A large steric-hindrance hydrophilic nanosilica, a preparation method and application thereof
By using modified nano-silica to compete with polymers for adsorption, the problem of reduced flow capacity of shale fracturing fractures caused by polymer adsorption was solved, thus achieving the technical effect of improving shale fracturing efficiency.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- CHINA NAT PETROLEUM CORP
- Filing Date
- 2024-11-26
- Publication Date
- 2026-05-26
AI Technical Summary
In existing shale oil and gas fracturing technologies, polyacrylamide adsorbs onto the shale surface to form large molecular clusters, which reduces the flow capacity of the fracturing fractures and affects the fracturing effect.
By modifying nano-silica with ethylene oxide and aniline, a large steric hindrance hydrophilic nano-silica was prepared. This nano-silica competitively adsorbed polymers, reducing polymer adsorption on the shale surface and maintaining the flow capacity of the fractures.
It effectively reduces polymer adsorption and blockage during shale fracturing, improves shale fracturing and stimulation effects, and enhances fracture flow capacity.
Smart Images
Figure CN122080910A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of unconventional shale oil and gas exploration and development technology, specifically to a large-steric-impeded hydrophilic nano-silica, its preparation method, and its application. Background Technology
[0002] Fracturing technology is the primary means of effectively developing shale oil and gas reservoirs. Shale lithology is dense with poor interlayer connectivity, necessitating fracturing to create a complex network of fractures and enhance shale gas flowability. However, the main component of the slickwater used in shale fracturing is high-molecular-weight polyacrylamide. The amide groups on the polyacrylamide molecular chain form hydrogen bonds with the shale rock surface, causing the polyacrylamide to adsorb onto the rock surface. This adsorbed polyacrylamide then connects to other polyacrylamide molecules through intermolecular forces, resulting in large polyacrylamide clusters at the adsorption sites. These clusters can reach diameters of tens or even hundreds of micrometers, severely reducing the flowability of the fracturing fractures and impacting post-fracturing productivity. Furthermore, the adsorption of polyacrylamide on the slickwater reduces the width of the fracturing fractures, affecting their flowability. Summary of the Invention
[0003] The purpose of this invention is to provide a sterically hindered hydrophilic nano-silica and its preparation method. The modified nano-silica obtained is a sterically hindered hydrophilic nano-silica, which can be used in the preparation of reagents to reduce fracturing fluid damage. This hydrophilic nano-silica will compete with polymers for adsorption, reducing polymer adsorption blockage, thereby reducing fracture damage.
[0004] This invention is achieved through the following technical solution: A sterically hindered hydrophilic nano-silica is prepared by modifying nano-silica with ethylene oxide and aniline. The nano-silica has a particle size of 2-5 nm, the mass percentage of ethylene oxide to nano-silica is 1.5-3:1, and the mass percentage of aniline to nano-silica is 0.8-3:1.
[0005] Furthermore, the aniline is 4-bromoaniline.
[0006] Furthermore, when modifying nano-silica with ethylene oxide and aniline, the solvent used is tetrahydrofuran, and the catalyst is an alkaline reagent.
[0007] Furthermore, the alkaline reagent is one or more of sodium hydroxide, potassium hydroxide, ammonia, ethanolamine, diethanolamine, triethanolamine, and urea.
[0008] A method for preparing large steric hindrance hydrophilic nano-silica as described above includes the following steps: Ⅰ. Introduce ethylene oxide into the reactor, add nano-silica and alkaline reagent, control the pressure in the reactor to 2~3MPa, control the reaction temperature to 120~150℃, and under stirring conditions, the reaction time is 40~60min; II. After the ethylene oxide reaction is complete, cool the temperature to 30±2℃, release the pressure to atmospheric pressure, add tetrahydrofuran solvent, 4-bromoaniline and alkaline reagent, and carry out the reaction for 3~4 hours under stirring. III. Reduce pressure and distill off unreacted 4-bromoaniline to obtain grafted modified, sterically hindered hydrophilic nano-silica that reduces fracturing fluid damage.
[0009] Furthermore, in steps I and II, the stirring rate is 100~150 r / min.
[0010] Furthermore, in step I, the amount of the basic metal reagent added is 1% of the mass of ethylene oxide; in step II, the amount of the basic metal reagent added is 0.5% of the mass of 4-bromoaniline.
[0011] Furthermore, in step II, the amount of tetrahydrofuran used is 5-8 times the mass of 4-bromoaniline.
[0012] The application of a sterically hindered hydrophilic nano-silica as described in any of the preceding claims in the preparation of a reagent to reduce fracturing fluid damage.
[0013] Furthermore, multiple experiments revealed that when applying large steric hindrance hydrophilic nano-silica, the mass concentration of the large steric hindrance hydrophilic nano-silica should be controlled between 0.1% and 0.5%. If the mass concentration exceeds 0.5%, the effect is not significantly improved.
[0014] Compared with the prior art, the present invention has the following advantages and beneficial effects: I. This invention proposes a sterically hindered hydrophilic nano-silica. This modified hydrophilic nano-silica competes with polymers for adsorption, reducing polymer adsorption and blockage, thereby reducing fracture damage. This modified hydrophilic nano-silica can effectively reduce the amount of polyacrylamide additives adsorbed and retained in the fracturing fractures in the slickwater during shale fracturing, thus helping to improve the fracturing and restoration effect of shale.
[0015] The principle involved in this process is as follows: Polyacrylamide in shale fracturing slickwater forms hydrogen bonds with the shale surface through its amide groups, causing it to adsorb onto the shale surface. The adsorbed polyacrylamide then connects with polyacrylamide molecules in the aqueous solution through hydrogen bonds, resulting in localized clustering of polyacrylamide. This reduces the width of the fracturing fracture, affecting its flow capacity and decreasing the fracturing effect. This invention constructs a method for preparing large-scale steric hindrance hydrophilic nano-silica to reduce fracturing fluid damage. The modified nano-silica particles of this invention contain a large number of hydrophilic groups, enabling them to form hydrogen bonds with the rock surface. However, the volume of the modified nano-particles is much smaller than that of polyacrylamide molecules. During the competitive interaction, the nano-silica particles preferentially act on the shale surface, occupying the sites on the shale surface, preventing polyacrylamide from interacting with the shale surface and avoiding narrowing of the shale fracturing fracture channel. The modified nano-silica particles can also interact with polyacrylamide molecules, reducing the formation of hydrogen bonds between polyacrylamide molecules, maintaining the linear state of the polyacrylamide, which is beneficial for its flow out of the fracture and back to the surface. Modified nano-silica particles reduce the adsorption of polyacrylamide on the shale surface, while allowing the polyacrylamide to exist in a linear molecular state, enabling it to flow out of the formation and greatly reducing damage to fractures after fracturing. Attached Figure Description
[0016] Figure 1 This is an NMR image of the shale sand-filled pipe in its original saturated water state in Example 5, specifically the No. 1 sand-filled pipe.
[0017] Figure 2 This is an NMR image of the shale sand-filled pipe in its original saturated water state in Example 5, specifically the No. 2 sand-filled pipe.
[0018] Figure 3 The images show the results of nuclear magnetic resonance imaging (NMR) detection after different displacement times of sand-filled tubes #1 and #2 in Example 5.
[0019] Figure 4 This is a morphological diagram of the pore space of the shale sand-filled pipe in the first group of Example 6.
[0020] Figure 5 This is a diagram showing the results of the pore-throat connectivity analysis before the first group of displacements in Example 6.
[0021] Figure 6 This is a CT scan result of the first group of shale-filled sand pipes after being displaced by slickwater in Example 6.
[0022] Figure 7 This is a diagram showing the results of the pore-throat connectivity analysis in the first group after being displaced by slickwater in Example 6.
[0023] Figure 8 This is a morphological diagram of the pore space of the shale sand-filled pipe in the second group of Example 6.
[0024] Figure 9 This is a diagram showing the results of the pore-throat connectivity analysis before the second group of displacements in Example 6.
[0025] Figure 10 This is a CT scan result of the shale sand-filled pipes in the second group of Example 6 after being displaced by slickwater + 0.2% hydrophilic nano silica C2.
[0026] Figure 11 This is a graph showing the pore-throat connectivity analysis results of the second group in Example 6 after displacement by slickwater + 0.2% hydrophilic nano-silica C2.
[0027] Figure 12 This is a particle size distribution diagram of the lye before and after adding a desorbent containing 0.2% hydrophilic nano-silica C3 to the slick water.
[0028] Figure 13 This is a SEM image of the drag-reducing agent morphology in slick water without the addition of hydrophilic nano-silica C3.
[0029] Figure 14 The second image shows the molecular morphology of drag reducer in slick water without the addition of hydrophilic nano-silica C3.
[0030] Figure 15 This is a SEM image of the drag-reducing agent morphology when 0.2% hydrophilic nano-silica C3 is added to slick water.
[0031] Figure 16 The second image shows the molecular morphology of the drag reducer in slick water when 0.2% hydrophilic nano-silica C3 is added.
[0032] Figure 17 This is a schematic diagram illustrating the synthesis route of the modified nano-silica particles of this invention. Detailed Implementation
[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.
[0034] Example 1 A method for preparing sterically hindered hydrophilic nano-silica, referenced Figure 17 It includes the following steps: I. Introduce 1.5 kg of ethylene oxide, 1 kg of nano-silica, and 0.015 kg of sodium hydroxide into a stainless steel batch reactor. Adjust the pressure inside the reactor with nitrogen and maintain it at 2 MPa. Control the reaction temperature at 120℃, stir at 100 rpm, and allow the reaction time to 40 min. Take a sample of the reaction solution from the sampling port of the reactor and analyze it using a gas chromatograph to monitor the ethylene oxide content and the entire reaction process.
[0035] In this step, based on the specifications of the reactor and corresponding process conditions, and after extensive experimental verification, it is advisable to add ethylene oxide, nano-silica, and alkaline reagents, control the pressure inside the reactor at 2-3 MPa, the reaction temperature at 120-150℃, and the reaction time at 40-60 min. The stirring rate should be set at 100-150 r / min.
[0036] II. After the ethylene oxide reaction is detected to be complete, the temperature is lowered to 30±2℃, the pressure is released to atmospheric pressure, 4 kg of tetrahydrofuran solvent, 0.8 kg of 4-bromoaniline and 4 g of sodium hydroxide are added, and the reaction is carried out by stirring at a rate of 100 r / min for 3 h under stirring conditions. III. After the reaction is complete, the unreacted 4-bromoaniline is removed by depressurization and distillation to obtain the grafted and modified hydrophilic nano-silica with large steric hindrance that reduces fracturing fluid damage, denoted as hydrophilic nano-silica C1.
[0037] Example 2 A method for preparing sterically hindered hydrophilic nano-silica, as shown in the figure, includes the following steps: I. Introduce 3.0 kg of ethylene oxide, 1 kg of nano-silica, and 0.03 kg of sodium hydroxide into a stainless steel batch reactor. Adjust the pressure inside the reactor with nitrogen and maintain it at 3 MPa. Control the reaction temperature at 150℃, stir at 150 r / min, and allow the reaction time to 60 min. Take a sample of the reaction solution from the sampling port of the reactor and analyze it using a gas chromatograph to monitor the ethylene oxide content and the entire reaction process.
[0038] II. After the ethylene oxide reaction is completed, the temperature is lowered to 30±2℃, the pressure is released to atmospheric pressure, 12kg of tetrahydrofuran solvent, 1.5kg of 4-bromoaniline and 7.5g of sodium hydroxide are added, and the reaction is carried out by stirring at a rate of 150r / min for 4h under stirring conditions. III. After the reaction is complete, the unreacted 4-bromoaniline is removed by depressurization and distillation to obtain the grafted and modified hydrophilic nano-silica with large steric hindrance that reduces fracturing fluid damage, denoted as hydrophilic nano-silica C2.
[0039] Example 3 A method for preparing sterically hindered hydrophilic nano-silica includes the following steps: I. Introduce 2.0 kg of ethylene oxide, 1 kg of nano-silica, and 0.02 kg of sodium hydroxide into a stainless steel batch reactor. Adjust the pressure inside the reactor with nitrogen and maintain it at 3 MPa. Control the reaction temperature at 140℃, stir at 130 r / min, and allow the reaction time to be 50 min. Take a sample of the reaction solution from the sampling port of the reactor and analyze it using a gas chromatograph to monitor the ethylene oxide content and the entire reaction process.
[0040] II. After the ethylene oxide reaction is completed, the temperature is lowered to 30±2℃, the pressure is released to atmospheric pressure, 7kg of tetrahydrofuran solvent, 1kg of 4-bromoaniline and 5g of sodium hydroxide are added, and the reaction is carried out at a stirring rate of 120r / min for 4h under stirring conditions. III. After the reaction is complete, the unreacted 4-bromoaniline is removed by depressurization and distillation to obtain the grafted and modified hydrophilic nano-silica with large steric hindrance that reduces fracturing fluid damage, denoted as hydrophilic nano-silica C3.
[0041] Example 4 A method for preparing sterically hindered hydrophilic nano-silica includes the following steps: I. Introduce 2.5 kg of ethylene oxide, 1 kg of nano-silica, and 0.025 kg of sodium hydroxide into a stainless steel batch reactor. Adjust the pressure inside the reactor with nitrogen and maintain it at 2 MPa. Control the reaction temperature at 140℃ and stir at 140 r / min for 60 min. Take a sample of the reaction solution from the sampling port of the reactor and analyze it using a gas chromatograph to monitor the ethylene oxide content and the entire reaction process.
[0042] II. After the ethylene oxide reaction is completed, the temperature is lowered to 30±2℃, the pressure is released to atmospheric pressure, and 8.4 kg of tetrahydrofuran solvent, 1.2 kg of 4-bromoaniline and 6 g of sodium hydroxide are added. The reaction is carried out by stirring at a rate of 130 r / min for 3 h. III. After the reaction is complete, the unreacted 4-bromoaniline is removed by depressurization and distillation to obtain the grafted and modified hydrophilic nano-silica with large steric hindrance that reduces fracturing fluid damage, denoted as hydrophilic nano-silica C4.
[0043] Example 5 A 0.1% slickwater solution was prepared using heavy water (D2O), and hydrophilic nano-silica C1 (i.e. drag reducer) obtained in Example 1 was added. Nuclear magnetic resonance imaging was used to detect the sand-filled pipes that had been displaced for different times to examine the ability of the drag reducer to reduce fracturing fluid damage.
[0044] Nuclear magnetic resonance imaging (MRI) can detect the properties and volume of fluids within the pores of a rock core, as well as the interaction between the fluid and the solid surface of the porous rock medium. Therefore, MRI images can reflect the distribution and accumulation of fluids in the rock core, as well as the interfacial effects between the fluid and the surrounding rock environment.
[0045] In this experiment, since heavy water does not contain 1H atoms, the 1H signal detected by nuclear magnetic resonance (NMR) in the solution originated solely from the 1H signal in the drag-reducing agent. According to the NMR imaging of the sand-filled tube, the microcrack size distribution of the original saturated water state of sand-filled tube #1 and #2 is basically the same. (Refer to...) Figure 1 , 2 , Figure 1 , 2 The images show NMR images of shale sand-filled pipes (No. 1 and No. 2) in their original saturated water state. Bright areas in the images represent hydrogen signals; the darker the color, the stronger the signal. Hydrophilic nano-silica C1 (i.e., drag-reducing agent) obtained in Example 1 was then added to sand-filled pipe No. 2. NMR imaging results of sand-filled pipes at different displacement times are referenced. Figure 3 , Figure 3 In the image, A, B, and C represent the nuclear magnetic resonance (NMR) images of the No. 1 sand-filled tube (with added slickwater) at 5, 10, and 15 min during the shale porous media displacement experiment, respectively. D, E, and F represent the NMR images of the No. 2 sand-filled tube (with added slickwater and desorbent) at 5, 10, and 15 min during the shale porous media displacement experiment, respectively.
[0046] Depend on Figures 1-3 It can be seen that with the increase of displacement time, due to the "filtering" effect of narrow fractures, the hydrogen signal of drag-reducing agent molecules in areas with smaller fracture widths continuously increases, resulting in greater retention. As some pores become blocked, subsequent drag-reducing agent molecules begin to be captured, and the hydrogen signal inside the entire sand-packed tube gradually increases, leading to a gradual increase in the adsorption and retention of the drag-reducing agent. After displacement with heavy water-based slickwater, significant retention of the drag-reducing agent can be observed, with a clear retention band observed in areas with smaller fracture widths. However, in the experimental group with the addition of a drag-reducing agent (i.e., hydrophilic nano-silica C1), the hydrogen signal of the drag-reducing agent is significantly reduced, and the retention amount is significantly decreased at the same displacement time. Therefore, the addition of hydrophilic nano-silica C1 as a drag-reducing agent can significantly reduce fracturing fluid damage.
[0047] Example 6 In this embodiment, CT scanning + 3D reconstruction + grayscale recognition technology is used to refine the adsorption and retention of drag-reducing agents in shale. At the same time, the changes in the pore throat connectivity before and after slickwater enters the shale sand-filled pipe are quantitatively calculated, thereby examining the application effect of hydrophilic nano-silica in the field of fracturing fluid damage reduction agents.
[0048] Group 1: By performing 3D reconstruction of the CT scan results of the shale sand-filled pipe before slickwater displacement, the three-dimensional structure of the shale sand-filled pipe can be obtained. At the same time, the rock skeleton and pore space can be divided based on grayscale recognition. Figure 4 This shows the pore space morphology of the shale sand-filled pipe, clearly indicating that the original rock sample had a relatively large pore space. Mathematical processing of the pore-throat connectivity using Avizo yielded the following results. Figure 5 The results of the pore-throat connectivity analysis show that the pore-throat connectivity is very good, and the calculated pore-throat ratio is 1:5.89.
[0049] Then, a CT scan was performed on the shale-filled sand pipe after slickwater displacement to observe the changes before and after the displacement. The results are referenced. Figure 6 .according to Figure 6 The results show that, in addition to pore space and rock skeleton, there are numerous drag-reducing agent signals (red substances), indicating a reduction in pore space in the shale sand-filled pipes after slickwater displacement. Furthermore, based on Avizo pore throat connectivity calculations (see reference...), Figure 7 The results show that the ratio of connecting pores to throats is 1:2.76, indicating that the pore-throat connectivity is significantly worse.
[0050] Group 2: Figure 8 This is another set of pore space morphology for shale sand-filled pipes, clearly showing that the original rock sample had a larger pore space. Using Avizo mathematical processing to analyze pore-throat connectivity, we obtained... Figure 9 The analysis of the pore-throat connectivity shown indicates that the ratio of the connecting pores to the throats in the original shale sand-filled pipes is 1:5.68, indicating good pore-throat connectivity.
[0051] After displacing the shale-filled pipe with slickwater and 0.2% hydrophilic nano-silica C2, the changes before and after the displacement were observed. The results are as follows. Figure 10 .according to Figure 10 The results show that, compared with the first group Figure 6 The results showed a significant reduction in the drag-reducing agent signal (red substance) in the shale-filled pipe. Mathematical processing of the pore-throat connectivity using Avizo yielded the following results. Figure 11 The pore-throat connectivity analysis shown has a pore-to-throat ratio of 1:4.32.
[0052] The results of the first and second groups show that the addition of a desorbent containing 0.2% hydrophilic nano-silica C2 can significantly reduce the blocking effect of drag-reducing agents in slickwater on shale pore channels, thereby improving the fluidity of shale pores.
[0053] Example 7 In this embodiment, the particle size and scanning electron microscopy were performed on slippery water and slippery water containing 0.2% hydrophilic nano silica C3 to examine the morphology of drag-reducing agent molecules in slippery water.
[0054] Reference to the particle size distribution investigation results of the two groups Figure 12 , Figure 12 This is a particle size distribution diagram of the desorbed liquid before and after adding 0.2% desorbent. Scanning electron microscopy results are for reference. Figures 13-16 , Figure 13 , 14 These are SEM images of the drag-reducing agent molecules in slick water without the addition of hydrophilic nano-silica C3. Figure 15 , 16 These are SEM images of the drag-reducing agent molecules in slick water with 0.2% hydrophilic nano-silica C3 added.
[0055] according to Figure 12 As can be seen, after adding the desorbent (hydrophilic nano silica C3), the median particle size of the slippery water molecule decreased from 626 nm to 428 nm, a reduction of 31.6%.
[0056] according to Figures 13-16 The SEM images show that the polymer molecular chains are finer, entanglement is reduced, and flexibility is enhanced after adding the desorbent containing hydrophilic nano-silica C3. This indicates that the desorbent can improve the flexibility of drag-reducing agent molecules in shale pores and fractures, reduce entanglement between drag-reducing agent molecules under low flow conditions, and reduce the particle size of drag-reducing agent molecules, thereby reducing the clogging effect of drag-reducing agent molecules on shale pores and fractures in slickwater, and thus improving the flowability of shale pores and fracture channels after fracturing.
[0057] As can be seen from Examples 5-7 above, the sterically hindered hydrophilic nano-silica in this scheme can be added as a desorbent to fracturing fluid slickwater, and is an effective reagent for reducing fracturing fluid reservoir damage. It can also be seen that this sterically hindered hydrophilic nano-silica can be used as one of the desorbents in the preparation of reagents to reduce fracturing fluid reservoir damage.
[0058] Furthermore, extensive experiments have shown that the sterically hindered hydrophilic nano-silica obtained using this method exhibits similar application effects, all demonstrating excellent ability to reduce fracturing fluid reservoir damage. It can be used in the preparation of reagents to reduce fracturing fluid reservoir damage, thus expanding the application range of hydrophilic nano-silica.
[0059] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications or equivalent changes made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.
Claims
1. A sterically hindered hydrophilic nano-silica, characterized in that: Nano-silica was modified with ethylene oxide and aniline. The nano-silica had a particle size of 2-5 nm, the mass percentage of ethylene oxide to nano-silica was 1.5-3:1, and the mass percentage of aniline to nano-silica was 0.8-3:
1.
2. The sterically hindered hydrophilic nano-silica according to claim 1, characterized in that: The aniline in question is 4-bromoaniline.
3. The sterically hindered hydrophilic nano-silica according to claim 1, characterized in that: When modifying nano-silica with ethylene oxide and aniline, the solvent used is tetrahydrofuran, and the catalyst is an alkaline reagent.
4. The sterically hindered hydrophilic nano-silica for reducing fracturing fluid damage according to claim 3, characterized in that: The alkaline reagent is one or more of sodium hydroxide, potassium hydroxide, ammonia, ethanolamine, diethanolamine, triethanolamine, and urea.
5. A method for preparing the sterically hindered hydrophilic nano-silica as described in claim 3, characterized in that, Includes the following steps: Ⅰ. Introduce ethylene oxide into the reactor, add nano-silica and alkaline reagent, control the pressure in the reactor to 2~3MPa, control the reaction temperature to 120~150℃, and under stirring conditions, the reaction time is 40~60min; II. After the ethylene oxide reaction is complete, cool the temperature to 30±2℃, release the pressure to atmospheric pressure, add tetrahydrofuran solvent, 4-bromoaniline and alkaline reagent, and carry out the reaction for 3~4 hours under stirring. III. Reduce pressure and distill off unreacted 4-bromoaniline to obtain grafted modified, sterically hindered hydrophilic nano-silica that reduces fracturing fluid damage.
6. The method for preparing large steric hindrance hydrophilic nano-silica according to claim 5, characterized in that: In steps I and II, the stirring rate is 100~150 r / min.
7. The method for preparing large steric hindrance hydrophilic nano-silica according to claim 5, characterized in that: In step I, the amount of alkaline reagent added is 1% of the mass of ethylene oxide; in step II, the amount of alkaline reagent added is 0.5% of the mass of 4-bromoaniline.
8. The method for preparing large steric hindrance hydrophilic nano-silica according to claim 5, characterized in that: In step II, the amount of tetrahydrofuran used is 5-8 times the mass of 4-bromoaniline.
9. The application of the sterically hindered hydrophilic nano-silica as described in any one of claims 1-8 in the preparation of a reagent to reduce fracturing fluid damage.
10. The application according to claim 9, characterized in that: The mass concentration of the sterically hindered hydrophilic nano-silica is 0.1~0.5%.