High-viscosity gel slug system capable of resisting temperature of 205 DEG C as well as preparation method and application of high-viscosity gel slug system

Abstract

The invention provides a 205 DEG C-resistant high-viscosity gel slug system as well as a preparation method and application thereof. The 205 DEG C-resistant high-viscosity gel slug system comprises sodium bentonite, NaCl, high-temperature-resistant gel, attapulgite, a high-temperature cross-linking agent, rigid particles, flexible fibers and water. The high-temperature cross-linking agent is selected from any one or more of sulfonated phenolic resin, water-soluble epoxy resin or melamine resin. According to the invention, the high-temperature cross-linking agent is added and is subjected to secondary cross-linking reaction with substances degraded by the high-temperature-resistant gel to form a cross-linked product which is difficult to degrade at ultrahigh temperature, so that a system is provided with ultrahigh viscosity and is matched with other substances, and finally, a gel slug with the viscosity of about million mPa.s can be obtained; the slug can be used for blocking a leakage layer while meeting the air stagnation requirement.

Description

Technical Field

[0001] The present invention belongs to the technical field of drilling, and in particular relates to a high-temperature-resistant 205°C high-viscosity gel slug system, a preparation method and an application thereof, specifically to a high-viscosity gel slug system for ensuring simultaneous overflow and leakage in ultra-deep wells during drilling operations, a too-fast upward migration speed of formation oil and gas, and lost circulation in ultra-high-temperature formations during drilling. Background Art

[0002] The western region (Tarim, Junggar, Turpan-Hami, Qaidam Basin, etc.) is the main replacement area for China's oil resource production. However, 73% of the oil resources in the western region are buried in deep formations. Therefore, the number of ultra-deep well drills has been increasing in recent years. According to statistics, since 2018, Sinopec has completed more than 20 ultra-deep wells over 8000 meters, and the bottom hole temperature of all wells has reached above 200°C.

[0003] However, the carbonate rock reservoirs in the western region have developed fractures and caves, and the safety density window of the drilling fluid is narrow, making it easy to simultaneously occur well leakage and overflow. Moreover, during the drilling process, due to severe gas invasion, the drilling cycle of the reservoir is long. To stabilize the gas layer and increase the density of the drilling fluid often leads to problems such as well leakage. Especially when drilling through large holes, the gas layer pressure is high, and the gas-liquid displacement speed is fast, not only losing a large amount of drilling fluid, but also causing more serious gas invasion. For example, among the 12 completed wells in the Tazhong area, 7 wells had lost circulation, including 2 wells that had blowouts in the upper section of the Yingshan Formation, with an average single-well lost circulation of 5281.45 m 3 ; 5 wells in the lower section of the Yingshan Formation had lost circulation, with an average single-well lost circulation of 1542.9 m 3 ; The exhaust time of the Ordovician reservoir section is long, and the average drilling cycle reaches 152.47 d, accounting for 54.56% of the whole well cycle.

[0004] At present, the main methods for dealing with the coexistence of overflow and leakage are kill and seal-off and isolation method for plugging. Among them, for kill and seal-off, by pumping kill fluid and plugging slurry into the well, the pressure-bearing capacity of the lost circulation zone is increased, the overflow fluid is discharged or squeezed into the formation, and a reasonable pressure distribution in the well is restored. There are mainly means such as normal and reverse circulation kill and seal-off, replacement method for controlling wellhead pressure, and hanging basket technology for reverse plugging. However, the key to this method lies in the preparation of bridge plugging slurry. Due to the lack of rich drilling data for ultra-deep wells and the unclear understanding of the size of the lost circulation channels in ultra-high temperature formations, and bridge plugging requires particle size grading according to the physical properties of the formation, resulting in a low success rate of the first plugging with bridge plugs, the need for repeated kill and seal-off operations, the loss of a large amount of high-cost anti-ultra-high temperature drilling fluid, and the extension of the drilling cycle. For the isolation method for plugging, by injecting a gas plug (thick bentonite slurry, polymer thick plug or highly thixotropic liquid plug) above the reservoir to first control the overflow, block the upward migration of oil and gas, ensure safe tripping, simplify the drill string and then plug the leak. However, after the high-viscosity gas plug is mixed into the well slurry, the viscosity increases severely, which is not conducive to the maintenance of high-density well slurry. At the same time, the tripping cycle in ultra-deep wells is long (2 - 3 days), and due to high temperature and long well section, the construction risk of cement and other consolidation-type plugging materials is high, while the anti-temperature resistance of conventional plugging materials is insufficient, they fail quickly underground and are prone to re-leakage, resulting in a low success rate of plugging and short efficiency.

[0005] CN112877045A discloses a swelling-type high-efficiency slug gel plugging agent, which uses a swelling plugging agent synthesized by reverse emulsion polymerization. The obtained plugging agent has the characteristics of being able to crosslink into gel underground and having a flexible adjustable gelation time, and after gelation, it has strong pressure-bearing capacity and high water absorption and swelling properties. However, the high-temperature resistance of this material is poor and it cannot be used for plugging ultra-high temperature formations. CN110066647B discloses a high-temperature resistant gas plug for drilling, which is composed of water, high-temperature resistant fluid loss reducer, high-temperature resistant shear enhancer, high-temperature resistant fiber, activity regulator, and pH regulator. After standing at 200 °C for a long time, this gas plug has high viscosity, shear force and good thixotropy, and can form a large blocking force on the oil and gas in the well, slowing down the upward migration speed of oil and gas. However, its viscosity is relatively low (funnel viscosity is greater than 200 s), and the ability to reduce gas channeling is limited. In the applied wells, the gas channeling speed of Well Shunbei 2 is reduced from 90 m / h to 15 m / h, the gas channeling speed of Well Shunbei Ping 1H is reduced from 300 m / h to 54 m / h, and the gas channeling speed of Well Shunbei 3 is reduced from 123 m / h to 14 m / h. However, their gas channeling speeds are all higher than the maximum gas channeling speed required for well control safety (the well control requirement is not higher than 9.8 m / h). Summary of the Invention

[0006] In view of this, the purpose of the present invention is to provide a high-viscosity gel slug system with a temperature resistance of 205 °C, its preparation method and application. This gel slug system has the characteristics of high-temperature resistance, high viscosity, long effective time, simple and safe construction, and good economic benefits.

[0007] To achieve this purpose, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a high-viscosity gel slug system resistant to 205 °C, which is prepared from 1-4 parts of sodium bentonite, 2-10 parts of NaCl, 1.5-8 parts of high-temperature resistant gel, 15-25 parts of attapulgite, 1.5-5 parts of high-temperature crosslinking agent, 1-5 parts of rigid particles, 0.2-1 part of flexible fiber, and 100 parts of water by weight;

[0009] The high-temperature resistant gel slug system is a network structure gel formed by crosslinking polymerization of a first monomer and a second monomer; the first monomer includes 2-acrylamido-2-methylpropanesulfonic acid, and the second monomer includes acrylamide;

[0010] The high-temperature crosslinking agent is selected from any one or more of sulfonated phenolic resin, water-soluble epoxy resin or melamine resin.

[0011] Preferably, the particle size of the high-temperature resistant gel is 1-3 mm.

[0012] Preferably, the rigid particles are selected from shell slag and / or oyster shell.

[0013] Preferably, the particle size of the rigid particles is 0.1-2 mm.

[0014] Preferably, the flexible fiber is selected from any one or more of asbestos wool, sepiolite wool or silicate fiber.

[0015] Preferably, the length of the flexible fiber is 75-380 μm.

[0016] In a second aspect, the present invention provides a preparation method of the above high-viscosity gel slug system resistant to 205 °C, including the following steps:

[0017] Mix 1-4 parts of sodium bentonite, 2-10 parts of NaCl, 1.5-8 parts of high-temperature resistant gel, 15-25 parts of attapulgite, 1.5-5 parts of high-temperature crosslinking agent, 1-5 parts of rigid particles, 0.2-1 part of flexible fiber, and 100 parts of water to obtain a high-viscosity gel slug system resistant to 205 °C;

[0018] The high-temperature resistant gel is a double-network structure gel formed by secondary crosslinking polymerization of a first monomer and a second monomer; the first monomer is 2-acrylamido-2-methylpropanesulfonic acid, and the second monomer includes acrylamide;

[0019] The high-temperature crosslinking agent is selected from any one or more of sulfonated phenolic resin, water-soluble epoxy resin or melamine resin.

[0020] In a third aspect, the present invention also provides an application of the above high-viscosity gel slug resistant to 205 °C in the drilling process.

[0021] Preferably, the above-mentioned 205°C temperature-resistant high-viscosity gel segment plug system is injected into a predetermined position in the wellbore, and after drilling to 50 to 100 m above the gel liquid level, the well is shut down and slowly and intermittently squeezed into the leaky layer to form a 205°C temperature-resistant high-viscosity gel segment plug.

[0022] Preferably, the drilling is started to 60 to 80 m above the gel liquid level.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The present invention provides a 205°C high-viscosity gel plug system for drilling fluid, comprising sodium bentonite, NaCl, high-temperature resistant gel, attapulgite, high-temperature crosslinking agent, rigid particles, flexible fibers and water. Among them, sodium bentonite provides the initial viscosity of the drilling fluid system, but its anti-stabilization ability is insufficient and it is easy to passivate and fail at high temperature; while attapulgite, as a salt-resistant soil, has strong high-temperature resistance and can provide a certain viscosity under high-temperature environment. In the present invention, the high-temperature resistant gel is a double-network structure gel formed by secondary cross-linking polymerization of 2-acrylamide-2-methylpropane sulfonic acid and acrylamide, which has good water absorption, can reduce the free water in the drilling fluid system, and make the system thicker, and the addition of NaCl can inhibit the water absorption rate of the high-temperature resistant gel to a certain extent, thereby ensuring that the viscosity of the drilling fluid system is low within 3 to 5 hours, meeting the requirements of preparation and pumping. After being pumped into the bottom of the well, under the action of the high temperature at the bottom of the well, as time goes by, the high temperature resistant gel begins to degrade to form large molecules and small molecules polymers, causing the viscosity of the system to continue to decrease, the high viscosity is maintained for a short time, or the system viscosity is insufficient to meet the need to block the rise of gas and cannot be used to plug the leaking layer. Therefore, the present invention innovatively uses sulfonated phenolic resin, water-soluble epoxy resin or melamine resin and other materials with a ring structure as a high temperature crosslinking agent, so that the high temperature resistant gel and the large and small molecule polymers generated by its degradation can undergo a secondary crosslinking reaction with the high temperature crosslinking agent. The crosslinked product formed contains a ring structure and is difficult to degrade at ultra-high temperatures. The reaction activity of this material is relatively low and is adjusted by adding a certain amount, so that this reaction is partial. Therefore, the molecular chain length of the high temperature resistant polymer (less body structure) formed provides the system with ultra-high viscosity. With other rigid particles and flexible fibers, a gel segment plug with a viscosity of up to one million mPa.s can be obtained in a high temperature bottom well environment, which can meet the needs of gas stagnation and can be used to plug the leaking layer.

[0025] The key to the application process of the temperature-resistant 205°C gel plug provided by the present invention is to utilize the synergistic enhancement effect of multi-component and multifunctional materials. The rigid particles, flexible fibers, and high-temperature resistant gel materials work together. The rigid particles reduce the pores from large to small, and the fiber materials are entangled with each other to increase the toughness and pressure resistance of the plugging layer. The deformation characteristics of the high-temperature resistant gel can adapt to leaking layers of different sizes to further improve the density of the plugging layer. At the same time, the water absorption and secondary cross-linking reaction thickening effect of the high-temperature resistant gel enable the formed gel plug system to maintain a long-term high viscosity state in the leaking layer to block pressure transmission. The second key is to squeeze and inject slowly to avoid continuous squeezing, aiming to give each component material enough migration time, enough accumulation time, and enough compaction time in the leaking formation, and finally form a high-viscosity plug that is resistant to high temperature, stable for a long time, and takes into account both gas stagnation and leakage prevention.

[0026] After testing, the viscosity of the temperature-resistant 205°C high-viscosity gel segment plug system provided by the present invention is 100-300 mPa.s within 5 hours at room temperature, which meets the requirements of preparation and pumping; after being pumped into the bottom of the well, the maximum viscosity of the gel segment plug formed under high temperature reaches one million mPa.s, which can block the gas from flowing up to prevent gas invasion on the one hand, and on the other hand, can form an isolation segment plug with high starting pressure in the leakage channel to seal the leakage layer. In addition, the formed gel segment plug maintains a viscosity of 1000000 mPa.s for more than 20 days at 205°C, which meets the needs of drilling operations, and has a high plugging success rate, good adaptability to the leakage channel, and no need for particle size grading. The temperature-resistant 205°C high-viscosity gel provided by the present invention has a simple construction process and high safety, and the system can pass through the drill bit and instruments smoothly without the need for drilling. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is an appearance diagram of the gel slug system obtained in Example 1 during the curing period at 205°C;

[0028] Figure 2 It is a schematic diagram of a plugging performance evaluation device and a gas stagnation performance evaluation device;

[0029] Among them, 1 is the air inlet; 2 is the sealing cover of the upper section of the glass tube; 3 is the liquid outlet at the lower end;

[0030] Figure 3 Schematic diagram of the sand bed formed by the product of Example 1 after curing at 205°C for 20 days;

[0031] Figure 4 A schematic diagram of a plugging layer formed by gel segments entering the pores of the sand bed after the sand bed formed by the product of Example 1 cured at 205°C for 20 days is removed;

[0032] Figure 5 This is a comparison diagram of the product of Example 2 after being cured at 205°C for 20 days and placed in the gas stagnation performance evaluation device without conducting the gas stagnation test;

[0033] Figure 6 This is the result of the gas stagnation test after the product of Example 2, which was cured at 205°C for 20 days, was placed in a gas stagnation performance evaluation device. DETAILED DESCRIPTION

[0034] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] In view of the problem that leakage and overflow coexist in the drilling process in the prior art, especially the low plugging rate of ultra-high temperature formations, the present invention provides a 205°C temperature-resistant high-viscosity gel segment plug system, which is preferably prepared by weight from 1 to 4 parts of sodium bentonite, 2 to 10 parts of NaCl, 1.5 to 8 parts of high-temperature resistant gel, 15 to 25 parts of attapulgite, 1.5 to 5 parts of high-temperature cross-linking agent, 1 to 5 parts of rigid particles, 0.2 to 1 part of flexible fiber, and 100 parts of water; more preferably, it includes 2 to 3 parts of sodium bentonite, 4 to 8 parts of NaCl, 3 to 6 parts of high-temperature resistant gel, 18 to 22 parts of attapulgite, 2 to 4 parts of high-temperature cross-linking agent, 2 to 4 parts of rigid particles, 0.5 to 0.8 parts of flexible fiber, and 100 parts of water.

[0036] In the present invention, the sodium bentonite is bentonite for drilling fluid slurry preparation, which can provide the initial viscosity for the gel system, but the anti-stabilization ability is insufficient and it is easy to passivate and fail at high temperature. Therefore, the present invention adds attapulgite, which is a salt-resistant soil for drilling fluid slurry preparation, has excellent high temperature resistance, and can provide a certain viscosity for the system under high temperature environment.

[0037] In the present invention, the high-temperature resistant gel is a network structure gel formed by crosslinking polymerization of a first monomer and a second monomer. Among them, the first monomer includes 2-acrylamido-2-methylpropanesulfonic acid, and the second monomer includes acrylamide. Specifically, it can be prepared according to Patent CN102295729B (Preparation Method of a Water Absorbing Resin Plugging Agent). In the present invention, the particle size of the high-temperature resistant gel is preferably 1-3 mm. In the present invention, the high-temperature resistant gel has good water absorption performance. It can absorb a large amount of water in the drilling fluid, resulting in a reduction of free water, making the drilling fluid system thicken, which is not conducive to the initial pumping requirements. Therefore, NaCl is added in the present invention, which inhibits the water absorption rate of the high-temperature resistant gel to a certain extent, thus ensuring that the viscosity of the system is relatively low within 3-5 h, meeting the requirements of preparation and pumping. In addition, the high-temperature resistant gel has the functions of water absorption and swelling and ductile deformation. It can deform and squeeze into pores, cracks of different sizes and the gaps of the plugging layer formed by bridge plugging materials under the action of pressure difference, cooperate with rigid particles and flexible fibers, and through reasonable particle size grading, improve the adaptability to the leakage layer and the compactness of the plugging layer.

[0038] After the formed high-temperature resistant gel slug enters the leakage layer, under the action of high temperature, as time goes by, it will gradually degrade to form macromolecular and small-molecular polymers, resulting in a continuous decrease in the viscosity of the system, a short maintenance time of high viscosity, or only meeting the need to block the rising of gas due to insufficient system viscosity and being unable to be used for plugging the leakage layer. Therefore, a high-temperature crosslinking agent is added to the gel slug system in the present invention. The high-temperature crosslinking agent is selected from any one or more of sulfonated phenolic resin, water-soluble epoxy resin or melamine resin, and preferably sulfonated phenolic resin. The above high-temperature crosslinking agents all have a cyclic structure, which can cause the high-temperature resistant gel and the macromolecular and small-molecular polymers generated by its degradation to undergo a secondary crosslinking reaction with the high-temperature crosslinking agent. At the same time, this crosslinking agent is also a part of the reactants, and can react with the gel slightly degraded in the high-temperature bottom hole environment to form a polymer containing a cyclic structure, which is difficult to degrade at ultra-high temperature. Since the crosslinking activity of the high-temperature crosslinking agent provided by the present invention is relatively low, a low dosage is difficult to react with the generated macromolecular and small-molecular polymers, and a high dosage is easy to form a three-dimensional polymer to form a solid, thus losing the characteristics of the viscous slug. The presence of NaCl added in the gel system can promote the progress of the secondary crosslinking reaction. Therefore, in practical applications, the dosage of the high-temperature crosslinking agent is in a relatively wide range. By adjusting the dosage, the secondary crosslinking reaction can be made partial. Therefore, the molecular chain length of the formed high-temperature resistant polymer (less three-dimensional structure) can provide an ultra-high viscosity for the system, up to about one million mPa·s, which can meet the need of gas blocking and can also be used for plugging the leakage layer.

[0039] In the present invention, the rigid particles can play roles such as rigid bridging, and can be specifically selected from shell slag and / or oyster shell. In some embodiments of the present invention, the particle size of the rigid particles is preferably 0.1 - 2 mm, more preferably 0.5 - 1 mm. The present invention has no special restrictions on the source of the rigid particles, and general commercially available products can be used.

[0040] In the present invention, the flexible fibers can be flexibly filled in the lost circulation channel and play a role of tension reinforcement, further improving the pressure-bearing capacity of the plugging layer, and can be specifically selected from any one or more of asbestos wool, sepiolite wool or silicate fibers. In some embodiments of the present invention, the length of the flexible fibers is preferably 75 - 380 μm. The present invention has no special restrictions on the source of the flexible fibers, and general commercially available products can be used.

[0041] Each component in the high-viscosity gel provided by the present invention coordinates with each other and promotes together. The slug formed by the high-viscosity gel has high-viscosity characteristics, up to millions of mPa·s. On the one hand, it can block the upward movement of gas to prevent gas invasion, and on the other hand, it can form an isolation slug with a high starting pressure in the lost circulation channel to plug the lost zone. After testing, the formed gel slug can maintain a viscosity of 1000000 mPa·s at 205°C for more than 20 days, meeting the requirements of drilling operations, with a high plugging success rate, good adaptability to the lost circulation channel, and no need for particle size grading.

[0042] The present invention also provides a preparation method of the above-mentioned high-viscosity gel with a temperature resistance of 205°C, including the following steps:

[0043] Mix 1 - 4 parts of sodium bentonite, 2 - 10 parts of NaCl, 1.5 - 8 parts of high-temperature resistant gel, 15 - 25 parts of attapulgite, 1.5 - 5 parts of high-temperature crosslinking agent, 1 - 5 parts of rigid particles, 0.2 - 1 part of flexible fibers and 100 parts of water to obtain a high-viscosity gel with a temperature resistance of 205°C.

[0044] Among them, the high-temperature resistant gel is a double-network structure gel formed by the secondary cross-linking polymerization of a first monomer and a second monomer; the first monomer is 2-acrylamide-2-methylpropanesulfonic acid, and the second monomer includes acrylamide; the high-temperature crosslinking agent is selected from any one or more of sulfonated phenolic resin, water-soluble epoxy resin or melamine resin.

[0045] In some embodiments of the present invention, mix sodium bentonite, NaCl, high-temperature resistant gel, attapulgite, high-temperature crosslinking agent, rigid particles, flexible fibers and water evenly with a mixing device. Among them, the content of each component is as described above and will not be elaborated here. In some preferred embodiments of the present invention, it is preferred to add sodium bentonite to water, stir evenly, stand for 12 - 24 h, then add NaCl to dissolve fully, and then successively add attapulgite, high-temperature crosslinking agent, rigid particles, high-temperature resistant gel and flexible fibers and disperse evenly.

[0046] The present invention tests the high-temperature stability of the obtained high-viscosity gel and finds that the viscosity of the formed gel slug system rises rapidly at high temperature, reaches the highest viscosity at 3 d, and then maintains its high viscosity for more than 20 d, indicating that the gel slug system has good high-temperature resistance.

[0047] The present invention tests the plugging and gas-retention performance of the obtained high-viscosity gel slug and finds that the formed gel slug immediately expands and fills the pore space after passing through the pore throat, forming a partitioned slug in the deep part of the wellbore and the leakage channel, thereby achieving the purpose of plugging. Moreover, under the action of gas pressure, the gas pushes the whole slug, but does not break through the slug (no bubbles emerge from the upper clear water), indicating that the gel slug can block the breakthrough of gas and has a significant gas-retention effect.

[0048] The present invention also evaluates the strength of the plugging layer formed by the high-viscosity gel slug. After system optimization, it is found that the 20-d bearing capacity of the formed gel slug (i.e., the plugging layer) reaches 8.8 MPa, which can meet the on-site requirements.

[0049] The present invention also provides an application process for the above high-viscosity gel slug system with a temperature resistance of 205 °C:

[0050] (1) Lower the drill string to above the clear leakage formation or suspected leakage formation and pump in the high-viscosity gel slug system with a temperature resistance of 205 °C. Pull out the drill string to 50 - 100 m above the gel liquid level, preferably 60 - 80 m, start the pump and circulate. Gradually increase the displacement from a low value, and circulate for at least one lag time or one week to ensure the uniformity of the density of the drilling fluid in the wellbore. Utilize the circulation pressure loss of the drilling fluid to initially establish a plugging layer in the leakage layer;

[0051] (2) Shut in the well and perform intermittent squeeze injection. The specific method is to continuously pump 5 times, stop the pump for 30 s - 40 s, observe the pressure rise, with each pump time of 10 - 20 s and a pump interval of 3 - 5 s; when the amount of gel squeezed into the leakage formation is 1 / 2 of the total gel amount, stop the pump for 10 - 15 min and observe the pressure stabilization situation; if the pressure stabilization effect is good, the pump time can be appropriately increased by 20 s - 30 s to tamp the formed plugging layer. If the pressure cannot be stabilized, keep the squeeze injection method unchanged;

[0052] (3) When the injection amount is 4 / 5 of the total gel amount, if the pressure cannot be built up, open the well and pull out the drill string to a safe well section; if the pressure can be built up well, after shutting in the well and statically plugging for 30 - 60 min, slowly relieve the pressure and open the well, controlling the pressure relief speed at 0.5 MPa / 5 - 10 min.

[0053] (4) Let it stand for 24 - 48 h until a high-viscosity gel slug with a temperature resistance of 205 °C is formed in the leakage formation, blocking the two pressure systems of the leakage layer and the wellbore to achieve the purpose of treating both leakage and overflow. Circulate and pull out the drill string in sections to clean the plug, and use the shale shaker to remove the gel-like plug and resume drilling.

[0054] To further illustrate the present invention, the following detailed description is provided through the following examples. The raw materials used in the following examples of the present invention are all commercially available, as follows:

[0055] Sodium bentonite and attapulgite were purchased from Bohai Drilling Engineering Co., Ltd., China National Petroleum Corporation.

[0056] NaCl: industrial grade.

[0057] High-temperature resistant gel: double-network gel DNG, Drilling Engineering Technology Research Institute, Zhongyuan Petroleum Engineering Co., Ltd., Sinopec, which can be prepared according to Patent CN102295729B (Preparation method of a water-absorbing resin plugging agent).

[0058] Sulfonated phenolic resin, water-soluble epoxy resin, and melamine resin were purchased from Jinan Shengquan Group Co., Ltd.

[0059] Rigid particles and flexible fibers: shell slag, oyster shell, asbestos wool, sepiolite wool, and silicate fiber were purchased from Hebei Lingshou Ore Factory.

[0060] Preparation Example 1

[0061] This preparation example provides a high-temperature resistant gel, and its preparation method is as follows:

[0062] NaOH was added to a 1 mol / L acrylamide solution to adjust the pH of the solution to neutral. Then, N,N-methylenebisacrylamide at 3% of the mass of acrylamide, silicon powder at 150% of the mass of acrylamide, ammonium persulfate and sulfurous acid at 0.01% of the mass of acrylamide were added in sequence. After stirring evenly, it was left to stand, and a block resin was obtained by reaction at room temperature. The resin was cut into small pieces, soaked in a 4 mol / L N,N-dimethylacrylamide and N,N-methylenebisacrylamide solution at 1% of the molar mass of N,N-dimethylacrylamide. After being saturated with liquid and taken out, it was heated to initiate polymerization and dried, and then granulated to 1 - 3 mm to obtain the high-temperature resistant gel.

[0063] Example 1

[0064] This example provides a high-viscosity gel slug system with a high temperature resistance of 205°C, and its preparation method is as follows:

[0065] 6 g of sodium bentonite was added to 300 g of water, stirred evenly, left to stand for 24 h, then 15 g of NaCl was added and fully dissolved. Then, 15 g of the high-temperature resistant gel obtained in Preparation 1, 60 g of attapulgite, 15 g of sulfonated phenolic resin, 15 g of 1 - 2 mm oyster shell, and 1.5 g of 75 - 380 μm sepiolite wool were added in sequence and dispersed evenly for standby.

[0066] Example 2

[0067] This embodiment provides a high-viscosity gel slug system with a temperature resistance of 205°C, and its preparation method is as follows:

[0068] Add 9 g of sodium bentonite to 300 g of water, stir evenly, let stand for 24 h, then add 20 g of NaCl and dissolve it fully. Then, add 17 g of the high-temperature-resistant gel obtained in Preparation 1, 65 g of attapulgite, 13 g of water-soluble epoxy resin, 6 g of 0.5 - 1 mm shell slag, and 1 g of 75 - 380 μm silicate fiber in sequence, and disperse them evenly for standby.

[0069] Example 3

[0070] This embodiment provides a high-viscosity gel slug system with a temperature resistance of 205°C, and its preparation method is as follows:

[0071] Add 5 g of sodium bentonite to 300 g of water, stir evenly, let stand for 24 h, then add 20 g of NaCl and dissolve it fully. Then, add 20 g of high-temperature-resistant gel, 60 g of attapulgite, 10 g of sulfonated phenolic resin, 6 g of 0.5 - 1 mm shell slag, and 1 g of 75 - 380 μm asbestos wool in sequence, and disperse them evenly for standby.

[0072] Example 4

[0073] This embodiment provides a high-viscosity gel slug system with a temperature resistance of 205°C, and its preparation method is as follows:

[0074] Add 12 g of sodium bentonite to 300 g of water, stir evenly, let stand for 24 h, then add 15 g of NaCl and dissolve it fully. Then, add 20 g of high-temperature-resistant gel, 50 g of attapulgite, 15 g of melamine resin, 9 g of 0.5 - 1 mm shell slag, and 2 g of 75 - 380 μm sepiolite wool in sequence, and disperse them evenly for standby.

[0075] Comparative Example 1

[0076] This comparative example provides a gel slug system without a high-temperature crosslinking agent, and its preparation method is as follows:

[0077] Add 9 g of sodium bentonite to 300 g of water, stir evenly, let stand for 24 h, then add 20 g of NaCl and dissolve it fully. Then, add 25 g of high-temperature-resistant gel, 55 g of attapulgite, 15 g of 0.5 - 1 mm shell slag, and 3 g of 75 - 380 μm sepiolite wool in sequence, and disperse them evenly for standby.

[0078] Comparative Example 2

[0079] This comparative example provides a gel slug system without a high-temperature-resistant gel, and its preparation method is as follows:

[0080] Add 9 g of sodium bentonite to 300 g of water, stir evenly, let stand for 24 h, then add 20 g of NaCl and dissolve it fully. Then add 55 g of attapulgite, 10 g of sulfonated phenolic resin, 15 g of 0.5 - 1 mm shell slag, and 3 g of 75 - 380 μm sepiolite wool in sequence and disperse evenly for standby.

[0081] Comparative Example 3

[0082] This comparative example provides a gel slug system. The high-temperature cross-linking agent is N,N'-methylenebisacrylamide, and its preparation method is as follows:

[0083] Add 12 g of sodium bentonite to 300 g of water, stir evenly, let stand for 24 h, then add 15 g of NaCl and dissolve it fully. Then add 20 g of high-temperature-resistant gel, 50 g of attapulgite, 1.5 g of N,N'-methylenebisacrylamide, 9 g of 0.5 - 1 mm shell slag, and 2 g of 75 - 380 μm sepiolite wool in sequence and disperse evenly for standby.

[0084] Comparative Example 4

[0085] This comparative example provides a gel slug system. The high-temperature cross-linking agent is potassium permanganate, and its preparation method is as follows:

[0086] Add 12 g of sodium bentonite to 300 g of water, stir evenly, let stand for 24 h, then add 15 g of NaCl and dissolve it fully. Then add 20 g of high-temperature-resistant gel, 50 g of attapulgite, 0.5 g of potassium permanganate, 9 g of 0.5 - 1 mm shell slag, and 2 g of 75 - 380 μm sepiolite wool in sequence and disperse evenly for standby.

[0087] High-temperature stability evaluation

[0088] Put the gel slug systems obtained in Examples 1 - 4 and Comparative Examples 1 - 4 into an aging tank. The viscosities after standing and curing at 205°C for different times are shown in Table 1 (measured by a Brookfield viscometer).

[0089] Table 1 High-temperature stability performance evaluation

[0090]

[0091] As can be seen from Table 1, the gel slug systems provided in Examples 1 to 4 have viscosities of 100 to 300 mPa·s within 5 h at room temperature, meeting the requirements for preparation and pumping. As the curing time increases, the viscosity of the system at high temperature rises rapidly, reaching the highest viscosity at 3 d, and then maintaining a high viscosity up to 20 d or more, indicating that the system has good high-temperature resistance. From the data of Examples 2 and 4, since water-soluble epoxy resin itself has a certain viscosity, the viscosity of the slurry prepared at room temperature is relatively high. Due to fewer active sites in melamine resin and water-soluble epoxy resin, the viscosity of the crosslinked system is slightly lower. From the data of Examples 1 and 3, using sulfonated phenolic resin as the crosslinking agent, its dosage range is relatively wide, and the system maintains a very high viscosity for a long time. Therefore, sulfonated phenolic resin is the optimal choice as the crosslinking agent.

[0092] For the gel slug system provided in Comparative Example 1, the high-temperature-resistant gel in the system absorbs free water within 3 d, causing the viscosity of the system to rise rapidly. After 3 d, the high-temperature-resistant gel begins to gradually degrade to form macromolecular and small-molecular polymers. Since no high-temperature crosslinking agent is added and no secondary crosslinking reaction can occur, the viscosity of the system decreases rapidly, indicating that the secondary crosslinking reaction promoted by the high-temperature crosslinking agent is the key component to maintain the high-temperature stability of the gel slug system. In the gel slug system provided in Comparative Example 2, no high-temperature-resistant gel is added. It can be seen that the viscosity change of the system during curing is not significant, indicating that the high-temperature-resistant gel is the main component to form a high-viscosity slug. In the gel slug systems provided in Comparative Examples 3 and 4, conventional crosslinking agents in the industry are respectively added to replace the high-temperature crosslinking agent in the present invention. Since the conventional crosslinking agent has a high activity, if the addition amount is the same as that of sulfonated phenolic resin, etc., the system will quickly self-crosslink to form a solid, which does not meet the application requirements. Therefore, the addition amount that can form a viscous slug is added. Experiments show that since this kind of crosslinking agent does not contain a high-temperature-resistant cyclic structure, the viscosity drops rapidly at high temperature and cannot meet the high-temperature requirements.

[0093] Taking the gel slug system obtained in Example 1 of the present invention as a sample, the appearance diagram during its curing at 205°C is as Figure 1 shown. It can be seen that the slug formed by the gel provided by the present invention is in a gel-like state and can be screened out by the vibrating screen with the circulation, without affecting the performance of the drilling fluid.

[0094] Plugging performance evaluation

[0095] The schematic diagram of the plugging performance evaluation device is as Figure 2 shown. The main body of the device is made of transparent organic glass for easy observation of experimental phenomena. The diameter of the hollow transparent organic glass tube is 18 cm. There is a sealing cover (2) at the upper section of the glass tube, an air inlet (1) on the cover body, and a liquid outlet (3) at the lower end. Gas can be injected from the air inlet (1) at the top and the liquid outlet (3) at the bottom of the device.

[0096] Add 200 g of 20 - 40 mesh sand to the visible sand bed (i.e., transparent plexiglass). After leveling, add the product of Example 1 cured at 205 °C for 20 d, seal it, and introduce nitrogen gas through the air inlet (1). After pressurizing to 1 MPa and maintaining for 10 min, the sand bed does not leak (see Figure 3 ). After the experiment, remove the visible section of the sand bed, and it can be seen that the slug enters the pores of the 20 - 40 mesh sand bed to form a 1.5 cm plugging layer (see Figure 4 ). All the sand grains in this plugging layer are uniform, and the slug is wrapped with a dense gel, and it has a certain strength, which proves that after the formed gel slug enters the leakage layer, it is stretched and contracted at the formation pore throats. When the gel slug passes through the pore throats, it immediately expands to fill the pore space, forming a partition slug deep in the wellbore and the leakage channel, thereby achieving the purpose of plugging.

[0097] Evaluation of gas retention performance

[0098] Use the plugging performance evaluation device as shown in Figure 2 to conduct the gas retention performance evaluation. The specific method is as follows:

[0099] Add 200 g of 20 - 40 mesh sand to the visible sand bed. After leveling, add the product of Example 2 cured at 205 °C for 20 d, seal it, and introduce nitrogen gas through the air inlet (1). After pressurizing to 1 MPa and maintaining for 10 min, open the sealing cover (2) and inject 100 mL of clear water (see Figure 5 ). Use nitrogen gas for reverse pressurization from the liquid outlet (3). The results are shown in Figure 6 . As can be seen from Figure 6 , under the action of gas pressure, the gas pushes the whole slug, but does not break through the slug (no bubbles emerge from the upper clear water), indicating that the formed gel slug can block the breakthrough of gas and has a significant gas retention effect.

[0100] Evaluation of plugging layer strength

[0101] Add the prepared sample to the simulated wellbore equipped with a simulated leakage layer module (5 - 10 mm gravel) for squeeze injection experiment. The process of squeeze injection is the process of forming the plugging layer; after the plugging layer is formed, use a heating jacket to heat the simulated wellbore to 205 °C to simulate downhole conditions, and then conduct a squeeze injection pressure-bearing experiment to test the pressure-bearing strength of the formed plugging layer.

[0102] The results are shown in Table 2 below:

[0103] Table 2 Evaluation of plugging layer strength

[0104]

[0105] As can be seen from the data in Table 2, Comparative Example 2 has no high-temperature crosslinked gel, lacking the water absorption swelling and deformation filling effects of the gel. Relying solely on the interlocking and winding effects between rigid particles and flexible fibers, it is difficult to effectively stay in the leakage layer to form a plugging layer. Therefore, the high-temperature gel is subjected to tensile contraction, water absorption deformation filling effects at the pore throats of the leakage layer, which plays an important role in the retention of the formed gel slug in the leakage layer; Comparative Example 1 has no high-temperature crosslinking agent, and the pressure-bearing capacity continues to decline after 3 days and fails at 5 days. The effective time is short and it is easy to re-leak, indicating that the secondary crosslinking reaction promoted by the high-temperature crosslinking agent is crucial for the slug to maintain a long-term stable pressure-bearing capacity at a high temperature of 205°C. Therefore, the addition of the high-temperature crosslinking agent is the key to the difference between the present invention and the conventional slug gel slug system; compared with Examples 1 to 4, Comparative Examples 3 and 4 use conventional crosslinking agents in the industry, and the pressure-bearing capacity continues to decline after 3 days, indicating that the secondary crosslinking reaction promoted by the conventional crosslinking agent cannot meet the requirements at high temperatures. However, the high-temperature resistant crosslinking agent preferably used in the present invention, especially sulfonated phenolic resin, can ensure that the pressure-bearing capacity of the formed gel slug still reaches 8.8 MPa after 20 days, meeting the on-site requirements.

[0106] The foregoing description of the disclosed embodiments enables those skilled in the art to practice or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Thus, the invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A high-temperature resistant 205°C high-viscosity gel slug system, characterized in that, by weight, it is prepared from 1-4 parts of sodium bentonite, 2-10 parts of NaCl, 1.5-8 parts of high-temperature resistant gel, 15-25 parts of attapulgite, 1.5-5 parts of high-temperature crosslinking agent, 1-5 parts of rigid particles, 0.2-1 part of flexible fiber, and 100 parts of water; The high-temperature resistant gel is a network structure gel formed by crosslinking polymerization of a first monomer and a second monomer; the first monomer includes 2-acrylamide-2-methylpropanesulfonic acid, and the second monomer includes acrylamide; The high-temperature crosslinking agent is selected from any one or more of sulfonated phenolic resin, water-soluble epoxy resin or melamine resin.

2. The high-temperature resistant 205°C high-viscosity gel slug system according to claim 1, characterized in that, the particle size of the high-temperature resistant gel is 1-3 mm.

3. The high-temperature resistant 205°C high-viscosity gel slug system according to claim 1, characterized in that, the rigid particles are selected from shell slag and / or oyster shell.

4. The high-temperature resistant 205°C high-viscosity gel slug system according to claim 3, wherein the particle size of the rigid particles is 0.1-2 mm.

5. The high-temperature resistant 205°C high-viscosity gel slug system according to claim 1, characterized in that, the flexible fiber is selected from any one or more of asbestos wool, sepiolite wool or silicate fiber.

6. The high-temperature resistant 205°C high-viscosity gel slug system according to claim 5, wherein the length of the flexible fiber is 75-380 μm.

7. A preparation method of the high-temperature resistant 205°C high-viscosity gel slug system according to any one of claims 1-6, characterized in that, comprises the following steps: Mix 1-4 parts of sodium bentonite, 2-10 parts of NaCl, 1.5-8 parts of high-temperature resistant gel, 15-25 parts of attapulgite, 1.5-5 parts of high-temperature crosslinking agent, 1-5 parts of rigid particles, 0.2-1 part of flexible fiber, and 100 parts of water to obtain a high-temperature resistant 205°C high-viscosity gel slug system; The high-temperature resistant gel is a double-network structure gel formed by secondary crosslinking polymerization of a first monomer and a second monomer; the first monomer is 2-acrylamide-2-methylpropanesulfonic acid, and the second monomer includes acrylamide; The high-temperature crosslinking agent is selected from any one or more of sulfonated phenolic resin, water-soluble epoxy resin or melamine resin.

8. Application of the high-temperature resistant 205°C high-viscosity gel slug system according to any one of claims 1-6 or the high-temperature resistant 205°C high-viscosity gel slug system prepared by the preparation method according to claim 7 in the drilling process.

9. The application according to claim 8, characterized in that, Inject the high-temperature resistant 205°C high-viscosity gel slug system according to any one of claims 1-6 or the high-temperature resistant 205°C high-viscosity gel slug system prepared by the preparation method according to claim 7 into the predetermined position of the wellbore. After pulling out the drill pipe to 50-100 m above the gel liquid level, shut in the well and slowly inject intermittently to make it enter the leakage layer to form a high-temperature resistant 205°C high-viscosity gel slug.

10. The application according to claim 9, characterized in that, The drill pipe is pulled out until it is 60 to 80 m above the gel level.

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