Extra-high water content oil reservoir oil displacement method

Abstract

The invention provides an extra-high water content oil reservoir oil displacement method which comprises the following steps: injecting water into an oil reservoir for water displacement until the water content of the oil reservoir is greater than 90%; respectively injecting a polymer solution and a supercritical carbon dioxide oil displacement agent; after the polymer solution or the supercritical carbon dioxide oil displacement agent is injected, water is injected for water flooding; wherein the injection amounts of the polymer solution and the supercritical carbon dioxide oil-displacing agent are respectively not less than 0.1 PV, and the total injection amount of the polymer solution and the supercritical carbon dioxide oil-displacing agent is 0.3-1.2 PV; the viscosity ratio of the polymer solution to the crude oil in the oil reservoir is 1: (0.8-10), and the viscosity ratio of the supercritical carbon dioxide oil displacement agent to the crude oil in the oil reservoir is 1: (10-800). By means of the oil displacement method, the swept volume of an oil layer can be remarkably increased, and then the recovery rate of crude oil is effectively increased.

Description

Technical Field

[0001] The invention belongs to the technical field of petroleum and natural gas engineering, and relates to an oil displacement method for an extremely high water-content oil reservoir. Background Art

[0002] my country's oil and gas fields are mainly distributed in continental sedimentary basins, with the characteristics of high viscosity and high wax content. After continuous water injection development, the eastern sandstone oil fields have gradually entered a period of ultra-high water content (water content ≥ 90%), which will make the remaining oil distributed in the upper part of the oil layer difficult to be affected, affecting the recovery rate, but the remaining reserves are still nearly 50%, with great potential. However, the existing oil recovery system cannot efficiently utilize the large amount of remaining oil in low permeability areas and upper parts of the oil layer, mainly affected by factors such as reservoir heterogeneity and gravity differentiation caused by the difference in oil and water density.

[0003] At present, the commonly used displacement systems mainly include carbon dioxide flooding, polymer flooding and supercritical carbon dioxide flooding. Among them, polymer flooding mainly relies on increasing the viscosity of the displacement fluid and reducing the mobility ratio of the displacement fluid and the displaced fluid to expand the swept volume. However, after long-term water flooding and polymer flooding in high-water-cut oil fields, high-seepage channels are usually formed at the bottom of the reservoir, resulting in inefficient or ineffective circulation of the injected medium, aggravated interlayer and intralayer conflicts in the reservoir, and highly dispersed residual oil; although carbon dioxide flooding can improve the recovery rate to a certain extent, carbon dioxide and crude oil have a large mobility ratio, resulting in serious "gas channeling" phenomenon in the top of the actual reservoir, affecting the swept volume and being unfavorable for the displacement of crude oil; the supercritical carbon dioxide (scCO2) oil flooding system has a smaller density than crude oil, and can produce a floating effect inside the formation. It has the potential to mobilize the remaining oil in the low permeability area above the reservoir and the upper area of ​​the mobilized oil layer. It is an oil recovery technology with great development potential. However, there are still many technical problems in the use process, such as premature gas breakthrough and small swept volume, which affect the recovery rate.

[0004] Therefore, it is urgent to develop a new oil recovery method to increase the swept volume of the oil layer and thus improve the oil recovery rate. Summary of the invention

[0005] In view of the above-mentioned defects, the present invention provides an oil recovery method for an ultra-high water-content oil reservoir, which can increase the swept volume of the oil layer and thus effectively improve the recovery rate of crude oil.

[0006] The present invention provides an oil recovery method for an ultra-high water content oil reservoir, comprising the following steps:

[0007] (1) Inject water into the reservoir for water flooding until the water content of the reservoir is greater than 90%;

[0008] (2) injecting a polymer solution and a supercritical carbon dioxide oil displacement agent respectively;

[0009] (3) After the polymer solution or supercritical carbon dioxide oil displacement agent is injected, water is injected for water flooding;

[0010] The injection amount of the polymer solution and the supercritical carbon dioxide oil-displacing agent is not less than 0.1 PV respectively, and the total injection amount of the polymer solution and the supercritical carbon dioxide oil-displacing agent is 0.3-1.2 PV;

[0011] The viscosity ratio of the polymer solution to the crude oil in the oil reservoir is 1:(0.8-10), and the viscosity ratio of the supercritical carbon dioxide oil displacement agent to the crude oil in the oil reservoir is 1:(10-800).

[0012] Furthermore, the viscosity of the polymer solution is not less than 1 mPa·s;

[0013] And / or, the viscosity of the supercritical carbon dioxide oil displacement agent is greater than the viscosity of pure supercritical carbon dioxide and less than the viscosity of crude oil in the oil reservoir.

[0014] Furthermore, the injection amount of the polymer solution is 0.1 to 0.6 PV, and / or the injection amount of the supercritical carbon dioxide oil displacement agent is 0.1 to 0.6 PV.

[0015] Further, step (2) is executed repeatedly;

[0016] The injection amount of the polymer solution is 0.05-0.2 PV, and the injection amount of the supercritical carbon dioxide oil displacement agent is 0.05-0.2 PV.

[0017] Furthermore, the internal pressure of the oil reservoir is less than the miscibility pressure of the supercritical carbon dioxide oil-displacing agent and crude oil.

[0018] Further, the polymer solution includes a polymer and water;

[0019] The polymer includes at least one of xanthan gum, a cross-linked polymer, a hydrophobic associating polymer, a comb polymer, and a star polymer.

[0020] Furthermore, the polymer solution also includes a surfactant and an alkaline compound;

[0021] The surfactant includes at least one of a nonionic surfactant, an anionic surfactant, and a zwitterionic surfactant;

[0022] The alkaline compound includes at least one of sodium hydroxide, sodium carbonate, sodium bicarbonate and ammonium hydroxide.

[0023] Furthermore, the average molecular weight of the polymer is 3 million to 21 million.

[0024] Furthermore, the supercritical carbon dioxide oil displacement agent comprises supercritical carbon dioxide and a base liquid dissolved in the supercritical carbon dioxide, and the base liquid comprises a thickener, a cosolvent, and water;

[0025] In the base liquid, the mass percentage of the thickener is 0.05-3wt%, the mass percentage of the co-solvent is 0.05-6wt%, and the balance is water;

[0026] The co-solvent includes at least one of kerosene, ether and n-decane.

[0027] Further, the thickener includes at least one of a siloxane thickener and a hydrocarbon thickener;

[0028] The siloxane thickener includes at least one of the compound shown in Formula 1, the compound shown in Formula 2, and the compound shown in Formula 3.

[0029]

[0030] In Formula 1, x and y are each independently selected from positive integers; in Formula 2, i, j, and k are each independently selected from positive integers; in Formula 3, h is selected from positive integers;

[0031] The hydrocarbon thickener includes at least one of the compound shown in Formula 4, the compound shown in Formula 5, and the compound shown in Formula 6.

[0032]

[0033] In Formula 4, a, b, and c are each independently selected from positive integers; in Formula 5, n is selected from a positive integer; and in Formula 6, m is selected from a positive integer.

[0034] The invention discloses an oil recovery method for an ultra-high water-content oil reservoir. The method comprises the following steps: firstly water-flooding the oil layer, displacing the crude oil at the bottom of the oil layer, and when the water content of the oil layer is greater than 90%, injecting a polymer solution of not less than 0.1 PV and a supercritical carbon dioxide oil recovery agent of not less than 0.1 PV into the oil layer, and the total injection amount of the polymer solution and the supercritical carbon dioxide oil recovery agent is 0.3-1.2 PV, and further displacing the crude oil at the bottom of the oil layer and the top of the oil layer respectively; wherein, when the viscosity ratio of the polymer solution to the crude oil in the oil reservoir is 1:(0.8-10), the polymer solution can not only block the dominant seepage channel formed by water flooding, but also increase the subsequent water flooding. The swept volume of flooding and polymer flooding can also form a larger viscosity ratio with crude oil, weaken the "fingering phenomenon", thereby increasing the swept volume of the polymer solution and improving the recovery rate of crude oil. At the same time, since the polymer solution has a certain viscoelasticity, it can also squeeze out the crude oil in the throat or blind end of the roar channel to improve the oil washing efficiency; and the supercritical carbon dioxide flooding agent will spread to the upper part of the oil layer. When the viscosity ratio of the supercritical carbon dioxide flooding agent to the crude oil in the reservoir is 1: (10~800), the "fingering phenomenon" can be weakened, the swept volume can be further increased, the recovery rate can be improved, and then water flooding can be carried out to comprehensively improve the crude oil recovery rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 is the oil-water relative permeability curve of the ideal numerical simulation model of the five-point method of the present invention;

[0036] Figure 2 The oil and gas relative permeability curve of the ideal numerical simulation model of the five-point method of the present invention;

[0037] Figure 3 It is the original reservoir oil saturation diagram in the ideal numerical simulation model of the five-point method of the present invention;

[0038] Figure 4 It is the oil saturation diagram of the reservoir when the water content of the reservoir reaches 90% in the ideal numerical simulation model of the five-point method of the present invention;

[0039] Figure 5 This is the oil saturation diagram of the reservoir after injecting 0.2PV polymer solution in Example 2 of the present invention;

[0040] Figure 6 This is the oil saturation diagram of the reservoir after the injection of 0.2PV supercritical carbon dioxide oil displacement agent in Example 2 of the present invention;

[0041] Figure 7 The oil saturation diagram of the oil reservoir when the water content of the oil reservoir reaches 98% or more in Example 2 of the present invention;

[0042] Figure 8 This is the oil saturation diagram of the reservoir after injecting 0.1 PV polymer solution in Example 3 of the present invention;

[0043] Fig. 9 This is the oil saturation diagram of the reservoir after injecting 0.1 PV supercritical carbon dioxide oil displacement agent in Example 3 of the present invention;

[0044] Fig.10 This is the oil saturation diagram of the reservoir after injecting 0.1 PV polymer solution in Example 3 of the present invention;

[0045] Fig.11 This is the oil saturation diagram of the reservoir after the injection of 0.1 PV supercritical carbon dioxide oil displacement agent in Example 3 of the present invention;

[0046] Fig.12 The oil saturation diagram of the oil reservoir when the water content of the oil reservoir reaches 98% or more in Example 3 of the present invention;

[0047] Fig.13 This is the oil saturation diagram of the reservoir after injecting 0.4 PV polymer solution in Comparative Example 4 of the present invention;

[0048] Fig.14 The oil saturation diagram of the oil reservoir when the water content of the oil reservoir reaches 98% or more in Comparative Example 4 of the present invention;

[0049] Fig.15 This is the oil saturation diagram of the reservoir after injecting 0.4PV supercritical carbon dioxide oil displacement agent in comparative example 9 of the present invention

[0050] Fig.16 The oil saturation diagram of the oil reservoir when the water content of the oil reservoir reaches 98% or more in Comparative Example 9 of the present invention;

[0051] Fig.17 It is a trend diagram of the recovery rate changing with the injection volume in Examples 11 to 16, Examples 19 to 22 and Comparative Example 14 of the present invention;

[0052] Fig.18 is a graph showing the variation trend of the recovery factor with the injection volume in Example 17 of the present invention;

[0053] Fig.19 This is a graph showing the variation trend of the recovery factor with the injection volume in Example 18 of the present invention. DETAILED DESCRIPTION

[0054] In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are 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.

[0055] The present invention provides an oil recovery method for an ultra-high water content oil reservoir, comprising the following steps:

[0056] (1) Inject water into the reservoir for water flooding until the water content of the reservoir is greater than 90%;

[0057] (2) injecting a polymer solution and a supercritical carbon dioxide oil displacement agent respectively;

[0058] (3) After the polymer solution or supercritical carbon dioxide flooding agent is injected, water is injected for water flooding;

[0059] The injection volume of the polymer solution and the supercritical carbon dioxide oil displacement agent is not less than 0.1PV respectively, and the total injection volume of the polymer solution and the supercritical carbon dioxide oil displacement agent is 0.3-1.2PV;

[0060] The viscosity ratio of the polymer solution to the crude oil in the reservoir is 1:(0.8-10), and the viscosity ratio of the supercritical carbon dioxide flooding agent to the crude oil in the reservoir is 1:(10-800).

[0061] For example, the total injection volume of the polymer solution and the supercritical carbon dioxide flooding agent is 0.3PV, 0.4PV, 0.5PV, 0.6PV, 0.7PV, 0.8PV, 0.9PV, 1.0PV, 1.1PV or 1.2PV.

[0062] For example, the viscosity ratio of the polymer solution to the crude oil in the reservoir is 1:0.8, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9 or 1:10.

[0063] For example, the viscosity ratio of the supercritical carbon dioxide flooding agent to the crude oil in the reservoir is 1:10, 1:100, 1:200, 1:300, 1:400, 1:500, 1:600, 1:700 or 1:800.

[0064] Specifically, in step (1), the water content of the reservoir can be calculated by formula 1:

[0065] Moisture content (%) = V1 / (V1+V2) Formula 1

[0066] In Formula 1, V1 represents the volume of crude oil recovered, and V2 represents the volume of water recovered.

[0067] The present invention does not impose any particular limitation on the thickness of the oil reservoir. Preferably, the thickness of the oil reservoir is not less than 10 m.

[0068] In step (2), a polymer solution and a supercritical carbon dioxide oil-displacing agent are respectively injected into an oil reservoir having a water content greater than 90%, wherein the injection amount of the polymer solution and the supercritical carbon dioxide oil-displacing agent is not less than 0.1 PV respectively, and the total injection amount of the polymer solution and the supercritical carbon dioxide oil-displacing agent is 0.3-1.2 PV.

[0069] The present invention does not specifically limit the injection order of the polymer solution and the supercritical carbon dioxide oil displacement agent. The polymer solution may be injected first and then the supercritical carbon dioxide oil displacement agent, or the supercritical carbon dioxide oil displacement agent may be injected first and then the polymer solution.

[0070] The supercritical carbon dioxide oil displacement agent in the present invention refers to a system comprising supercritical carbon dioxide (scCO2) and a base fluid dissolved in the supercritical carbon dioxide.

[0071] The supercritical carbon dioxide in the present invention refers to carbon dioxide in a state between liquid and gas under conditions higher than its critical temperature of 31.1° C. and critical pressure of 7.38 MPa.

[0072] In step (3), after the injection of the polymer solution or supercritical carbon dioxide oil displacement agent is completed, water flooding is continued.

[0073] The oil displacement method of the present invention firstly performs water displacement on the oil layer. Since the density of water is greater than that of crude oil, water will flow at the bottom of the oil layer to displace the crude oil at the bottom of the oil layer. When the water content of the oil layer is greater than 90%, a polymer solution of not less than 0.1PV and a supercritical carbon dioxide oil displacement agent of not less than 0.1PV are injected into the oil layer, and the total injection amount of the polymer solution and the supercritical carbon dioxide oil displacement agent is 0.3-1.2PV, respectively, to further displace the crude oil at the bottom and top of the oil layer. The density of the polymer solution is greater than that of the crude oil, and the polymer solution will flow at the bottom of the oil layer to block the dominant seepage channel formed by water displacement, thereby increasing the swept volume of subsequent water displacement and polymer displacement, and improving the crude oil recovery rate. The viscosity ratio of the polymer solution to the crude oil is When the viscosity ratio of supercritical carbon dioxide flooding agent to crude oil is 1:(0.8-10), a larger viscosity ratio can be formed with crude oil, the "fingering phenomenon" can be weakened, thereby further increasing the swept volume of the polymer solution and improving the recovery rate of crude oil. At the same time, since the polymer solution has a certain viscoelasticity, the crude oil in the throat or blind end of the roar channel can be squeezed out to improve the oil washing efficiency. The density of the supercritical carbon dioxide flooding agent is less than that of the crude oil, so it will sweep to the upper part of the oil layer and increase the swept volume. When the viscosity ratio of the supercritical carbon dioxide flooding agent to the crude oil in the reservoir is 1:(10-800), a larger viscosity ratio can be formed with crude oil, the "fingering phenomenon" can be weakened, the swept volume can be further increased, and then the recovery rate can be improved. After that, water flooding can be carried out to comprehensively improve the recovery rate of crude oil.

[0074] In addition, in the oil recovery method of the present invention, after the supercritical carbon dioxide oil recovery agent is injected, the density of the supercritical carbon dioxide oil recovery agent is close to the density of crude oil, so it can avoid the supercritical carbon dioxide oil recovery agent directly passing through the top of the oil layer during the oil recovery process due to its too low density, thereby further improving the recovery rate of crude oil.

[0075] In a specific embodiment, the viscosity of the polymer solution is not less than 1 mPa·s. Within this range, the polymer solution can form a larger viscosity ratio with the crude oil in the reservoir, further increasing the swept volume, thereby improving the oil recovery rate.

[0076] In a specific embodiment, the viscosity of the supercritical carbon dioxide oil-displacing agent is greater than the viscosity of pure supercritical carbon dioxide and less than the viscosity of crude oil in the oil reservoir. The inventors of the present invention have found that when the viscosity of the supercritical carbon dioxide oil-displacing agent is greater than the viscosity of crude oil in the oil reservoir, it is not conducive to further increasing the swept volume. Therefore, when the viscosity of the supercritical carbon dioxide oil-displacing agent is greater than the viscosity of pure supercritical carbon dioxide and less than the viscosity of crude oil in the oil reservoir, the volume of crude oil swept by supercritical carbon dioxide injected into the oil reservoir can be further increased; at the same time, the cost can also be reduced.

[0077] In a specific embodiment, the injection volume of the polymer solution is 0.1 to 0.6 PV. For example, the injection volume of the polymer solution is 0.1 PV, 0.2 PV, 0.3 PV, 0.4 PV, 0.5 PV or 0.6 PV. Within this range, not only can the swept volume of the polymer solution be further increased, the recovery rate can be improved, but also the cost can be reduced to achieve economic maximization.

[0078] In a specific embodiment, the injection amount of the supercritical carbon dioxide oil displacement agent is 0.1 to 0.6 PV. For example, the injection amount of the supercritical carbon dioxide oil displacement agent is 0.1 PV, 0.2 PV, 0.3 PV, 0.4 PV, 0.5 PV or 0.6 PV. Within this range, the supercritical carbon dioxide oil displacement agent can achieve a higher swept volume in the reservoir while also saving costs.

[0079] In one embodiment, step (2) is performed in multiple cycles;

[0080] The injection amount of the polymer solution is 0.05-0.2 PV, and the injection amount of the supercritical carbon dioxide flooding agent is 0.05-0.2 PV. By performing step (2) in multiple cycles, that is, alternately injecting the polymer solution and the supercritical carbon dioxide flooding agent, a larger swept volume can be achieved, which can further improve the oil recovery rate.

[0081] The present invention does not specifically limit the number of cycles, and only requires that the injection amount of the polymer solution and the supercritical carbon dioxide oil displacement agent each time be between 0.05 and 0.2 PV. For example, the injection amount of the polymer solution each time is 0.05 PV, 0.1 PV, 0.15 PV or 0.2 PV; for example, the injection amount of the supercritical carbon dioxide oil displacement agent each time is 0.05 PV, 0.1 PV, 0.15 PV or 0.2 PV.

[0082] The present invention does not impose any particular limitation on the number of times the polymer solution and the supercritical carbon dioxide oil displacement agent are injected. For example, the polymer solution may be injected n times and the supercritical carbon dioxide oil displacement agent may be injected n+1 times; the polymer solution may be injected n times and the supercritical carbon dioxide oil displacement agent may be injected n-1 times; or the polymer solution may be injected n times and the supercritical carbon dioxide oil displacement agent may be injected n times.

[0083] In a specific embodiment, the internal pressure of the oil reservoir is less than the miscibility pressure of the supercritical carbon dioxide oil displacement agent and the crude oil. The miscibility pressure refers to the minimum pressure at which the supercritical carbon dioxide oil displacement agent reaches miscibility with the crude oil in the oil reservoir at the oil layer temperature. When the internal pressure of the oil reservoir is less than the miscibility pressure of the supercritical carbon dioxide oil displacement agent and the crude oil, the crude oil displacement effect can be improved, thereby improving the crude oil recovery rate.

[0084] In a specific embodiment, the polymer solution includes a polymer and water; the polymer includes at least one of xanthan gum, a cross-linked polymer, a hydrophobic associating polymer, a comb polymer, and a star polymer. It can be understood that the above five types of compounds include multiple specific compounds, and the selected compounds in the present invention can be well dispersed and dissolved in water. When the aforementioned polymer is a mixture of multiple specific compounds, the present invention does not make too many restrictions on the ratio between the specific compounds.

[0085] The present invention does not impose any specific restrictions on the ratio of polymer to water, and it is only necessary that the viscosity of the polymer solution prepared by the polymer and water and the viscosity of the crude oil be in the ratio of 1: (0.8-10).

[0086] The present invention does not impose any particular limitation on the source of the polymer, and any commercially available product or a product prepared by a conventional preparation method well known to those skilled in the art may be used.

[0087] In one embodiment, the polymer solution further comprises a surfactant and an alkaline compound;

[0088] The surfactant includes at least one of a nonionic surfactant, an anionic surfactant, and a zwitterionic surfactant;

[0089] The alkaline compound includes at least one of sodium hydroxide, sodium carbonate, sodium bicarbonate, and ammonium hydroxide.

[0090] Further, the nonionic surfactant includes at least one of a long-chain amino surfactant, a long-chain guanidine surfactant, and an alkyl glycoside; the anionic surfactant can be selected from a long-chain carboxylate and / or a long-chain sulfate; the zwitterionic surfactant can be selected from a carboxylic acid betaine and / or a sulfobetaine. Among them, the long-chain amino surfactant can be, for example, a long-chain alkylamide dimethylamine such as erucic acid amide alkyl dimethylamine (erucic acid amide propyl dimethylamine), and the long-chain guanidine surfactant can be a long-chain alkyl tetramethylguanidine such as dodecyltetramethylguanidine; the long-chain carboxylate can be selected from at least one of sodium oleate, potassium oleate, and sodium linoleate; the long-chain sulfate can be a long-chain alkyl sodium sulfate such as sodium dodecyl sulfate; the carboxylic acid betaine can be selected from a long-chain alkyl carboxylic acid betaine and / or a fatty amide carboxylic acid betaine; the sulfobetaine can be selected from at least one of a long-chain alkyl sulfobetaine, a fatty amide propyl sulfobetaine, and a fatty amide hydroxypropyl sulfobetaine. Specifically, the above-mentioned "long chain" generally refers to C12 or above, such as C12-C18, etc. When the above-mentioned surfactant is a mixture of multiple specific compounds, the present invention does not impose too many restrictions on the ratio between the specific compounds.

[0091] The present invention does not specifically limit the source of the surfactant, and any commercially available product or a product prepared by a conventional preparation method well known to those skilled in the art may be used.

[0092] Furthermore, when the basic compound is a mixture of multiple specific compounds, the present invention does not impose too many restrictions on the ratios between the specific compounds.

[0093] In a specific embodiment, the average molecular weight of the polymer is 3 million to 21 million. For example, the average molecular weight of the polymer is 3 million, 5 million, 7 million, 9 million, 11 million, 13 million, 15 million, 17 million, 19 million or 21 million. Within this range, it can better match the pore throat size inside the oil reservoir, further improving the recovery effect of crude oil.

[0094] In a specific embodiment, the supercritical carbon dioxide oil displacement agent includes supercritical carbon dioxide and a base liquid dissolved in the supercritical carbon dioxide, and the base liquid includes a thickener, a cosolvent, and water;

[0095] In the base liquid, the mass percentage of the thickener is 0.05-3wt%, the mass percentage of the co-solvent is 0.05-6wt%, and the balance is water;

[0096] The auxiliary solvent includes at least one of kerosene, ether and n-decane.

[0097] For example, the mass percentage of the thickener is 0.05wt%, 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt% or 3wt%, and the mass percentage of the co-solvent is 0.05wt%, 1wt%, 2wt%, 3wt%, 4wt%, 5wt% or 6wt%.

[0098] When the composition of the supercritical carbon dioxide oil displacement agent is the above composition and the mass percentage of each component is within the above range, the viscosity characteristics of the supercritical carbon dioxide oil displacement agent can be further improved, thereby improving its viscosity ratio with crude oil, and further increasing the crude oil recovery rate.

[0099] The present invention does not specifically limit the ratio of supercritical carbon dioxide oil displacement agent to base liquid, and only requires that the viscosity ratio of the supercritical carbon dioxide oil displacement agent prepared by supercritical carbon dioxide and base liquid to the crude oil in the reservoir be between 1: (10-800).

[0100] In a specific embodiment, the thickener includes at least one of a silicone thickener and a hydrocarbon thickener;

[0101] The siloxane thickener includes at least one of the compound represented by Formula 1, the compound represented by Formula 2, and the compound represented by Formula 3.

[0102]

[0103] In Formula 1, x and y are each independently selected from positive integers; in Formula 2, i, j, and k are each independently selected from positive integers; in Formula 3, h is selected from positive integers;

[0104] The hydrocarbon thickener includes at least one of the compound shown in Formula 4, the compound shown in Formula 5, and the compound shown in Formula 6.

[0105]

[0106]

[0107] In Formula 4, a, b, and c are each independently selected from positive integers; in Formula 5, n is selected from a positive integer; and in Formula 6, m is selected from a positive integer.

[0108] The present invention does not specifically limit the source of the thickener, and any commercially available product or a product prepared by a conventional preparation method well known to those skilled in the art may be used.

[0109] The present invention does not limit the preparation method of the supercritical carbon dioxide oil-displacing agent. For example, the supercritical carbon dioxide oil-displacing agent can be prepared by a method comprising the following process:

[0110] Add the thickener and the cosolvent into water, stir until dissolved, and prepare a base liquid; under the supercritical condition of carbon dioxide, mix and dissolve the base liquid with supercritical carbon dioxide to obtain a supercritical carbon dioxide oil-displacing agent. Generally, the conventional method in the art can be used to regulate the above-mentioned supercritical condition of carbon dioxide. In one embodiment, a conventional intermediate container can be used to prepare a supercritical carbon dioxide oil-displacing agent, and the supercritical condition that makes carbon dioxide in a supercritical state is controlled by regulating the temperature and pressure in the intermediate container. Specifically, the interior of the intermediate container is divided into an upper part and a lower part by a piston, and the upper part is used to prepare a supercritical carbon dioxide oil-displacing agent, and the lower part contains water and other media, and the lower part can be connected to a device containing water and other media through an ISCO pump, etc., and the ISCO pump can be used to introduce / absorb water and other media into the lower part of the intermediate container, so that the piston moves, and the volume of the upper part of the intermediate container is changed, thereby realizing the control of the pressure on the upper part of the intermediate container; at the same time, the intermediate container can be placed in a thermostat to realize the control of the temperature in the intermediate container.

[0111] Hereinafter, the method for oil recovery from an ultra-high water-content reservoir including the present invention will be described in detail through specific examples using different methods.

[0112] 1. Numerical simulation method

[0113] In order to study the oil recovery effect of the method for recovering oil from an ultra-high water-content reservoir of the present invention, an ideal model of a 5-point well pattern including 1 injection well and 4 production wells was established. The model includes three phases: gas, water, and oil. A black oil simulator was used. Under a fixed injection rate system, the injection rate of the polymer solution was 1000 m / s. 3 / d, the injection rate of supercritical carbon dioxide flooding agent is 12000m 3 / d, the bottom hole pressure of the injection well is 40MPa; the bottom hole pressure of the production well is 8MPa, and the simulation time is 60 years. Table 1 shows the basic parameters of the ideal numerical simulation model of the five-point method. Figure 1 is the oil-water relative permeability curve of the ideal numerical simulation model of the five-point method, Figure 2 is the oil and gas relative permeability curve of the ideal numerical simulation model of the five-point method, Figure 3 This is the oil saturation diagram of the original reservoir in the ideal numerical simulation model of the five-point method.

[0114] Table 1

[0115] parameter Parameter Value Grid Dimension I*J*K=80*80*10 Grid size (m) L*W*H=10*10*3 Depth(m) 500 <![CDATA[Permeability (10 -3 μm 2 )]]> PERMX*PERMX*PERMX=500*500*50 Porosity 0.28 <![CDATA[Density (kg / m 3 )]]> <![CDATA[Water: 1000; Crude oil: 850; Polymer solution: 1000; scCO2: 540]]> Viscosity (mPa·s) <![CDATA[Water: 0.6; Crude oil: 12; Polymer solution: 8; scCO2: 0.014]]> <![CDATA[Polymer solution concentration (kg / m 3 )]]> 0.8

[0116] The above reservoir model was flooded with water until the water content reached 90%, at which time the crude oil recovery was 26.25%. On the basis that the water content of the reservoir reached 90%, the crude oil recovery under different flooding methods was simulated. Figure 4 This is the oil saturation diagram of the reservoir when the water content of the reservoir reaches 90% in the ideal numerical simulation model of the five-point method.

[0117] Example 1

[0118] 0.2PV of supercritical carbon dioxide flooding agent (viscosity of 1.12mPa·s) was further injected into the above-mentioned reservoir model with a water content of 90%, and then 0.2PV of polymer solution (viscosity of 8mPa·s) was injected, and then water flooding was carried out. When the water content of the reservoir reached more than 98%, the crude oil recovery rate was 62.81%.

[0119] Example 2

[0120] 0.2PV of polymer solution (viscosity of 8mPa·s) was further injected into the above-mentioned reservoir model with a water content of 90%, and then 0.2PV of supercritical carbon dioxide oil displacement agent (viscosity of 1.12mPa·s) was injected, and then water flooding was carried out. When the water content of the reservoir reached more than 98%, the crude oil recovery rate was 62.15%.

[0121] Figure 5 This is the oil saturation diagram of the reservoir after injecting 0.2PV polymer solution. Figure 6 This is the oil saturation diagram of the reservoir after injecting 0.2PV supercritical carbon dioxide flooding agent. Figure 7 This is the oil saturation diagram of the reservoir when the water content of the reservoir reaches more than 98%.

[0122] Example 3

[0123] 0.1PV of polymer solution (viscosity of 8mPa·s) was continued to be injected into the above-mentioned reservoir model with a water content of 90%, and then 0.1PV of supercritical carbon dioxide oil displacement agent (viscosity of 1.12mPa·s) was injected. Then 0.1PV of polymer solution (viscosity of 8mPa·s) and 0.1PV of supercritical carbon dioxide oil displacement agent (viscosity of 1.12mPa·s) were injected in sequence and then water flooding was carried out. When the water content of the reservoir reached more than 98%, the crude oil recovery factor was 64.11%.

[0124] Figure 8 This is the oil saturation diagram of the reservoir after injecting 0.1PV polymer solution. Fig. 9 This is the oil saturation diagram of the reservoir after injecting 0.1PV supercritical carbon dioxide flooding agent. Fig.10 This is the oil saturation diagram of the reservoir after injecting 0.1 PV polymer solution. Fig.11 This is the oil saturation diagram of the reservoir after injecting 0.1PV supercritical carbon dioxide flooding agent. Fig.12 This is the oil saturation diagram of the reservoir when the water content of the reservoir reaches more than 98%.

[0125] Example 4

[0126] Into the above-mentioned reservoir model with a water content of 90%, 0.05 PV of polymer solution (viscosity of 8 mPa·s) and 0.05 PV of supercritical carbon dioxide oil displacement agent (viscosity of 1.12 mPa·s) were injected in sequence. The injection was cyclically injected four times according to the above-mentioned injection method, and then water flooding was carried out. When the water content of the reservoir reached more than 98%, the crude oil recovery rate was 81.31%.

[0127] Example 5

[0128] The method for flooding an ultra-high water-content reservoir in this embodiment is basically the same as that in Example 1, except that the injection amount of the polymer solution is changed, specifically: 0.2PV of supercritical carbon dioxide flooding agent (viscosity of 1.12mPa·s) is continuously injected into the reservoir model with a water content of 90%, and then 0.8PV of polymer solution (viscosity of 8mPa·s) is injected, and then water flooding is performed. When the water content of the reservoir reaches more than 98%, the crude oil recovery factor is 73.34%.

[0129] Example 6

[0130] The method for flooding an ultra-high water-content reservoir in this embodiment is basically the same as that in Example 1, except that the injection amount of the supercritical carbon dioxide flooding agent is changed, specifically: 0.8PV of supercritical carbon dioxide flooding agent (viscosity of 1.12mPa·s) is continued to be injected into the reservoir model with a water content of 90%, and then 0.2PV of polymer solution (viscosity of 8mPa·s) is injected, and then water flooding is performed. When the water content of the reservoir reaches more than 98%, the crude oil recovery factor is 74.48%.

[0131] Comparative Example 1

[0132] Water is continuously injected into the reservoir model with a water content of 90% to carry out water flooding. When the water content of the reservoir reaches above 98%, the crude oil recovery rate is 44.15%.

[0133] Comparative Example 2

[0134] 0.2 PV of polymer solution (viscosity of 8 mPa·s) was continuously injected into the reservoir model with a water content of 90%, and then water flooding was performed. When the water content of the reservoir reached more than 98%, the crude oil recovery rate was 45.60%.

[0135] Comparative Example 3

[0136] 0.2 PV of pure supercritical carbon dioxide (viscosity 0.014 mPa·s) was continuously injected into the reservoir model with a water content of 90%, and then water flooding was performed. When the water content of the reservoir reached more than 98%, the crude oil recovery rate was 46.17%.

[0137] Comparative Example 4

[0138] 0.4 PV of polymer solution (viscosity of 8 mPa·s) was continuously injected into the reservoir model with a water content of 90%, and then water flooding was performed. When the water content of the reservoir reached more than 98%, the crude oil recovery rate was 48.18%.

[0139] Fig.13 This is the oil saturation diagram of the reservoir after injecting 0.4PV polymer solution. Fig.14 This is the oil saturation diagram of the reservoir when the water content of the reservoir reaches more than 98%.

[0140] Comparative Example 5

[0141] 0.4 PV of pure supercritical carbon dioxide (viscosity 0.014 mPa·s) was continuously injected into the reservoir model with a water content of 90%, and then water flooding was performed. When the water content of the reservoir reached more than 98%, the crude oil recovery rate was 46.95%.

[0142] Comparative Example 6

[0143] 0.4 PV of supercritical carbon dioxide flooding agent (viscosity of 0.14 mPa·s) was continuously injected into the above reservoir model with a water content of 90%, and then water flooding was performed. When the water content of the reservoir reached more than 98%, the crude oil recovery rate was 52.50%.

[0144] Comparative Example 7

[0145] 0.4 PV of supercritical carbon dioxide flooding agent (viscosity of 0.28 mPa·s) was continuously injected into the above reservoir model with a water content of 90%, and then water flooding was performed. When the water content of the reservoir reached more than 98%, the crude oil recovery rate was 55.36%.

[0146] Comparative Example 8

[0147] 0.4 PV of supercritical carbon dioxide flooding agent (viscosity of 0.56 mPa·s) was continuously injected into the above reservoir model with a water content of 90%, and then water flooding was performed. When the water content of the reservoir reached more than 98%, the crude oil recovery rate was 50.45%.

[0148] Comparative Example 9

[0149] 0.4 PV of supercritical carbon dioxide flooding agent (viscosity of 1.12 mPa·s) was continuously injected into the above reservoir model with a water content of 90%, and then water flooding was performed. When the water content of the reservoir reached more than 98%, the crude oil recovery rate was 54.22%.

[0150] Fig.15 This is the oil saturation diagram of the reservoir after injecting 0.4PV supercritical carbon dioxide flooding agent. Fig.16 This is the oil saturation diagram of the reservoir when the water content of the reservoir reaches more than 98%.

[0151] Comparative Example 10

[0152] The method for flooding an ultra-high water-content reservoir in this comparative example is basically the same as that in Example 1, except that the injection amounts of the supercritical carbon dioxide flooding agent and the polymer solution are changed so that the injection amounts of both are lower than 0.1PV, specifically: 0.08PV of supercritical carbon dioxide flooding agent (viscosity of 1.12mPa·s) is continuously injected into the reservoir model with a water content of 90%, and then 0.08PV of polymer solution (viscosity of 8mPa·s) is injected, and then water flooding is performed. When the water content of the reservoir reaches more than 98%, the crude oil recovery factor is 43.40%.

[0153] Comparative Example 11

[0154] The method for flooding an ultra-high water-content reservoir in this comparative example is basically the same as that in Example 1, except that the injection amounts of the supercritical carbon dioxide flooding agent and the polymer solution are changed so that the total injection amount of the two is greater than 1.2PV, specifically: 0.65PV of supercritical carbon dioxide flooding agent (viscosity of 1.12mPa·s) is continuously injected into the reservoir model with a water content of 90%, and then 0.65PV of polymer solution (viscosity of 8mPa·s) is injected, and then water flooding is performed. When the water content of the reservoir reaches more than 98%, the crude oil recovery factor is 76.28%.

[0155] Comparative Example 12

[0156] The method for flooding an ultra-high water-content reservoir in this comparative example is basically the same as that in Example 1, except that the viscosity of the polymer solution is changed so that the viscosity ratio of the polymer solution to the crude oil in the reservoir is 1:0.6, specifically: 0.2PV of supercritical carbon dioxide flooding agent (viscosity of 1.12mPa·s) is continuously injected into the reservoir model with a water content of 90%, and then 0.2PV of polymer solution (viscosity of 20mPa·s) is injected, and then water flooding is performed. When the water content of the reservoir reaches more than 98%, the crude oil recovery factor is 51.73%.

[0157] Comparative Example 13

[0158] The method for flooding an ultra-high water-content reservoir in this comparative example is basically the same as that in Example 1, except that the viscosity of the polymer solution is changed so that the viscosity ratio of the polymer solution to the crude oil in the reservoir is 1:12, specifically: 0.2PV of supercritical carbon dioxide flooding agent (viscosity of 1.12mPa·s) is continuously injected into the reservoir model with a water content of 90%, and then 0.2PV of polymer solution (viscosity of 1mPa·s) is injected, and then water flooding is performed. When the water content of the reservoir reaches more than 98%, the crude oil recovery factor is 43.02%.

[0159] Comparative Example 14

[0160] The method for flooding an ultra-high water-content oil reservoir in this comparative example is basically the same as that in Example 1, except that the viscosity of the supercritical carbon dioxide flooding agent is changed so that the viscosity ratio of the supercritical carbon dioxide flooding agent to the crude oil in the reservoir is 1:850, specifically: 0.2PV of supercritical carbon dioxide flooding agent (viscosity of 0.0141mPa·s) is continuously injected into the above-mentioned reservoir model with a water content of 90%, and then 0.2PV of polymer solution (viscosity of 8mPa·s) is injected, and then water flooding is performed. When the water content of the reservoir reaches more than 98%, the crude oil recovery factor is 46.52%.

[0161] See Table 2 for specific data.

[0162] Table 2

[0163]

[0164]

[0165] From Table 1 and Table 2, we can see that:

[0166] The method for oil recovery from an ultra-high water-content reservoir in Examples 1 to 6 can achieve a higher crude oil recovery rate than that of Comparative Examples 1 to 10 and Comparative Examples 12 to 14, up to 81.31%; wherein, although the crude oil recovery rates of Examples 5 and 6 are higher than those of Example 1, during the injection process, the injection amount of the polymer solution or supercritical carbon dioxide oil recovery agent is also larger, so there are deficiencies in terms of improving economic benefits; although the crude oil recovery rate of Comparative Example 11 is higher than that of Example 1, the cost is higher and the economic benefits are lower. It can be seen from this that the method for oil recovery from an ultra-high water-content reservoir of the present invention can increase the swept volume of the oil layer and significantly improve the crude oil recovery rate.

[0167] Depend on Figure 3-Figure 7 It can be seen that in Example 2, when the water content reached 90%, 0.2PV of polymer solution and 0.2PV of thickened supercritical CO2 were injected into the reservoir respectively, and the oil saturation of the reservoir produced a continuous decline process. After water flooding to a water content of 98%, the overall oil saturation of the reservoir was significantly reduced.

[0168] Depend on Figure 8-Figure 12 It can be seen that in Example 3, when the water cut reached 90%, 0.1PV of polymer solution and thickened supercritical CO2 were injected into the reservoir alternately twice, and the overall oil saturation of the reservoir continued to decrease. After water flooding to a water cut of 98%, the final overall oil saturation of the reservoir was higher than that of Example 2, indicating that the increase in the number of alternations has improved the overall recovery rate of the reservoir.

[0169] Fig.13 and Fig.14It can be seen that in Comparative Example 4, after the water content reached 90% and only 0.4PV of polymer solution was injected, compared with the results of Example 2 or Example 3 in which the total alternating injection volume was 0.4PV, the oil saturation field was higher and the surface enhanced oil recovery effect was poor, indicating that the injection method of the present invention is significantly better than the single injection method.

[0170] Fig.15 and Fig.16 It can be seen that in Comparative Example 9, after the water content reached 90%, only 0.4PV of thickened supercritical CO2 was injected. Compared with the results of Example 2 or Example 3 in which the total alternating injection volume was 0.4PV, the oil saturation field was higher and the surface enhanced oil recovery effect was poor, indicating that the injection method of the present invention is significantly better than the single injection method.

[0171] 2. Indoor test method

[0172] In order to study the influence of polymer solutions of different components and supercritical carbon dioxide oil displacement agent of the present invention on oil displacement effect, a cuboid artificial core with a size of 4.5×4.5×30 cm was used, and the average air permeability of the core was 500 mD; the test fluid was prepared, wherein: the simulated oil was crude oil from Daqing Oilfield, with a viscosity of 12 mPa·s, a temperature of 45°C, and a pressure of 10 MPa, and the simulated water ion content was as shown in Table 3.

[0173] Table 3

[0174] Ion type <![CDATA[K + +That + ]]> <![CDATA[Ca 2+ ]]> <![CDATA[HCO3 - ]]> <![CDATA[Cl - ]]> <![CDATA[CO3 2- ]]> Total mineralization Content (mg / L) 1768 122.75 884.79 2357.89 60.02 5193.46

[0175] Step 1: Weigh the core and place it in a core holder. Keep it under a confining pressure of 2MPa and evacuate for 24h. Then connect the inlet of the core holder to simulated water. Use simulated water to displace 30PV at a flow rate of 5mL / min to saturate the core with simulated water. Weigh it again and calculate the porosity.

[0176] Step 2: After the core is saturated with simulated water, simulated oil is used to displace 20 PV at 5 mL / min, and then 10 PV at 10 mL / min. The saturated oil volume is read to calculate the oil saturation;

[0177] Step 3: using the polymer to prepare a polymer solution according to the petroleum and natural gas industry standard SY / T 6576-2003;

[0178] Step 4: The base liquid is introduced into an intermediate container, and then pure supercritical carbon dioxide (viscosity of 0.014 MPa·s) is added to fully dissolve the base liquid to prepare a thickened supercritical carbon dioxide oil displacement agent.

[0179] Step 5: After the core is saturated with simulated oil, it is maintained at a confining pressure of 12 MPa, and simulated water is used to displace at a rate of 0.5 mL / min. After the water content reaches 90%, the oil displacement method of the present invention is used to displace oil. During this process, the pressure, water yield, and oil yield are read every 2 minutes.

[0180] Embodiment 11

[0181] The polymer is a hydrophobic associating polymer (mass percentage is 1wt%), the hydrophobic associating polymer is partially hydrolyzed polyacrylamide (HPAM), the average molecular weight is 16 million, the solid content is greater than 88%, and it is produced by Daqing Refining and Chemical Company of China National Petroleum Corporation. The surfactant is alkyl polyglycoside (APG, mass percentage is 0.1wt%) and sodium hydroxide (mass percentage is 1.2wt%), and a polymer solution with a solution viscosity of 9.5mPa·s is prepared;

[0182] The thickener is polydimethylsiloxane (average molecular weight of 25000, mass percentage of 3wt%), and the cosolvent is kerosene (mass percentage of 2wt%), and the pure supercritical carbon dioxide is thickened by 20 times to obtain a supercritical carbon dioxide oil displacement agent with a viscosity of 0.28MPa·s;

[0183] At an injection pressure of 10 MPa, 0.4 PV of polymer solution and 0.4 PV of supercritical carbon dioxide oil displacement agent were injected into the core with a water content of 90% in sequence, and then water flooding was performed. When the water content reached 98%, the crude oil recovery rate was recorded. The crude oil recovery rate in this embodiment was 86.03%.

[0184] Example 12

[0185] The polymer is xanthan gum (average molecular weight of 16 million, mass percentage of 1wt%), the surfactant is alkyl polyglycoside (APG, mass percentage of 0.1wt%), and the alkali is sodium hydroxide (mass percentage of 1.2wt%), and a polymer solution with a solution viscosity of 7.2mPa·s is prepared;

[0186] The thickener is polydimethylsiloxane (average molecular weight of 25000, mass percentage of 3wt%), and the cosolvent is kerosene (mass percentage of 0.2wt%), and the pure supercritical carbon dioxide is thickened by 5 times to obtain a supercritical carbon dioxide oil displacement agent with a viscosity of 0.07MPa·s;

[0187] At an injection pressure of 10 MPa, 0.4 PV of polymer solution and 0.4 PV of supercritical carbon dioxide oil displacement agent were injected into the core with a water content of 90% in sequence, and then water flooding was performed. When the water content reached 98%, the crude oil recovery factor was recorded. The crude oil recovery factor in this embodiment was 73.12%.

[0188] Embodiment 13

[0189] The polymer used was star polymer SD-6800 (mass percentage of 1wt%), with a solid content of 89.7%, an average molecular weight of 16 million, and a hydrolysis degree of 22.7%, provided by Zhangjiakou Shengda Polymer Priority Company, the surfactant was alkyl polyglycoside (APG, mass percentage of 0.1wt%), and the alkali was sodium hydroxide (mass percentage of 1.2wt%), and a polymer solution with a solution viscosity of 8.2mPa·s was prepared;

[0190] The thickener is polydimethylsiloxane (average molecular weight of 25000, mass percentage of 3wt%), and the cosolvent is kerosene (mass percentage of 6wt%), and the pure supercritical carbon dioxide is thickened by 50 times to obtain a supercritical carbon dioxide oil displacement agent with a viscosity of 0.7MPa·s;

[0191] At an injection pressure of 10 MPa, 0.4 PV of polymer solution and 0.4 PV of supercritical carbon dioxide oil displacement agent were injected into the core with a water content of 90% in sequence, and then water flooding was performed. When the water content reached 98%, the crude oil recovery rate was recorded. The crude oil recovery rate in this embodiment was 88.05%.

[0192] Embodiment 14

[0193] The polymer is a hydrophobic polymer (mass percentage is 1wt%), the hydrophobic associating polymer is partially hydrolyzed polyacrylamide (HPAM), the average molecular weight is 16 million, the solid content is greater than 88%, and it is produced by Daqing Refining and Chemical Company of China National Petroleum Corporation. It is alkyl polyglycoside (APG, mass percentage is 0.1wt%) and sodium hydroxide (mass percentage is 1.2wt%), and a polymer solution with a solution viscosity of 9.5mPa·s is prepared;

[0194] The thickener is vinyl polysiloxane (average molecular weight of 25,000, mass percentage of 3wt%), and the cosolvent is kerosene (mass percentage of 2.5wt%), and the pure supercritical carbon dioxide is thickened by 24 times to obtain a supercritical carbon dioxide oil displacement agent with a viscosity of 0.336MPa·s;

[0195] At an injection pressure of 10 MPa, 0.4 PV of polymer solution and 0.4 PV of supercritical carbon dioxide oil displacement agent were injected into the core with a water content of 90% in sequence, and then water flooding was performed. When the water content reached 98%, the crude oil recovery rate was recorded. The crude oil recovery rate in this embodiment was 90.38%.

[0196] Embodiment 15

[0197] The polymer is a hydrophobic associating polymer (mass percentage is 1wt%), the hydrophobic associating polymer is partially hydrolyzed polyacrylamide (HPAM), the average molecular weight is 16 million, the solid content is greater than 88%, and it is produced by Daqing Refining and Chemical Company of China National Petroleum Corporation. The surfactant is alkyl polyglycoside (APG, mass percentage is 0.1wt%) and sodium hydroxide (mass percentage is 1.2wt%), and a polymer solution with a solution viscosity of 9.5mPa·s is prepared;

[0198] The thickener is polydimethylsiloxane (average molecular weight of 25000, mass percentage of 0.05wt%), and the cosolvent is kerosene (mass percentage of 2wt%), and the pure supercritical carbon dioxide is thickened by 2.5 times to obtain a supercritical carbon dioxide oil displacement agent with a viscosity of 0.035MPa·s;

[0199] At an injection pressure of 10 MPa, 0.4 PV of polymer solution and 0.4 PV of supercritical carbon dioxide oil displacement agent were injected into the core with a water content of 90% in sequence, and then water flooding was performed. When the water content reached 98%, the crude oil recovery rate was recorded. The crude oil recovery rate in this embodiment was 72.01%.

[0200] Example 16

[0201] The polymer is a hydrophobic associating polymer (mass percentage is 1wt%), the hydrophobic associating polymer is partially hydrolyzed polyacrylamide (HPAM), the average molecular weight is 16 million, the solid content is greater than 88%, and it is produced by Daqing Refining and Chemical Company of China National Petroleum Corporation. The surfactant is alkyl polyglycoside (APG, mass percentage is 0.1wt%) and sodium hydroxide (mass percentage is 1.2wt%), and a polymer solution with a solution viscosity of 9.5mPa·s is prepared;

[0202] The thickener is polydimethylsiloxane (average molecular weight of 25000, mass percentage of 2wt%), and the cosolvent is kerosene (mass percentage of 2wt%), and the pure supercritical carbon dioxide is thickened by 13 times to obtain a supercritical carbon dioxide oil displacement agent with a viscosity of 0.182MPa·s;

[0203] At an injection pressure of 10 MPa, 0.4 PV of polymer solution and 0.4 PV of supercritical carbon dioxide oil displacement agent were injected into the core with a water content of 90% in sequence, and then water flooding was performed. When the water content reached 98%, the crude oil recovery rate was recorded. The crude oil recovery rate in this embodiment was 81.23%.

[0204] Embodiment 17

[0205] The polymer is a hydrophobic associating polymer (mass percentage is 1wt%), the hydrophobic associating polymer is partially hydrolyzed polyacrylamide (HPAM), the average molecular weight is 16 million, the solid content is greater than 88%, and it is produced by Daqing Refining and Chemical Company of China National Petroleum Corporation. The surfactant is alkyl polyglycoside (APG, mass percentage is 0.1wt%) and sodium hydroxide (mass percentage is 1.2wt%), and a polymer solution with a solution viscosity of 9.5mPa·s is prepared;

[0206] The thickener is polydimethylsiloxane (average molecular weight of 25000, mass percentage of 3wt%), and the cosolvent is kerosene (mass percentage of 2wt%), and the pure supercritical carbon dioxide is thickened by 20 times to obtain a supercritical carbon dioxide oil displacement agent with a viscosity of 0.28MPa·s;

[0207] At an injection pressure of 10 MPa, 0.8 PV of polymer solution and 0.4 PV of supercritical carbon dioxide oil displacement agent were injected into the core with a water content of 90% in sequence, and then water flooding was performed. When the water content reached 98%, the crude oil recovery rate was recorded. The crude oil recovery rate in this embodiment was 89.80%.

[0208] Embodiment 18

[0209] The polymer is a hydrophobic associating polymer (mass percentage is 1wt%), the hydrophobic associating polymer is partially hydrolyzed polyacrylamide (HPAM), the average molecular weight is 16 million, the solid content is greater than 88%, and it is produced by Daqing Refining and Chemical Company of China National Petroleum Corporation. The surfactant is alkyl polyglycoside (APG, mass percentage is 0.1wt%) and sodium hydroxide (mass percentage is 1.2wt%), and a polymer solution with a solution viscosity of 9.5mPa·s is prepared;

[0210] The thickener is polydimethylsiloxane (average molecular weight of 25000, mass percentage of 3wt%), and the cosolvent is kerosene (mass percentage of 2wt%), and the pure supercritical carbon dioxide is thickened by 20 times to obtain a supercritical carbon dioxide oil displacement agent with a viscosity of 0.28MPa·s;

[0211] At an injection pressure of 10 MPa, 0.4 PV of polymer solution and 0.8 PV of supercritical carbon dioxide oil displacement agent were injected into the core with a water content of 90% in sequence, and then water flooding was performed. When the water content reached 98%, the crude oil recovery rate was recorded. The crude oil recovery rate in this embodiment was 90.08%.

[0212] Embodiment 19

[0213] The polymer is a hydrophobic associating polymer (mass percentage is 1wt%), the hydrophobic associating polymer is partially hydrolyzed polyacrylamide (HPAM), the average molecular weight is 3 million, the solid content is greater than 88%, and it is produced by Daqing Refining and Chemical Company of China National Petroleum Corporation. The surfactant is an alkyl polyglycoside (mass percentage is 0.1wt%) and sodium hydroxide (mass percentage is 1.2wt%), and a polymer solution with a solution viscosity of 2.5mPa·s is prepared;

[0214] The thickener is polydimethylsiloxane (average molecular weight of 25000, mass percentage of 3wt%), and the cosolvent is kerosene (mass percentage of 2wt%), and the pure supercritical carbon dioxide is thickened by 20 times to obtain a supercritical carbon dioxide oil displacement agent with a viscosity of 0.28MPa·s;

[0215] At an injection pressure of 10 MPa, 0.4 PV of polymer solution and 0.4 PV of supercritical carbon dioxide oil displacement agent were injected into the core with a water content of 90% in sequence, and then water flooding was performed. When the water content reached 98%, the crude oil recovery rate was recorded. The crude oil recovery rate in this embodiment was 77.43%.

[0216] Embodiment 20

[0217] The polymer is a hydrophobic associating polymer (mass percentage is 1wt%), the hydrophobic associating polymer is partially hydrolyzed polyacrylamide (HPAM), the average molecular weight is 20 million, the solid content is greater than 88%, and it is produced by Daqing Refining and Chemical Company of China National Petroleum Corporation. The surfactant is an alkyl polyglycoside (mass percentage is 0.1wt%) and sodium hydroxide (mass percentage is 1.2wt%), and a polymer solution with a solution viscosity of 14mPa·s is prepared;

[0218] The thickener is polydimethylsiloxane (average molecular weight of 25000, mass percentage of 3wt%), and the cosolvent is kerosene (mass percentage of 2wt%), and the pure supercritical carbon dioxide is thickened by 20 times to obtain a supercritical carbon dioxide oil displacement agent with a viscosity of 0.28MPa·s;

[0219] At an injection pressure of 10 MPa, 0.4 PV of polymer solution and 0.4 PV of supercritical carbon dioxide oil displacement agent were injected into the core with a water content of 90% in sequence, and then water flooding was performed. When the water content reached 98%, the crude oil recovery rate was recorded. The crude oil recovery rate in this embodiment was 85.36%.

[0220] Embodiment 21

[0221] The polymer is a hydrophobic associating polymer (mass percentage is 1wt%), the hydrophobic associating polymer is partially hydrolyzed polyacrylamide (HPAM), the average molecular weight is 2 million, the solid content is greater than 88%, and it is produced by Daqing Refining and Chemical Company of China National Petroleum Corporation. The surfactant is an alkyl polyglycoside (mass percentage is 0.1wt%) and sodium hydroxide (mass percentage is 1.2wt%), and a polymer solution with a solution viscosity of 1.2mPa·s is prepared;

[0222] The thickener is polydimethylsiloxane (average molecular weight of 25000, mass percentage of 3wt%), and the cosolvent is kerosene (mass percentage of 2wt%), and the pure supercritical carbon dioxide is thickened by 20 times to obtain a supercritical carbon dioxide oil displacement agent with a viscosity of 0.28MPa·s;

[0223] At an injection pressure of 10 MPa, 0.4 PV of polymer solution and 0.4 PV of supercritical carbon dioxide oil displacement agent were injected into the core with a water content of 90% in turn, and then water flooding was performed. When the water content reached 98%, the crude oil recovery rate was recorded. The crude oil recovery rate in this embodiment was 72.22%.

[0224] Embodiment 22

[0225] The polymer is a hydrophobic associating polymer (mass percentage is 1wt%), the hydrophobic associating polymer is partially hydrolyzed polyacrylamide (HPAM), the average molecular weight is 24 million, the solid content is greater than 88%, and it is produced by Daqing Refining and Chemical Company of China National Petroleum Corporation. The surfactant is an alkyl polyglycoside (mass percentage is 0.1wt%) and sodium hydroxide (mass percentage is 1.2wt%), and a polymer solution with a solution viscosity of 15mPa·s is prepared;

[0226] The thickener is polydimethylsiloxane (average molecular weight of 25000, mass percentage of 3wt%), and the cosolvent is kerosene (mass percentage of 2wt%), and the pure supercritical carbon dioxide is thickened by 20 times to obtain a supercritical carbon dioxide oil displacement agent with a viscosity of 0.28MPa·s;

[0227] At an injection pressure of 10 MPa, 0.4 PV of polymer solution and 0.4 PV of supercritical carbon dioxide oil displacement agent were injected into the core with a water content of 90% in sequence, and then water flooding was performed. When the water content reached 98%, the crude oil recovery rate was recorded. The crude oil recovery rate in this embodiment was 83.14%.

[0228] Comparative Example 14

[0229] The polymer is xanthan gum (average molecular weight of 16 million, mass percentage of 0.1wt%), the surfactant is alkyl polyglycoside (APC, mass percentage of 0.1wt%), and the alkali is sodium hydroxide (mass percentage of 1.2wt%), and a polymer solution with a solution viscosity of 0.8mPa·s is prepared;

[0230] The thickener is polydimethylsiloxane (average molecular weight of 25000, mass percentage of 3wt%), and the cosolvent is kerosene (mass percentage of 2wt%), and the pure supercritical carbon dioxide is thickened by 20 times to obtain a supercritical carbon dioxide oil displacement agent with a viscosity of 0.28MPa·s;

[0231] At an injection pressure of 10 MPa, 0.4 PV of polymer solution and 0.4 PV of supercritical carbon dioxide oil displacement agent were injected into the core with a water content of 90% in sequence, and then water flooding was performed. When the water content reached 98%, the crude oil recovery factor was recorded. The crude oil recovery factor in this embodiment was 69.15%.

[0232] For detailed data, see Table 4 and Figure 17-Figure 19 .

[0233] Table 4

[0234]

[0235] From Table 3 and Table 4, we can see that:

[0236] Examples 11 to 22 respectively use different polymers and thickeners to displace extremely high water-content reservoirs at different viscosities, and can achieve a high recovery rate, up to 90.38%; while the recovery rate of comparative example 14 is only 69.15%; among them, although the recovery rates of examples 17 and 18 are higher than those of example 11, the costs are also increased accordingly, and the economic benefits are relatively low. It can be seen that the oil displacement method of the present invention can achieve a higher recovery rate for extremely high water-content reservoirs.

[0237] like Fig.17 , Fig.18 , Fig.19 Shown are the trends of recovery rate versus injection volume in various embodiments and comparative examples.

[0238] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for oil recovery from an extremely high water content reservoir, characterized in that: The following steps are involved: (1) Inject water into the reservoir for water flooding until the water content of the reservoir is greater than 90%; (2) injecting a polymer solution and a supercritical carbon dioxide flooding agent respectively; (3) After the polymer solution or supercritical carbon dioxide oil displacement agent is injected, water is injected for water flooding; The injection amount of the polymer solution and the supercritical carbon dioxide oil-displacing agent is not less than 0.1 PV respectively, and the total injection amount of the polymer solution and the supercritical carbon dioxide oil-displacing agent is 0.3-1.2 PV; The viscosity ratio of the polymer solution to the crude oil in the oil reservoir is 1:(0.8-10), and the viscosity ratio of the supercritical carbon dioxide oil displacement agent to the crude oil in the oil reservoir is 1:(10-800).

2. The method for oil displacement from an ultra-high water-cut reservoir according to claim 1, characterized in that: The viscosity of the polymer solution is not less than 1 mPa·s; And / or, the viscosity of the supercritical carbon dioxide oil displacement agent is greater than the viscosity of pure supercritical carbon dioxide and less than the viscosity of crude oil in the oil reservoir.

3. The method for oil displacement from an ultra-high water-cut reservoir according to claim 1 or 2, characterized in that: The injection amount of the polymer solution is 0.1 to 0.6 PV, and / or the injection amount of the supercritical carbon dioxide oil displacement agent is 0.1 to 0.6 PV.

4. The method for displacing oil from an ultra-high water-cut reservoir according to any one of claims 1 to 3, characterized in that: Repeat step (2) multiple times; The injection amount of the polymer solution is 0.05-0.2 PV, and the injection amount of the supercritical carbon dioxide oil displacement agent is 0.05-0.2 PV.

5. The method for oil displacement from an ultra-high water-cut reservoir according to any one of claims 1 to 4, characterized in that: The internal pressure of the oil reservoir is less than the miscibility pressure of the supercritical carbon dioxide oil displacement agent and crude oil.

6. The method for oil displacement from an ultra-high water-cut reservoir according to any one of claims 1 to 5, characterized in that: The polymer solution comprises a polymer and water; The polymer includes at least one of xanthan gum, a cross-linked polymer, a hydrophobic associating polymer, a comb polymer, and a star polymer.

7. The method for displacing oil from an ultra-high water content reservoir according to any one of claims 1 to 6, characterized in that: The polymer solution also includes a surfactant and an alkaline compound; The surfactant includes at least one of a nonionic surfactant, an anionic surfactant, and a zwitterionic surfactant; The alkaline compound includes at least one of sodium hydroxide, sodium carbonate, sodium bicarbonate and ammonium hydroxide.

8. The method for oil displacement from an ultra-high water-cut reservoir according to claim 7, characterized in that: The average molecular weight of the polymer is 3 million to 21 million.

9. The method for oil displacement from an ultra-high water-cut reservoir according to any one of claims 1 to 8, characterized in that: The supercritical carbon dioxide oil displacement agent comprises supercritical carbon dioxide and a base liquid dissolved in the supercritical carbon dioxide, wherein the base liquid comprises a thickener, a cosolvent and water; In the base liquid, the mass percentage of the thickener is 0.05-3wt%, the mass percentage of the co-solvent is 0.05-6wt%, and the balance is water; The co-solvent includes at least one of kerosene, ether and n-decane.

10. The method for oil displacement from an ultra-high water-cut reservoir according to claim 9, characterized in that: The thickener includes at least one of a siloxane thickener and a hydrocarbon thickener; The siloxane thickener includes at least one of the compound represented by Formula 1, the compound represented by Formula 2, and the compound represented by Formula 3. In Formula 1, x and y are each independently selected from positive integers; in Formula 2, i, j, and k are each independently selected from positive integers; in Formula 3, h is selected from positive integers; The hydrocarbon thickener includes at least one of the compound shown in Formula 4, the compound shown in Formula 5, and the compound shown in Formula 6. In Formula 4, a, b, and c are each independently selected from positive integers; in Formula 5, n is selected from a positive integer; in Formula 6, m is selected from a positive integer.

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