Foam workover fluid system and preparation method thereof

Abstract

The invention discloses a foam workover fluid system and a preparation method thereof. The foam workover fluid system is prepared from a foaming agent, a foam stabilizer, a high-temperature stabilizer, water and the like. The foaming agent is a composition of sodium alpha-olefin sulfonate and sodium dodecyl benzene sulfonate; the foam stabilizer is a composition of xanthan gum and polyacrylamide; and the high-temperature stabilizer is thiourea. The use amount of the foaming agent accounts for 0.50%-0.70% of the mass of the water, the use amount of the foam stabilizer accounts for 0.10%-0.30% of the mass of the water, and the use amount of the high-temperature stabilizer accounts for 0.05%-0.20% of the mass of the water. The method comprises the following steps: adding a foam stabilizer into water at 50-60 DEG C, and uniformly stirring; adding a high-temperature stabilizer, and continuously stirring; and finally, adding the foaming agent and stirring for 30 minutes to obtain the foam workover fluid. The foam workover fluid system has excellent foaming performance and foam stabilizing performance, is low in density, strong in salt resistance and oil resistance and good in high-temperature stability, can effectively reduce the leakage problem in workover operation, meets the requirements of low-pressure oil and gas well workover operation, and is suitable for popularization and application in the low-pressure oil and gas well workover operation.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas field development, in particular to a foam well repairing fluid system and a preparation method thereof. Background Art

[0002] In the later stages of oil and gas well development, serious problems such as sand accumulation, fluid accumulation, wax deposition, and oil contamination in the wellbore hinder normal production. Due to years of exploitation, formation energy depletion and low formation pressure have led to the current use of water-based workover fluids, such as solid-free brine and polymer-solidified brine workover fluids, which suffer from inefficient workover efficiency and are prone to leakage into the formation, causing reservoir damage. Furthermore, poor compatibility between the workover fluid and the reservoir fluid can further exacerbate the damage. Therefore, it is crucial to utilize an appropriate workover fluid system tailored to the characteristics of low-pressure oil and gas wells. Foam workover technology utilizes the advantages of foam fluids, such as their low density and their ability to carry sand, clean well oil, and remove bottomhole debris, enabling specialized foam workover operations for oil and gas wells. Foam workover fluids effectively clean bottomhole debris, strip wax deposits from the wellbore, and create negative or low-pressure circulation in the bottomhole oil layer, stimulating the producing zone and unblocking the flow path. This technology is an effective technique for inducing production or restoring the productivity of older wells.

[0003] However, foam workover fluids also present some challenges in their use. First, with the increasing number of deep and ultra-deep wells in China, the high temperature and high pressure conditions at the bottom of the well reduce the stability of the foam. Furthermore, due to the severe water accumulation at the bottom of older wells and the high salinity of the formation water, the foam stability of the foam workover fluid decreases significantly after it is introduced into the well, limiting well cleaning efficiency and making it difficult to meet the requirements of well repair operations. Furthermore, the foam has insufficient salt tolerance. Therefore, developing a foam workover fluid system with low density, strong foaming and stabilizing properties, and high resistance to temperature, salt, and oil contamination is of great significance for low-pressure oil and gas well repair operations. Summary of the Invention

[0004] To address the problem of poor foam stability in high-temperature and high-salt conditions in existing foam workover fluids, the present invention provides a foam workover fluid system. This foam workover fluid system has excellent foaming and foam stabilization properties, low density, and excellent salt and oil resistance and high temperature resistance.

[0005] The foam well repair fluid system provided by the present invention is made of raw materials such as a foaming agent, a foam stabilizer, a high-temperature stabilizer, and water. The usage ratio of each raw material component is as follows:

[0006] The amount of foaming agent used accounts for 0.50% to 0.70% of the water mass, the amount of foam stabilizer used accounts for 0.10% to 0.30% of the water mass, and the amount of high-temperature stabilizer used accounts for 0.05% to 0.20% of the water mass.

[0007] The foaming agent is a composition of sodium α-olefin sulfonate and sodium dodecylbenzene sulfonate.

[0008] Preferably, the foaming agent is a composition of sodium α-olefin sulfonate and sodium dodecylbenzene sulfonate in a mass ratio of 1:1.

[0009] The sodium α-olefin sulfonate and sodium dodecylbenzene sulfonate are used in combination, and through the synergistic effect of the two, the foaming ability of the foam well repair fluid system can be further increased.

[0010] The foam stabilizer is a combination of xanthan gum and polyacrylamide. Preferably, the foam stabilizer is a combination of xanthan gum and polyacrylamide in a mass ratio of 1:4. Further preferably, the polyacrylamide has a molecular weight of 200,000 to 600,000 and a degree of hydrolysis of ≤20%.

[0011] Xanthan gum has strong temperature resistance, strong viscosity increasing performance, and strong foam stabilizing performance, but it will reduce the foaming performance of the foam workover fluid system to a certain extent; polyacrylamide has weak temperature resistance. By adding low molecular weight and low hydrolysis degree polyacrylamide, it works synergistically with xanthan gum to ensure the foaming ability of the system without affecting the temperature resistance of the foam workover fluid system.

[0012] The high-temperature stabilizer is thiourea. The addition of thiourea can effectively improve the stability of the foam under high temperature conditions and prolong the foam stability time.

[0013] The preparation method of the foam well repair fluid system is as follows:

[0014] Add foam stabilizer, high temperature stabilizer and foaming agent into hot water at 50-60℃ and stir evenly to obtain foam well repairing fluid.

[0015] Specifically, a foam stabilizer is added to hot water at 50-60°C, and the mixture is stirred at a constant temperature of 200-300 rpm for 30 minutes; a high-temperature stabilizer is then added, and the stirring is continued for 5-10 minutes; and finally a foaming agent is added, stirred for 30 minutes, and then cooled to room temperature to obtain a foamed well repair fluid.

[0016] Compared with the prior art, the present invention is beneficial in that:

[0017] (1) The foam workover fluid system provided by the present invention still has excellent foaming ability and foam stability under the conditions of 20 wt% CaCl2 concentration and 20% kerosene contamination, and can meet the workover requirements of high-salinity and oil wells.

[0018] (2) The foam produced by the foam workover fluid system provided by the present invention has excellent foam stability under high temperature environment, which has significant advantages in deep well workover operations.

[0019] (3) The foam well repair fluid system provided by the present invention has excellent foaming and foam stabilization properties, and has the advantages of low density, strong salt and oil resistance, and no damage to the reservoir. It can effectively solve the problem of low well repair efficiency caused by insufficient salt resistance of conventional well repair fluids, and can effectively reduce the leakage problem in well repair operations, meeting the needs of low-pressure oil and gas well repair operations.

[0020] (4) The foam workover fluid provided by the present invention has a simple formula, is easy to prepare, has a wide range of raw material sources, is low in cost, is easy to construct on site, has good economic and environmental benefits, and is suitable for promotion and application in low-pressure oil and gas well workover operations.

[0021] Other advantages, objectives and features of the present invention will be reflected in part from the following description and will be understood by those skilled in the art through study and practice of the present invention. DETAILED DESCRIPTION

[0022] The preferred embodiments of the present invention are described below. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0023] Example 1

[0024] The foam workover fluid system is composed of: 100g of clean water, 0.1g of foam stabilizer, 0.05g of high-temperature stabilizer (thiourea), and 0.5g of foaming agent; wherein the foam stabilizer is composed of xanthan gum and polyacrylamide in a ratio of 1:4, i.e., 0.02g of xanthan gum and 0.08g of polyacrylamide, with a molecular weight of 200,000 and a degree of hydrolysis of ≤20%; and the foaming agent is composed of sodium α-olefin sulfonate and sodium dodecylbenzene sulfonate in a ratio of 1:1, i.e., 0.25g of sodium α-olefin sulfonate and 0.25g of sodium dodecylbenzene sulfonate.

[0025] The preparation method of the foam workover fluid system is as follows: first heat clean water to 60°C and then maintain constant temperature, add a foam stabilizer and stir at a constant temperature of 250 rpm for 30 minutes; then add a high-temperature stabilizer and continue stirring for 10 minutes; finally, add a foaming agent and stir for 30 minutes, and cool to room temperature to obtain the foam workover fluid.

[0026] Example 2

[0027] The foam workover fluid system is composed of: 100g of clean water, 0.2g of foam stabilizer, 0.01g of high-temperature stabilizer (thiourea), and 0.5g of foaming agent; wherein the foam stabilizer is composed of xanthan gum and polyacrylamide in a ratio of 1:4, i.e., 0.04g of xanthan gum and 0.16g of polyacrylamide, the molecular weight of polyacrylamide is 500,000, and the degree of hydrolysis is ≤20%; the foaming agent is composed of sodium α-olefin sulfonate and sodium dodecylbenzene sulfonate in a ratio of 1:1, i.e., 0.25g of sodium α-olefin sulfonate and 0.25g of sodium dodecylbenzene sulfonate.

[0028] The preparation method of the foam workover fluid system is the same as that of Example 1.

[0029] Example 3

[0030] The foam workover fluid system is composed of: 100g of clean water, 0.2g of foam stabilizer, 0.01g of high-temperature stabilizer (thiourea), and 0.6g of foaming agent; wherein the foam stabilizer is composed of xanthan gum and polyacrylamide in a ratio of 1:4, i.e., 0.04g of xanthan gum and 0.16g of polyacrylamide, with a molecular weight of 500,000 and a degree of hydrolysis of ≤20%; and the foaming agent is composed of sodium α-olefin sulfonate and sodium dodecylbenzene sulfonate in a ratio of 1:1, i.e., 0.3g of sodium α-olefin sulfonate and 0.3g of sodium dodecylbenzene sulfonate.

[0031] The preparation method of the foam workover fluid system is the same as that of Example 1.

[0032] Example 4

[0033] The foam workover fluid system is composed of: 100g of clean water, 0.2g of foam stabilizer, 0.01g of high-temperature stabilizer (thiourea), and 0.7g of foaming agent; wherein the foam stabilizer is composed of xanthan gum and polyacrylamide in a ratio of 1:4, i.e., 0.04g of xanthan gum and 0.16g of polyacrylamide, the molecular weight of polyacrylamide is 500,000, and the degree of hydrolysis is ≤20%; the foaming agent is composed of sodium α-olefin sulfonate and sodium dodecylbenzene sulfonate in a ratio of 1:1, i.e., 0.35g of sodium α-olefin sulfonate and 0.35g of sodium dodecylbenzene sulfonate.

[0034] The preparation method of the foam workover fluid system is the same as that of Example 1.

[0035] Example 5

[0036] The foam workover fluid system is composed of: 100g of clean water, 0.3g of foam stabilizer, 0.01g of high-temperature stabilizer (thiourea), and 0.7g of foaming agent; wherein the foam stabilizer is composed of xanthan gum and polyacrylamide in a ratio of 1:4, i.e., 0.06g of xanthan gum and 0.24g of polyacrylamide, with a molecular weight of 600,000 and a degree of hydrolysis of ≤20%; and the foaming agent is composed of sodium α-olefin sulfonate and sodium dodecylbenzene sulfonate in a ratio of 1:1, i.e., 0.35g of sodium α-olefin sulfonate and 0.35g of sodium dodecylbenzene sulfonate.

[0037] The preparation method of the foam workover fluid system is the same as that of Example 1.

[0038] Comparative Example 1

[0039] On the basis of Example 1, the foam stabilizer was adjusted to directly use 0.1 g of xanthan gum; the other parameters remained unchanged.

[0040] Comparative Example 2

[0041] On the basis of Example 1, the foam stabilizer was adjusted to directly use 0.1 g of polyacrylamide; the molecular weight of the polyacrylamide was 200,000, and the degree of hydrolysis was ≤20%, and other contents remained unchanged.

[0042] Comparative Example 3

[0043] On the basis of Example 1, the foaming agent was adjusted to directly use 0.5 g of sodium α-olefin sulfonate; the other parameters remained unchanged.

[0044] Comparative Example 4

[0045] On the basis of Example 1, the foaming agent was adjusted to directly use 0.5 g of sodium dodecylbenzenesulfonate; the other parameters remained unchanged.

[0046] Comparative Example 5

[0047] On the basis of Example 1, the polyacrylamide with a molecular weight of 200,000 and a hydrolysis degree of ≤20% was replaced with a polyacrylamide with a high molecular weight of 1,000,000 and a hydrolysis degree of ≤20%, and the other conditions remained unchanged.

[0048] Comparative Example 6

[0049] On the basis of Example 1, the polyacrylamide with a molecular weight of 200,000 and a hydrolysis degree ≤ 20% was replaced with a polyacrylamide with a molecular weight of 200,000 and a hydrolysis degree of 25%, and the other conditions remained unchanged.

[0050] Comparative Example 7

[0051] On the basis of Example 1, the addition of 0.05 g of high-temperature stabilizer (thiourea) was omitted, and the other conditions remained unchanged.

[0052] The performance of the foam well repair fluids prepared in Examples 1 to 5 and Comparative Examples 1 to 7 was tested:

[0053] (1) Foaming and foam stabilization performance test of foam workover fluid system

[0054] The test method is as follows: take 100mL of foam workover fluid, stir it with a high-speed stirrer at 10,000rpm for 3 minutes, and immediately pour it into a 1,000mL graduated cylinder; record the foam volume V0 (indicating the foaming ability of the foaming fluid), and also record the time required for 50mL of liquid to precipitate from the foam, which is called the foam half-life t 50(Characterizing the stability of the foam). The test results are shown in Table 1. It can be seen that the foam workover fluid system provided by the present invention has excellent foaming performance and foam stability, and can meet the requirements of low-pressure oil and gas well workover operations; when the foaming agent is a synergistic effect of sodium α-olefin sulfonate and dodecylbenzenesulfonic acid, the resulting foam workover fluid system has even better foaming performance; while the foaming performance of a single-component foaming agent with the same dosage is significantly lower than that of the combination of sodium α-olefin sulfonate and dodecylbenzenesulfonic acid. When a two-component foam stabilizer of xanthan gum and polyacrylamide is used, the foam stability is significantly better than that of a single-component foam stabilizer with the same dosage; this is because the use of xanthan gum and polyacrylamide as the foam stabilizer can produce a synergistic effect, while ensuring the foaming performance and foam stability of the foam workover fluid system.

[0055] Table 1 Performance test results of foam workover fluids of Examples 1 to 5 and Comparative Examples 1 to 7

[0056]

[0057]

[0058] 2. Test of CaCl2 resistance of foam workover fluid system

[0059] The experimental method involved replacing the clean water in the foam workover fluid system with a 20,000 mg / L CaCl2 solution. The foaming ability and foam stability of the foam system were tested using the aforementioned experimental method. The test results are shown in Table 2. It can be seen that the foam workover fluid system provided by the present invention exhibits excellent CaCl2 resistance, and contamination with 25,000 mg / L CaCl2 does not substantially alter the foaming performance of the foam. During workover operations, the system is not restricted by on-site water preparation and the salinity of the wellbore fluid. While this does affect the foam stability of the foam system, it still meets the requirements of workover operations. Furthermore, the combination of the foaming agent and foam stabilizer provided by the present invention exhibits better foaming performance and foam stability than a single agent alone.

[0060] Table 2 Anti-CaCl2 performance of foam workover fluids of Examples 1 to 5 and Comparative Examples 1 to 6

[0061]

[0062]

[0063] 3. Test of the anti-oil pollution ability of foam workover fluid system

[0064] The foam workover fluids prepared in Examples 1-5 were tested for their resistance to oil contamination. The test method consisted of replacing the clean water in the foam workover fluid system with an oil-water mixture consisting of clean water and kerosene at a ratio of 4:1. The foaming ability and foam stability of the foam system were tested using the aforementioned test method. The test results are shown in Table 3. It can be seen that the foam workover fluid system provided by the present invention exhibits excellent resistance to oil contamination. Even 20% contamination does not substantially alter the foaming performance of the foam. Although it has a slight negative impact on the foam stability of the foam system, it still meets the requirements of well workover operations.

[0065] Table 3 Oil pollution resistance of foam workover fluids of Examples 1 to 5

[0066] Serial number Foam workover fluid system <![CDATA[Bubble volume V0 / mL]]> <![CDATA[Half-life t 50 / min]]> 1 Example 1 630 146 2 Example 2 590 208 3 Example 3 620 188 4 Example 4 630 218 5 Example 5 610 358

[0067] 4. Temperature resistance test of foam workover fluid system

[0068] The experimental method involved foaming a well-serving foam system, placing the foam in a 90°C thermostat, and testing its stability. The test results are shown in Table 4. It can be seen that the foam well-serving foam system provided by the present invention has excellent temperature resistance and meets the requirements of well-serving operations. Specifically, the dual-component foam stabilizer provided by the present invention exhibits stronger foam stabilization performance at high temperatures than a single-component foam stabilizer. The two components of the foam stabilizer produce a synergistic effect, achieving a 1+1 greater than 2 effect. Furthermore, the addition of the high-temperature stabilizer effectively prolongs the stability of the foam in high-temperature environments.

[0069] Table 4 Temperature resistance of foams produced by the foam workover fluid systems of Examples 1 to 5 and Comparative Examples 1 to 7

[0070]

[0071]

[0072] In summary, the present invention provides a foam workover fluid system composed of water, a foaming agent, a foam stabilizer, and a high-temperature stabilizer. This foam workover fluid system exhibits excellent foaming and foam stabilization properties, low density, strong salt and oil resistance, and good high-temperature stability. It can effectively reduce leakage during workover operations, meeting the needs of low-pressure oil and gas well workover operations. It offers excellent economic and environmental benefits and is suitable for widespread application in low-pressure oil and gas well workover operations.

[0073] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as a preferred embodiment as above, it is not intended to limit the present invention. Any technician familiar with this profession can make some changes or modifications to equivalent embodiments of the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A foam well repairing fluid system, characterized in that: It includes raw material components of foaming agent, foam stabilizer, high temperature stabilizer and water; The foaming agent is a combination of sodium α-olefin sulfonate and sodium dodecylbenzene sulfonate; The foam stabilizer is a composition of xanthan gum and polyacrylamide; The high temperature stabilizer is thiourea.

2. The foam well repairing fluid system according to claim 1, characterized in that: The usage ratio of each raw material component is as follows: The amount of foaming agent used accounts for 0.50% to 0.70% of the water mass, the amount of foam stabilizer used accounts for 0.10% to 0.30% of the water mass, and the amount of high-temperature stabilizer used accounts for 0.05% to 0.20% of the water mass.

3. The foam well repairing fluid system according to claim 2, characterized in that: The foaming agent is a composition of sodium α-olefin sulfonate and sodium dodecylbenzene sulfonate in a mass ratio of 1:

1.

4. The foam well repairing fluid system according to claim 2, characterized in that: The foam stabilizer is a composition of xanthan gum and polyacrylamide in a mass ratio of 1:

4.

5. The foam well repairing fluid system according to claim 4, characterized in that: The molecular weight of the polyacrylamide is 200,000-600,000, and the degree of hydrolysis is ≤20%.

6. A method for preparing a foam well repairing fluid system according to any one of claims 1 to 5, characterized in that: Add foam stabilizer, high temperature stabilizer and foaming agent into hot water at 50-60℃ and stir evenly to obtain foam well repairing fluid.

7. The method for preparing a foam well repairing fluid system according to claim 6, characterized in that: Add a foam stabilizer to hot water at 50-60°C and stir evenly; then add a high-temperature stabilizer and continue stirring evenly; finally add a foaming agent and stir for 30 minutes before cooling to room temperature to obtain a foam well repairing fluid.

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