A gas channeling prevention system and a nitrogen flooding gas channeling prevention method

Abstract

The application provides a gas channeling prevention system and a nitrogen flooding gas channeling prevention method. The gas channeling prevention system comprises a temperature-resistant and salt-resistant gel system, a nitrogen gel foam system and a nitrogen thickened foam system. The nitrogen flooding gas channeling prevention method adopts the gas channeling prevention system and carries out gas channeling prevention in the form of slug combination. The temperature-resistant and salt-resistant gel system is used as a pre-slug to block 100-500m wide nitrogen gas channeling channels; the nitrogen gel foam system is used as a first main slug to block 10-100m wide nitrogen gas channeling channels; the nitrogen thickened foam system is used as a second main slug to block 0.1-10m wide nitrogen gas channeling channels; finally, water is preferably injected as a displacement slug to squeeze the foregoing slugs into the formation, so as to improve the gas channeling prevention effect and avoid plugging of the foregoing slugs in the wellbore.

Description

Technical Field

[0001] This invention belongs to the field of nitrogen flooding development technology for fractured-vuggy reservoirs, and particularly relates to a gas channeling prevention system and a nitrogen flooding prevention method. Background Technology

[0002] Fractured-vuggy reservoirs are highly heterogeneous, with diverse spatial relationships between fractures and cavities, varied inter-well reservoir distribution, and are characterized by high temperature and high salinity. Following breakthroughs in unit-based nitrogen flooding in 2015 as water injection development in oilfields entered its later stages, unit-based nitrogen flooding was widely adopted in the field. However, with the expansion of nitrogen flooding, gas channeling occurred in some well groups, leading to a significant decrease in nitrogen utilization. Early methods for preventing nitrogen channeling primarily employed a combination of multi-segment thickened foam segments and nitrogen segments, which suffered from poor temperature and salinity resistance, short sealing effectiveness, and minimal oil production increase. Current research on gas injection-based gas channeling prevention mainly focuses on sandstone CO2 anti-channeling plugging agents, which are unsuitable for nitrogen channeling prevention in highly heterogeneous fractured-vuggy reservoirs. Furthermore, a complete design method for nitrogen channeling prevention segments is lacking. In summary, there is an urgent need to develop a slug design method for preventing gas channeling in nitrogen-driven fractured-vuggy reservoirs, which can improve the current gas channeling situation in nitrogen-driven well groups and provide support for the efficient operation of nitrogen-driven fractured-vuggy reservoir units. Summary of the Invention

[0003] To address the aforementioned problems, the present invention aims to provide a method for preventing gas channeling in nitrogen-driven fractured-vuggy reservoir units, thereby improving the current gas channeling situation in nitrogen-driven well groups and providing support for the efficient operation of nitrogen-driven fractured-vuggy reservoir units.

[0004] One of the present inventions provides an anti-gas channeling system, which includes a temperature and salt resistant gel system, a nitrogen gel foam system, and a nitrogen thickened foam system.

[0005] According to a specific embodiment of the present invention, the temperature- and salt-resistant gel system comprises a first anionic polyacrylamide, carboxymethyl cellulose, a first phenolic crosslinking agent, and a first aldehyde crosslinking agent; and / or

[0006] The nitrogen gel foam system includes nitrogen and gel foam; and / or

[0007] The nitrogen-thickened foam system includes nitrogen and thickened foam;

[0008] Preferably, the gel foam comprises a second anionic polyacrylamide, polyurethane, a second phenolic crosslinking agent, a second aldehyde crosslinking agent, and a surfactant; and / or

[0009] The thickened foam includes a foaming agent and a foam stabilizer.

[0010] According to a specific embodiment of the present invention, the heat-resistant and salt-resistant gel system is 100% by mass, and the heat-resistant and salt-resistant gel system includes 0.6 to 1 wt% of the first anionic polyacrylamide, 0.4 to 1 wt% of the carboxymethyl cellulose, 0.2 to 0.6 wt% of the first phenolic crosslinking agent, 0.2 to 0.6 wt% of the first aldehyde crosslinking agent, and the balance being water.

[0011] According to one specific embodiment of the present invention, the gel foam is 100% by weight, and the gel foam comprises 0.8 to 1 wt% of the second anionic polyacrylamide, 1 to 1.2 wt% of the polyurethane, 0.4 to 0.6 wt% of the second phenolic crosslinking agent, 0.4 to 0.6 wt% of the second aldehyde crosslinking agent, 0.6 to 1 wt% of the surfactant, and the balance being water.

[0012] According to one specific embodiment of the present invention, the thickened foam is 100% by mass, and the thickened foam comprises 1 to 1.5 wt% of the foaming agent, 1 to 1.5 wt% of the foam stabilizer and the balance being water.

[0013] According to a specific embodiment of the present invention, the weight-average molecular weight of the first anionic polyacrylamide is 10 × 10⁻⁶. 4 ; and / or

[0014] The weight-average molecular weight of the second anionic polyacrylamide is 14 × 10⁻⁶. 4 ; and / or

[0015] The polyurethane has a weight-average molecular weight of 322; and / or

[0016] The first phenolic crosslinking agent and the second phenolic crosslinking agent are hydroquinone; and / or

[0017] The first aldehyde crosslinking agent and the second aldehyde crosslinking agent are hexamethylenetetramine; and / or

[0018] The surfactant is sodium dodecylbenzenesulfonate; and / or

[0019] The foaming agent is dodecyl dimethylamine hydantoin; and / or the foam stabilizer is polyacrylamide.

[0020] The second invention provides a nitrogen-driven gas channeling prevention method, which uses the gas channeling prevention system described in the first invention and performs nitrogen-driven gas channeling prevention in a slug combination manner;

[0021] 1) Inject the temperature- and salt-resistant gel system as a pre-block to seal a 100 to 500 m wide nitrogen gas leakage channel;

[0022] 2) Inject the nitrogen gel foam system as the first main block to seal the nitrogen gas leakage channel 10 to 100m wide;

[0023] 3) Inject the nitrogen-thickened foam system as the second main block to seal the nitrogen gas leakage channel with a width of 0.1 to 10m.

[0024] According to a specific embodiment of the present invention, the method further includes step 4), injecting water as a replacement slug.

[0025] According to a specific embodiment of the present invention, the total injection volume of the pre-segment plug, the gel foam in the first main segment plug, the thickened foam in the second main segment plug, and the displacement plug is taken as 100%, wherein the injection volume of the pre-segment plug accounts for 10 to 15%, the injection volume of the gel foam in the first main segment plug accounts for 20 to 25%, the injection volume of the thickened foam in the second main segment plug accounts for 30 to 35%, and the injection volume of the displacement plug accounts for 25 to 40%.

[0026] In this invention, the injection rates and total injection volumes of the pre-slug, the gel foam in the first main slug, the thickened foam in the second main slug, and the displacement slug can be determined based on the actual on-site construction conditions of the target reservoir.

[0027] Application of the gas channeling prevention system according to one of the present inventions or the nitrogen-driven gas channeling prevention method according to another of the present invention in nitrogen-driven gas channeling prevention in fractured-vuggy reservoir units.

[0028] The beneficial effects of this invention are:

[0029] To address the problems of poor temperature and salt resistance, short sealing period, and insignificant oil recovery in existing nitrogen gas channeling prevention methods, this invention provides a gas channeling prevention system and a nitrogen-driven gas channeling prevention method. The gas channeling prevention system includes a temperature and salt resistant gel system, a nitrogen gel foam system, and a nitrogen thickened foam system. The nitrogen-driven gas channeling prevention method uses the aforementioned gas channeling prevention system, employing a slug combination approach for gas channeling prevention. Specifically, the temperature and salt resistant gel system serves as a pre-slug, sealing nitrogen gas channeling channels 100 to 500 meters wide; the nitrogen gel foam system serves as a first main slug, sealing nitrogen gas channeling channels 10 to 100 meters wide; the nitrogen thickened foam system serves as a second main slug, sealing nitrogen gas channeling channels 0.1 to 10 meters wide; finally, water is preferably injected as a replacement slug to push the aforementioned slugs into the formation, enhancing the gas channeling prevention effect while preventing the aforementioned slugs from clogging in the wellbore. The gas channeling prevention system and nitrogen-driven gas channeling prevention method provided by this invention have been practically applied in gas channeling wells in fractured-vuggy reservoirs. After treatment, the production of wells THX1, THX2, and THX3 is as follows: daily oil production increased from 9.9t, 9.1t, and 11.3t before treatment to 16.9t, 15.8t, and 21.1t after treatment; continuous production for 170 days, 160 days, and 70 days; and the cumulative oil increase was 643.4t, 697.2t, and 612.7t respectively, and all are still increasing oil production, indicating good treatment effect. Attached Figure Description

[0030] Figure 1 This reflects the treatment of well THX1 using the gas channeling prevention system and nitrogen-driven gas channeling prevention method provided by the present invention in Example 1;

[0031] Figure 2 This reflects the treatment of well THX2 using the gas channeling prevention system and nitrogen-driven gas channeling prevention method provided by the present invention in Example 2;

[0032] Figure 3 This reflects the treatment of well THX3 using the gas channeling prevention system and nitrogen-driven gas channeling prevention method provided by the present invention in Example 3. Detailed Implementation

[0033] The present invention will be further described below with reference to the embodiments. However, the embodiments of the present invention are merely illustrative examples and should not be construed as limiting the present invention under any circumstances.

[0034] One of the present inventions provides an anti-gas channeling system, which includes a temperature and salt resistant gel system, a nitrogen gel foam system, and a nitrogen thickened foam system.

[0035] According to a specific embodiment of the present invention, the temperature- and salt-resistant gel system comprises a first anionic polyacrylamide, carboxymethyl cellulose, a first phenolic crosslinking agent, and a first aldehyde crosslinking agent; and / or

[0036] The nitrogen gel foam system includes nitrogen and gel foam; and / or

[0037] The nitrogen-thickened foam system includes nitrogen and thickened foam;

[0038] Preferably, the gel foam comprises a second anionic polyacrylamide, polyurethane, a second phenolic crosslinking agent, a second aldehyde crosslinking agent, and a surfactant; and / or

[0039] The thickened foam includes a foaming agent and a foam stabilizer.

[0040] According to a specific embodiment of the present invention, the heat- and salt-resistant gel system is taken as 100% by mass, and the heat- and salt-resistant gel system comprises 0.6 to 1 wt% of the first anionic polyacrylamide, 0.4 to 1 wt% of the carboxymethyl cellulose, 0.2 to 0.6 wt% of the first phenolic crosslinking agent, 0.2 to 0.6 wt% of the first aldehyde crosslinking agent, and the balance being water; and / or

[0041] The gel foam, by weight 100%, comprises 0.8 to 1 wt% of the second anionic polyacrylamide, 1 to 1.2 wt% of the polyurethane, 0.4 to 0.6 wt% of the second phenolic crosslinking agent, 0.4 to 0.6 wt% of the second aldehyde crosslinking agent, 0.6 to 1 wt% of the surfactant, and the balance being water; and / or

[0042] The thickened foam is 100% by mass, and the thickened foam comprises 1 to 1.5 wt% of the foaming agent, 1 to 1.5 wt% of the foam stabilizer and the balance being water.

[0043] According to a specific embodiment of the present invention, the heat- and salt-resistant gel system is taken as 100% by mass, and the heat- and salt-resistant gel system comprises 0.6 wt% of the first anionic polyacrylamide, 0.4 wt% of the carboxymethyl cellulose, 0.2 wt% of the first phenolic crosslinking agent, 0.2 wt% of the first aldehyde crosslinking agent, and the balance being water; and / or

[0044] The gel foam, by weight 100%, comprises 0.8 wt% of the second anionic polyacrylamide, 1 wt% of the polyurethane, 0.4 wt% of the second phenolic crosslinking agent, 0.4 wt% of the second aldehyde crosslinking agent, 0.6 wt% of the surfactant, and the balance being water; and / or

[0045] The mass of the thickened foam is 100%, and the thickened foam comprises 1 wt% of the foaming agent, 1 wt% of the foam stabilizer, and the balance being water.

[0046] According to a specific embodiment of the present invention, the heat- and salt-resistant gel system is taken as 100% by mass, and the heat- and salt-resistant gel system comprises 0.8 wt% of the first anionic polyacrylamide, 0.6 wt% of the carboxymethyl cellulose, 0.4 wt% of the first phenolic crosslinking agent, 0.4 wt% of the first aldehyde crosslinking agent, and the balance being water; and / or

[0047] The gel foam, by weight 100%, comprises 0.9 wt% of the second anionic polyacrylamide, 1.1 wt% of the polyurethane, 0.5 wt% of the second phenolic crosslinking agent, 0.5 wt% of the second aldehyde crosslinking agent, 0.8 wt% of the surfactant, and the balance being water; and / or

[0048] The thickened foam is 100% by mass, and the thickened foam comprises 1.2 wt% of the foaming agent, 1.2 wt% of the foam stabilizer and the balance being water.

[0049] According to a specific embodiment of the present invention, the heat- and salt-resistant gel system is taken as 100% by mass, and the heat- and salt-resistant gel system comprises 1 wt% of the first anionic polyacrylamide, 1 wt% of the carboxymethyl cellulose, 0.6 wt% of the first phenolic crosslinking agent, 0.6 wt% of the first aldehyde crosslinking agent, and the balance being water; and / or

[0050] The gel foam, by weight 100%, comprises 1 wt% of the second anionic polyacrylamide, 1.2 wt% of the polyurethane, 0.6 wt% of the second phenolic crosslinking agent, 0.6 wt% of the second aldehyde crosslinking agent, 1 wt% of the surfactant, and the balance being water; and / or

[0051] The thickened foam is 100% by mass, and the thickened foam comprises 1.5 wt% of the foaming agent, 1.5 wt% of the foam stabilizer and the balance being water.

[0052] According to a specific embodiment of the present invention, the temperature-resistant and salt-resistant gel system has a temperature resistance of not less than 130°C; and / or a salt resistance of not less than 20 × 10⁻⁶. 4 mg / L; and / or gelation time at 130℃ for 1 to 4 hours; and / or gelation strength not lower than H grade;

[0053] And / or the gel foam has a foaming ratio of not less than 3 times under conditions of 130°C and 3MPa; and / or a foam half-life of not less than 250 min; and / or

[0054] The thickened foam has a foaming ratio of not less than 6 times under the conditions of 130℃ and 3MPa; and / or a foam half-life of not less than 210min.

[0055] In this invention, the gel strength grade H is the gel strength level measured by the Sydansk visual code method. A gel strength grade H refers to a slightly deformable, non-flowing gel, where only the gel surface deforms upon inversion.

[0056] In this invention, the Waring-Blender method is used to determine the foaming volume, foam half-life, and liquid separation half-life of gel foam and thickened foam.

[0057] According to a specific embodiment of the present invention, the weight-average molecular weight of the first anionic polyacrylamide is 10 × 10⁻⁶. 4 ; and / or

[0058] The weight-average molecular weight of the second anionic polyacrylamide is 14 × 10⁻⁶. 4 ; and / or

[0059] The polyurethane has a weight-average molecular weight of 322; and / or

[0060] The first phenolic crosslinking agent and the second phenolic crosslinking agent are hydroquinone; and / or

[0061] The first aldehyde crosslinking agent and the second aldehyde crosslinking agent are hexamethylenetetramine; and / or

[0062] The surfactant is sodium dodecylbenzenesulfonate; and / or

[0063] The foaming agent is dodecyl dimethylamine hydantoin; and / or the foam stabilizer is polyacrylamide;

[0064] Preferably, the CAS number of the carboxymethyl cellulose is 9000-11-7; and / or

[0065] The molecular weight of the polyacrylamide is 14 × 10⁻⁶. 4 .

[0066] The second invention provides a nitrogen-driven gas channeling prevention method, which uses the gas channeling prevention system described in the first invention and performs nitrogen-driven gas channeling prevention in a slug combination manner;

[0067] 1) Inject the temperature- and salt-resistant gel system as a pre-block to seal a 100 to 500 m wide nitrogen gas leakage channel;

[0068] 2) Inject the nitrogen gel foam system as the first main block to seal the nitrogen gas leakage channel 10 to 100m wide;

[0069] 3) Inject the nitrogen-thickened foam system as the second main block to seal the nitrogen gas leakage channel with a width of 0.1 to 10m.

[0070] According to a specific embodiment of the present invention, the method further includes step 4), injecting water as a replacement slug.

[0071] According to a specific embodiment of the present invention, the total injection volume of the pre-segment plug, the gel foam in the first main segment plug, the thickened foam in the second main segment plug, and the displacement plug is taken as 100%, wherein the injection volume of the pre-segment plug accounts for 10 to 15%, the injection volume of the gel foam in the first main segment plug accounts for 20 to 25%, the injection volume of the thickened foam in the second main segment plug accounts for 30 to 35%, and the injection volume of the displacement plug accounts for 25 to 40%.

[0072] According to a specific embodiment of the present invention, the injection rates of the pre-slug, the gel foam in the first main slug, the thickened foam in the second main slug, and the displacement slug are independently 18 to 30 m / s. 3 / h;

[0073] Preferably, the injection rates of the pre-slug, the gel foam in the first main slug, the thickened foam in the second main slug, and the displacement slug are 24 m / s. 3 / h.

[0074] According to a specific embodiment of the present invention, to ensure the anti-gas channeling effect, the total injection volume of the pre-plug, the gel foam in the first main plug, the thickened foam in the second main plug, and the displacement plug is not higher than 3000 m³. 3 .

[0075] Application of the gas channeling prevention system according to one of the present inventions or the nitrogen-driven gas channeling prevention method according to another of the present invention in nitrogen-driven gas channeling prevention in fractured-vuggy reservoir units.

[0076] The nitrogen-driven gas channeling prevention method provided by this invention first addresses the characteristics of fractured-vuggy reservoirs—large-scale, highly heterogeneous, and prone to individual nitrogen gas channeling. A temperature- and salt-resistant gel system is injected downhole as a pre-plug. After injection, the gel slowly condenses under formation pressure and temperature, sealing large nitrogen gas channeling channels of 100 to 500 meters. Next, a nitrogen gel foam system is injected downhole as the first main plug. Specifically, while injecting nitrogen into the well, a foam generator at the wellhead injects gel foam downhole. The gel foam itself seals larger nitrogen gas channeling channels of 10 to 100 meters. The accompanying nitrogen continuously disturbs the gel foam, causing it to regenerate and allowing it to penetrate into higher areas of the wellbore. The affected area is used to start the remaining oil production; then, a nitrogen-thickened foam system is injected downhole as the second main slug through the foam generator at the wellhead. Specifically, while injecting nitrogen into the well, thickened foam is injected downhole using the foam generator at the wellhead. Based on the aforementioned slug blocking of large and relatively large nitrogen gas channeling channels, the thickened foam uniformly blocks small nitrogen gas channeling channels of 0.1 to 10m. The nitrogen injected along with the thickened foam continuously disturbs the thickened foam, causing it to regenerate and continue to enter the unaffected areas of the wellbore to further start the remaining oil production; finally, oilfield water is preferably injected downhole as a replacement slug to squeeze the aforementioned slug into the formation, further enhancing the gas channeling prevention effect of the aforementioned slug, while also avoiding blockage in the wellbore.

[0077] Anti-gas leakage system

[0078] The raw material information used in Examples 1 to 3 is as follows:

[0079] First anionic polyacrylamide: purchased from Hebei Wanrui Chemical Co., Ltd., molecular weight 10×10 4 ;

[0080] Second anionic polyacrylamide: purchased from Henan Duohui Chemical Products Co., Ltd., molecular weight 14×10 4 ;

[0081] Carboxymethyl cellulose: purchased from Jinan Xinguang Chemical Products Co., Ltd., CAS No. 9000-11-7;

[0082] Polyurethane: Purchased from Guangzhou Haoyi New Material Technology Co., Ltd., Guangdong Province; molecular weight: 322.36.

[0083] First phenolic crosslinking agent, second phenolic crosslinking agent: hydroquinone;

[0084] First aldehyde crosslinking agent, second aldehyde crosslinking agent: hexamethylenetetramine;

[0085] Surfactant: Sodium dodecylbenzenesulfonate, purchased from Shandong Xingang Chemical Co., Ltd.;

[0086] Foaming agent: Dodecyl dimethylamine acetyl lactone, purchased from Sichuan Guanghan Rongxin Fine Chemical Co., Ltd., with a half-life of ≥250 min.

[0087] Foam stabilizer: (for oil displacement in Type II zones) polyacrylamide, molecular weight 14×10 4 Purchased from Shandong Juxing Petroleum Technology Co., Ltd.

[0088] Example 1

[0089] The anti-gas migration system provided in this embodiment is as follows:

[0090] (1) Temperature and salt resistant gel system: The total mass of the temperature and salt resistant gel system is taken as 100%. The temperature and salt resistant gel system includes 0.6 wt% of the first anionic polyacrylamide, 0.4 wt% of carboxymethyl cellulose, 0.2 wt% of the first phenolic crosslinking agent hydroquinone, 0.2 wt% of the first aldehyde crosslinking agent hexamethylenetetramine and the balance water;

[0091] (2) Nitrogen gel foam system: including nitrogen and gel foam; the total mass of gel foam is 100%, and the gel foam includes 0.8 wt% second anionic polyacrylamide, 1.0 wt% polyurethane, 0.4 wt% second phenolic crosslinking agent hydroquinone, 0.4 wt% second aldehyde crosslinking agent hexamethylenetetramine, 0.6 wt% surfactant and the balance water;

[0092] (3) Nitrogen-thickened foam system: includes nitrogen and thickened foam; the total mass of thickened foam is 100%, and the thickened foam includes 1 wt% foaming agent, 1 wt% foam stabilizer and the balance water.

[0093] Example 2

[0094] The anti-gas migration system provided in this embodiment is as follows:

[0095] (1) Temperature and salt resistant gel system: The total mass of the temperature and salt resistant gel system is taken as 100%. The temperature and salt resistant gel system includes 0.8 wt% of the first anionic polyacrylamide, 0.6 wt% of carboxymethyl cellulose, 0.4 wt% of the first phenolic crosslinking agent hydroquinone, 0.4 wt% of the first aldehyde crosslinking agent hexamethylenetetramine and the balance water;

[0096] (2) Nitrogen gel foam system: including nitrogen and gel foam; the total mass of gel foam is 100%, and the gel foam includes 0.9 wt% second anionic polyacrylamide, 1.1 wt% polyurethane, 0.5 wt% second phenolic crosslinking agent hydroquinone, 0.5 wt% second aldehyde crosslinking agent hexamethylenetetramine, 0.8 wt% surfactant and the balance water;

[0097] (3) Nitrogen-thickened foam system: includes nitrogen and thickened foam; the total mass of thickened foam is 100%, and the thickened foam includes 1.2 wt% foaming agent, 1.2 wt% foam stabilizer and the balance water.

[0098] Example 3

[0099] The anti-gas migration system provided in this embodiment is as follows:

[0100] (1) Temperature and salt resistant gel system: The total mass of the temperature and salt resistant gel system is 100%. The temperature and salt resistant gel system includes 1.0 wt% of the first anionic polyacrylamide, 1.0 wt% of carboxymethyl cellulose, 0.6 wt% of the first phenolic crosslinking agent hydroquinone, 0.6 wt% of the first aldehyde crosslinking agent hexamethylenetetramine and the balance water;

[0101] (2) Nitrogen gel foam system: including nitrogen and gel foam; the total mass of gel foam is 100%, and the gel foam includes 1.0 wt% second anionic polyacrylamide, 1.2 wt% polyurethane, 0.6 wt% second phenolic crosslinking agent hydroquinone, 0.6 wt% hexamethylenetetramine, 1.0 wt% surfactant and the balance water;

[0102] (3) Nitrogen-thickened foam system: includes nitrogen and thickened foam; the total mass of thickened foam is 100%, and the thickened foam includes 1.5 wt% foaming agent, 1.5 wt% foam stabilizer and the balance water.

[0103] Test Example 1 - Performance Evaluation of the Anti-Gas Channeling System

[0104] i. Determination of the properties of heat and salt resistant gel

[0105] At room temperature, using a mineralization of 20 × 10 4 The simulated formation water at a concentration of mg / L was used to weigh the raw materials according to the proportions of each component recorded in Examples 1 to 3, and each raw material was completely dissolved in the simulated formation water to obtain temperature and salt resistant gel-1, temperature and salt resistant gel-2, and temperature and salt resistant gel-3 for testing.

[0106] Determination of gelation time and gelation strength: Weigh 10g each of the temperature and salt resistant gels-1 to-3 prepared in this test example, and place them in a constant temperature chamber set at 130℃ for aging. During the aging process, observe the gelation condition of each gel, and measure the gelation time and gelation strength of each gel according to the Sydansk visual code method. The results are shown in Table 1.

[0107] High-temperature stability test: Weigh 30g each of the temperature and salt resistant gels-1 to-3 prepared in this test example and place them in separate containers. Seal the containers and start aging in a constant temperature chamber set at 130℃. After gel formation, continue aging at 130℃ and observe the dehydration of the gel. Observe the amount of water dehydrated by visual inspection. Divide the amount of water dehydrated by the volume of the gel after gel formation to obtain the dehydration rate. The number of aging days when the dehydration rate reaches 10% is taken as the time to achieve high-temperature stability. The results are shown in Table 1.

[0108] Table 1. Performance determination of temperature and salt resistant gels in anti-gas migration systems

[0109] gel number gelation time rubber strength High temperature stability Temperature and salt resistant gel-1 3 to 4 hours H-class 90 days Temperature and salt resistant gel-2 2 to 3 hours Level I 100 days Temperature and salt resistant gel-3 1 to 2 hours Level I 120 days

[0110] ii. Performance testing of gel foam and thickened foam

[0111] The foaming ratio, liquid half-life, and foam half-life of the foam system were determined by the Waring-Blender method to evaluate the performance of gel foam and thickened foam.

[0112] The specific steps are as follows:

[0113] Step 1: Weigh the gel foam from the anti-gas channeling compositions provided in Examples 1 to 3 according to the proportions and prepare test solutions 1 to 3 in sequence; weigh the thickened foam according to the proportions and prepare test solutions 4 to 6 in sequence.

[0114] Step 2: Under test conditions of (25±1)℃ and normal pressure, measure 10mL of any one of the test solutions 1 to 6 using a graduated cylinder, record the initial height of the liquid, start the stirrer, stir at a speed of 4000 to 13000r / min for 30 seconds, stop stirring, record the initial height of the foam, and continuously observe the height of the foam and the height of the precipitated liquid.

[0115] When the height of the precipitated liquid is half of the initial height of the liquid, the recorded time is the precipitated liquid half-life;

[0116] The foaming ratio is the initial height of the foam divided by the initial height of the liquid.

[0117] The time when the foam height decreases to half of the initial foam height is recorded as the foam half-life.

[0118] Following step 2, the foaming ratio, precipitation half-life, and foam half-life of the test solutions 1 to 6 prepared in step 1 were determined. The specific results are shown in Table 2.

[0119] The test conditions in step 2 were adjusted to 130℃ and 3MPa. The foaming ratio and foam half-life of the test solutions 1 to 6 prepared in step 1 were determined. The specific results are shown in Table 3.

[0120] Table 2. Foaming ratio, liquid half-life and foam half-life at (25±1)℃ and atmospheric pressure

[0121]

[0122] Table 3.1 Foaming ratio and foam half-life at 130℃ and 3MPa

[0123]

[0124] As can be seen from the measurement results in Tables 1 to 3, the anti-gas channeling system provided by the present invention has a suitable gelation time, sufficient gelation strength, good high-temperature stability and excellent foaming performance, and is suitable for preventing gas channeling during nitrogen drive in fractured-vuggy oil reservoir well groups.

[0125] Implement nitrogen-based gas channeling prevention method

[0126] During nitrogen-driven development of fractured-vuggy reservoirs, gas channeling occurred in 20 out of 93 well groups, accounting for 21.5%. The gas channeling prevention system and nitrogen-driven gas channeling prevention method provided in this invention were applied to address this issue. The following detailed explanation uses wells THX1, THX2, and THX3 as examples.

[0127] Example 4

[0128] Using the gas channeling prevention system provided in Example 1, the nitrogen-driven gas channeling prevention method of this invention was implemented on the THX1 well, and the reverse injection method with the tubing string stationary was used for construction:

[0129] 1) Inject the temperature- and salt-resistant gel system provided in Example 1 as a pre-block to seal a 100 to 500 m wide nitrogen gas channel;

[0130] 2) Inject the nitrogen gel foam system provided in Example 1 as the first main slug: at 1000m 3 Nitrogen is injected into the well at an injection rate of / h, while a foam generator at the wellhead is used to inject gel foam into the well to block nitrogen gas leakage channels that are 10 to 100m wide.

[0131] 3) Inject the nitrogen-thickened foam system provided in Example 1 as the second main slug: with a density of 1000m 3 Nitrogen is injected into the well at an injection rate of / h, while thickened foam is injected into the well using a foam generator at the wellhead to block nitrogen gas leakage channels that are 0.1 to 10m wide.

[0132] 4) Inject oilfield water as a replacement slug to squeeze the pre-slug, the first main slug, and the second main slug into the formation, which helps to block the nitrogen gas channel. After the well is shut down, it will start flowing production.

[0133] During construction, the injection rates of the pre-plug, the gel foam in the first main plug, the thickened foam in the second main plug, and the displacement plug were all 18m. 3 / h, cumulative injection 1000m 3 Of which, the pre-slug injection volume accounts for 10%, with a cumulative injection volume of 100m³. 3 The volume of gel foam injected into the first main body plug accounts for 20% of the total volume, with a cumulative injection volume of 200m³. 3 The thickened foam injected into the second main body plug accounts for 30% of the total volume, with a cumulative injection volume of 300 m³. 3 The displacement slug injection volume accounted for 40%, with a cumulative injection volume of 400 m³. 3 .

[0134] Figure 1 This example demonstrates the treatment of well THX1. As can be seen, after treatment, well THX1's daily fluid production increased to 23.3 tons, and its daily oil production increased from 9.9 tons before treatment to 16.9 tons after treatment, with a water cut of 27.6%. The well has been producing continuously for 170 days, accumulating an additional 643.4 tons of oil, and is still increasing its oil production.

[0135] Example 5

[0136] Using the gas channeling prevention system provided in Example 2, the nitrogen-driven gas channeling prevention method of this invention was implemented on the THX2 well, and the reverse injection method with the tubing string stationary was used for construction. Specifically:

[0137] 1) Inject the temperature- and salt-resistant gel system provided in Example 2 as a pre-block to seal a 100 to 500 m wide nitrogen gas channel;

[0138] 2) Inject the nitrogen gel foam system provided in Example 2 as the first main slug: at 1000m 3 Nitrogen is injected into the well at an injection rate of / h, while a foam generator at the wellhead is used to inject gel foam into the well to block nitrogen gas leakage channels that are 10 to 100m wide.

[0139] 3) Inject the nitrogen-thickened foam system provided in Example 2 as the second main slug: with a 1000m... 3 Nitrogen is injected into the well at an injection rate of / h, while thickened foam is injected into the well using a foam generator at the wellhead to block nitrogen gas leakage channels that are 0.1 to 10m wide.

[0140] 4) Inject oilfield water as a replacement slug to squeeze the pre-slug, the first main slug, and the second main slug into the formation, which helps to block the nitrogen gas channel. After the well is shut down, it will start flowing production.

[0141] During construction, the injection rates of the pre-plug, the gel foam in the first main plug, the thickened foam in the second main plug, and the displacement plug were all 24m. 3 / h, cumulative injection 1500m 3 The pre-slug injection volume accounts for 12%, with a cumulative injection volume of 180m³. 3 The volume of gel foam injected into the first main body plug segment accounts for 22%, with a cumulative injection volume of 330m³. 3 The thickened foam injected into the second main body plug accounts for 32% of the total volume, with a cumulative injection volume of 480m³. 3 The replacement slug injection volume accounted for 34%, with a cumulative oilfield water injection volume of 510 m³. 3 .

[0142] Figure 2 This example demonstrates the treatment of well THX2. As can be seen, after treatment, well THX2's daily fluid production increased to 29.5 tons, and its daily oil production increased from 9.1 tons before treatment to 15.8 tons after treatment, with a water cut of 46.5%. The well has been producing continuously for 160 days, with a cumulative increase in oil production of 697.2 tons, and is still increasing oil production.

[0143] Example 6

[0144] Using the gas channeling prevention system provided in Example 3, the nitrogen-driven gas channeling prevention method of this invention was implemented on the THX3 well, and the reverse injection method with the tubing string stationary was used for construction. Specifically:

[0145] 1) Inject the temperature- and salt-resistant gel system provided in Example 3 as a pre-block to seal the nitrogen gas channel with a width of 100 to 500 m;

[0146] 2) Inject the nitrogen gel foam system provided in Example 3 as the first main slug: at 1000m 3 Nitrogen is injected into the well at an injection rate of / h, while a foam generator at the wellhead is used to inject gel foam into the well to block nitrogen gas leakage channels that are 10 to 100m wide.

[0147] 3) Inject the nitrogen-thickened foam system provided in Example 3 as the second main slug: with 1000m 3 Nitrogen is injected into the well at an injection rate of / h, while thickened foam is injected into the well using a foam generator at the wellhead to block nitrogen gas leakage channels that are 0.1 to 10m wide.

[0148] 4) Inject oilfield water as a replacement slug to squeeze the pre-slug, the first main slug, and the second main slug into the formation, which helps to block the nitrogen gas channel. After the well is shut down, it will start flowing production.

[0149] During construction, the injection rates of the pre-plug, the gel foam in the first main plug, the thickened foam in the second main plug, and the displacement plug were all 30m. 3 / h, cumulative injection 2000m 3 Of this, the pre-slug injection volume accounted for 15%, with a cumulative injection volume of 300m³. 3 The volume of gel foam injected into the first main body plug accounts for 25%, with a cumulative injection volume of 500m³. 3 The thickened foam injected into the second main body plug accounts for 35% of the total volume, with a cumulative injection volume of 700 m³. 3 The displacement slug injection volume accounted for 25%, with a cumulative injection volume of 500m³. 3 .

[0150] Figure 3 This example demonstrates the treatment of well THX3. As can be seen, after treatment, well THX3's daily fluid production increased to 29.3 tons, and its daily oil production increased from 11.3 tons before treatment to 21.1 tons after treatment, with a water cut of 27.9%. The well has been producing continuously for 70 days, accumulating an additional 612.7 tons of oil, and is still increasing its oil production.

[0151] While the present invention has been described with reference to specific embodiments, those skilled in the art will understand that various changes can be made without departing from the true spirit and scope of the invention. Furthermore, numerous modifications can be made to the subject, spirit, and scope of the invention to suit specific situations, materials, material compositions, and methods. All such modifications are included within the scope of the claims of the present invention.

Claims

1. An anti-gas leakage system, comprising a temperature- and salt-resistant gel system, a nitrogen gel foam system, and a nitrogen-thickened foam system; The temperature- and salt-resistant gel system includes a first anionic polyacrylamide, carboxymethyl cellulose, a first phenolic crosslinking agent, and a first aldehyde crosslinking agent; The nitrogen gel foam system includes nitrogen and gel foam; The nitrogen-thickened foam system includes nitrogen and thickened foam; The gel foam comprises a second anionic polyacrylamide, polyurethane, a second phenolic crosslinking agent, a second aldehyde crosslinking agent, and a surfactant; The thickened foam includes a foaming agent and a foam stabilizer; The weight-average molecular weight of the first anionic polyacrylamide is 10 × 10⁻⁶. 4 ; The weight-average molecular weight of the second anionic polyacrylamide is 14 × 10⁻⁶. 4 ; The first phenolic crosslinking agent and the second phenolic crosslinking agent are hydroquinone; The first aldehyde crosslinking agent and the second aldehyde crosslinking agent are hexamethylenetetramine.

2. The anti-gas migration system according to claim 1, characterized in that, The heat- and salt-resistant gel system is 100% by mass, and the heat- and salt-resistant gel includes 0.6 to 1 wt% of the first anionic polyacrylamide, 0.4 to 1 wt% of the carboxymethyl cellulose, 0.2 to 0.6 wt% of the first phenolic crosslinking agent, 0.2 to 0.6 wt% of the first aldehyde crosslinking agent, and the balance being water.

3. The anti-gas migration system according to claim 1, characterized in that, The gel foam is 100% by weight, and the gel foam comprises 0.8 to 1 wt% of the second anionic polyacrylamide, 1 to 1.2 wt% of the polyurethane, 0.4 to 0.6 wt% of the second phenolic crosslinking agent, 0.4 to 0.6 wt% of the second aldehyde crosslinking agent, 0.6 to 1 wt% of the surfactant, and the balance being water.

4. The anti-gas migration system according to claim 1, characterized in that, The thickened foam is 100% by mass, and the thickened foam comprises 1 to 1.5 wt% of the foaming agent, 1 to 1.5 wt% of the foam stabilizer, and the balance being water.

5. The anti-gas leakage system according to any one of claims 1 to 4, characterized in that, The polyurethane has a weight-average molecular weight of 322; and / or The surfactant is sodium dodecylbenzenesulfonate; and / or The foaming agent is dodecyl dimethylamine hydantoin; and / or The foam stabilizer is polyacrylamide.

6. A nitrogen-based method for preventing gas channeling, characterized in that, The gas channeling prevention system according to any one of claims 1 to 5 is used to perform nitrogen-driven gas channeling prevention in a slug combination manner; 1) Inject the temperature- and salt-resistant gel system as a pre-block to seal a 100 to 500 m wide nitrogen gas leakage channel; 2) Inject the nitrogen gel foam system as the first main block to seal the nitrogen gas leakage channel 10 to 100m wide; 3) Inject the nitrogen-thickened foam system as the second main block to seal the nitrogen gas leakage channel with a width of 0.1 to 10m.

7. The method according to claim 6, characterized in that, The method also includes step 4), injecting water as a replacement plug.

8. The method according to claim 7, characterized in that, The total injection volume of the pre-segment plug, the gel foam in the first main segment plug, the thickened foam in the second main segment plug, and the displacement plug is taken as 100%. The injection volume of the pre-segment plug accounts for 10 to 15%, the injection volume of the gel foam in the first main segment plug accounts for 20 to 25%, the injection volume of the thickened foam in the second main segment plug accounts for 30 to 35%, and the injection volume of the displacement plug accounts for 25 to 40%.

9. The application of the gas channeling prevention system according to any one of claims 1 to 5 or the nitrogen-driven gas channeling prevention method according to any one of claims 6 to 8 in nitrogen-driven gas channeling prevention in fractured-vuggy reservoir units.

Images