Slow cross-linked polymer gel suitable for water shutoff of high-temperature and high-salt oil reservoir and application of low cross-linked polymer gel

Abstract

The invention provides slow cross-linked polymer gel suitable for high-temperature and high-salt oil reservoir water shutoff and application thereof.The slow cross-linked polymer gel is prepared from acrylamide / 2-acrylamide-2-methylpropanesulfonic acid copolymer, a phenolic aldehyde composite cross-linking agent, a deoxidant, a cross-linking control agent A, a cross-linking control agent B and the balance water, and the cross-linking control agent B is sodium p-toluenesulfonate, sodium isopropyl benzene sulfonate or sodium salicylate. The gel system disclosed by the invention is long in gelling time and good in stability, has important significance on improving the oil and gas recovery ratio, and can be used for further improving the crude oil recovery ratio in the technical field of oil and gas field development engineering.

Description

Technical Field

[0001] The present invention belongs to the technical field of oil and gas field development engineering, and specifically belongs to a slow-crosslinking polymer gel suitable for water plugging in high-temperature and high-salinity reservoirs and its application. Background Technique

[0002] In the middle and late stages of waterflooding development of oilfields, there is usually a serious problem of water channeling, and polymer gels need to be used for plugging. With the exploration and development moving towards high-temperature and high-salinity reservoirs, higher requirements are also put forward for the performance of polymer gels. On the one hand, the gel should have good stability at high temperature and high salinity to extend the plugging validity period. On the other hand, it should have a long enough gelation time to ensure construction safety and achieve deep profile control. However, there is a contradiction between the requirements of gel stability and gelation time at high temperature. Usually, to increase the gel stability, the amounts of polymer and crosslinking agent in the gel need to be increased, which will lead to too short gelation time of the gel; conversely, reducing the amounts of polymer and crosslinking agent to extend the gelation time will result in poor stability. At present, there is no effective solution to this contradiction.

[0003] To improve the stability of the gel under high-temperature and high-salinity conditions, the polymer is changed from conventional HPAM to temperature- and salt-resistant polymers, such as AM-AMPS copolymer, AM-AMPS-NVP copolymer, etc., and the crosslinking agent used is also changed from inorganic metal crosslinking agents to organic phenolic aldehyde crosslinking agents. At present, many studies on temperature- and salt-resistant gels have been carried out by scientific research workers, but they generally focus on reservoir conditions with a temperature not exceeding 130°C and a salinity not exceeding 20×10 4 mg / L, while the temperature of some reservoirs is as high as 150°C and the salinity reaches 25×10 4 mg / L. According to the gelation time of the gel under different temperature and salinity conditions in the existing research, it can be inferred that the gelation time of these gels at 150°C and 25×10 4 mg / condition is far lower than the 10 h required for field construction. For example, Patent CN 111808585A discloses a slow-crosslinking temperature- and salt-resistant high-strength gel and its preparation method and application. The gelation time of this gel at 130°C is only 1.5 - 2 h, which cannot meet the requirements of field construction. Patent CN106749899A discloses a preparation method of a polymer gelator for high-temperature and high-salt profile control and water plugging. The gelation time of this gel at 110°C and 10×10 4 mg / L condition is 15 - 24 h, but this patent does not provide experimental data at higher temperatures and higher salinities. According to the influence law of temperature on gelation time, it can be inferred that the gelation time of this system at 150°C will be much lower than 15 h. Patent CN105131921A discloses a salt- and high-temperature-resistant high-strength gel water plugging agent. The salt- and high-temperature-resistant high-strength gel water plugging agent has a gelation time at a temperature of 120°C and a salinity of 20×104 At the condition of mg / L, the gel strength is 4×10 4 ~10×10 4 mPa·s, but the gelation time is only 4 - 6 h. Patent CN103232839A discloses a water plugging agent suitable for water shutoff and profile control in high-temperature and high-salinity oil reservoirs. This water plugging agent is applicable to water shutoff and profile control of oil layers with a temperature of 90 - 150°C and a salinity greater than 2×10 5 mg / L. The gelation time is 5 - 28 h, the formed gel strength is 0.060 - 0.085 MPa, the integrity of the water plugging agent is good, and the plugging rate of the core reaches more than 92%. However, the gelation time of this system in clear water at 150°C is only 5.4 h. Therefore, at present, the gelation time of temperature- and salt-resistant gels cannot meet the construction requirements of high-temperature and high-salinity oil reservoirs (temperature 150°C, salinity 25×10 4 mg / L), deep profile control cannot be achieved, and construction accidents are likely to occur. Summary of the Invention

[0004] Aiming at the problems existing in the prior art, such as the fast gelation and poor stability of gels used for water plugging in high-salinity oil reservoirs, and the contradiction between improving gel stability and delaying gelation time, the present invention proposes a slow-crosslinking polymer gel and its application suitable for water plugging in high-temperature and high-salinity oil reservoirs. This gel system has a long gelation time and good stability, which is of great significance for improving oil and gas recovery rate and can further improve crude oil recovery rate in the field of oil and gas field development engineering technology.

[0005] To achieve the above object, the present invention provides the following technical solution: A slow-crosslinking polymer gel suitable for water plugging in high-temperature and high-salinity oil reservoirs, the raw materials of which include acrylamide / 2-acrylamido-2-methylpropanesulfonic acid copolymer, phenolic aldehyde composite crosslinking agent, deoxidizer, crosslinking control agent A, crosslinking control agent B and the balance of water. Among them, the crosslinking control agent A is alkylpyridinium bromide, and the crosslinking control agent B is sodium p-toluenesulfonate, sodium isopropylbenzenesulfonate or sodium salicylate.

[0006] Further, by mass percentage, the total amount is 100%, and the raw materials include: 0.5% - 1.0% of acrylamide / 2-acrylamido-2-methylpropanesulfonic acid copolymer, 0.2% - 0.8% of phenolic aldehyde composite crosslinking agent, 0.3% of deoxidizer, 0.2% - 0.3% of crosslinking control agent A, 0.05% - 0.075% of crosslinking control agent B and the balance of water.

[0007] Further, the phenolic aldehyde composite crosslinking agent includes a first crosslinking agent and a second crosslinking agent. The first crosslinking agent is hydroquinone, resorcinol, catechol or pyrogallol; the second crosslinking agent is formaldehyde, hexamethylenetetramine or terephthalaldehyde.

[0008] Furthermore, the mass ratio of the first crosslinking agent to the second crosslinking agent is 1:1.

[0009] Furthermore, the first crosslinking agent is hydroquinone and the second crosslinking agent is hexamethylenetetramine.

[0010] Furthermore, the crosslinking control agent A is one of cetylpyridinium bromide or octadecylpyridinium bromide.

[0011] Furthermore, the content of 2-acrylamido-2-methylpropanesulfonic acid in the acrylamide / 2-acrylamido-2-methylpropanesulfonic acid copolymer is 50%-80%, and the molecular weight is 6 million - 8 million.

[0012] Furthermore, the deoxidizer is thiourea.

[0013] Furthermore, the gel system has a gelation time of more than 12 h under the conditions of a temperature of 150°C and a salinity of 25×10 4 mg / L.

[0014] The present invention also provides an application of the above-mentioned delayed-crosslinking polymer gel in water plugging for high-temperature and high-salinity oil reservoirs.

[0015] Compared with the prior art, the present invention has at least the following beneficial effects:

[0016] The present invention provides a delayed-crosslinking polymer gel suitable for water plugging in high-temperature and high-salinity oil reservoirs. A delayed-crosslinking system is constructed by a crosslinking agent, a deoxidizer, a crosslinking control agent A, a crosslinking control agent B and water. The alkylpyridinium bromide of the crosslinking control agent A can form micelles in the gelling solution, and the phenolic aldehyde composite crosslinking agent can be solubilized in the micelles formed by the crosslinking control agent A, resulting in a reduced diffusion rate. The p-toluenesulfonate of the crosslinking control agent B can also increase the effect of the aggregation number of the alkylpyridinium bromide micelles, strengthening the solubilization effect of the micelles on the crosslinking agent. Furthermore, the rate of formation of the phenolic aldehyde prepolymer by the crosslinking agent is slowed down, thereby delaying the crosslinking reaction between the phenolic aldehyde prepolymer and the acrylamide / 2-acrylamido-2-methylpropanesulfonic acid copolymer, and finally achieving the purpose of delaying the gelation of the gel. The gel for water plugging in high-temperature and high-salinity oil reservoirs of the present invention is of great significance for improving the oil and gas recovery rate and can further improve the crude oil recovery rate in the field of oil and gas field development engineering technology.

[0017] The gel for water plugging in high-temperature and high-salinity oil reservoirs prepared by the present invention has a long gelation time. Under the conditions of a temperature of 150°C and a salinity of 25×10 4 mg / L, the gelation time is more than 12 h, which can meet the injection time requirements during field construction, thereby ensuring construction safety and achieving deep water plugging; and it has good stability and strong plugging ability in a high-temperature and high-salinity environment. The dehydration rate after aging for 90 days under the conditions of 150°C and 25×10 4 mg / L salinity does not exceed 8%, and at a permeability of 2μm2 The breakthrough pressure gradient generated by water shutoff in the core on both sides is higher than 60 MPa / m, meeting the requirement of the gel water shutoff strength. Specific Embodiments

[0018] The specific embodiments of the present invention will be further described in detail below in combination with the examples and comparative examples. Here, the illustrative examples and descriptions of the present invention are used to explain the present invention, but not to limit the present invention.

[0019] Aiming at the problems that the gel has poor stability and short gelation time in high-temperature and high-salt reservoirs, and it is difficult to meet the requirements of gel injection and stability, the present invention provides a gel for water shutoff with a long gelation time and good stability in high-temperature and high-salt reservoirs, specifically as follows:

[0020] A slow-crosslinking polymer gel applicable to water shutoff in high-temperature and high-salt reservoirs is composed of 0.5% - 1.0% acrylamide / 2-acrylamido-2-methylpropanesulfonic acid (AM / AMPS) copolymer, 0.2% - 0.8% phenolic composite crosslinking agent, 0.3% thiourea, 0.2% - 0.3% crosslinking control agent A, 0.05% - 0.075% crosslinking control agent B, and the balance of water by mass percentage.

[0021] Preferably, the content of AMPS monomer in the AM / AMPS copolymer is 50 - 80%, and the molecular weight is 6 - 8 million. In the present invention, the AM / AMPS copolymer is a temperature- and salt-resistant polymer, and a large amount of temperature- and salt-resistant monomer AMPS is introduced into the molecule, which can be stable for a long time in a high-temperature and high-salt environment, so that the prepared gel can be stable in a reservoir at 150 °C and 25 × 10 4 mg / L for a long time.

[0022] Preferably, the phenolic composite crosslinking agent includes a first crosslinking agent and a second crosslinking agent with a mass ratio of 1:1. The first crosslinking agent is hydroquinone, resorcinol, catechol, or pyrogallol, preferably hydroquinone; the second crosslinking agent is formaldehyde, terephthalaldehyde, or hexamethylenetetramine, preferably hexamethylenetetramine;

[0023] The crosslinking reaction involving the use of this phenolic composite crosslinking agent is divided into 3 steps:

[0024] (1) Hexamethylenetetramine is hydrolyzed by hot water to formaldehyde;

[0025] (2) Formaldehyde and hydroquinone are polycondensed to form a phenolic prepolymer;

[0026] (3) The phenolic prepolymer is crosslinked with the polymer through covalent bonds to form a gel with a three-dimensional network, which has strong temperature resistance;

[0027] Preferably, thiourea in the gelling solution is used as an oxygen scavenger, which can consume the dissolved oxygen in water, reduce the oxidative degradation of the polymer gel, and increase the gel stability.

[0028] Preferably, the crosslinking control agent A is one of cetylpyridinium bromide or octadecylpyridinium bromide;

[0029] Preferably, the crosslinking control agent B is sodium p-toluenesulfonate, sodium isopropylbenzenesulfonate or sodium salicylate. Further preferably, the crosslinking control agent B is sodium p-toluenesulfonate;

[0030] Preferably, the dosage of the crosslinking control agent B is 25% of that of the crosslinking control agent A.

[0031] In the present invention, the crosslinking control agent A and the crosslinking control agent B are used to reduce the crosslinking reaction rate and prolong the gelation time of the gel, so as to ensure construction safety and achieve deep water plugging of the gel. Among them, the alkylpyridinium bromide of the crosslinking control agent A can form micelles in the gel-forming solution, and hydroquinone in the crosslinking agent can be solubilized in the micelles formed by the crosslinking control agent A, resulting in a reduced diffusion rate. Furthermore, the rate of reaction with formaldehyde to form the phenolic prepolymer is controlled, and finally the effect of delaying the gelation of the gel is achieved. Sodium p-toluenesulfonate of the crosslinking control agent B can increase the aggregation number of the alkylpyridinium bromide micelles, strengthen the solubilization effect of the micelles on hydroquinone, and further delay the gelation of the gel.

[0032] The gel-forming system constructed in the present invention has a relatively long gelation time at high temperatures, and can achieve large-dose and high-intensity injection of the gel system. According to the water plugging requirements, usually several hundred to several thousand cubic meters of gel-forming solution are prepared and injected into the formation. The gel-forming solution enters the water channeling channel, and after aging in the formation for a period of time, the gel gels in the formation to form a plug, causing the injected water to migrate to the uninvaded reservoir.

[0033] Example 1:

[0034] The present invention provides a slow-crosslinking polymer gel suitable for water plugging in high-temperature and high-salt oil reservoirs, specifically as follows:

[0035] First, 0.3 g of thiourea, 0.4 g of hydroquinone, 0.4 g of hexamine, 0.3 g of cetylpyridinium bromide and 0.075 g of sodium p-toluenesulfonate are added to 97.525 g of simulated formation water. After being stirred evenly on the stirrer support, the stirrer is adjusted to 400 r / min, and then 1 g of AM-AMPS is slowly added. After stirring for 10 min, the rotation speed is reduced to 200 r / min and stirred for 4 h to obtain a uniform gel-forming solution. The gelation time of the gel at 150 °C is 18 h, the breakthrough pressure gradient after aging for 2 days is 78 MPa / m, and the dehydration rate of the gel after aging for 90 days is 3%.

[0036] Example 2:

[0037] The present invention provides a slow-crosslinking polymer gel suitable for water plugging in high-temperature and high-salt oil reservoirs, specifically as follows:

[0038] First, add 0.3 g of thiourea, 0.4 g of resorcinol, 0.4 g of hexamethylenetetramine, 0.2 g of cetylpyridinium bromide, and 0.05 g of sodium p-toluenesulfonate to 97.65 g of simulated formation water. Place it on the stirrer bracket and stir evenly. Then, adjust the stirrer speed to 400 r / min, and slowly add 1 g of AM-AMPS. After stirring for 10 min, reduce the speed to 200 r / min and stir for 4 h to obtain a uniform gelling solution. The gelling time of the gel at 150 °C is 12 h, the breakthrough pressure gradient after aging for 2 days is 81 MPa / m, and the dehydration rate of the gel after aging for 90 days is 2%.

[0039] Example 3:

[0040] The present invention provides a slow-crosslinking polymer gel suitable for water plugging in high-temperature and high-salt oil reservoirs, specifically as follows:

[0041] First, add 0.3 g of thiourea, 0.1 g of catechol, 0.1 g of hexamethylenetetramine, 0.3 g of cetylpyridinium bromide, and 0.075 g of sodium p-toluenesulfonate to 98.125 g of simulated formation water. Place it on the stirrer bracket and stir evenly. Then, adjust the stirrer speed to 400 r / min, and slowly add 1.0 g of AM-AMPS. After stirring for 10 min, reduce the speed to 200 r / min and stir for 4 h to obtain a uniform gelling solution. The gelling time of the gel at 150 °C is 30 h, the breakthrough pressure gradient after aging for 2 days is 50 MPa / m, and the dehydration rate of the gel after aging for 90 days is 9%.

[0042] Example 4

[0043] The present invention provides a slow-crosslinking polymer gel suitable for water plugging in high-temperature and high-salt oil reservoirs, specifically as follows:

[0044] First, add 0.3 g of thiourea, 0.4 g of hydroquinone, 0.4 g of formaldehyde, 0.2 g of octadecylpyridinium bromide, and 0.05 g of sodium p-toluenesulfonate to 98.15 g of simulated formation water. Place it on the stirrer bracket and stir evenly. Then, adjust the stirrer speed to 400 r / min, and slowly add 0.5 g of AM-AMPS. After stirring for 10 min, reduce the speed to 200 r / min and stir for 4 h to obtain a uniform gelling solution. The gelling time of the gel at 150 °C is 24 h, the breakthrough pressure gradient after aging for 2 days is 62 MPa / m, and the dehydration rate of the gel after aging for 90 days is 8%.

[0045] Example 5:

[0046] The present invention provides a slow-crosslinking polymer gel suitable for water plugging in high-temperature and high-salt oil reservoirs, specifically as follows:

[0047] First, add 0.3 g of thiourea, 0.4 g of pyrogallol, 0.4 g of terephthalaldehyde, 0.3 g of cetylpyridinium bromide, and 0.075 g of sodium isopropylbenzene sulfonate to 97.825 g of simulated formation water. Place it on the stirrer support and stir evenly. Then, adjust the stirrer speed to 400 r / min, and slowly add 0.7 g of AM-AMPS. After stirring for 10 min, reduce the speed to 200 r / min and stir for 4 h to obtain a uniform gel-forming solution. The gelation time of the gel at 150 °C is 20 h, the breakthrough pressure gradient after aging for 2 days is 68 MPa / m, and the dehydration rate of the gel after aging for 90 days is 5%.

[0048] Example 6:

[0049] The present invention provides a slow-crosslinking polymer gel suitable for water plugging in high-temperature and high-salinity oil reservoirs, specifically as follows:

[0050] First, add 0.3 g of thiourea, 0.2 g of hydroquinone, 0.2 g of hexamethylenetetramine, 0.3 g of cetylpyridinium bromide, and 0.075 g of sodium salicylate to 97.925 g of simulated formation water. Place it on the stirrer support and stir evenly. Then, adjust the stirrer speed to 400 r / min, and slowly add 1 g of AM-AMPS. After stirring for 10 min, reduce the speed to 200 r / min and stir for 4 h to obtain a uniform gel-forming solution. The gelation time of the gel at 150 °C is 26 h, the breakthrough pressure gradient after aging for 2 days is 57 MPa / m, and the dehydration rate of the gel after aging for 90 days is 5%.

[0051] Example 7:

[0052] The present invention provides a slow-crosslinking polymer gel suitable for water plugging in high-temperature and high-salinity oil reservoirs, specifically as follows:

[0053] First, add 0.3 g of thiourea, 0.4 g of hydroquinone, 0.4 g of hexamethylenetetramine, 0.25 g of cetylpyridinium bromide, and 0.0625 g of sodium p-toluenesulfonate to 97.5875 g of simulated formation water. Place it on the stirrer support and stir evenly. Then, adjust the stirrer speed to 400 r / min, and slowly add 1 g of AM-AMPS. After stirring for 10 min, reduce the speed to 200 r / min and stir for 4 h to obtain a uniform gel-forming solution. The gelation time of the gel at 150 °C is 15 h, the breakthrough pressure gradient after aging for 2 days is 80 MPa / m, and the dehydration rate of the gel after aging for 90 days is 2%.

[0054] Comparative Example 1:

[0055] First, add 0.3 g of thiourea, 0.4 g of hydroquinone, and 0.4 g of hexamethylenetetramine to 97.9 g of simulated formation water. Place it on the stirrer support and stir evenly. Then, adjust the stirrer speed to 400 r / min, and slowly add 1 g of AM-AMPS. After stirring for 10 min, reduce the speed to 200 r / min and stir for 4 h to obtain a uniform gel-forming solution. The gelation time of the gel at 150 °C is 3.5 h, the breakthrough pressure gradient after aging for 2 days is 82 MPa / m, and the gel does not dehydrate after aging for 90 days.

[0056] Table 1 Summary of the component ratios and performance parameters of the gel in the present invention

[0057]

[0058] In the comparative examples and examples, the gelation time, thermal stability, and plugging performance of the polymer gel were evaluated. The gelation time was determined according to the gel strength code standard (i.e., Gel Strength Codes) proposed by Sydansk. The time required for the gel strength in the visually inverted ampoule to reach grade F was defined as the gelation time. The thermal stability of the gel was characterized by the dehydration rate corresponding to aging for 90 days at 150 °C and a salinity of 25×10 4 mg / L. The dehydration rate was the mass percentage of the water dehydrated from the gel to the initial gel-forming solution. The plugging performance of the gel was represented by evaluating the breakthrough pressure gradient of the gel in a core with a permeability of about 2 μm 2 rock core.

[0059] Different from Examples 1-7: In Comparative Example 1, crosslinking control agent A and crosslinking control agent B were not included, and the gelation time of the gel system was only 3.5 h, which was too short to meet the on-site construction requirements. In Examples 1-7, by adding crosslinking control agent A and crosslinking control agent B, the gelation time of the gel was effectively delayed. According to the dosage of the crosslinking control agent, the gelation time of the gel could be controlled to 12-30 hours, greatly meeting the on-site injection requirements. In addition, the plugging performance and thermal stability of the gel still met the requirements of on-site injection after adding the crosslinking control agent.

[0060] The results of the examples of the present invention show that the temperature- and salt-resistant gel of the present invention has a gelation time of more than 12 h under the conditions of 150 °C and 25×10 4 mg / L salinity brine, which can greatly meet the on-site construction requirements; the breakthrough pressure gradient after aging for 2 days is above 60 MPa / m, and the plugging performance is good; moreover, the dehydration rate does not exceed 8% after aging for 90 days, and the thermal stability is excellent, which can solve the problem that the gelation time of high-temperature and high-salt-resistant gels is not easy to control.

Claims

1. A slow-crosslinking polymer gel suitable for water plugging in high-temperature and high-salinity oil reservoirs, characterized in that: The raw materials include acrylamide / 2-acrylamide-2-methylpropane sulfonic acid copolymer, phenolic composite crosslinking agent, deoxidizer, crosslinking control agent A, crosslinking control agent B and balance water, wherein the crosslinking control agent A is alkylpyridinium bromide, and the crosslinking control agent B is sodium p-toluenesulfonate, sodium isopropylbenzenesulfonate or sodium salicylate.

2. The slow-crosslinking polymer gel suitable for water plugging in high-temperature and high-salinity oil reservoirs according to claim 1, characterized in that: Calculated by mass percentage, the total amount is 100%, and the raw materials include: 0.5% to 1.0% of acrylamide / 2-acrylamide-2-methylpropane sulfonic acid copolymer, 0.2% to 0.8% of phenolic composite crosslinking agent, 0.3% of deoxidizer, 0.2% to 0.3% of crosslinking control agent A, 0.05% to 0.075% of crosslinking control agent B and the balance of water.

3. The slow-crosslinking polymer gel suitable for water plugging in high-temperature and high-salinity oil reservoirs according to claim 1, characterized in that: The phenolic composite crosslinking agent comprises a first crosslinking agent and a second crosslinking agent, wherein the first crosslinking agent is hydroquinone, resorcinol, catechol or pyrogallol; and the second crosslinking agent is formaldehyde, hexamethylenetetramine or terephthalaldehyde.

4. The slow-crosslinking polymer gel suitable for water plugging in high-temperature and high-salinity oil reservoirs according to claim 3, characterized in that: The mass ratio of the first cross-linking agent to the second cross-linking agent is 1:

1.

5. The slow-crosslinking polymer gel suitable for water plugging in high-temperature and high-salinity oil reservoirs according to claim 3, characterized in that: The first cross-linking agent is hydroquinone, and the second cross-linking agent is hexamethylenetetramine.

6. The slow-crosslinking polymer gel suitable for water plugging in high-temperature and high-salinity oil reservoirs according to claim 1, characterized in that: The cross-linking control agent A is one of cetylpyridinium bromide and octadecylpyridinium bromide.

7. The slow-crosslinking polymer gel suitable for water plugging in high-temperature and high-salinity oil reservoirs according to claim 1, characterized in that: The content of 2-acrylamide-2-methylpropanesulfonic acid in the acrylamide / 2-acrylamide-2-methylpropanesulfonic acid copolymer is 50%-80%, and the molecular weight is 6 million-8 million.

8. The slow-crosslinking polymer gel suitable for water plugging in high-temperature and high-salinity oil reservoirs according to claim 1, characterized in that: The deoxidizer is thiourea.

9. The slow-crosslinking polymer gel suitable for water plugging in high-temperature and high-salinity oil reservoirs according to claim 1, characterized in that: The gel system is heated to 150°C and 25×10 4 The gelation time under the conditions of mg / L mineralization is more than 12h.

10. Use of the slow-crosslinking polymer gel according to any one of claims 1 to 9 in water plugging in high-temperature and high-salinity oil reservoirs.

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