Rough fracture model and method for evaluating foam fluidity control ability in rough fractures

Abstract

The present invention discloses a rough fracture model and a method for evaluating the foam fluidity control ability in a rough fracture, wherein the rough fracture model comprises a spliced ​​cap layer and a bottom layer, grooves are provided on the opposite surfaces of the cap layer and the bottom layer to form a fracture wall, and circular grooves are provided on the two opposite fracture walls of the cap layer and the bottom layer to form a rough fracture; the method comprises the following steps: S1: placing the rough fracture model into a core holder of a displacement system; S2: injecting gas and foam system using the displacement system until the pressure difference standard deviation is less than the pressure difference standard deviation threshold, and recording the pressure difference value at this time; S3: calculating the foam apparent viscosity according to the pressure difference value obtained in step S2, and characterizing the foam fluidity control ability with the foam apparent viscosity. The present invention can obtain a rough fracture model of the target fracture roughness, thereby more accurately evaluating the foam fluidity control ability in a rough fracture.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas reservoir development, and in particular to a rough fracture model and a method for evaluating the foam fluidity control capability in the rough fracture. Background Art

[0002] Low-permeability oil reservoirs in my country are widely distributed and have huge resources. They are an important force supporting my country's oil and gas production. However, low-permeability oil reservoirs have small pore throats, low natural production capacity and high injection pressure, making it difficult to effectively develop them on a large scale using conventional mining methods. CO2 can significantly increase crude oil recovery through a variety of mechanisms, such as reducing crude oil viscosity and interfacial tension and expanding crude oil volume. Under most reservoir conditions, CO2 is in a supercritical state, its density is similar to that of liquid, and its gravity differentiation is weaker than that of other gases. At the same time, its viscosity is close to that of gas, making it particularly suitable for low-permeability oil reservoirs with injectability problems.

[0003] However, the rock in low-permeability reservoirs is hard and brittle, and often has cracks and strong reservoir heterogeneity. CO2 is very easy to flow in the cracks, and it is difficult to enter the matrix to displace crude oil, resulting in low CO2 sweep efficiency and serious impact on crude oil recovery. Controlling CO2 mobility is the key to solving the CO2 sweep problem. Common methods include: alternating water and gas injection, gel injection and foam injection. Compared with the first two methods, foam injection does not have the problem of matrix damage and can achieve deep migration. It has received widespread attention in recent years. The ability of foam to control mobility in fractures is closely related to factors such as reservoir temperature, pressure and fracture roughness. However, due to the lack of physical models that can accurately simulate the real fracture reservoir environment, how to accurately characterize the ability of foam to control mobility in fractures is still a research difficulty. Summary of the invention

[0004] In view of the above problems, the present invention aims to provide a rough fracture model and a method for evaluating the foam fluidity control capability in rough fractures.

[0005] The technical solution of the present invention is as follows:

[0006] On the one hand, a rough crack model is provided, comprising a spliced ​​cover layer and a bottom layer, wherein grooves are provided on the opposite surfaces of the cover layer and the bottom layer to form crack walls, and circular grooves are provided on the two opposite crack walls of the cover layer and the bottom layer to form a rough crack.

[0007] Preferably, the depth of the groove is half of the preset hydraulic radius of the crack.

[0008] Preferably, the number of the circular grooves is determined by a target crack roughness, thereby obtaining a rough crack model of the target crack roughness.

[0009] Preferably, the number of the circular grooves is calculated by the following formula:

[0010] (1)

[0011] Where: n is the number of circular grooves, dimensionless; R s is the target crack roughness, dimensionless; L is the crack length, mm; W is the crack width, mm; h is the depth of the lowest point of the circular groove, mm.

[0012] Preferably, when making the rough crack model, firstly, the model plate is cut using wire cutting technology to obtain the cover layer and the bottom layer, then the grooves are dug on the cover layer and the bottom layer using a milling cutter, and then the circular grooves are drilled on the grooves using a spherical milling cutter, and finally the cover layer and the bottom layer are assembled to obtain the rough crack model.

[0013] Preferably, the model plate is made of steel.

[0014] In another aspect, a method for evaluating the fluidity control capability of foam in a rough fracture is provided, comprising the following steps:

[0015] S1: placing any of the above-mentioned rough fracture models into a core holder of a displacement system;

[0016] S2: injecting gas and foam system by using the displacement system until the pressure difference standard deviation is less than the pressure difference standard deviation threshold, and recording the pressure difference value at this time;

[0017] S3: Calculate the foam apparent viscosity according to the pressure difference value obtained in step S2, and use the foam apparent viscosity to characterize the foam fluidity control ability.

[0018] Preferably, in step S1, the displacement system includes an injection system, a core holder, a confining pressure system, a back pressure system, a collecting device and a constant temperature oven, the injection system includes a foam system injection system and a gas injection system in parallel, the output end of the injection system is connected to the input end of the core holder, the confining pressure system is connected to the side wall of the core holder, and the back pressure system and the collecting device are connected to the output end of the core holder.

[0019] Preferably, in step S2, when injecting the gas and foam system, the gas injection rate and the liquid injection rate are calculated by the following formulas:

[0020] (2)

[0021] (3)

[0022] Where: q g is the gas injection rate, mL / min; q is the preset injection rate, mL / min; f gis the foam quality, %;q l is the injection rate, mL / min.

[0023] Preferably, in step S3, the foam apparent viscosity is calculated by the following formula:

[0024] (4)

[0025] Where: μ app is the apparent viscosity of the foam, mPa·s; ∆P is the pressure difference.

[0026] The beneficial effects of the present invention are:

[0027] The present invention can accurately design a rough fracture model with quantitative characterization of fracture roughness, and the rough fracture model is easy to manufacture, highly variable, and can be reused to simulate the actual temperature and pressure environment of the reservoir. The present invention can accurately evaluate the foam fluidity control ability in the rough fracture according to the rough fracture model, and provide technical support for the exploitation of low-permeability reservoirs. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0029] Figure 1 This is a schematic diagram of the manufacturing process of the rough crack model of the present invention;

[0030] Figure 2 It is a schematic diagram of circular groove parameters of the rough crack model of the present invention;

[0031] Figure 3 FIG. 4 is a schematic diagram of the structure of a displacement system in a specific embodiment. DETAILED DESCRIPTION

[0032] The present invention is further described below in conjunction with the accompanying drawings and embodiments. It should be noted that, in the absence of conflict, the embodiments in this application and the technical features in the embodiments can be combined with each other. It should be noted that, unless otherwise specified, all technical and scientific terms used in this application have the same meanings as those generally understood by those of ordinary skill in the art to which this application belongs. The words "including" or "comprising" and the like used in the disclosure of the present invention mean that the elements or objects appearing before the word cover the elements or objects listed after the word and their equivalents, without excluding other elements or objects.

[0033] On the one hand, if Figure 1-2As shown, the present invention provides a rough crack model, including a spliced ​​cover layer and a bottom layer, wherein grooves are provided on the opposite surfaces of the cover layer and the bottom layer to form crack walls, and circular grooves are provided on the two opposite crack walls of the cover layer and the bottom layer to form a rough crack.

[0034] In a specific embodiment, the depth of the groove is half of the preset hydraulic radius of the crack. In this embodiment, the depth of the grooves on the cover layer and the bottom layer are both half of the preset hydraulic radius of the crack, and the crack radius is evenly divided on the cover layer and the bottom layer, which enables the present invention to have the same force on the cover layer and the bottom layer in subsequent experiments, and the experimental results are more accurate. It should be noted that, as needed, the depth of the groove of the cover layer can be set deeper than the depth of the groove of the bottom layer, or the depth of the groove of the cover layer can be set shallower than the depth of the groove of the bottom layer, as long as the sum of the depths of the two is the preset hydraulic radius of the crack, a crack with a preset hydraulic radius of the crack can be obtained.

[0035] In a specific embodiment, the number of circular grooves is determined by the target crack roughness, thereby obtaining a rough crack model of the target crack roughness. The number of circular grooves is calculated by the following formula:

[0036] (1)

[0037] Where: n is the number of circular grooves, dimensionless; R s is the target crack roughness, dimensionless; L is the crack length, mm; W is the crack width, mm; h is the depth of the lowest point of the circular groove, mm.

[0038] In a specific embodiment, when making the rough crack model, firstly, the model plate is cut using wire cutting technology to obtain the cover layer and the bottom layer, then the grooves are dug on the cover layer and the bottom layer using a milling cutter, and then the circular grooves are drilled on the grooves using a spherical milling cutter, and finally the cover layer and the bottom layer are assembled to obtain the rough crack model.

[0039] In a specific embodiment, the model plate is made of steel. In this embodiment, the rough fracture model is made of steel, which can improve the heat and pressure resistance of the present invention, so that the present invention can simulate the high temperature and high pressure environment of the oil reservoir.

[0040] In another aspect, the present invention also provides a method for evaluating the fluidity control capability of foam in a rough fracture, comprising the following steps:

[0041] S1: placing any of the above-mentioned rough fracture models into a core holder of a displacement system;

[0042] S2: injecting gas and foam system by using the displacement system until the pressure difference standard deviation is less than the pressure difference standard deviation threshold, and recording the pressure difference value at this time;

[0043] S3: Calculate the foam apparent viscosity according to the pressure difference value obtained in step S2, and use the foam apparent viscosity to characterize the foam fluidity control ability.

[0044] In a specific embodiment, Figure 3 As shown, the displacement system includes an injection system, a core holder, a confining pressure system, a back pressure system, a collecting device and a constant temperature oven. The injection system includes a foam system injection system and a gas injection system in parallel. The output end of the injection system is connected to the input end of the core holder, the confining pressure system is connected to the side wall of the core holder, and the back pressure system and the collecting device are connected to the output end of the core holder.

[0045] It should be noted that the internal size of the core holder must correspond to the size of the rough fracture model. In addition, the displacement system of the above embodiment is only a preferred device of the present invention. Other displacement systems capable of injection output in the prior art can also be applied to the present invention. The main point of the method of the present invention is that the rough fracture model of the present invention is used in the core holder, so that the present invention can accurately study the foam fluidity control ability under specific fracture roughness.

[0046] In a specific embodiment, in step S2, when injecting the gas and foam system, the gas injection rate and the liquid injection rate are calculated by the following formulas:

[0047] (2)

[0048] (3)

[0049] Where: q g is the gas injection rate, mL / min; q is the preset injection rate, mL / min; f g is the foam quality, %;q l is the injection rate, mL / min.

[0050] In a specific embodiment, in step S3, the foam apparent viscosity is calculated by the following formula:

[0051] (4)

[0052] Where: μ app is the apparent viscosity of the foam, mPa·s; ∆P is the pressure difference.

[0053] Example 1

[0054] A method for evaluating the mobility control capability of foam in rough fractures comprises the following steps:

[0055] (1) Making a rough crack model

[0056] In this embodiment, first, a steel block with a size of 200×45×45 mm is cut in half using wire cutting technology to form a cap layer and a bottom layer; the hydraulic radius of the fracture is preset to be d h The grooves with a depth of 0.5 mm and a width of 36 mm were dug in the middle of the cover layer and the bottom layer by a milling cutter to form the crack wall, and 4.5 mm was left on both edges to facilitate the splicing of the cover layer and the bottom layer; then, a certain number of circular grooves were drilled on the two crack surfaces by a spherical milling cutter to form a rough crack. The crack roughness R was preset. s is 1.048, the depth of the lowest point of the circular groove h is 0.11 mm, and the number of circular grooves n is calculated by formula (1) to be 9096; finally, the cover layer and the bottom layer are combined to obtain the crack roughness R s The rough crack model is 1.048.

[0057] (2) Place the rough fracture model into the core holder and press Figure 3 The structural schematic diagram shown connects the various components of the displacement system;

[0058] (3) Increase the temperature of the constant temperature oven to 55°C, increase the back pressure to 13 MPa through the advection pump, and the surrounding pressure to 16 MPa;

[0059] (4) Preset foam mass f g The injection rate q is 40% and 0.5 mL / min. The injection rate q is calculated by formula (2): g The injection speed q is 0.2 mL / min, and is calculated by formula (3): l is 0.3mL / min. According to the injection speed q g and injection speed q l Inject CO2 gas and sodium dodecyl sulfate solution until the pressure difference standard deviation is less than 0.01, and record the pressure difference value ∆P at this time as 0.287MPa;

[0060] (5) Based on the pressure difference value obtained in step (4), the foam apparent viscosity μ is calculated by combining formula (4): app It is 517.482 mPa·s, which is used to characterize the foam fluidity control ability.

[0061] Example 2

[0062] A method for evaluating the mobility control capability of foam in rough fractures comprises the following steps:

[0063] (1) Making a rough crack model

[0064] In this embodiment, first, a steel block with a size of 250×45×45 mm is cut in half using wire cutting technology to form a cap layer and a bottom layer; the hydraulic radius of the fracture is preset to be d h The grooves with a depth of 0.75 mm and a width of 36 mm were dug in the middle of the cover layer and the bottom layer by a milling cutter to form the crack wall, and 4.5 mm was left on both edges to facilitate the splicing of the cover layer and the bottom layer; then, a certain number of circular grooves were drilled on the two crack surfaces by a spherical milling cutter to form a rough crack. The crack roughness R was preset. s is 1.077, the depth of the lowest point of the circular groove h is 0.13 mm, and the number of circular grooves n is calculated by formula (1) to be 13059; finally, the cover layer and the bottom layer are combined to obtain the crack roughness R s The rough crack model is 1.077.

[0065] (2) Place the rough fracture model into the core holder and press Figure 3 The structural schematic diagram shown connects the various components of the displacement system;

[0066] (3) Increase the temperature of the constant temperature oven to 60°C, increase the back pressure to 17 MPa through a horizontal flow pump, and increase the surrounding pressure to 20 MPa;

[0067] (4) Preset foam mass f g The injection rate q is 60% and 1.0 mL / min. The injection rate q is calculated by formula (2): g The injection speed q is 0.6 mL / min, and is calculated by formula (3): l is 0.4mL / min. According to the injection speed q g and injection speed q l Inject CO2 gas and sodium dodecyl sulfate solution until the pressure difference standard deviation is less than 0.01, and record the pressure difference value ∆P at this time as 0.312MPa;

[0068] (5) Based on the pressure difference value obtained in step (4), the foam apparent viscosity μ is calculated by combining formula (4): app It is 758.16 mPa·s, which is used to characterize the foam fluidity control ability.

[0069] Example 3

[0070] A method for evaluating the mobility control capability of foam in rough fractures comprises the following steps:

[0071] (1) Making a rough crack model

[0072] In this embodiment, first, a steel block with a size of 300×45×45 mm is cut in half using wire cutting technology to form a cap layer and a bottom layer; the hydraulic radius of the fracture is preset to be d hThe diameter of the crack is 2.0 mm, and a milling cutter is used to dig grooves with a depth of 1 mm and a width of 36 mm in the middle of the cover layer and the bottom layer to form the crack wall. 4.5 mm is left on both edges to facilitate the splicing of the cover layer and the bottom layer. Then, a certain number of circular grooves are drilled on the two crack surfaces using a spherical milling cutter to form a rough crack. The crack roughness R is preset. s is 1.112, the depth of the lowest point of the circular groove h is 0.15 mm, and the number of circular grooves n is calculated by formula (1) to be 17121; finally, the cover layer and the bottom layer are combined to obtain the crack roughness R s The rough crack model is 1.112.

[0073] (2) Place the rough fracture model into the core holder and press Figure 3 The structural schematic diagram shown connects the various components of the displacement system;

[0074] (3) Increase the temperature of the constant temperature oven to 65°C, increase the back pressure to 15 MPa through the advection pump, and increase the surrounding pressure to 18 MPa;

[0075] (4) Preset foam mass f g The injection rate q is 80% and 1.0 mL / min. The injection rate q is calculated by formula (2): g The injection speed q is 0.8 mL / min, and is calculated by formula (3): l is 0.2mL / min. According to the injection speed q g and injection speed q l Inject CO2 gas and sodium dodecyl sulfate solution until the pressure difference standard deviation is less than 0.01, and record the pressure difference value ∆P at this time as 0.275MPa;

[0076] (5) Based on the pressure difference value obtained in step (4), the foam apparent viscosity μ is calculated by combining formula (4): app It is 1320 mPa·s, which is used to characterize the foam fluidity control ability.

[0077] The above description is only a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as a preferred embodiment as above, it is not intended to limit the present invention. Any technician familiar with the profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the scope of the technical solution of the present invention.

Claims

1. A rough crack model, characterized in that: The invention comprises a cap layer and a bottom layer which are assembled together, grooves are arranged on the opposite surfaces of the cap layer and the bottom layer to form crack walls, circular grooves are arranged on the two opposite crack walls of the cap layer and the bottom layer to form a rough crack, and the number of the circular grooves is determined by the target crack roughness, so as to obtain a rough crack model of the target crack roughness; the number of the circular grooves is calculated by the following formula: （1） Where: n is the number of circular grooves, dimensionless; R s is the target crack roughness, dimensionless; L is the crack length, mm; W is the crack width, mm; h is the depth of the lowest point of the circular groove, mm.

2. The rough crack model according to claim 1, characterized in that: The depth of the groove is half of the preset hydraulic radius of the crack.

3. The rough crack model according to claim 1 or 2, characterized in that: When making the rough crack model, first use the wire cutting technology to cut the model plate to obtain the cover layer and the bottom layer, then use a milling cutter to dig the grooves on the cover layer and the bottom layer, then use a spherical milling cutter to drill the circular grooves on the grooves, and finally splice the cover layer and the bottom layer to obtain the rough crack model.

4. The rough crack model according to claim 3, characterized in that: The model plate is made of steel.

5. A method for evaluating the ability of foam fluidity control in rough fractures, characterized in that: The following steps are involved: S1: placing the rough fracture model according to any one of claims 1 to 4 into a core holder of a displacement system; S2: injecting gas and foam system by using the displacement system until the pressure difference standard deviation is less than the pressure difference standard deviation threshold, and recording the pressure difference value at this time; S3: Calculate the foam apparent viscosity according to the pressure difference value obtained in step S2, and use the foam apparent viscosity to characterize the foam fluidity control ability; the foam apparent viscosity is calculated by the following formula: （4） Where: μ app is the apparent viscosity of the foam, mPa·s; W is the crack width, mm; d h is the preset fracture hydraulic radius, mm; q is the preset injection rate, mL / min; ∆P is the pressure difference; L is the fracture length, mm.

6. The method for evaluating the foam fluidity control ability in rough fractures according to claim 5, characterized in that: In step S1, the displacement system includes an injection system, a core clamp, a confining pressure system, a back pressure system, a collecting device and a constant temperature oven, the injection system includes a foam system injection system and a gas injection system in parallel, the output end of the injection system is connected to the input end of the core clamp, the confining pressure system is connected to the side wall of the core clamp, and the back pressure system and the collecting device are connected to the output end of the core clamp.

7. The method for evaluating the foam fluidity control ability in rough fractures according to claim 5, characterized in that: In step S2, when the gas and foam system are injected, the gas injection rate and the liquid injection rate are calculated by the following formulas: （2） （3） Where: q g is the gas injection rate, mL / min; q is the preset injection rate, mL / min; f g is the foam quality, %;q l is the injection rate, mL / min.

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