Modified cellulose cross-linked gel for profile control of oil field as well as preparation method and application of modified cellulose cross-linked gel

Abstract

The invention relates to modified cellulose cross-linked gel for profile control of an oil field and a preparation method and application of the modified cellulose cross-linked gel. The modified cellulose cross-linked gel for oilfield profile control is prepared from the following components in parts by weight: 0.5 to 2 parts of modified cellulose, 0.01 to 0.1 part of polymer, 0.2 to 1 part of cross-linking agent, 0.05 to 0.2 part of coagulant and 1000 parts of water. The modified cellulose cross-linked gel for profile control of the oil field, provided by the invention, is organic cross-linked, has dual functions of profile control and oil displacement, and can effectively reduce the influence of other mineral ions in a stratum and factors such as shearing, adsorption and the like on the gelling performance of the modified cellulose cross-linked gel. The main body of the modified cellulose cross-linked gel is self-made modified cellulose, the molecular weight is small, the dosage of a polymer is effectively reduced, the initial viscosity of a gel system is greatly reduced, and the shear resistance is improved.

Description

Technical Field

[0001] The invention relates to a modified cellulose cross-linked gel for oil field profile control and a preparation method and application thereof, belonging to the technical field of oil and gas development. Background Art

[0002] Among the profile control agents and profile control methods currently used, underground gelling profile control agents are relatively common. They are mainly polymers, cross-linking agents, additives, etc. that are injected into the formation together. Cross-linking reactions occur in the underground oil layer to form gel profile control agents. However, during the underground gelling process, due to formation conditions such as mineralization, pressure, and temperature in the formation, the gelling agent often fails to gel or partially fails to gel in the formation, or the strength of the formed gel is weak, and the purpose of plugging cannot be achieved. In addition, factors such as the porous medium environment, mineral ions, dilution, shear, and adsorption in the oil layer make the gelling reaction difficult to control.

[0003] Moreover, the polymers of the profile control agents currently in use are mainly partially hydrolyzed polyacrylamide, which are easily sheared and degraded by the formation during the gelation process underground after injection, resulting in the failure to gel and play the role of profile control and sealing. Therefore, it is necessary to study a gel-type profile control agent suitable for horizontal wells in deep high-temperature oil reservoirs. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention provides a modified cellulose cross-linked gel for oil field profile control and its preparation method and application. The modified cellulose cross-linked gel for oil field profile control can effectively improve the anti-shear and anti-adsorption capabilities of the formation and enhance the gelling performance in the formation.

[0005] The technical solution of the present invention is as follows:

[0006] A modified cellulose cross-linked gel for oil field profile control, comprising the following components by weight:

[0007] 0.5-2 parts of modified cellulose, 0.01-0.1 parts of polymer, 0.2-1 parts of cross-linking agent, 0.05-0.2 parts of coagulant, and 1000 parts of water.

[0008] Preferably, according to the present invention, the modified cellulose is prepared according to the following method:

[0009] The natural cellulose is soaked in a 0.5 mol / L sodium hydroxide solution for 1.5 to 2.5 hours to obtain swollen cellulose; the swollen cellulose is then added to an etherifying agent, reacted at 40 to 80° C. for 2 to 6 hours, and the modified cellulose is obtained through neutralization, washing, impurity removal, drying and pulverization.

[0010] More preferably, the etherifying agent is ethylene oxide or chloroacetic acid.

[0011] More preferably, the mass ratio of the swollen cellulose to the etherifying agent is 1:(0.3-0.5).

[0012] Preferably according to the present invention, the cross-linking agent is an organic chromium cross-linking agent.

[0013] More preferably, the cross-linking agent is chromium acetate.

[0014] Preferably according to the present invention, the coagulant is ferric chloride.

[0015] Preferably according to the present invention, the polymer is partially hydrolyzed polyacrylamide, and the viscosity average molecular weight is 25 to 30 million.

[0016] According to the present invention, the method for preparing the modified cellulose cross-linked gel for oil field profile control comprises the following steps:

[0017] Modified cellulose, a coagulant, a polymer and a cross-linking agent are added to part of the water in sequence according to the proportion while stirring to obtain a mixed solution; the remaining water is added to the mixed solution and stirred evenly; the remaining polymer is then added and stirred to dissolve to obtain a modified cellulose cross-linked gel for oil field profile control.

[0018] Preferably according to the present invention, the stirring speed is 380-420 r / min.

[0019] The modified cellulose cross-linked gel for oil field profile control is used in the exploitation of oil and gas reservoirs.

[0020] Beneficial effects of the present invention:

[0021] 1. The modified cellulose cross-linked gel for oil field profile control provided by the present invention is organically cross-linked and has the dual functions of profile control and oil displacement, and can effectively reduce the influence of other mineral ions in the formation and factors such as shearing and adsorption on its gelling properties.

[0022] 2. The modified cellulose cross-linked gel for oilfield profile control provided by the present invention is mainly composed of self-made modified cellulose with a small molecular weight, which effectively reduces the amount of polymer used, greatly reduces the initial viscosity of the gel system, and increases the shear resistance.

[0023] 3. The method for preparing the modified cellulose cross-linked gel for oil field profile control of the present invention is simple to operate, has strong operability, mild conditions, is easy to be industrially produced on a large scale, and has good quality stability of the obtained product. DETAILED DESCRIPTION

[0024] The technical scheme of the present invention is further described below in conjunction with the embodiments, but the protection scope of the present invention is not limited thereto. The materials involved in the embodiments, unless otherwise specified, are all common commercially available products; the experimental operations involved in the embodiments, unless otherwise specified, are all conventional operations in the art.

[0025] The modified cellulose described in this embodiment is prepared according to the following method:

[0026] The natural cellulose is soaked in a 0.5 mol / L sodium hydroxide solution for 1.5 to 2.5 hours to obtain swollen cellulose; then 1 g of the swollen cellulose is added to 0.4 g of ethylene oxide, reacted at 60° C. for 4 hours, and the modified cellulose is obtained through neutralization, washing, impurity removal, drying and pulverization.

[0027] The chromium acetate can be purchased directly or prepared as follows: glacial acetic acid is added to deionized water to prepare an acetic acid solution of appropriate concentration. Under stirring conditions, a certain mass of chromium trichloride is gradually added and stirring is continued until it is completely dissolved. As needed, the pH of the solution is adjusted by adding an acidic or alkaline solution to meet the use requirements. Finally, the prepared chromium acetate solution is stored in a closed container and kept away from light to prevent oxidation and maintain stability.

[0028] Example 1

[0029] A modified cellulose cross-linked gel for oil field profile control, comprising the following components by weight:

[0030] Modified cellulose 1.00g, partially hydrolyzed polyacrylamide 0.31g, chromium acetate 1.00g, ferric chloride 0.20g, water 1000g.

[0031] The method for preparing the modified cellulose cross-linked gel for oil field profile control comprises the following steps:

[0032] At a stirring speed of 400 r / min, add 1.00 g of homemade modified cellulose to 100 g of water while stirring, and stir for 20 minutes; then add 0.20 g of ferric chloride and stir for 10 minutes; then add 0.01 g of partially hydrolyzed polyacrylamide and stir for 40 minutes; then add 1.00 g of chromium acetate and stir for 10 minutes to obtain a mixed solution; add the remaining 900 g of water to the mixed solution and stir for 20 minutes; then add the remaining 0.3 g of partially hydrolyzed polyacrylamide and stir for 120 minutes to obtain a modified cellulose cross-linked gel for oil field profile control.

[0033] Example 2

[0034] A modified cellulose cross-linked gel for oil field profile control, comprising the following components by weight:

[0035] 0.50g modified cellulose, 0.31g partially hydrolyzed polyacrylamide, 0.25g chromium acetate, 0.10g ferric chloride, 1000g water.

[0036] The method for preparing the modified cellulose cross-linked gel for oil field profile control comprises the following steps:

[0037] At a stirring speed of 400 r / min, add 0.50 g of homemade modified cellulose to 100 g of water while stirring, and stir for 20 minutes; then add 0.10 g of ferric chloride and stir for 10 minutes; then add 0.01 g of partially hydrolyzed polyacrylamide and stir for 40 minutes; then add 0.25 g of chromium acetate and stir for 10 minutes to obtain a mixed solution; add the remaining 900 g of water to the mixed solution and stir for 20 minutes; then add the remaining 0.3 g of partially hydrolyzed polyacrylamide and stir for 120 minutes to obtain a modified cellulose cross-linked gel for oil field profile control.

[0038] Comparative Example 1

[0039] A cellulose cross-linked gel for oilfield profile control, the specific components and preparation method are the same as those described in Example 1, except that no homemade modified cellulose is added and partially hydrolyzed polyacrylamide is used instead.

[0040] Test Example 1

[0041] The performance of the modified cellulose cross-linked gel for oil field profile control prepared in Example 1 and the cellulose cross-linked gel for oil field profile control prepared in Comparative Example 1 were evaluated.

[0042] 1. Determination of initial viscosity

[0043] After the modified cellulose cross-linked gel for oil field profile control in Example 1 and the cellulose cross-linked gel for oil field profile control prepared in Comparative Example 1 are stirred evenly, 250 mL of each sample is measured and placed in a 500 mL tall beaker, a rotor that meets the required measurement range is selected and connected to the viscometer, and the measurement is performed at a speed of 6 r / min. After the reading is stable, the viscosity data at this time is recorded, which is the initial viscosity.

[0044] 2. Determination of gelation time and gelation viscosity

[0045] Use a 500mL measuring cylinder to measure 250mL of the modified cellulose cross-linked gel for oil field profile control in Example 1 and the cellulose cross-linked gel for oil field profile control prepared in Comparative Example 1, respectively, and pour them into 10 to 12 500mL sample bottles, tightly seal them, and place them in an electric heated air drying oven with the temperature set to 45°C. Take them out regularly according to product performance, test their apparent viscosity using a Brookfield viscometer, and draw an apparent viscosity-time curve. The time elapsed when the curve begins to have an inflection point is taken as the gelation time of the product, and the maximum viscosity value on the curve is its gelation viscosity.

[0046] The specific results of the determination of initial viscosity, gelation time and gelation viscosity are shown in Table 1.

[0047] Table 1. Gel-forming properties of Example 1 and Comparative Example 1

[0048]

[0049] As can be seen from Table 1, the initial viscosity of the modified cellulose cross-linked gel used for oil field profile control in Example 1 is about 30.1 times lower than the initial viscosity of the cellulose cross-linked gel in Comparative Example 1. Moreover, unlike the gelation in Comparative Example 1 within 16 hours, the gelation process of Example 1 is slowly formed, the gelation time is longer than that of Comparative Example 1, and the final gelation viscosity is higher than the final gelation viscosity of Comparative Example 1. The above data comparison proves that the modified cellulose cross-linked gel used for oil field profile control in Example 1 of the present invention can enhance the gelation strength and prolong the gelation time of the gel system by adding modified cellulose as part of the main agent constituting the gel network, which is beneficial for the profile control system to effectively adjust the water absorption profile of the deep part of the reservoir.

[0050] 3. Determination of shear resistance

[0051] 250 mL of the modified cellulose cross-linked gel for oil field profile control prepared in Example 1 and the cellulose cross-linked gel for oil field profile control prepared in Comparative Example 1 were measured and placed in a 500 mL beaker. The samples were sheared at a speed of 5000 r / min for 5 minutes. The performance of the samples after shearing was tested according to the determination methods in 1 and 2. The results are shown in Table 2.

[0052] Table 2. Gel properties after shearing of Example 1 and Comparative Example 1

[0053]

[0054]

[0055] As can be seen from Table 2, the initial viscosity of the modified cellulose cross-linked gel for oil field profile control in Example 1 after shearing is about 4.7 times lower than the initial viscosity of the cellulose cross-linked gel in Comparative Example 1. Moreover, unlike the situation in which the cellulose cross-linked gel in Comparative Example 1 initially gelled after shearing for 24 hours, the modified cellulose cross-linked gel for oil field profile control in Example 1 only began to initially gel after 48 hours, and the gelling time was longer than that in Comparative Example 1, and the final gelling viscosity was about 1.8 times the final gelling viscosity of Comparative Example 1. The above data comparison proves that the modified cellulose cross-linked gel for oil field profile control in Example 1 of the present invention can enhance the gelling strength and prolong the gelling time of the gel system after shearing by adding modified cellulose as part of the main agent constituting the gel network, and has good anti-shear performance, which is beneficial for the profile control system to effectively adjust the water absorption profile in the deep part of the reservoir.

[0056] 4. Determination of anti-adsorption performance

[0057] 250 mL of the modified cellulose cross-linked gel for oil field profile control prepared in Example 1 and the cellulose cross-linked gel for oil field profile control prepared in Comparative Example 1 were measured and placed in a 500 mL beaker. 225 g of core was added respectively and the mixture was shaken and adsorbed for 24 h. The performance of the samples after adsorption was tested according to the determination methods in 1 and 2. The results are shown in Table 3.

[0058] Table 3. Gel properties after shearing of Example 1 and Comparative Example 1

[0059]

[0060] As can be seen from Table 3, the initial viscosity of the modified cellulose cross-linked gel for oil field profile control in Example 1 after adsorption is about 3.1 times lower than the initial viscosity of the cellulose cross-linked gel in Comparative Example 1. In addition, unlike the situation in which the cellulose cross-linked gel in Comparative Example 1 initially gelled after 36 hours of adsorption, the modified cellulose cross-linked gel for oil field profile control in Example 1 began to initially gel after 24 hours, and the final gelling viscosity was about 5.3 times the final gelling viscosity of Comparative Example 1. The above data comparison proves that the modified cellulose cross-linked gel for oil field profile control in Example 1 of the present invention can enhance the gelling strength and prolong the gelling time of the gel system after adsorption by adding modified cellulose as part of the main agent constituting the gel network, and has good anti-adsorption performance, which is beneficial for the profile control system to effectively adjust the water absorption profile of the reservoir.

[0061] The above-described embodiments are only preferred specific implementation schemes of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A modified cellulose cross-linked gel for oil field profile control, characterized in that: The components are as follows by weight: 0.5-2 parts of modified cellulose, 0.01-0.1 parts of polymer, 0.2-1 parts of cross-linking agent, 0.05-0.2 parts of coagulant, and 1000 parts of water.

2. The modified cellulose cross-linked gel for oil field profile control according to claim 1, characterized in that: The modified cellulose is prepared according to the following method: The natural cellulose is soaked in a 0.5 mol / L sodium hydroxide solution for 1.5 to 2.5 hours to obtain swollen cellulose; the swollen cellulose is then added to an etherifying agent, reacted at 40 to 80° C. for 2 to 6 hours, and the modified cellulose is obtained through neutralization, washing, impurity removal, drying and pulverization.

3. The modified cellulose cross-linked gel for oil field profile control according to claim 2, characterized in that: The etherifying agent is ethylene oxide or chloroacetic acid.

4. The modified cellulose cross-linked gel for oil field profile control according to claim 3, characterized in that: The mass ratio of the swelled cellulose to the etherifying agent is 1:(0.3-0.5).

5. The modified cellulose cross-linked gel for oil field profile control according to claim 1, characterized in that: The cross-linking agent is an organic chromium cross-linking agent; More preferably, the cross-linking agent is chromium acetate.

6. The modified cellulose cross-linked gel for oil field profile control according to claim 1, characterized in that: The coagulant is ferric chloride.

7. The modified cellulose cross-linked gel for oil field profile control according to claim 1, characterized in that: The polymer is partially hydrolyzed polyacrylamide, and the viscosity average molecular weight is 25 to 30 million.

8. The method for preparing the modified cellulose cross-linked gel for oil field profile control according to claim 1, characterized in that: The steps include: Modified cellulose, a coagulant, a polymer and a cross-linking agent are added to part of the water in sequence according to the proportion while stirring to obtain a mixed solution; the remaining water is added to the mixed solution and stirred evenly; the remaining polymer is then added and stirred to dissolve to obtain a modified cellulose cross-linked gel for oil field profile control.

9. The preparation method according to claim 8, characterized in that: The stirring speed is 380-420 r / min.

10. Use of the modified cellulose cross-linked gel for oil field profile control according to claim 1 in oil and gas reservoir exploitation.

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