Temperature / co2 dual-responsive zwitterionic hydrogel profile control agent and preparation method thereof

Abstract

The application discloses a temperature / CO2 dual-response zwitterionic hydrogel profile control agent, and a preparation method thereof. The preparation method comprises the following steps: taking monomer A, monomer B and monomer C as raw materials, adding a crosslinking agent and an initiator, and performing a polymerization reaction in a water medium to obtain the profile control agent. The monomer A is selected from any one of acrylamide, acrylic acid and 1-vinyl-2-pyrrolidone; the monomer B is selected from any one of [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl) ammonium hydroxide, 2-methacryloyloxyethylphosphocholine and 3-((2-(methacryloyloxy)ethyl)dimethylamino)propanoate inner salt; and the monomer C is selected from any one of 2-(dimethylamino)methyl acrylate, dimethylaminopropyl methacrylamide and polyethyleneimine. The profile control agent has a dual-swelling mechanism, has outstanding temperature resistance and salt resistance, can resist 220,000 mg / L of mineralized water, is suitable for high-salt reservoirs, and has good long-term aging resistance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of oilfield chemical water shutoff profile control agents, and particularly relates to a temperature / CO2 dual-response zwitterionic hydrogel profile control agent and a preparation method thereof. BACKGROUND

[0002] With the deepening of oilfield development, the permeability of the oil reservoir is becoming more and more complex. In particular, in the water-gas alternating displacement process, water injection and gas injection are alternately performed, which can cause excessive water absorption or rapid gas loss in part of the high-permeability layer, resulting in failure of the injected water or gas, and seriously affecting the oil recovery of the oilfield. In particular, in the process of water-gas alternating injection, due to water-gas mismatch, excessive water injection often occurs in some areas, which cannot effectively displace the crude oil in the oil reservoir, resulting in uneven oil displacement effect and reducing the oil recovery. In the water-gas alternating displacement process, there is also the problem of water channeling. Therefore, how to solve the problem of water shutoff in water-gas alternating displacement and improve the oil recovery of the oilfield has become a technical problem to be solved. Although the profile control agents used in the field have achieved certain results, the water-swellable speed of the profile control and water shutoff material particles is fast, the injection depth is limited, the particle material is easy to break after water saturation, and precise plugging cannot be achieved, resulting in poor plugging effect and high cost.

[0003] For example, patent CN107445857A discloses a preparation method of long-chain alkyl acid amide propyl dimethylamine with CO2 response performance, and the aqueous solution thereof can be used as a CO2 response gel. The prepared compound can also be used for enhanced oil recovery in oil and gas fields. The aqueous solution belongs to an in-situ formed gel, which can cause chromatographic separation effect in the formation, and the preparation conditions are harsh, and the response mechanism is single.

[0004] Patent CN118772327A discloses a CO2 response deep profile control agent, a preparation method and application thereof. The prepared deep profile control agent can be injected into the deep formation with an injection pressure close to that of water, and after reacting with CO2 in the deep formation, the deep profile control agent is secondarily swelled, thereby achieving the purpose of selectively plugging CO2 channeling layers. However, the plugging is performed only through a single CO2 response mechanism, the response condition is single, and the formation extreme environment tolerance and long-term aging are not considered.

[0005] In summary, the existing pre-prepared particle type profile control agents are difficult to migrate in the deep formation, not only hydrolysis occurs under high temperature conditions, but also salt shrinkage occurs under high salinity conditions, and the deformability is generally poor, which is not suitable for reservoir stimulation work under harsh conditions. In order to cope with the profile control and water shutoff work under the conditions of medium-high temperature and high salinity, the present application designs a dual-intelligent response profile control agent, which has excellent mechanical properties and temperature and salt resistance. SUMMARY

[0006] In view of the fact that the existing pre-prepared particle profile control agent cannot migrate to the far well zone, the response condition is single and uncontrollable, and the profile control agent cannot play the expected effect in the face of high-salt oil reservoirs and long-term aging conditions, the present application provides a temperature / CO2 dual-response zwitterionic hydrogel profile control agent.

[0007] The temperature / CO2 dual-response zwitterionic hydrogel profile control agent provided by the present application has the following preparation method:

[0008] The monomer A, monomer B and monomer C are dissolved in water to form an aqueous solution, a crosslinking agent is added, and the mixture is uniformly dispersed in an ultrasonic instrument, then nitrogen is introduced for 30 minutes, an initiator is added, the mixture is uniformly stirred by a magnetic stirrer, and then the mixture is reacted at 50-70 DEG C for 10-15 hours, after the reaction is completed, the product is taken out, cut, dried and crushed to obtain the target hydrogel profile control agent.

[0009] The monomer A is selected from any one of acrylamide, acrylic acid and 1-vinyl-2-pyrrolidone.

[0010] The monomer B is a zwitterionic monomer, and is selected from any one of [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide, 2-methacryloyloxyethylphosphocholine and 3-((2-(methacryloyloxy)ethyl)dimethylamino)propanoate inner salt.

[0011] The monomer C is a carbon dioxide response monomer containing a tertiary amine group, and is selected from any one of 2-(dimethylamino)ethyl methacrylate, dimethylaminopropyl methacrylamide and polyethyleneimine.

[0012] The crosslinking agent is selected from any one of N,N-methylenebisacrylamide, 1,6-hexanediol diacrylate and divinylbenzene.

[0013] The initiator is selected from any one of potassium persulfate, ammonium persulfate and sodium persulfate.

[0014] The amount of each raw material is, for example, as follows:

[0015] The monomer A accounts for 10-30% of the mass of water, the monomer B accounts for 5-30% of the mass of the monomer A, the monomer C accounts for 20-40% of the mass of the monomer A, the crosslinking agent accounts for 0.5-1% of the mass of the monomer A, and the initiator accounts for 0.2-2% of the total mass of the three monomers.

[0016] Preferably, the polymerization reaction condition is 60 DEG C for 12 hours.

[0017] The present application solves the problem of the high swelling performance of conventional profile control agents in low-salt environment and the poor swelling performance in high-salt environment by adding the zwitterionic monomer B. The monomer B belongs to the betaine zwitterionic monomer, and the zwitterion with upper critical solution temperature (UCST) shows the hydrophilicity of temperature rise because the electrostatic inter- and intra-association will be destroyed in the positively and negatively charged parts. In addition, the solubility of the zwitterionic polymer in the salt water solution is also improved. When swelling in pure water, the anions and cations in the gel network will attract each other, so as to control the swelling ratio of the whole gel not to be too large, and in the high-salt environment, the anions and cations will be attracted by the positive and negative charges in the environment, so as to be dispersed, so that the main chain can fully absorb water. This feature is called the anti-polyelectrolyte effect, which is rarely used in the particle profile control agent, but the use of the feature can make it cope with the high-salt reservoir conditions that the conventional profile control agent cannot cope with. And the zwitterionic monomer used in the present application has UCST, mainly C-UCST relying on the coulomb electrostatic force, and the response temperature can be adjusted. The same unit positive and negative ions in the zwitterionic polyelectrolyte molecule, the ions between different units in the molecule, and the positive and negative ion groups on different molecular chains can form ion pairs through electrostatic interaction, at this time the polymer molecular chain is in a crumpled state, and the water solubility is poor, and when the temperature is increased to exceed the UCST, the interaction between the positive and negative ion groups is weakened under the action of heat energy, the interaction between the polymer molecular chain and the water molecules is enhanced, and the molecular chain is in an extended state, showing hydrophilicity.

[0018] The monomer C is a CO2 response monomer, so that the prepared polymer profile control agent has CO2 response performance. CO2 is a greenhouse gas, and the CO2 response performance can improve the oil recovery and store the greenhouse gas at the same time, which meets the concept of green development. In the water alternating gas flooding, the double response swelling solves the problem that the conventional prefabricated particle gel is difficult to deep migration, and the particle is easy to inject at low temperature and in the absence of response stimulation, and the swelling plays a profile control role when the target reservoir temperature is reached and the stimulation point exists.

[0019] The polymer profile control agent of the present application takes the formation temperature and the greenhouse gas CO2 as the response point, is environment-friendly and low in economic cost, is beneficial to industrialized production, and the response condition is controllable and the transition temperature is adjustable.

[0020] Compared with the prior art, the present application has the following advantages:

[0021] (1) The hydrogel profile control agent of the present application has better swelling performance, more intelligent response and more significant salt resistance compared with the existing pre-made particle gel profile control agent. The existing CO2-responsive gel profile control agent can cope with a salinity of 10000 mg / L, while the profile control agent of the present application can resist a salinity of 220000 mg / L, has a high content of divalent ions and is suitable for high-salt reservoirs. In the core displacement experiment, the displacement pressure difference of the particle after response is significantly improved compared with that of the particle before response.

[0022] (2) The hydrogel profile control agent of the present application has the characteristics of shrinking in pure water and swelling in salt water, and can cope with harsh oilfield production environments.

[0023] (3) The process equipment and steps of the present application are simple, the reaction conditions are simple and convenient, the system is low in price and easy to obtain, and the cost is saved.

[0024] (4) The present application solves the problem of environmental pollution caused by direct emission of greenhouse gas CO2, and the resources are reused. While carrying out CO2 oil displacement, the greenhouse gas is stored, which meets the green development.

[0025] (5) The present application has a dual-response mechanism, breaks through the limitation of single trigger, and adapts to complex formation conditions.

[0026] Other advantages, objects and features of the present application will be partly embodied in the following description, and partly understood by those skilled in the art through research and practice of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 is a scanning electron microscope image of the gel profile control agent of Example 1.

[0028] Figure 2 is the temperature and salt resistance aging performance test result of the profile control agent particles of Example 1.

[0029] Figure 3 is a comparison chart of the profile control agent particles of Example 1 before swelling under different salinities, from left to right are the corresponding charts of 5x10 4 mg / L, 10x10 4 mg / L, 15x10 4 mg / L and 22x10 4 mg / L.

[0030] Figure 4 is a comparison chart of the profile control agent particles of Example 1 after swelling under different salinities, from left to right are the corresponding charts of 5x10 4 mg / L, 10x10 4 mg / L, 15x10 4 mg / L and 22x10 4mg / L corresponding graph.

[0031] Figure 5 is the core transport differential pressure characteristic curve result graph of the profile control agent particles of example 1. DETAILED DESCRIPTION

[0032] The preferred embodiments of the present application are described below in conjunction with the accompanying drawings, it should be understood that the preferred embodiments described here are only used to illustrate and explain the present application, and are not used to limit the present application.

[0033] Example 1

[0034] A temperature / CO2 dual-response zwitterionic hydrogel profile control agent, the preparation method is as follows:

[0035] After 10g of acrylamide is dissolved in 90g of deionized water, 1.5g of [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl) ammonium hydroxide, 2mL of 2-(dimethylamino)ethyl methacrylate, 0.05g of N,N-methylene bisacrylamide crosslinking agent are added, and then magnetically stirred uniformly, and then dispersed uniformly in an ultrasonic instrument; nitrogen is passed for 30 minutes, then 0.07g of potassium persulfate is added, and then magnetically stirred uniformly, and then reacted at 60℃ for 12h, and then cut after taking out, dried, and then crushed to obtain the target product hydrogel profile control agent.

[0036] Figure 1 is the scanning electron microscope graph of the gel profile control agent prepared in example 1.

[0037] Comparative example 1

[0038] On the basis of example 1, [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl) ammonium hydroxide is replaced with an equal amount of 2-acrylamido-2-methylpropanesulfonic acid to prepare a profile control agent.

[0039] Comparative example 2

[0040] On the basis of example 1, [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl) ammonium hydroxide is replaced with an equal amount of dimethyldiallylammonium chloride to prepare a profile control agent.

[0041] Comparative example 3

[0042] After 10g of acrylamide is dissolved in 90g of deionized water, 0.05g of N,N-methylene bisacrylamide crosslinking agent is added, and then magnetically stirred uniformly, and then dispersed uniformly in an ultrasonic instrument, and then 0.07g of potassium persulfate is added, and then magnetically stirred uniformly, and then reacted at 60℃ for 12h, and then cut after taking out, dried, and then crushed to obtain the profile control agent.

[0043] Example 2

[0044] A temperature / CO2 dual-responsive zwitterionic hydrogel profile control agent, the preparation method is as follows:

[0045] After 15 mL of acrylic acid is dissolved in 85 g of deionized water, 3 g of 2-methyl acryloyloxyethyl phosphocholine, 4.5 mL of dimethylaminopropyl methacrylamide, and 0.075 mL of divinylbenzene crosslinking agent are added, and then the mixture is uniformly stirred and dispersed in an ultrasonic instrument. Nitrogen is passed for 30 minutes, and then 0.1 g of ammonium persulfate is added. After uniform magnetic stirring, the mixture is reacted at 60°C for 12 h. After being taken out, the mixture is cut, dried, and crushed to obtain the hydrogel profile control agent.

[0046] Example 3

[0047] A temperature / CO2 dual-responsive zwitterionic hydrogel profile control agent, the preparation method is as follows:

[0048] After 10 g of 1-vinyl-2-pyrrolidone is dissolved in 90 g of deionized water, 1 g of 3-((2-(methacryloyloxy)ethyl)dimethylamino)propionate inner salt, 2 mL of polyethyleneimine, and 0.05 g of N,N-methylenebisacrylamide crosslinking agent are added, and then the mixture is uniformly stirred and dispersed in an ultrasonic instrument. Nitrogen is passed for 30 minutes, and then 0.07 g of sodium persulfate is added. After uniform magnetic stirring, the mixture is reacted at 60°C for 12 h. After being taken out, the mixture is cut, dried, and crushed to obtain the hydrogel profile control agent.

[0049] Experimental Example 1

[0050] The dry profile control agent particles prepared in Examples 1-3 and Comparative Examples 1-3 are respectively placed in pure water and mineralized water (the composition is shown in Table 1) for swelling for 24 h, and then the swelling performance at room temperature is compared. The results are shown in Table 2.

[0051] Table 1 Composition of mineralized water

[0052]

[0053] Table 2 Comparison test results of swelling performance (swelling ratio)

[0054]

[0055] From the data of Table 2, it can be seen that the ordinary gel (Comparative Example 3) without adding any salt-resistant and responsive monomer has a very low swelling ratio in the water with salinity, and is prone to hydrolysis or salt shrinkage. The general solution to this problem is to add a single ion property temperature-resistant and salt-resistant monomer (such as Comparative Examples 1 and 2) to improve the swelling ratio in salt water. According to the experimental data, compared with the ordinary gel of Comparative Example 3, the profile control agents of Comparative Examples 1 and 2 have better swelling ratio in water with salinity, but because of the same sex repulsion, the swelling ratio in pure water increases more obviously, which is called polyelectrolyte effect. This characteristic makes the particle profile control agent with single ion property only block the shallow layer with low salinity, and cannot migrate to the deep layer with higher salinity. In view of this situation, the present application adds zwitterionic monomers to make the profile control agent have the reverse polyelectrolyte effect. For example, the swelling ratio of the profile control agents of Examples 1-3 is obviously lower than that of Comparative Examples 1-3 in pure water because of the zwitterionic attraction between the anion and cation monomers, and the swelling ratio of Example 2 is the smallest. However, in salt water, the swelling ratio of Examples 1-3 is obviously higher than that of Comparative Examples 1-3, and the swelling ratio of Example 2 is the highest. This is because the amount of zwitterionic monomer added in Example 2 is the largest among the three groups of examples, so the swelling ratio is the lowest in pure water and the highest in salt water among the three groups of examples. This abnormal swelling performance makes the profile control agent of the present application more suitable for actual profile control operation. After adding zwitterions, the salt resistance of the profile control agent of the present application is significantly improved, and the zwitterions also have UCST, and act as salt-resistant monomers and temperature-responsive monomers. The [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl) ammonium hydroxide used in Example 1 has a UCST adjustable at 40-80℃, which can cope with different temperature formations.

[0056] Experimental Example 2

[0057] Salt-resistant aging performance test: The profile control agent particles in Example 1 were loaded into a pressure-resistant bottle, and the same salinity water as described above was added. During the period, the pH of the solution was adjusted to about 5.5, CO2 was introduced to saturation, and the solution was aged in a 70℃ aging box for 45 days. Photographs were taken to record the observation at 0d, 5d, 10d, 20d, 30d and 45d, respectively. The temperature-resistant and salt-resistant stability of the particles was evaluated, the sample shape was observed, the swelling ratio was measured and calculated, and the test results are shown in Table 4. Figure 2

[0058] Visual code method was used to describe the gel strength during the aging process. In the laboratory, the gel sample strength can be quickly observed by this method. By observing the gel shape at different aging times and referring to the strength code table, the temperature-resistant performance can be directly judged. The specific content of the gel strength code table is shown in Table 3.

[0059] Table 3 Gel strength code standard table​

[0060]

[0061] From the experimental results, it can be seen that the gel profile control agent particles of Example 1 can effectively withstand high temperature and harsh high-salt environment, and still have CO2 and temperature response, and still maintain elasticity and do not degrade after 45 days of aging.

[0062] Experimental Example 3

[0063] Swelling test under different salinities: The profile control agent particles of Examples 1-3 were taken and loaded into pressure-resistant bottles, 40 mL of salinity water with different salinities (5×10 4 mg / L, 10×10 4 mg / L, 15×10 4 mg / L, 22×10 4 mg / L) were added, in addition to the salinity water indicated in Table 1, the remaining salinity water only had monovalent ions, and was placed in a 70°C aging oven for swelling performance comparison. The results are shown in Tables 4-6, and the comparison of swelling before and after of Example 1 is shown in Figure 3 and Figure 4 .

[0064] Table 4 Swelling comparison test of Example 1 at 70°C under different salinities

[0065] Salinity (mg / L) 5 x 10 4 ]] 10 x 10 4 ]] 15 x 10 4 ]] 22 x 10 4 ]] Swelling ratio (g / g) 28.62 31.16 33.81 35.02

[0066] Table 5 Swelling comparison test of Example 2 at 70°C under different salinities

[0067] Salinity (mg / L) 5 x 10 4 ]] 10 x 10 4 ]] 15 x 10 4 ]] 22 x 10 4 ]] Swelling ratio (g / g) 28.83 32.52 34.98 36.59

[0068] Table 6 Swelling comparison test of Example 3 at 70°C under different salinities

[0069] Salinity (mg / L) 5 x 10 4 ]] 10 x 10 4 ]] 15 x 10 4 ]] 22 x 10 4 ]] Swelling ratio (g / g) 27.58 29.85 33.52 34.82

[0070] At the same time, Comparative Example 1, Comparative Example 2, and Comparative Example 3 particles were taken for comparison test under the same conditions, to illustrate the swelling of the profile control agent particles of the present application and the particles of the comparative examples under different salinities, to compare their salt tolerance, and the results are shown in Tables 7, 8, and 9, Table 7 Swelling comparison test of Comparative Example 1 at 70°C under different salinities

[0071] Salinity (mg / L) 5 x 10 4 ]]> 10 x 10 4 ]] 15 x 10 4 ]]> 22 x 10 4 ]] Swelling ratio (g / g) 21.98 21.26 19.96 18.59

[0072] Table 8 Swelling comparison test of Comparative Example 2 at 70°C under different salinities

[0073] Salinity (mg / L) 5 x 10 4 ]] 10 x 10 4 ]] 15 x 10 4 ]] 22 x 10 4 ]] Swelling ratio (g / g) 19.81 18.96 17.08 15.78

[0074] Table 9 Swelling comparison test of Comparative Example 3 at 70℃ under different salinities

[0075] Salinity (mg / L) 5 x 10 4 ]]> 10 x 10 4 ]] 15 x 10 4 ]] 22 x 10 4 ]] Swelling ratio (g / g) 14.57 14.06 13.67 12.59

[0076] From the swelling test results of the samples under different salinities, it can also be seen that the hydrogel profile control agent prepared in the present application has more significant temperature resistance and salt resistance than the profile control agents of Comparative Examples 1-3, and has better swelling performance in water with different salinities. With the increase of salinity, the swelling ratio of Examples 1-3 shows an overall upward trend, and the swelling performance is also good under the condition of high salinity water of 220000 mg / L; while the swelling ratio of Comparative Examples 1-3 shows a gradually downward trend, and cannot tolerate high salinity water.

[0077] Experimental Example 4

[0078] The plugging performance of the profile control agent particles of Example 1 was tested by core flooding experiment: the core parameters used are shown in Table 10, and the experimental conditions are: the injection pressure is higher than 4.5 MPa by back pressure regulator, the injection rate is 1.5 mL / min, the experimental temperature is room temperature, and the particle size of the profile control agent is 20-40 mesh. In order to control the variable, the core flooding experiment before and after the particle response was tested in the same core, and the results are shown in Table 11. Figure 5 In the core flooding experiment, the displacement pressure difference of the particles after the response is significantly improved compared with the particles before the response.

[0079] Table 10 Core basic parameters

[0080]

[0081] The above is only the preferred embodiment of the present application, and does not limit the present application in any form. Although the present application has been disclosed as above with the preferred embodiment, it is not intended to limit the present application. Any skilled person in the art can make some changes or modifications to the above disclosed technical content without departing from the technical solution of the present application, and any simple modification, equivalent change and modification of the above embodiment based on the technical essence of the present application are still within the scope of the technical solution of the present application.

Claims

1. A method for preparing a temperature / CO2 dual responsive zwitterionic hydrogel profile control agent, characterized in that, The monomer A, the monomer B and the monomer C are used as raw materials, a crosslinking agent and an initiator are added, and a polymerization reaction is carried out in a water medium to prepare the water gel profile control agent; The monomer A is selected from any one of acrylamide, acrylic acid and 1-vinyl-2-pyrrolidone; The monomer B is selected from any one of [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide, 2-methacryloyloxyethylphosphocholine and 3-((2-(methacryloyloxy)ethyl)dimethylamino)propanoate inner salt; The monomer C is selected from any one of 2-(dimethylamino)methyl acrylate, dimethylaminopropyl methacrylamide and polyethyleneimine. The usage ratio of each raw material is as follows: The monomer A accounts for 10%-30% of the mass of water, the monomer B accounts for 5-30% of the mass of the monomer A, the monomer C accounts for 20-40% of the mass of the monomer A, the crosslinking agent accounts for 0.5-1% of the mass of the monomer A, and the initiator accounts for 0.2%-2% of the total mass of the three monomers.

2. The method of claim 1, wherein the temperature / CO2 dual responsive zwitterionic hydrogel profile control agent is prepared by the steps of: The polymerization reaction temperature is 50-70℃, and the reaction time is 10-15h.

3. The method of claim 1, wherein the temperature / CO2 dual responsive zwitterionic hydrogel profile control agent is prepared by the steps of: The crosslinking agent is selected from any one of N,N-methylene bisacrylamide, 1,6-hexanediol diacrylate and divinylbenzene.

4. The method of claim 1, wherein the temperature / CO2 dual responsive zwitterionic hydrogel profile control agent is prepared by the steps of: The initiator is selected from any one of potassium persulfate, ammonium persulfate and sodium persulfate.

5. The method of claim 1, wherein the temperature / CO2 dual responsive zwitterionic hydrogel profile control agent is prepared by the steps of: (a) mixing a first solution comprising a first polymer and a second solution comprising a second polymer to form a mixture; (b) adding a crosslinking agent to the mixture; and (c) allowing the mixture to form a hydrogel. The steps are as follows: The monomer A, the monomer B and the monomer C are dissolved in water to prepare an aqueous solution, the crosslinking agent is added and uniformly dispersed in an ultrasonic instrument, the initiator is added after oxygen removal by nitrogen blowing, and the mixture is uniformly stirred by a magnetic stirrer, and then the reaction is carried out at 50-70℃ for 10-15h, and the product is obtained after cutting, drying and crushing to obtain the target water gel profile control agent.

6. The method of claim 5, wherein the temperature / CO2 dual responsive zwitterionic hydrogel profile control agent is prepared by the steps of: The polymerization reaction condition is 60℃ for 12h.

7. A temperature / CO2 dual responsive zwitterionic hydrogel profile control agent, characterized in that, The water gel profile control agent is prepared by the preparation method of any one of claims 1-6. The water gel profile control agent is prepared by the preparation method of any one of claims 1-6.

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