CO2 clustering oil displacement method for remaining oil in compact conglomerate oil reservoir

Abstract

The invention relates to the technical field of unconventional oil and gas development, and discloses a CO2 clustering oil displacement method for remaining oil in a compact conglomerate oil reservoir. The method comprises the following steps: performing staged fracturing on a horizontal well in a compact conglomerate reservoir to form a region I containing a plurality of crack clusters perpendicular to the horizontal well; the horizontal well is a horizontal well subjected to depletion type mining; establishing a numerical model of the oil displacement unit; a continuous oil pipe is arranged on the horizontal well section in the area I, a packer is arranged on a first oil displacement unit, and high-pressure CO2 is continuously injected into an annular space between the continuous oil pipe and a horizontal well casing pipe; and when high-pressure CO2 reaches the first fracture cluster, oil displacement is started to be conducted on the first oil displacement unit, and the packer is continuously moved to be placed in the oil displacement unit with the remaining oil to be exploited till the remaining oil in all the oil displacement units is displaced. According to the method provided by the invention, the remaining oil between the fractures can be displaced to the oil pipe, and the recovery efficiency of the compact conglomerate oil reservoir is remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of unconventional oil and gas development, and in particular to a CO2 clustering oil recovery method for residual oil in a tight conglomerate reservoir. Background Art

[0002] Tight conglomerate reservoirs are characterized by low permeability and strong heterogeneity. After staged and clustered fracturing of horizontal wells, the initial oil production is large, but the oil production rate decays severely after a period of production. At the same time, there is still a large amount of residual oil in the strata between the fractures, which is difficult to inject into the reservoir by conventional water drive and chemical drive.

[0003] At present, the main problem in the development of tight conglomerate reservoirs is how to effectively develop the remaining oil between reservoir fractures to increase the recovery of crude oil.

[0004] According to field practice and theoretical research, supercritical CO2 has the properties of low viscosity, high permeability and zero surface tension, and can effectively displace crude oil in dense conglomerate reservoirs.

[0005] CN109025940A discloses a CO2 fracturing and oil recovery integrated method for tight oil reservoirs, the method comprising: starting from the toe of the horizontal well and sequentially toward the heel, the segmented units are respectively fractured and oil driven, in the fracturing stage, liquid carbon dioxide is used to perform segmented closed fracturing on the horizontal well; in the oil recovery stage, after the horizontal well segmented unit is fractured, high-pressure carbon dioxide is continuously injected into the segmented unit for segmented closed oil recovery. The method adopts the state of always injecting CO2 without backflow, and has the functions of carrying sand, creating fractures, replenishing formation energy, and displacement. It not only effectively utilizes the fracturing fluid to supplement energy, but also realizes the displacement oil recovery of tight oil reservoirs, and can select the injection amount and injection time according to the actual development needs, realizing the integration of reservoir production increase fracturing transformation and oil recovery. However, the method in the prior art is aimed at brand new oil reservoirs, and cannot increase the production of depleted oil reservoirs, and does not consider the storage efficiency of CO2 in the oil reservoir. Summary of the invention

[0006] The purpose of the present invention is to overcome the problem in the prior art that the remaining oil in the depleted oil reservoir is difficult to exploit.

[0007] In order to achieve the above object, the present invention provides a CO2 clustering flooding method for residual oil in a tight conglomerate reservoir, the method comprising:

[0008] (1) performing staged fracturing on a horizontal well in a tight conglomerate reservoir to form a region I containing a plurality of fracture clusters perpendicular to the horizontal well; the horizontal well is a horizontal well that has undergone depletion production;

[0009] (2) Establishing a numerical model of the oil displacement unit by simulating the flow of oil, gas and water in the oil displacement unit and the deformation characteristics of the rock matrix during the CO2 clustering oil displacement in the horizontal well section of the tight conglomerate reservoir;

[0010] Wherein, the oil displacement unit is the space between two adjacent fracture clusters;

[0011] The CO2 phase and crude oil phase in the oil displacement unit both satisfy formula (1):

[0012]

[0013] Among them, α corresponds to each mobile phase in the oil displacement unit; ρ α is the density of each mobile phase in the oil displacement unit, in kg / m 3 ; is the porosity of the oil displacement unit; q α is the Darcy velocity of mobile phase α; t is the displacement time, in seconds;

[0014] Fluid saturation S α Satisfies formula (2):

[0015] ∑ α S α =1 (2);

[0016] Darcy velocity q of mobile phase α α Satisfies formula (3):

[0017]

[0018] Where K is the permeability tensor, in mD; k rα is the relative permeability; μ α is the dynamic viscosity of each fluid phase, in mPa·s; g is the gravity vector, in m / s 2 ;P α is the fluid pressure, in MPa;

[0019] Fluid pressure and capillary pressure P of crude oil phase and CO2 phase c The relationship between satisfies formula (4):

[0020]

[0021] Among them, P o is the fluid pressure of crude oil phase, in MPa; is the fluid pressure of CO2 phase, in MPa;

[0022] Based on the solid mechanics deformation equation, the total rock strain ε in the oil displacement unit satisfies formula (5):

[0023]

[0024] Where, E is the elastic modulus of rock, in MPa; F is the volume force per unit volume of rock, in MPa;

[0025] Formula (1) to formula (5) are combined and solved by finite element software to obtain the crude oil saturation distribution, cumulative crude oil production and CO2-crude oil volume ratio, CO2 injection pressure and CO2 wellhead injection displacement in the oil displacement unit at different oil displacement times.

[0026]

[0027] β is the coefficient of CO2 volume change; is the Darcy velocity of CO2, in m / s; h is the oil layer thickness, in m; l is the length of the fracture cluster, in m;

[0028] (3) placing a coiled tubing in the horizontal well section in the region I, placing a packer in the first oil displacement unit, and continuously injecting high-pressure CO2 into the annular space between the coiled tubing and the horizontal well casing;

[0029] Determining the wellhead injection displacement of the CO2 according to step (2);

[0030] The fracture cluster that the high-pressure CO2 first reaches is defined as the first fracture cluster, the fracture cluster adjacent to the first fracture cluster is defined as the second fracture cluster, and the fracture cluster adjacent to the right side of the Nth fracture cluster is defined as the (N+1)th fracture cluster; the first oil displacement unit is defined as the space between the first fracture cluster and the second fracture cluster, and the Nth oil displacement unit is defined as the space between the Nth fracture cluster and the (N+1)th fracture cluster;

[0031] When the high-pressure CO2 reaches the first fracture cluster, the first oil displacement unit starts to be displaced, and the remaining oil in the first oil displacement unit is displaced by the high-pressure CO2;

[0032] When the first oil recovery unit finishes oil recovery, the packer is moved to the second oil recovery unit, at which time the remaining oil in the second oil recovery unit is displaced by high-pressure CO2; the packer is continuously moved to the oil recovery unit for the remaining oil to be recovered, until the remaining oil in each oil recovery unit is displaced and flows into the continuous oil pipe to increase the production of the tight gravel reservoir.

[0033] By adopting the method provided by the present invention, the remaining oil between the seams can be effectively displaced into the coiled tubing, thereby significantly improving the recovery rate of the dense conglomerate reservoir; and the injection of CO2 into the formation can replenish the formation energy and realize the geological storage of CO2. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a schematic diagram of the oil displacement process of the residual oil in the tight conglomerate reservoir according to the present invention;

[0035] Figure 2 is a crude oil saturation distribution diagram of the oil displacement unit on the 30th day, the 200th day, the 500th day, and the 800th day in Example 1 of the present invention;

[0036] Figure 3 It is a schematic diagram of the cumulative crude oil production and CO2-crude oil volume ratio of the oil displacement unit within 800 days in Example 1 of the present invention.

[0037] Description of Reference Numerals

[0038] 1. High-pressure CO2 injection direction; 2. Crude oil flow direction; 3. Horizontal well casing; 4. Coiled tubing; 5. Packer; 6. First fracture cluster; 7. Second fracture cluster; 8. Dense conglomerate formation; 9. Producing oil layer. DETAILED DESCRIPTION

[0039] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0040] As mentioned above, the present invention provides a CO2 clustering flooding method for residual oil in a tight conglomerate reservoir, the method comprising:

[0041] (1) performing staged fracturing on a horizontal well in a tight conglomerate reservoir to form a region I containing a plurality of fracture clusters perpendicular to the horizontal well; the horizontal well is a horizontal well that has undergone depletion production;

[0042] (2) Establishing a numerical model of the oil displacement unit by simulating the flow of oil, gas and water in the oil displacement unit and the deformation characteristics of the rock matrix during the CO2 clustering oil displacement in the horizontal well section of the tight conglomerate reservoir;

[0043] Wherein, the oil displacement unit is the space between two adjacent fracture clusters;

[0044] The CO2 phase and crude oil phase in the oil displacement unit both satisfy formula (1):

[0045]

[0046] Among them, α corresponds to each mobile phase in the oil displacement unit; ρ α is the density of each mobile phase in the oil displacement unit, in kg / m3 ; is the porosity of the oil displacement unit; q α is the Darcy velocity of mobile phase α; t is the displacement time, in seconds;

[0047] Fluid saturation S α Satisfies formula (2):

[0048] ∑ α S α =1 (2);

[0049] Darcy velocity q of mobile phase α α Satisfies formula (3):

[0050]

[0051] Where K is the permeability tensor, in mD; k rα is the relative permeability; μ α is the dynamic viscosity of each fluid phase, in mPa·s; g is the gravity vector, in m / s 2 ;P α is the fluid pressure, in MPa;

[0052] Fluid pressure and capillary pressure P of crude oil phase and CO2 phase c The relationship between satisfies formula (4):

[0053]

[0054] Among them, P o is the fluid pressure of crude oil phase, in MPa; is the fluid pressure of CO2 phase, in MPa;

[0055] Based on the solid mechanics deformation equation, the total rock strain ε in the oil displacement unit satisfies formula (5):

[0056]

[0057] Where, E is the elastic modulus of rock, in MPa; F is the volume force per unit volume of rock, in MPa;

[0058] Formula (1) to formula (5) are combined and solved by finite element software to obtain the crude oil saturation distribution, cumulative crude oil production and CO2-crude oil volume ratio, CO2 injection pressure and CO2 wellhead injection displacement in the oil displacement unit at different oil displacement times.

[0059]

[0060] β is the coefficient of CO2 volume change; is the Darcy velocity of CO2, in m / s; h is the oil layer thickness, in m; l is the length of the fracture cluster, in m;

[0061] (3) placing a coiled tubing in the horizontal well section in the region I, placing a packer in the first oil displacement unit, and continuously injecting high-pressure CO2 into the annular space between the coiled tubing and the horizontal well casing;

[0062] Determining the wellhead injection displacement of the CO2 according to step (2);

[0063] The fracture cluster that the high-pressure CO2 first reaches is defined as the first fracture cluster, the fracture cluster adjacent to the first fracture cluster is defined as the second fracture cluster, and the fracture cluster adjacent to the right side of the Nth fracture cluster is defined as the (N+1)th fracture cluster; the first oil displacement unit is defined as the space between the first fracture cluster and the second fracture cluster, and the Nth oil displacement unit is defined as the space between the Nth fracture cluster and the (N+1)th fracture cluster;

[0064] When the high-pressure CO2 reaches the first fracture cluster, the first oil displacement unit starts to be displaced, and the remaining oil in the first oil displacement unit is displaced by the high-pressure CO2;

[0065] When the first oil recovery unit finishes oil recovery, the packer is moved to the second oil recovery unit, at which time the remaining oil in the second oil recovery unit is displaced by high-pressure CO2; the packer is continuously moved to the oil recovery unit for the remaining oil to be recovered, until the remaining oil in each oil recovery unit is displaced and flows into the continuous oil pipe to increase the production of the tight gravel reservoir.

[0066] It should be noted that the injection pressure of CO2 in the present invention is numerically the same as equal.

[0067] It should be noted that, in the present invention, when α is a CO2 phase,

[0068] In the present invention, the CO2 volume variation coefficient is the ratio of the CO2 density at the wellhead of the horizontal well to the CO2 density at the bottom of the horizontal well.

[0069] In the present invention, the remaining oil in each oil displacement unit is displaced to the adjacent oil production fracture cluster on the right side of each oil displacement unit to flow into the coiled tubing. For example, when the first oil displacement unit is displaced, the remaining oil in the first oil displacement unit is first displaced to the second fracture cluster to flow into the coiled tubing.

[0070] The present invention Figure 1 A schematic diagram of the oil recovery process of the remaining oil in the above-mentioned tight conglomerate reservoir is provided as an example.

[0071] exist Figure 1 In the present invention, in the area of ​​dense conglomerate formation 8, the coiled tubing 4 is lowered into the horizontal well section in the production oil layer 9, the packer 5 is placed in the oil recovery unit (the first oil recovery unit), and high-pressure CO2 is continuously injected into the annular space between the coiled tubing 4 and the horizontal well casing 3 along the direction opposite to the crude oil flow direction 2, that is, along the high-pressure CO2 injection direction 1; the high-pressure CO2 first reaches the first fracture cluster 6, and the fracture cluster adjacent to the first fracture cluster is the second fracture cluster 7 (i.e., the oil production fracture cluster).

[0072] It should be noted that Figure 1 The rightmost red line represents the end of the horizontal well; Figure 1 There are 5 middle crack clusters; the above shall not be construed as any limitation to the present invention.

[0073] It should be noted that the number of horizontal wells in the tight conglomerate reservoir in the present invention is one.

[0074] Preferably, in step (1), the staged fracturing time is 10-30 hours.

[0075] Preferably, the number of the fracture clusters is ≥5, and the fracture clusters are all main fractures, and there are no branch fractures in the region I. The inventors of the present invention have found that in this preferred case, the oil recovery method of the present invention has better economic benefits.

[0076] Preferably, in step (1), the fracture conductivity of the fracture cluster is ≥ 8 μm 2 The inventors of the present invention have found that, in this preferred case, the recovery rate of the tight conglomerate reservoir is higher.

[0077] Preferably, in step (1), the sorting coefficient of gravel in the tight conglomerate reservoir is less than 1.5. The inventors of the present invention have found that in this preferred embodiment, the recovery efficiency of the remaining oil in the tight conglomerate reservoir is higher.

[0078] Preferably, in formula (1), ρα=50-2000kg / m 3 ,

[0079] Preferably, in formula (3), μ α =0.01-100mPa·s, g=9.7-10m / s 2 ;

[0080] Preferably, in formula (4), P c =0.01-0.5;

[0081] Preferably, in formula (5), E = 10,000-80,000 MPa.

[0082] Preferably, in formula (6), h=2-50m, and l=160-400m.

[0083] Preferably, in step (1), when the crude oil production is ≤0.05t / 24h, it is determined that the depletion-type production is terminated.

[0084] Preferably, in step (3), before the high-pressure CO2 is injected, the saturation of the remaining oil in each oil displacement unit is ≥30 vol%.

[0085] Preferably, when the crude oil production is less than 0.5 t / 24h or the CO2-crude oil volume ratio is greater than 300, the packer is adjusted to be placed in the oil displacement unit for the remaining oil to be recovered.

[0086] It should be noted that the distance and position should be controlled when adjusting the packer to achieve the separation of CO2 and crude oil and the stability of the coiled tubing.

[0087] The present invention will be described in detail below by way of examples. In the following examples, unless otherwise specified, the instruments, reagents, materials, etc. involved are all conventional instruments, reagents, materials, etc., which can be obtained through regular commercial channels. Among them, unless otherwise specified, the reagents used are all commercially available analytically pure products.

[0088] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, the following example uses a horizontal well section in the H block of Mahu Depression in Xinjiang Uygur Autonomous Region (oil layer reserves of about 530,000 tons) to illustrate the specific implementation of the present invention, but it does not serve as any limitation to the present invention.

[0089] Example 1

[0090] (1) A horizontal well in a tight conglomerate reservoir was subjected to staged fracturing for 25 h to form a fracture cluster containing 25 fractures perpendicular to the horizontal well (all of which were main fractures, with no branch fractures and a fracture conductivity of 15 μm). 2 ·cm) in area I (the sorting coefficient of gravel in the tight conglomerate reservoir is 1.2); the horizontal well is a horizontal well that has undergone depletion production (depletion production ends when the crude oil production is 0.05t / 24h);

[0091] (2) Establishing a numerical model of the oil displacement unit by simulating the flow of oil, gas and water in the oil displacement unit and the deformation characteristics of the rock matrix during the CO2 clustering oil displacement in the horizontal well section of the tight conglomerate reservoir;

[0092] Wherein, the oil displacement unit is the space between two adjacent fracture clusters;

[0093] The CO2 phase and crude oil phase in the oil displacement unit both satisfy formula (1):

[0094]

[0095] Among them, α corresponds to each mobile phase in the oil displacement unit; ρ α is the density of each mobile phase in the oil displacement unit, in kg / m 3 ; is the porosity of the oil displacement unit; q α is the Darcy velocity of mobile phase α; t is the displacement time, in seconds;

[0096] Fluid saturation S α Satisfies formula (2):

[0097] Σ α S α =1 (2);

[0098] Darcy velocity q of mobile phase α α Satisfies formula (3):

[0099]

[0100] Where K is the permeability tensor; k rα is the relative permeability; μ α is the dynamic viscosity of each fluid phase, in mPa·s; g is the gravity vector, in m / s 2 ;P α is the fluid pressure, in MPa;

[0101] Fluid pressure and capillary pressure P of crude oil phase and CO2 phase c The relationship between satisfies formula (4):

[0102]

[0103] Among them, P o is the fluid pressure of crude oil phase, in MPa; is the fluid pressure of CO2 phase, in MPa;

[0104] Based on the solid mechanics deformation equation, the total rock strain ε in the oil displacement unit satisfies formula (5):

[0105]

[0106] Where, E is the elastic modulus of rock, in MPa; F is the volume force per unit volume of rock, in MPa;

[0107] The known parameters involved in the above formula are obtained through logging data and simulation experiments;

[0108] in K = 50mD; g = 9.81m / s2 ;E=14,800MPa; F=32.21MPa;

[0109] When α is in the CO2 phase, ρ α =350kg / m 3 ;μ α =0.08mPa·s;

[0110] When α is the crude oil phase, ρ α =800kg / m 3 ;μ α =5mPa·s; P α =P o ;

[0111] Formula (1)-Formula (5) are combined and solved by finite element software to obtain the crude oil saturation distribution in the oil displacement unit when the oil displacement time is 30 days, 200 days, 500 days and 800 days respectively (see Figure 2 ), the cumulative crude oil production of the oil displacement unit within 800 days and the CO2-crude oil volume ratio (see Figure 3 As shown in ), CO2 injection pressure and CO2 wellhead injection displacement

[0112] Among them, the injection pressure of CO2 =

[0113]

[0114] β is the CO2 volume variation coefficient (the ratio of the CO2 density at the wellhead of the horizontal well to the CO2 density at the bottom of the horizontal well); is the Darcy velocity of CO2, in m / s; h is the oil layer thickness, in m; l is the length of the fracture cluster, in m;

[0115] In the above formula, β = 1.35; h = 5m; l = 200m;

[0116] (3) placing a coiled tubing in the horizontal well section in the region I, placing a packer in the first oil displacement unit, and continuously injecting high-pressure CO2 into the annular space between the coiled tubing and the horizontal well casing;

[0117] According to step (2), the wellhead injection rate of the CO2 is determined to be 67.5m 3 / sky;

[0118] The fracture cluster that the high-pressure CO2 first reaches is the first fracture cluster, and the fracture cluster adjacent to the first fracture cluster is the second fracture cluster; the first oil displacement unit is the space between the first fracture cluster and the second fracture cluster, and the second oil displacement unit is the space between the second fracture cluster and the third fracture cluster;

[0119] When the high-pressure CO2 reaches the first fracture cluster, the first oil displacement unit starts to be displaced, and the remaining oil in the first oil displacement unit is displaced by the high-pressure CO2;

[0120] When the first oil recovery unit finishes oil recovery, the packer is moved to the second oil recovery unit, at which time the remaining oil in the second oil recovery unit is displaced by high-pressure CO2; the packer is continuously moved to the oil recovery unit for the remaining oil to be recovered, until the remaining oil in each oil recovery unit is displaced and flows into the continuous oil pipe to increase the production of the tight gravel reservoir.

[0121] pass Figure 2 It can be seen that the crude oil saturation distribution of a single oil displacement unit at the 30th, 200th, 500th and 800th day of displacement time; specifically, with the increase of displacement time, the crude oil saturation area becomes smaller and smaller, and there is a certain fingering phenomenon in the displacement process.

[0122] pass Figure 3 It can be seen that the optimal single oil recovery unit has an oil recovery time of 500 days; after 500 days of oil recovery, the output of a single oil recovery unit is 2,432 tons. At this time, the crude oil in the oil recovery unit is basically produced, and the CO2 leakage is relatively small; therefore, the oil recovery time of a single oil recovery unit cycle can be set to 500 days, and then the packer can be moved to the next oil recovery unit.

[0123] According to the CO2 wellhead injection displacement and CO2 density (when α is CO2 phase, ρ α =350kg / m 3 ) It can be calculated that the CO2 injection volume within 500 days is 4560 tons. Figure 3 Integrating the red line area, we can get a 500-day CO2 leakage of 660 tons, and the 500-day CO2 storage capacity of a single oil recovery unit is 3,900 tons;

[0124] There are 48 oil displacement units in this horizontal well section after CO2 flooding:

[0125] Cumulative oil production = 2432 tons × 48 = 116,700 tons;

[0126] Total CO2 storage capacity = 3,900 tons × 48 = 187,200 tons;

[0127] CO2 storage efficiency = 3900 tons / 4560 tons × 100% = 85.5%;

[0128] The crude oil recovery factor increased by 21.99% (= cumulative oil production / oil layer reserves × 100%), achieving the dual benefits of increased production of depleted tight conglomerate reservoirs and CO2 storage.

[0129] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A CO2 cluster flooding method for residual oil in a tight conglomerate reservoir, characterized in that: The method includes: (1) performing staged fracturing on a horizontal well in a tight conglomerate reservoir to form a region I containing a plurality of fracture clusters perpendicular to the horizontal well; the horizontal well is a horizontal well that has undergone depletion production; (2) Establishing a numerical model of the oil displacement unit by simulating the flow of oil, gas and water in the oil displacement unit and the deformation characteristics of the rock matrix during the CO2 clustering oil displacement in the horizontal well section of the tight conglomerate reservoir; Wherein, the oil displacement unit is the space between two adjacent fracture clusters; The CO2 phase and crude oil phase in the oil displacement unit both satisfy formula (1): Among them, α corresponds to each mobile phase in the oil displacement unit; ρ α is the density of each mobile phase in the oil displacement unit, in kg / m 3 ; is the porosity of the oil displacement unit; q α is the Darcy velocity of mobile phase α; t is the displacement time, in seconds; Fluid saturation S α Satisfies formula (2): ∑ α S α ＝1 (2)； Darcy velocity q of mobile phase α α Satisfies formula (3): Where K is the permeability tensor, in mD; k rα is the relative permeability; μ α is the dynamic viscosity of each fluid phase, in mPa·s; g is the gravity vector, in m / s 2 ;P α is the fluid pressure, in MPa; Fluid pressure and capillary pressure P of crude oil phase and CO2 phase c The relationship between satisfies formula (4): Among them, P o is the fluid pressure of crude oil phase, in MPa; is the fluid pressure of CO2 phase, in MPa; Based on the solid mechanics deformation equation, the total rock strain ε in the oil displacement unit satisfies formula (5): Where, E is the elastic modulus of rock, in MPa; F is the volume force per unit volume of rock, in MPa; Formula (1) to formula (5) are combined and solved by finite element software to obtain the crude oil saturation distribution, cumulative crude oil production and CO2-crude oil volume ratio, CO2 injection pressure and CO2 wellhead injection displacement in the oil displacement unit at different oil displacement times. β is the coefficient of CO2 volume change; is the Darcy velocity of CO2, in m / s; h is the oil layer thickness, in m; l is the length of the fracture cluster, in m; (3) placing a coiled tubing in the horizontal well section in the region I, placing a packer in the first oil displacement unit, and continuously injecting high-pressure CO2 into the annular space between the coiled tubing and the horizontal well casing; Determining the wellhead injection displacement of the CO2 according to step (2); The fracture cluster that the high-pressure CO2 first reaches is defined as the first fracture cluster, the fracture cluster adjacent to the first fracture cluster is defined as the second fracture cluster, and the fracture cluster adjacent to the right side of the Nth fracture cluster is defined as the (N+1)th fracture cluster; the first oil displacement unit is defined as the space between the first fracture cluster and the second fracture cluster, and the Nth oil displacement unit is defined as the space between the Nth fracture cluster and the (N+1)th fracture cluster; When the high-pressure CO2 reaches the first fracture cluster, the first oil displacement unit starts to be displaced, and the remaining oil in the first oil displacement unit is displaced by the high-pressure CO2; When the first oil recovery unit finishes oil recovery, the packer is moved to the second oil recovery unit, at which time the remaining oil in the second oil recovery unit is displaced by high-pressure CO2; the packer is continuously moved to the oil recovery unit for the remaining oil to be recovered, until the remaining oil in each oil recovery unit is displaced and flows into the continuous oil pipe to increase the production of the tight gravel reservoir.

2. The method according to claim 1, wherein: In step (1), the staged fracturing time is 10-30 hours.

3. The method according to claim 1 or 2, wherein: The number of the crack clusters is ≥5, and all the crack clusters are main cracks. There are no branch cracks in the region I.

4. The method according to claim 1 or 2, wherein: In step (1), the fracture conductivity of the fracture cluster is ≥ 8 μm 2 ·cm.

5. The method according to claim 1 or 2, wherein: In step (1), the sorting coefficient of gravel in the tight conglomerate reservoir is less than 1.

5.

6. The method according to claim 1 or 2, wherein: In formula (1), ρ α =50-2000kg / m 3 , And / or, in formula (3), μ α =0.01-100mPa·s, g=9.7-10m / s 2 ; And / or, in formula (4), P c =0.01-0.5; And / or, in formula (5), E = 10,000-80,000 MPa.

7. The method according to claim 1 or 2, wherein: In formula (6), h=2-50 m, and l=160-400 m.

8. The method according to claim 1 or 2, wherein: In step (1), when the crude oil production is ≤0.05t / 24h, it is determined that the depletion-type production is terminated.

9. The method according to claim 1 or 2, wherein: In step (3), before the high-pressure CO2 is injected, the saturation of the remaining oil in each oil displacement unit is ≥30 vol%.

10. The method according to claim 1 or 2, wherein: When the crude oil production is less than 0.5t / 24h or the CO2-crude oil volume ratio is greater than 300, the packer is adjusted to be placed in the oil displacement unit where the remaining oil is to be recovered.

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