligent expansibility instrument produced by Qingdao Hengtaida Electromechanical Equipment Co., LTD. [39]. The test conditions selected were as follows: the pressure was 3 Mpa, the temperature was 80 \({}^{\circ}\)C, and the density of plugging slurry prepared with water of 1.5 \(\times\) 10\({}^{5}\) mg/L salinity was 1.65 g/cm\({}^{3}\). Then, the expansion rate of the plugging agent over time was measured. Reological properties of plugging agent. In this experiment, different densities of plugging agent slurry commonly used in the field (1.45 g/cm\({}^{3}\), 1.60 g/cm\({}^{3}\), 1.70 g/cm\({}^{3}\)) were prepared.