Nanoarchitectonics and performance evaluation of a Fe 3 O 4 -stabilized Pickering emulsion-type di ﬀ erential pressure plugging agent

: With the rapid growth of natural gas consumption capacity, the important role of gas storage in seasonal peak shaving and emergency response is gradually emerging. Long-term forced production and injection of gas storage will lead to problems such as wellhead equipment leakage and string seal failure. Replacing the string is not only costly but also takes a long time. Aiming at thread leakage caused by multiple rounds of forced production and injection in gas storage, a Pickering emulsion di ﬀ er-ential pressure plugging agent with a self-sealing function under a certain pressure di ﬀ erence was developed. We selected carboxyl nitrile latex with a self-polymerization function and modi ﬁ ed the nano-stabilizer Fe 3 O 4 @SiO 2 . The Pickering di ﬀ erential pressure plugging agent with excellent plugging performance was prepared by the combination of modi ﬁ ed particles and non-ionic emulsi ﬁ er OP-10. The plug-ging test was carried out for the simulated oil pipe thread. When the leakage rate was 50 mL/min, no leakage occurred under a pressure of 20 MPa after plugging. The di ﬀ erential pressure plugging agent is expected to achieve plugging without moving the pipe string and rebuild the integrity of the wellbore.


Introduction
After multiple rounds of high-intensity and periodic injection and production in Shuang6 gas storage of Liaohe Oilfield, annulus pressure has appeared.Through preliminary analysis of 15 old wells that have injected and produced gas in Shuang6 gas storage, it can be determined that the pressure of annulus A in some wells is due to the leakage of sealing components such as tubing and packer.Long-term annulus pressure will not only cause additional corrosion to the casing but also cause additional corrosion to the casing.This can lead to the failure of wellhead shielding, leading to well control risks.At present, the disposal methods of annulus A band pressure all require the disposal of the original production and completion pipe string, and the workover cost of a single well is up to 10 million yuan (to investigate similar wells of Huabai gas storage and Dagang gas storage).Besides, the workover cycle of gas storage wells is lengthy, and there are many uncontrollable factors in the workover process, which are easy to lead to unexpected conditions such as reservoir pollution caused by killing wells and casing damage caused by milling packers, resulting in irreversible damage.In order to reduce the cost of workover, low-cost and safe workover, there is an urgent need to conduct research on differential pressure plugging technology, plug the loss channel in a nonselective way, and re-establish well integrity.
In recent years, researchers have reported a pressure differential plugging agent with a short repair cycle and simple operation.The sealant has a bionic sealing effect similar to wound blood coagulation.It can only activate the liquid-solid conversion reaction under the effect of the leak point pressure difference, coalesce and precipitate at the edge of the leak hole, and finally form a ductile solid, block the leak point, and complete the sealing repair.However, the remaining sealant remains in a flowing state and will not block other production systems [1][2][3].Compared with the traditional sealing repair injection agent, the differential pressure plugging agent has stable chemical properties, does not react during transportation, and is not affected by the transmission time, ambient temperature, and pressure.Its sealing characteristics only depend on the nature of the leak point and the differential pressure [4,5].A differential pressure plugging agent shows important application value in oil and gas development, storage and transportation, and other fields.Xu et al. [6] studied a differential pressure-type plugging agent with a polydisperse system.The plugging agent uses butadiene nitrile latex particles as an emulsifier and removes the surface water film of butadiene nitrile latex particles by adding electrolyte, so that the butadiene nitrile latex can be agglomerated under the cooperation of the viscosityincreasing agent, and can effectively seal the 5 mm 3 leak under 5.7 MPa.Guo et al. [7] developed a differential pressure-activated sealant with nitrile latex as the main agent, CH 3 COONa as the activator, and OP-40 as the terminator, which can effectively repair the leakage and withstand a liquid pressure of 40 MPa after repair.Chang [8] verified that the differential pressure-activated sealant can effectively seal high-pressure and high-leakage rate oil and gas wells with an environmental pressure of 35 MPa.At the same time, the tubing foam simulation plugging experiment verified that the foam differential pressure-activated sealant can effectively seal low-pressure and low leakage rate oil and gas wells with an environmental pressure of less than 10 MPa.
The most important thing in preparing a differential pressure plugging agent is the selection of latex and stabilizer.On the one hand, latex determines the performance of the plugging agent; on the other hand, the stabilizer determines whether the plugging agent can effectively prevent the excessive aggregation and solidification of latex and maintain excellent stability.In addition to the most basic latex, herein, in preparation for the differential pressure-type plugging agent, a certain amount of sodium cellulose solution is added to thicken the latex, and potassium chloride solution is used as an activator to achieve the aggregation and the growth of latex particles by destroying the liquid film outside the latex particles and increasing the particle size.After the size of the colloidal particles increases to a certain extent, a stabilizer is added to emulsify the colloidal particles again, and the liquid film is coated on the outside again to form a stable O/W Pickering emulsion [9,10], preventing its continuous aggregation.The stabilizer adopts solid nanometer Fe 3 O 4 @SiO 2 and compounds with an emulsifier OP-10.Solid nano Fe 3 O 4 @SiO 2 can be obtained by the modification of the nano-Fe 3 O 4 .Fe 3 O 4 has strong hydrophilicity due to its small wetting angle, which is not conducive to the formation of stable O/W emulsion [11].Through modification, SiO 2 can be coated on the outer layer of Fe 3 O 4 , which partially wets the particles and improves the stability of the emulsion.When the modified nanoparticles are combined with OP-10, a skeleton structure is formed between the colloidal particles and the liquid film.This skeleton structure increases the mechanical resistance between lotion particles, blocks further aggregation and growth of latex particles, and thus increases the stability.

Instrumentation and characterization
The instruments used in the study are as follows: precision electronic balance ( (1) Nano-Fe 3 O 4 particles were prepared by the solvothermal method.An analytical balance was used to weigh 0.12 g of sodium citrate (C 6 H 5 Na 3 O 7 ) and was added to 50 mL of EG.After dissolution, 0.36 g of sodium acetate (CH 3 COONa) was added.After stirring and dissolving, 0.14 g of ferric chloride hexahydrate (FeCl 3 •6H 2 O) was added.After 30 min of ultrasonic treatment, a yellow uniform solution was obtained.The obtained homogeneous solution was transferred to the polyfluoroethylene lining and then placed it in a stainless steel reactor to initiate the reaction at 200℃ for 8 h.After the reaction, the reactor was cooled to room temperature, and the solution was taken out.The reaction liquid was poured into the centrifugal tube and centrifuged.Ethanol and water were used to wash the reactants during centrifugation, and the centrifugal speed was 4,000 rpm and allowed to stand for 5 min.After washing, it was placed in a constant temperature oven at 60℃.After drying, nano-Fe (2) To 60 mL ethanol, 0.1 g of Fe 3 O 4 particles, 5 mL of water, and 1.5 mL of NH 3 •H 2 O were added, stirred for 1 h, and then 0.18 mL of tetraethyl silicate (ethyl orthosilicate, TEOS) was added to the above solution.After the reaction for 8 h, the mixture was washed three times with ethanol and water to obtain Fe 3 O 4 @SiO 2 particles.The principle of preparing Fe 3 O 4 @SiO 2 particles is shown in Figure 2.

Determination of particle wettability
About 0.05 g of Fe 3 O 4 particles was added to 10 g of anhydrous ethanol and then dispersed ultrasonically for 30 min.Then, a microsampler was used to absorb 1 μL of the solution and drop it on the slide.The solution was dried in a vacuum drying oven at 60℃ for 12 h.After drying, the contact angle of Fe 3 O 4 particle coating was analyzed with an optical contact angle measuring instrument.The water contact angle of Fe 3 O 4 @SiO 2 particles was measured by the same method.(1) About 140 mL of carboxyl nitrile latex and 60 mL of 0.2% sodium cellulose solution were added into a 500 mL three-necked flask and stirred at 550 rpm at normal temperature.Then, 20 mL of 20% potassium chloride solution (activator) and 1 mL of defoamer were added to the flask and mixed.The mixing was stopped after dropping within 10 min, and allowed to stand for 15 min.(2) The mixing is turned on again after standing with the rotating speed maintained at 550 rpm.Then, 0.1 g of Fe 3 O 4 @SiO 2 particles and 10 mL of 20% OP-10 solution were added to the mixture and stirred for 15 min.After mixing, the stable Pickering-type differential pressure plugging agent was obtained.The principle of preparing the Pickering differential pressure plugging agent is shown in Figure 3.

Simulation plugging process of the differential pressure plugging agent
For the prepared differential pressure plugging agent, the plugging performance experiment was preliminarily simulated under different differential pressure conditions (5, 10, 15, 20 MPa) at different leakage speeds (50, 80, 100 mL/min).The gas leakage rates were adjusted through the throttle valve, which were 50, 80, and 100 mL/min, respectively.After the leakage rate was stable, the container valve was opened and a differential pressure-type plugging agent was injected.Then, the injection pressure was adjusted to 5 MPa via the pressure regulating valve of the highpressure gas cylinder, and the same differential pressure was maintained for 30 min after the injection pressure was stable.Considering 30 min as the node, pressurize for 5 MPa each time, and the pressure change was measured within 30 min after the pressure increases to 10, 15, and 20 MPa.The experimental method is shown in Figure 4.

Plugging test of the differential pressure plugging agent on the simulated tubing thread
The leakage of the tubing thread is generally small and the leakage channel is tortuous and narrow.The prepared plugging agent lotion has a small particle size and can enter into the tiny pores of the tubing thread to form a plugging.By adjusting the number of turns of the screw thread in the simulated tubing screw thread device, the different gas leakage speeds were adjusted, which were 50, 80, and 100 mL/min, respectively.The high-pressure gas cylinder was opened to inject the plugging agent into the short connection of the oil pipe, and plugged the leaking thread, with a test pressure of 6 MPa.After the simulated tubing thread was plugged, the pressure was increased to 20 MPa, stabilized for 30 min, and the leakage rate of the simulated tubing thread was measured.The experimental apparatus is shown in Figure 5.

Plugging test of the differential pressure plugging agent for simulated corrosion perforation
In the plugging experiment of the differential pressuretype plugging agent for simulating corrosion perforation, an orifice plate with a hole diameter of 1 mm was selected.
After the differential pressure-type plugging agent was kept still for 48 h, 200 mL of it was injected into the container of the high-temperature and high-pressure filter, and the orifice plate and filter paper with a diameter of  1 mm were added in turn.Different differential pressures were applied to the differential pressure-type plugging agent, and at the time when the differential pressuretype plugging agent stopped flowing out, the film thickness was recorded.The orifice plate and 1 mm hole diameter are shown in Figure 6.
3 Results and discussion The obtained product was analyzed by infrared spectroscopy.The infrared spectra of the product and the modified product are shown in Figure 7.It can be observed from the spectrogram (Figure 7, black curve) that the stretching vibration peak of Fe-O appears at 568, 621, 1,445, and 2,915 cm −1 , and the absorption peak of -OH appears at 3,438 cm −1 , which proves that nano-Fe 3 O 4 particles have been successfully prepared by the thermal solvent method.
It can be seen from the spectrogram (Figure 7, red curve) that there is a strong and wide characteristic absorption peak of Si-O-Si at 1,062-1,237 cm −1 , which indicates that there is a characteristic absorption peak of SiO 2 in the modified product.This proves that SiO 2 is successfully coated on the surface of Fe 3 O 4 .
Figure 8 shows the SEM images of nano-Fe 3 O 4 and Fe 3 O 4 @SiO 2 .It can be seen from the observation images that they are regular in appearance, mostly spherical, and almost no agglomeration occurs.The particle size of Fe 3 O 4 is about 120 nm, which is relatively uniform, and the average particle size of the modified product Fe 3 O 4 @SiO 2 is about 130 nm, which is also relatively uniform.
Figure 9 shows the measurement results of the static water contact angle of Fe   stabilizing emulsified colloidal particles.The water contact angle of Fe 3 O 4 particles is 30.0°, while that of Fe 3 O 4 @SiO 2 particles is 53.0°.The closer the contact angle is to 90°, according to Gibbs' free energy formula, the greater the desorption energy required for solid particles to separate from the two-phase interface, and the more stable the Pickering emulsion is formed.This shows that the wettability of the particles has been improved through modification, which has the characteristics of partial wettability.This is conducive to improving the stability of the formed Pickering lotion.
The magnetic properties of the modified particles were tested, and the hysteresis curve is shown in Figure 10.The saturation magnetization of the modified particles is 76.97 emu g −1 .When the external magnetic field reaches 4.3 kOe, the magnetic response of the modified particles tends to be saturated.In addition, the hysteresis curve of the obtained particles passes through the origin, which indicates that the coercivity and remanence of the modified particles are both 0, that is, superparamagnetic particles are successfully prepared.The saturation magnetic response intensity per unit length and unit mass of the product particles is about 0.32 emu g −1 nm −1 .The particles have superparamagnetism, which can accelerate the breaking of the stability of colloidal emulsion by applying an external magnetic field when plugging the leakage point with a differential pressure plugging agent.Under the double action of the differential pressure and magnetic force, the   hydration film on the surface of latex particles will be removed more quickly.As a result, the consolidation process of colloidal particles will also be accelerated and the plugging efficiency will be increased.

Characterization analysis and
performance evaluation of the differential pressure plugging agent

Particle size analysis
The particle size analysis of the prepared differential pressure plugging agent shows that the particle size dispersion of the prepared latex is narrow, the distribution range is 160.57-319.50nm, and the average particle size is 240.86 nm, as shown in Figure 11.

Plugging morphology of the differential pressure plugging agent
The differential pressure plugging agent is a white emulsion with fluidity before plugging the leak point, as shown in Figure 12(a); after plugging, it forms an elastic rubber body, which can only deform under a certain pressure; brittle failure does not occur, as shown in Figure 12(b).

Magnetic response experiment
Fe 3 O 4 @SiO 2 is not only used as a stabilizer but also has magnetic response characteristics.After the pressure difference plugging agent is injected, an external magnetic field can be applied at the leakage point.Fe 3 O 4 @SiO 2 has magnetic response characteristics, and it will be separated from the latex droplets by magnetic force adsorption.The framework constructed by Fe 3 O 4 @SiO 2 particles and OP-10 will be destroyed, which will accelerate the coalescence of latex particles and seal the leakage point more quickly.In addition, when the on-site construction is completed, there will inevitably be a redundant differential pressure-type plugging agent.The liquid is not convenient for transportation and treatment relative to the solid.Applying an external magnetic field to the residual poor leakage plugging agent will destroy the skeleton constructed by Fe 3 O 4 @SiO 2 and OP-10, thus destroying the stability of the leakage plugging agent.After the stability of the plugging agent is damaged, it will start to solidify and become a solid colloid after a certain time, which is conducive to on-site treatment after construction.The magnetic response of the differential pressure plugging agent is shown in Figure 13.

Plugging performance with different pressure differences and leakage rates
The differential pressure change of the pressure gauge after plugging with a differential plugging agent under different leakage rates and differential pressures are shown in Figures 15-17.
It can be seen from Figure 15 that when the leakage rate reaches 50 mL/min, even if the differential pressure increases from 5 to 20 MPa, the pressure can be kept stable within 30 min under each differential pressure.This shows that the differential pressure plugging agent has a good plugging effect for the leakage of 50 mL/min, and the maximum pressure can be reached at 20 MPa.
According to Figure 16, when the leakage rate reaches 80 mL/min, the pressure gauge can be kept constant in the pressure range of 5-15 MPa after plugging the leakage point with a differential pressure plugging agent.However, leakage occurred again after the pressure increased to 20 MPa, and it stabilized after the pressure dropped to 10 MPa.Therefore, the differential pressure plugging agent can only withstand a maximum differential pressure of 15 MPa after effectively plugging the leakage point with a leakage rate of 80 mL/min.
As shown in Figure 17, the gas leakage rate reaches 100 mL/min.After the differential pressure plugging agent blocks the leakage point and the injection pressure is stabilized at 5 MPa for 30 min, the pressure increases to 10 MPa, and the leakage occurs immediately.At the same time, the pressure drops rapidly to 2.4 MPa.It can be seen that for the leakage point with a leakage rate of 100 mL/ min, the pressure bearing performance of the differential  pressure plugging agent configured is poor, and the maximum pressure difference can only be 5 MPa.
To sum up, the differential pressure plugging agent is sensitive to the differential pressure.The larger the differential pressure, the smaller the leakage channel at the same leakage speed, the stronger the dehydration ability of the surface of the nano lotion, and the dehydrated lotion particles will be crosslinked more easily and solidified via coalescence, resulting in an excellent plugging effect.The larger the leakage channel, the nano-sized lotion particles can still block the leakage point under a small pressure difference.However, when the pressure difference increases, the cured latex has poor pressure-bearing performance, resulting in leakage again.Therefore, when the leakage rate is low, the plugging performance of the differential pressure plugging agent is excellent, and it can withstand high differential pressure (≤20 MPa).However, when the leakage rate is high, the differential pressure plugging agent can only achieve plugging under a small differential pressure (≤5 MPa).

Plugging performance of the differential pressure plugging agent on simulated tubing threads
The plugging capacity of the differential pressure-type plugging agent to analog tubing threads is shown in Table 1.By using a simulated tubing thread plugging device, the relation table between different leakage speeds and plugging performance is formed.As shown in the table, the differential pressure plugging agent has a good plugging effect on the leakage of the simulated tubing thread.When the leakage speed is 50 or 80 mL/min, the plugging effect is very good, and no leakage occurs when the pressure increases to 20 MPa.When the leakage rate is 100 mL/min,   the leakage rate is high, and the plugging effect becomes worse.When the pressure increases to 20 MPa, leakage occurs and the leakage rate is 25 mL/min.It can be seen that when the leakage rate is small, the configured differential pressure-type plugging agent has a good plugging effect.However, when the leakage rate is too high, there is still leakage after the injection of the plugging agent, and the leakage point of the simulated tubing thread cannot be completely plugged but the leakage point is improved, and the leakage rate is significantly smaller than before the injection of the plugging agent.
According to previous literature reports, differential pressure plugging agents can handle leaks with a pressure difference of 7 MPa.The performance of the pressure difference-type plugging agent synthesized herein is superior.Even if the test pressure reaches 20 MPa, the sealing work can be completed well.The plugging performance results of the differential pressure plugging agent for a 1 mm orifice plate are shown in Table 2 and Figure 18.
For the orifice plate with a diameter of 1 mm used to simulate corrosion perforation, all the differential pressure-type leakage plugging agents leaked out under pressures of 5, 10, 15, 20, and 25 MPa, and the hole diameter could not be blocked.The colloidal particle of the differential pressure leakage plugging agent is a composite droplet, and its outer liquid film can isolate the protective colloidal particle and maintain the thermodynamic and dynamic stability of the sealing fluid.The reason why the differential pressure plugging agent cannot show the plugging effect is that the lotion particle size of the differential pressure plugging agent is in the nano-meter range, and the pore size of the material simulating corrosion perforation is relatively large and the pore size is a cylinder shape, which is different from the stepped shape of the gradually narrow oil pipe thread.Such leakage points do not have a differential pressure effect.The colloidal particles do not dehydrate and their stability is not damaged, so they cannot be dehydrated and accumulated in the pores.On the contrary, the colloidal particles will directly pass through the pores.At this time, there is no differential pressure between the inside and outside, so there will be no solidification, and no effective plugging can be formed, as shown in Figure 19.

Analysis of the plugging mechanism of the differential pressure plugging agent
The differential pressure plugging agent is a multiphase fluid composed of latex particles and the dispersion medium [12].As a dispersion phase, the colloidal particles have regular morphology.The inner layer is a polymer cross-linked by hydrophobic chains and hydrophilic chains through covalent bonds, while the outer layer is a liquid film wrapped around the core.This structure can be understood as an O/W Pickering emulsion.The electrolyte is introduced to reduce the zeta potential.The potential will destroy the stability of the Pickering emulsion, resulting in the two-phase separation of latex and water film, and improving the aggregation performance of colloidal particles to increase the size of colloidal particles.By adjusting the aggregation growth time of colloidal particles, the size of the colloidal particles can be controlled.Carboxybutyronitrile latex is selected to prepare the differential pressure plugging agent because its latex molecular weight and particle size distribution are relatively uniform, and it has good oil resistance, high salinity resistance, acid and alkaline resistance, which can greatly increase the universality of differential pressure plugging agent.In addition, because there are strong polar carboxyl groups on the macromolecular chain of the carboxyl nitrile latex, its activity and adhesive strength have also been significantly improved [13][14][15].The size of the colloidal particles is determined by the time when the stabilizer is added.The stabilizer can block the aggregation of the colloidal particles and play the role of emulsification, so that the colloidal particles are once again wrapped by the liquid film to form a stable Pickering emulsion, preventing the excessive aggregation of the latex and curing.
The interfacial tension of the composite liquid drop causes it to exhibit a special dynamic deformation behavior under the effect of the leak point pressure difference, which is the key to achieving adaptive sealing of the sealing fluid [16,17].In the narrow and tortuous pores of the tubing thread, due to the pressure difference at the leak point, after the differential pressure plugging agent enters the leak point, the latex particles rotate, swing, wall slip, and impact, and the force on the phase interface changes.The skeleton constructed by the solid particles Fe 3 O 4 @SiO 2 and OP-10 was destroyed, resulting in the overall transient deformation, the surface dehydration of the latex particles, and the destruction of the water film on the surface.At this time, the dehydrated colloidal particles show strong selfagglomeration.By overlapping, diffusion, and adsorption of molecular chains in the inner and outer layers, the multiparticles coalesce and fuse to form a solid with a certain structural strength, which fills the leak holes [18][19][20][21].A seal repair is achieved, as shown in Figure 20 (DOI: CNKI:-SUN:TRQG.0.2020-03-021).

Conclusions
Aiming at the problem of thread leakage of oil pipes in gas storage, the plugging performance and mechanism of the differential pressure plugging agent were studied.Based on nano-Fe 3 O 4 , hydrophilic Fe 3 O 4 @SiO 2 particles were obtained by modification.This particle, as a stabilizer, cooperates with the emulsifier OP-10 in the preparation of the Pickering emulsion-type differential pressure plugging agent to build a skeleton on the surface of the rubber particles, playing an excellent emulsification and stability effect so that the dewatered latex particles are covered by the liquid film again and stop aggregating, without curing.Carboxybutyronitrile latex in this differential pressure plugging agent has high activity and bonding strength, ensuring the excellent plugging ability of the plugging agent.Its average particle size is about 241 nm, and its size is small.For the throttling valve plugging test, the pressure of the 50 mL/min leak point can be 20 MPa after the differential pressure plugging agent effectively plugs the leak point.When the leakage rate reaches 80 mL/min, the differential pressure plugging agent can only withstand 15 MPa after plugging.When the leakage rate reaches 100 mL/min, the differential pressure plugging agent can complete plugging under an injection pressure of 5 MPa, but it can no longer bear higher pressure and has poor pressure-bearing performance.In addition, the differential pressure plugging agent can effectively block the tubing thread within a pressure difference of 20 MPa and a leakage rate of less than 100 mL/min.The differential pressure-type plugging agent prepared in this article can meet the requirements of rapid, economical, and safe repair of sealing damage such as oil pipe threads in gas storage, and provides a new technical reference for rapid recovery of gas storage integrity.

Figure 1 :
Figure 1: Schematic diagram of the preparation of nano-Fe 3 O 4 particles by the hot solvent method.

Figure 3 :
Figure 3: Schematic diagram for the preparation of the Pickering differential pressure plugging agent.

Figure 4 :
Figure 4: Simulated plugging process of a differential pressure plugging agent.

Figure 5 :
Figure 5: The flowchart of the simulated tubing thread plugged with the differential pressure plugging agent.

Figure 13 :
Figure 13: (a) Differential pressure plugging agent.(b) The magnetic field is applied to the differential pressure plugging agent.(c) Fe 3 O 4 particles are adsorbed to one side of the cup wall.(d) The differential pressure plugging agent begins to cure after its stability is destroyed.

3. 2 . 4
Figure14(a) shows the shape of the solid particles after being diluted with deionized water for the differential pressure-type plugging agent.The solid particles are regularly shaped, spindle and spherical, forming hydrated colloidal particles with a particle size greater than 100 mm.Some particles are overlapped to form large particles with irregular shapes.Figure14(b) shows the aggregation morphology of the hydrated colloidal particles after dehydration.Obviously, the activity of colloidal particles increases after dehydration, and they spread, overlap, and stack on the surface to form a ductile solid with a certain hierarchical structure.This phenomenon shows that dehydrated colloidal particles have strong self-coalescence ability and can self-assemble into solids in space.

Figure 15 :
Figure 15:The pressure change at a gas leakage rate of 50 mL/min.

Figure 17 :Figure 16 :
Figure 17: The pressure change at a gas leakage rate of 100 mL/min.

Figure 18 :
Figure 18: Sealing effect of a 1 mm orifice plate under pressure (the right-hand side picture is taken after standing still).

Figure 19 :
Figure 19: Schematic diagram of the rubber particles directly passing through a 1 mm aperture.

Figure 20 :
Figure 20: Plugging mechanism of the differential pressure plugging agent.

Table 2 :
Plugging performance of the differential pressure plugging agent for a 1 mm orifice plate

Table 1 :
Plugging effect of the differential pressure plugging agent on analog tubing threads