Gel for assisting huff and puff of carbon dioxide and application of gel

Abstract

The invention provides gel for assisting huff and puff of carbon dioxide and application of the gel, and relates to the technical field of huff and puff of carbon dioxide in oil fields, and the gel comprises the following components in percentage by mass: 0.20%-0.60% of a main agent, 0.10%-0.30% of a cross-linking agent, 0.01%-0.04% of sodium sulfite and the balance of water, the main agent is sodium alginate and sodium carboxymethyl cellulose, and the cross-linking agent is chromium acetate and chromium citrate. When the gel provided by the invention is used for effectively blocking a dominant seepage channel, carbon dioxide can be prevented from forming gas channeling along the dominant seepage channel, so that the sweep range of the carbon dioxide in an oil layer is expanded, and more carbon dioxide is further mixed and dissolved in crude oil; the utilization efficiency of carbon dioxide is improved, and the huff and puff validity period of carbon dioxide is prolonged, so that the crude oil recovery rate is improved. In addition, the gel provided by the invention also has the characteristics of simple components and wide application range.

Description

Technical Field

[0001] The present invention relates to the technical field of carbon dioxide throughput in oil fields, and in particular to a gel for assisting carbon dioxide throughput and application thereof. Background Art

[0002] Currently, natural energy development is primarily used in areas where establishing a reasonable injection-production relationship is difficult. However, if the continuously diminishing natural energy resources are not replenished promptly, the development results of the area will deteriorate dramatically. Existing technologies often employ carbon dioxide huff-and-puff (CO2) in these areas to replenish formation energy, enhance oil recovery, and improve development outcomes. The principle is that large quantities of liquid CO2 are injected into the oil reservoir. At formation temperatures, the CO2 rapidly vaporizes and dissolves in the crude oil, significantly reducing oil-water interfacial tension, lowering crude oil viscosity, and increasing its flowability. Simultaneously, the volume of the underground crude oil expands, raising pore pressure in the reservoir and forming localized saturated zones, displacing some of the remaining oil. This can increase the volume of the oil by 10% to 30%, increasing the kinetic energy of the fluid, and thus improving oil displacement efficiency and recovery. Therefore, CO2 huff-and-puff is an important technique for enhancing oil recovery.

[0003] Due to the influence of reservoir heterogeneity (reservoirs with different properties) and dominant seepage channels, the carbon dioxide injected from the oil well will form gas channeling along the dominant seepage channels, greatly reducing the scope of the carbon dioxide, resulting in the carbon dioxide being unable to dissolve in some crude oil, thereby greatly reducing the crude oil recovery rate; in addition, after the well is soaked, the carbon dioxide will return along the original injection channel during the well opening and production process, forming an ineffective cycle of carbon dioxide.

[0004] Therefore, in the field of oilfield carbon dioxide throughput technology, how to effectively block the dominant channels to improve the carbon dioxide throughput effect has become a technical problem that needs to be solved urgently. Summary of the Invention

[0005] To solve the above problems, in a first aspect, the present invention provides a gel for assisting carbon dioxide intake and exhalation, the gel comprising the following components by mass percentage: 0.20% to 0.60% of a main agent, 0.10% to 0.30% of a cross-linking agent, 0.01% to 0.04% of sodium sulfite, and the balance being water; the main agent is sodium alginate and sodium carboxymethyl cellulose, and the cross-linking agent is chromium acetate and chromium citrate.

[0006] Preferably, the mass ratio of the sodium alginate to the sodium carboxymethyl cellulose is 1:2 to 2:1; the mass ratio of the chromium acetate to the chromium citrate is 2:1 to 5:1.

[0007] Preferably, the gel comprises the following components in mass percentage: 0.6% main agent, 0.3% cross-linking agent, 0.04% sodium sulfite, and 99.06% water; wherein the main agent is sodium alginate and sodium carboxymethyl cellulose in a mass ratio of 1:2, and the cross-linking agent is chromium acetate and chromium citrate in a mass ratio of 5:1.

[0008] In a second aspect, the present invention provides an application of a gel for assisting carbon dioxide huff and puff, wherein the gel is used to assist carbon dioxide huff and puff oil production, and the application includes:

[0009] S1, injecting a gel pre-slug into the oil layer, then displacing it with clean water and waiting for solidification; wherein the gel pre-slug is the gel according to any one of claims 1 to 3 above;

[0010] S2, injecting a main slug of carbon dioxide into the oil layer;

[0011] S3, stewing time setting;

[0012] S4, after the set time is reached, the well is opened for production.

[0013] Preferably, after S2 and before S3, the application further includes:

[0014] A gel rear slug is injected into the oil layer, and clean water is used to displace the oil, and the oil is allowed to solidify. The gel used in the gel rear slug is the same as that used in the gel front slug.

[0015] Preferably, the gel front slug or the gel rear slug comprises the following components by mass percentage: 0.20% to 0.60% of a main agent, 0.10% to 0.30% of a cross-linking agent, 0.01% to 0.04% of sodium sulfite, and the balance being water; the main agent is sodium alginate and sodium carboxymethyl cellulose, and the cross-linking agent is chromium acetate and chromium citrate.

[0016] Preferably, the mass ratio of the sodium alginate to the sodium carboxymethyl cellulose is 1:2 to 2:1; the mass ratio of the chromium acetate to the chromium citrate is 2:1 to 5:1.

[0017] Preferably, in S1, the amount of the gel front plug is 500t to 800t, and the displacement is 1t / h to 5t / h; the amount of clean water displacement is 10t to 30t; and the waiting time for coagulation is 72h.

[0018] Preferably, the amount of the carbon dioxide main body slug is 500t to 1000t, the displacement is 5t / h to 10t / h; and the setting time is 20d to 40d.

[0019] Preferably, the amount of the gel rear plug is 10t to 50t, and the displacement is 1t / h to 5t / h; the amount of the clean water displacement is 10t to 30t.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] The present invention provides a gel for assisting carbon dioxide huff and puff, and its application, relating to the technical field of carbon dioxide huff and puff in oil fields. The gel comprises the following components, by mass percentage: a main agent (0.20% to 0.60%), a cross-linking agent (0.10% to 0.30%), sodium sulfite (0.01% to 0.04%), and water (the balance). The main agents are sodium alginate and sodium carboxymethyl cellulose, and the cross-linking agents are chromium acetate and chromium citrate. The gel provided by the present invention effectively blocks dominant seepage channels, preventing carbon dioxide from channeling along these channels. This expands the reach of carbon dioxide in the oil reservoir, further allowing more carbon dioxide to dissolve in crude oil, improving carbon dioxide utilization efficiency and extending the effective period of carbon dioxide huff and puff, thereby increasing crude oil recovery. Furthermore, the gel provided by the present invention has the advantages of simple composition and a wide range of applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0023] Figure 1 This is a graph showing the viscosity change of the gel provided in an embodiment of the present invention;

[0024] Figure 2 This is a flow chart of a carbon dioxide huff and puff oil production process in the prior art;

[0025] Figure 3 This is a flow chart of gel-assisted carbon dioxide huff and puff oil production according to an embodiment of the present invention. DETAILED DESCRIPTION

[0026] The following examples are provided for a better understanding of the present invention and are not intended to limit the best mode of implementation. They do not limit the content and scope of protection of the present invention. Any product identical or similar to the present invention obtained by anyone under the guidance of the present invention or by combining the features of the present invention with other prior arts shall fall within the scope of protection of the present invention.

[0027] Where specific experimental steps or conditions are not specified in the examples, the conventional experimental steps or conditions described in the prior art in the art may be used. The reagents and other instruments used, for which the manufacturer is not specified, are all conventional reagent products that can be obtained commercially. Furthermore, the accompanying drawings are merely schematic illustrations of the embodiments of the present disclosure and are not necessarily drawn to scale. Identical reference numerals in the figures represent identical or similar parts, and their repeated descriptions will be omitted. Some block diagrams shown in the accompanying drawings are functional entities and do not necessarily correspond to physically or logically independent entities.

[0028] In a first aspect, the present invention provides a gel for assisting carbon dioxide intake and exhalation, the gel comprising the following components by mass percentage: 0.20% to 0.60% of a main agent, 0.10% to 0.30% of a cross-linking agent, 0.01% to 0.04% of sodium sulfite, and the remainder being water; the main agent is sodium alginate and sodium carboxymethyl cellulose, and the cross-linking agent is chromium acetate and chromium citrate.

[0029] In the embodiments of the present invention, the gel provided by the present invention is used to effectively block the dominant seepage channels, thereby preventing carbon dioxide from forming gas channeling along the dominant seepage channels, thereby expanding the scope of carbon dioxide in the oil layer, further allowing more carbon dioxide to be miscible with crude oil, improving the utilization efficiency of carbon dioxide and extending the effective period of carbon dioxide throughput, thereby increasing crude oil recovery. In addition, the gel provided by the embodiments of the present invention has the characteristics of simple composition and wide range of applications.

[0030] The dominant seepage channel is a low-resistance seepage channel formed locally in the reservoir due to geology and development. Since the oil field has been in the process of long-term water injection development, in the later stage of water injection development, the injected water forms an obvious dominant flow along the dominant seepage channel and produces an invalid circulation. Especially in the formation where the dominant seepage channel is developed, the injected water forms an invalid crossflow in the dominant seepage channel, the injection efficiency is reduced, the water drive swept volume is reduced, the water content of the oil well increases rapidly, the water drive effect is reduced, and the oil reservoir recovery rate and development efficiency gradually deteriorate.

[0031] Specifically, sodium alginate and sodium carboxymethyl cellulose act synergistically to enhance the heat and salt resistance of the gel. In the present embodiment, the main agent adopts sodium alginate and sodium carboxymethyl cellulose simultaneously. On the one hand, sodium alginate and sodium carboxymethyl cellulose are natural polymer materials, are not easily degraded, and have good stability; On the other hand, the six-membered rings carried by sodium alginate and sodium carboxymethyl cellulose molecules can improve the heat resistance of the gel, and more importantly, the six-membered ring structure makes the main agent molecular chain not easy to curl under the action of underground salt, further improving the salt resistance of the gel, and sodium alginate and sodium carboxymethyl cellulose are low molecular weight materials, making the main agent molecular chain more not easy to curl; Because the main agent molecular chain is not easy to curl, the sodium alginate molecular chain and the sodium carboxymethyl cellulose molecular chain are cross-linked to form an interpenetrating network structure, and the interpenetrating network structure formed is conducive to strengthening the heat and salt resistance of the material. It should also be noted that the main agent in this embodiment does not use common artificial synthetic polymer materials such as polyacrylamide or partially hydrolyzed polyacrylamide because the molecular chains of polyacrylamide or partially hydrolyzed polyacrylamide are linear and easily curled, and the gel formed thereby has poor temperature and salt resistance.

[0032] Under high-temperature conditions, the viscosity retention rate of the gel provided in this embodiment is above 95.00%, demonstrating its strong heat and salt tolerance. Due to its strong heat and salt tolerance, the gel provided in this embodiment can be used to block advantageous seepage channels, thereby reducing the impact of reservoir temperature and formation water salinity on gel stability. This can further extend the effective period of carbon dioxide huff and puff, thereby improving the economic benefits of carbon dioxide huff and puff.

[0033] Furthermore, the gel provided in this embodiment has a high viscosity retention rate at a temperature of 115° C., which can meet the requirements for blocking the advantageous seepage channels in medium- and high-temperature oil reservoirs.

[0034] Figure 1 This is a graph showing the viscosity change of the gel provided in the embodiment of the present invention, as shown in FIG. Figure 1 As shown, the viscosity of the gel provided in this embodiment is in the range of 30,000 mPa·s to 43,000 mPa·s. The gel obtained by using the above components and proportions has a high viscosity, and thus can tightly block the dominant seepage channel, with a good blocking effect.

[0035] Specifically, chromium acetate and chromium citrate are used to cross-link the main agent, making the gel non-flowable and reducing the permeability of the oil layer where the gel is injected, thereby achieving plugging and preventing carbon dioxide from forming gas channeling along the dominant seepage channel. Furthermore, in this embodiment, the chromium ions in the chromium acetate and chromium citrate form polar bonds and coordination bonds with the carboxyl groups on the main agent molecules to generate cross-linking to form a gel, thereby improving the strength of the gel.

[0036] Specifically, the sodium sulfite in the gel is used to prevent oxygen in the water from oxidizing and degrading the gel, thereby improving the stability of the gel and thus extending the effective sealing period of the gel.

[0037] In this embodiment, since the effective ingredients in the gel have a good blocking effect, the proportion of the effective ingredients in the gel in this embodiment is extremely small, and the gel has the characteristics of low cost and good injectability; if the total proportion of effective ingredients such as the main agent and cross-linking agent in this embodiment is greater than 1%, it will lead to high cost of gel raw materials and poor injectability, thereby resulting in higher pressure required for injection, further increasing the cost of use.

[0038] In some embodiments, the mass ratio of the sodium alginate to the sodium carboxymethyl cellulose is 1:2 to 2:1; the mass ratio of the chromium acetate to the chromium citrate is 2:1 to 5:1.

[0039] In this embodiment, by utilizing chromium acetate and chromium citrate together and their ratio, the release rate of chromium ions can be controlled so that the main agent can completely gel in the oil layer, thereby controlling the gelation time and gelation strength of the gel, thereby meeting the requirements for gel performance.

[0040] In some embodiments, the gel comprises the following components in mass percentage: a main agent 0.6%, a cross-linking agent 0.3%, sodium sulfite 0.04%, and water 99.06%; wherein the main agent is sodium alginate and sodium carboxymethyl cellulose in a mass ratio of 1:2, and the cross-linking agent is chromium acetate and chromium citrate in a mass ratio of 5:1.

[0041] In this embodiment, the gel with this ratio has a higher viscosity, a higher blocking rate, and a better blocking effect.

[0042] like Figure 2 As shown, Figure 2 This is a flow chart of a carbon dioxide huff-and-puff oil recovery process in the prior art, including:

[0043] S01, injecting a main slug of carbon dioxide into the oil layer; S02, shutting down the well; S03, opening the well for production.

[0044] When using this method for crude oil extraction, the CO2 injected into the well may channel along unblocked, dominant seepage pathways, significantly reducing the CO2's reach and rendering it insoluble in some crude oil, significantly reducing the oil recovery rate. Furthermore, after soaking the well, the CO2 can return along the original injection pathway during production, creating an ineffective cycle of CO2.

[0045] In order to solve the problem that carbon dioxide may form gas channeling along the dominant seepage channel during carbon dioxide huff and puff, resulting in poor carbon dioxide huff and puff effect, in a second aspect, the present invention provides an application of a gel for assisting carbon dioxide huff and puff, wherein the gel is used to assist carbon dioxide huff and puff oil production, such as Figure 3 As shown, Figure 3 This is a flow chart of a gel-assisted carbon dioxide huff and puff oil recovery according to an embodiment of the present invention, wherein the application includes:

[0046] S1, injecting a gel pre-slug into the oil layer, then displacing it with clean water and waiting for solidification; wherein the gel pre-slug is the gel described in the first aspect above; S2, injecting a carbon dioxide main slug into the oil layer; S3, setting a shut-in time; S4, opening the well for production after the set time has elapsed.

[0047] and Figure 2 Compared to the process shown in the figure, the present invention uses gel to effectively block the dominant seepage channels before injecting the main CO2 slug into the oil layer. This prevents CO2 from channeling along these channels, thereby expanding the CO2's reach within the oil layer and further allowing more CO2 to dissolve in the crude oil. This improves CO2 utilization efficiency and extends the effective period of CO2 throughput, thereby increasing crude oil recovery. Furthermore, the application provided by the present invention has the advantages of a wide range of applications and simple process implementation; specifically, the application provided by the present invention is suitable for oil reservoirs with temperatures below 115°C.

[0048] In step S1, a heat-resistant and salt-resistant gel pre-slug is injected into the oil layer to assist carbon dioxide huff-and-puff oil production, and then the heat-resistant and salt-resistant gel is displaced to the dominant seepage channel using clean water. Within a preset time, the heat-resistant and salt-resistant gel in the viscous solution is completely gelled in the dominant seepage channel, thereby effectively blocking the dominant seepage channel.

[0049] In step S2, carbon dioxide is injected again. Since the dominant seepage channel has been blocked by the salt-resistant and temperature-resistant gel, gas channeling of carbon dioxide along the dominant seepage channel can be prevented. Therefore, the carbon dioxide enters the low-permeability channel with a high crude oil content, expanding the scope of carbon dioxide in the oil layer. In the soaking process of step S3, more carbon dioxide is fully diffused in the oil layer and reacts with the crude oil, thereby improving the utilization efficiency of carbon dioxide and extending the effective period of carbon dioxide throughput, thereby increasing the crude oil recovery rate. After the soaking is completed, additional crude oil can be produced.

[0050] Since the gel used in the oil production process of this embodiment has strong temperature and salt resistance, when the heat-resistant and salt-resistant gel is used to block the dominant seepage channel, the influence of reservoir temperature and formation water salinity on gel stability can be reduced, and the effective period of carbon dioxide throughput can be further extended, thereby improving the economic benefits of carbon dioxide throughput.

[0051] Specifically, sodium alginate and sodium carboxymethyl cellulose act synergistically to enhance the heat and salt resistance of the gel. In the present embodiment, the main agent adopts sodium alginate and sodium carboxymethyl cellulose simultaneously. On the one hand, sodium alginate and sodium carboxymethyl cellulose are natural polymer materials, are not easily degraded, and have good stability; On the other hand, the six-membered rings carried by sodium alginate and sodium carboxymethyl cellulose molecules can improve the heat resistance of the gel, and more importantly, the six-membered ring structure makes the main agent molecular chain not easy to curl under the action of underground salt, further improving the salt resistance of the gel, and sodium alginate and sodium carboxymethyl cellulose are low molecular weight materials, making the main agent molecular chain more not easy to curl; Because the main agent molecular chain is not easy to curl, the sodium alginate molecular chain and the sodium carboxymethyl cellulose molecular chain are cross-linked to form an interpenetrating network structure, and the interpenetrating network structure formed is conducive to strengthening the heat and salt resistance of the material. It should also be noted that the main agent in this embodiment does not use common artificial synthetic polymer materials such as polyacrylamide or partially hydrolyzed polyacrylamide because the molecular chains of polyacrylamide or partially hydrolyzed polyacrylamide are linear and easily curled, and the gel formed thereby has poor temperature and salt resistance.

[0052] The viscosity retention rate of the gel provided in this embodiment is above 95.00% in high-temperature environments, demonstrating its strong heat and salt tolerance. Because of this strong heat and salt tolerance, using this heat and salt-resistant gel to block dominant seepage channels can reduce the impact of reservoir temperature and formation water salinity on gel stability, further extending the effective period of CO2 throughput and improving the economic benefits of CO2 throughput. Furthermore, the maximum temperature in high-temperature environments can reach 115°C; therefore, the application provided by this embodiment is particularly suitable for oil reservoirs at 115°C.

[0053] Specifically, chromium acetate and chromium citrate are used to cross-link the main agent, making the gel non-flowable and reducing the permeability of the oil layer where the gel is injected, thereby achieving plugging and preventing carbon dioxide from forming gas channeling along the dominant seepage channel. Furthermore, in this embodiment, the chromium ions in the chromium acetate and chromium citrate form polar bonds and coordination bonds with the carboxyl groups on the main agent molecules to generate cross-linking to form a gel, thereby improving the strength of the gel.

[0054] Specifically, sodium sulfite is used to prevent oxygen in water from oxidizing and degrading the gel, so as to improve the stability of the gel, thereby extending the effective sealing period of the gel.

[0055] In some implementations, after S2 and before S3, the application further includes:

[0056] A gel rear slug is injected into the oil layer, and clean water is used to displace the oil, and the oil is allowed to solidify. The gel used in the gel rear slug is the same as that used in the gel front slug.

[0057] Compared to Figure 2 The process shown uses the application provided by this embodiment. Before and after the injection of the carbon dioxide slug, a heat-resistant and salt-resistant gel slug is injected. This not only effectively blocks the dominant seepage channel to prevent carbon dioxide from channeling along the dominant seepage channel, thereby expanding the scope of carbon dioxide in the oil layer, but also prevents carbon dioxide from returning along the original injection channel during the well opening and production process in step S4, thereby avoiding ineffective circulation of carbon dioxide, achieving "sealing" and further improving the utilization rate of carbon dioxide.

[0058] In some embodiments, the gel front slug or the gel rear slug comprises the following components by mass percentage: 0.20% to 0.60% of a main agent, 0.10% to 0.30% of a cross-linking agent, 0.01% to 0.04% of sodium sulfite, and the balance being water; the main agent is sodium alginate and sodium carboxymethyl cellulose, and the cross-linking agent is chromium acetate and chromium citrate.

[0059] In some embodiments, the mass ratio of the sodium alginate to the sodium carboxymethyl cellulose is 1:2 to 2:1; the mass ratio of the chromium acetate to the chromium citrate is 2:1 to 5:1.

[0060] In this embodiment, by utilizing chromium acetate and chromium citrate together and their ratio, the release rate of chromium ions can be controlled so that the main agent can completely gel in the oil layer, thereby controlling the gelation time and gelation strength of the gel, thereby meeting the requirements for gel performance.

[0061] In some embodiments, in S1, the amount of the gel front plug is 500t to 800t, the displacement is 1t / h to 5t / h; the amount of clean water displacement is 10t to 30t; and the waiting time for coagulation is 72h.

[0062] In some embodiments, the amount of the carbon dioxide main body plug is 500t to 1000t, the displacement is 5t / h to 10t / h; and the setting time is 20d to 40d.

[0063] In some embodiments, the amount of the gel rear plug is 10t to 50t, and the displacement is 1t / h to 5t / h; the amount of the clean water displacement is 10t to 30t.

[0064] In order to enable those skilled in the art to better understand the present invention, the gel for assisting carbon dioxide intake and exhalation and its application provided by the present invention are described below through multiple specific embodiments.

[0065] Example 1

[0066] First, 9954 kg of preparation water (mineralization 89585 mg / L) was added to the preparation tank, followed by 20 kg of sodium alginate and 10 kg of sodium carboxymethyl cellulose, and stirred to completely dissolve them. 10 kg of chromium acetate and 5 kg of chromium citrate were added to the completely dissolved main agent solution, and stirred to completely dissolve them to obtain a mixed solution. 1 kg of sodium sulfite, a stabilizer, was added to the mixed solution, and stirred to mix uniformly to obtain 10,000 kg of ungelled gel A.

[0067] Example 2

[0068] First, 9906 kg of preparation water (mineralization 89585 mg / L) was added to the preparation tank, followed by 20 kg of sodium alginate and 40 kg of sodium carboxymethyl cellulose, and stirred to completely dissolve them. 25 kg of chromium acetate and 5 kg of chromium citrate were added to the completely dissolved main agent solution, and stirred to completely dissolve them to obtain a mixed solution. 4 kg of sodium sulfite, a stabilizer, was added to the mixed solution, and stirred to mix uniformly to obtain 10,000 kg of ungelled gel B.

[0069] Example 3

[0070] First, 9935 kg of preparation water (mineralization 89585 mg / L) was added to the preparation tank, followed by 20 kg of sodium alginate and 20 kg of sodium carboxymethyl cellulose, and stirred to completely dissolve them. 17.5 kg of chromium acetate and 5 kg of chromium citrate were added to the completely dissolved main agent solution, and stirred to completely dissolve them to obtain a mixed solution. 2.5 kg of sodium sulfite, a stabilizer, was added to the mixed solution, and stirred to mix uniformly to obtain 10,000 kg of ungelled gel C.

[0071] The three gels obtained above were tested for their temperature and salt resistance.

[0072] The gels A, B, and C obtained above were all viscous solutions. 1000 g of each of the gels A, B, and C were taken and divided into 20 vials, which were sealed and placed in a constant temperature box at 115°C. One vial was taken out every month and the viscosity of the gel was measured using a viscometer. Figure 1 Table 1 is a viscosity change curve of the gel provided in the embodiment of the present invention, and Table 2 is a viscosity change table of the three gels. Figure 1 As can be seen from Table 1, the viscosity of the gel provided by the present invention is in the range of 30,000 mPa·s to 43,000 mPa·s, thus being able to tightly block the dominant seepage channels with good blocking effect. After 20 months, gels A, B, and C still maintained relatively high viscosities, and the viscosity of the three gel solutions decreased only slightly compared to the initial viscosity. The corresponding viscosity retention rates of gel solutions A, B, and C were 95.28%, 95.01%, and 95.00%, respectively, indicating that all three gels exhibited good temperature and salt resistance.

[0073] Table 1 Viscosity changes of three gels

[0074]

[0075] The following is a test of the oil-increasing effect of three gel-assisted carbon dioxide huff and puff

[0076] Test wells A, B, and C are three adjacent oil wells in the same block. The temperature of the oil layer where test wells A, B, and C are located is 115°C, the permeability is 252mD, the porosity is 13.7%, the oil layer thickness is 7.6m, the number of oil layers is 1, the wells are vertical, the formation water salinity is 89585mg / L, and the surface crude oil viscosity is 23.5mPa·s (115°C).

[0077] In the late stage of waterflooding development, the injected water forms a significant dominant flow along the dominant seepage channel, resulting in ineffective circulation. In formations with well-developed dominant seepage channels, the injected water forms ineffective crossflow in the dominant seepage channel, causing the water cut in the oil well to rise rapidly, the water drive effect to decrease, and the reservoir recovery rate and development efficiency to gradually deteriorate. The basic conditions of the test wells A, B, and C before plugging are as follows:

[0078] In the initial stage of production, the test well A produced 20 tons of oil per day and 0.2 tons of water per day. After it was put into production, the water content gradually increased. Currently, the water content in the produced oil is 99.2%, and production cannot continue. The cumulative oil production is 15,282 tons; in the initial stage of production, the test well B produced 21 tons of oil per day and 0.3 tons of water per day. After it was put into production, the water content gradually increased. Currently, the water content in the produced oil is 99.4%, and production cannot continue. The cumulative oil production is 15,715 tons; in the initial stage of production, the test well C produced 23 tons of oil per day and 0.1 tons of water per day. After it was put into production, the water content gradually increased. Currently, the water content in the produced oil is 99.5%, and production cannot continue. The cumulative oil production is 15,010 tons.

[0079] In order to increase oil well production, temperature-resistant and salt-resistant gel-assisted carbon dioxide huff-and-puff was performed on test wells A, B, and C:

[0080] In test well A, the dosage of the Gel A front plug was 500 tons, with a displacement of 1 ton / hour. After the injection of the Gel A front plug, 10 tons of clean water were injected to displace it, and the well was left to solidify for 72 hours. The dosage of the carbon dioxide main plug was 500 tons, with a displacement of 5 tons / hour. The dosage of the Gel A rear plug was 10 tons, with a displacement of 1 ton / hour. After the injection of the Gel A rear plug, 10 tons of clean water were injected to displace it, and the well was started for production after being shut down for 20 days.

[0081] After the well was shut down for 20 days after the gel-assisted carbon dioxide huff-and-puff operation, drainage production was carried out. On the second day, the oil production was 3.4 tons / day and the daily water production was 5.8 tons. On the third day, the oil production was 3.6 tons / day and the daily water production was 6.0 tons. The daily oil and water production tended to be stable for the next six months. After four months, the daily oil production showed a downward trend and the daily water production showed an upward trend. After nine months, the water cut increased to 99.4%, and the carbon dioxide huff-and-puff operation failed. The gel A-assisted carbon dioxide huff-and-puff operation had a net increase of 812 tons in oil production.

[0082] In test well B, the dosage of the Gel B front plug was 800 tons, with a displacement of 5 tons / hour. After the injection of the Gel B front plug, 30 tons of clean water were injected to displace it, and the well was left to solidify for 72 hours. The dosage of the carbon dioxide main plug was 1,000 tons, with a displacement of 10 tons / hour. The dosage of the Gel B rear plug was 50 tons, with a displacement of 5 tons / hour. After the injection of the Gel B rear plug, 30 tons of clean water were injected to displace it, and the well was started for production after being shut down for 40 days.

[0083] After the well was shut down for 40 days with the implementation of gel B-assisted carbon dioxide huff and puff operation, drainage production was carried out. On the second day, the oil production was 4.1 tons / day and the daily water production was 5.2 tons. On the third day, the oil production was 4.2 tons / day and the daily water production was 5.3 tons. The daily oil production and daily water production tended to be stable for the next 6 months. After 5 months, the daily oil production showed a downward trend and the daily water production showed an upward trend. After 10 months, the water cut increased to 99.3%, and the carbon dioxide huff and puff operation failed. The net increase in oil production from this gel B-assisted carbon dioxide huff and puff operation was 1,034 tons.

[0084] In test well C, the dosage of the Gel C front plug was 650 tons, with a displacement of 3 tons / hour. After the injection of the Gel C front plug, 20 tons of clean water were injected to displace it, and the well was left to solidify for 72 hours. The dosage of the carbon dioxide main plug was 750 tons, with a displacement of 7.5 tons / hour. The dosage of the Gel C rear plug was 30 tons, with a displacement of 3 tons / hour. After the injection of the Gel C rear plug, 20 tons of clean water were injected to displace it, and the well was started for production after being shut down for 30 days.

[0085] After the well was shut down for 30 days with the implementation of the gel C-assisted carbon dioxide huff and puff operation, drainage production was carried out. On the second day, the oil production was 4.5 tons / day and the daily water production was 4.4 tons. On the third day, the oil production was 4.4 tons / day and the daily water production was 4.3 tons. The daily oil and water production tended to be stable for the next six months. After six months, the daily oil production showed a downward trend and the daily water production showed an upward trend. After 12 months, the water cut increased to 99%, and the carbon dioxide huff and puff operation failed. The net increase in oil production from this gel C-assisted carbon dioxide huff and puff operation was 1,100 tons.

[0086] The above-mentioned test wells A, B, and C all achieved good oil-increasing effects, indicating that the gel-assisted carbon dioxide huff and puff provided by the present invention has good application prospects.

[0087] It should be pointed out that the steps and methods in the various embodiments of the present application are not limited to the corresponding embodiments, and the operating details and precautions of each embodiment are corresponding to each other.

[0088] The applicant declares that the present invention uses the above-described embodiments to illustrate the detailed process flow of the present invention, but the present invention is not limited to the above-described detailed process flow, that is, it does not mean that the present invention must rely on the above-described detailed process flow to be implemented. Those skilled in the art should understand that any simple modification of the present invention, equivalent substitution of raw materials for the products of the present invention, addition of auxiliary ingredients, selection of specific methods, etc., are all within the scope of protection and disclosure of the present invention.

[0089] For simplicity of description, the method embodiments are described as a series of actions. However, those skilled in the art should be aware that the present invention is not limited by the order of the actions described, as certain steps can be performed in other orders or simultaneously according to the present invention. Furthermore, those skilled in the art should also be aware that the embodiments described in this specification are preferred embodiments, and the actions and components involved are not necessarily required for the present invention.

[0090] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present disclosure. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification.

[0091] The above is a detailed introduction to a gel for assisting carbon dioxide intake and exhalation and its application provided by the present invention. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core concept. At the same time, for those skilled in the art, according to the concept of the present invention, there may be changes in the specific implementation methods and application scopes. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A gel for assisting carbon dioxide inhalation and exhalation, characterized in that: The gel comprises the following components by mass percentage: 0.20% to 0.60% of a main agent, 0.10% to 0.30% of a cross-linking agent, 0.01% to 0.04% of sodium sulfite, and the balance being water; the main agent is sodium alginate and sodium carboxymethyl cellulose, and the cross-linking agent is chromium acetate and chromium citrate.

2. The gel according to claim 1, characterized in that The mass ratio of the sodium alginate to the sodium carboxymethyl cellulose is 1:2 to 2:1; the mass ratio of the chromium acetate to the chromium citrate is 2:1 to 5:

1.

3. The gel according to claim 1, characterized in that The gel comprises the following components by mass percentage: a main agent 0.6%, a cross-linking agent 0.3%, sodium sulfite 0.04%, and water 99.06%; wherein the main agent is sodium alginate and sodium carboxymethyl cellulose in a mass ratio of 1:2, and the cross-linking agent is chromium acetate and chromium citrate in a mass ratio of 5:

1.

4. An application of a gel for assisting carbon dioxide intake and exhalation, characterized in that: The gel is used to assist carbon dioxide huff and puff oil recovery, and the applications include: S1, injecting a gel pre-slug into the oil layer, then displacing it with clean water and waiting for solidification; wherein the gel pre-slug is the gel according to any one of claims 1 to 3 above; S2, injecting a main slug of carbon dioxide into the oil layer; S3, stewing time setting; S4, after the set time is reached, the well is opened for production.

5. The oil production method according to claim 4, characterized in that: After S2 and before S3, the application further includes: A gel rear slug is injected into the oil layer, and clean water is used to displace the oil, and the oil is allowed to solidify. The gel used in the gel rear slug is the same as that used in the gel front slug.

6. The use according to claim 4, characterized in that The gel front slug or the gel rear slug comprises the following components by mass percentage: 0.20% to 0.60% of a main agent, 0.10% to 0.30% of a cross-linking agent, 0.01% to 0.04% of sodium sulfite, and the balance being water; the main agent is sodium alginate and sodium carboxymethyl cellulose, and the cross-linking agent is chromium acetate and chromium citrate.

7. The use according to claim 4, characterized in that The mass ratio of the sodium alginate to the sodium carboxymethyl cellulose is 1:2 to 2:1; the mass ratio of the chromium acetate to the chromium citrate is 2:1 to 5:

1.

8. The use according to claim 4, characterized in that In S1, the amount of the gel front plug is 500t to 800t, and the displacement is 1t / h to 5t / h; the amount of clean water displacement is 10t to 30t; and the waiting time for coagulation is 72h.

9. The use according to claim 4, characterized in that The usage of the carbon dioxide main body slug is 500t to 1000t, the displacement is 5t / h to 10t / h; and the setting time is 20d to 40d.

10. The use according to claim 5, characterized in that The amount of the gel rear plug is 10t to 50t, and the displacement is 1t / h to 5t / h; the amount of the clean water displacement is 10t to 30t.

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