Heterogeneous reservoir combined fracturing and displacement simulation experiment method and device

Abstract

The invention discloses a heterogeneous reservoir combined fracturing and displacement simulation experiment method and device.The method comprises the following steps that S1, natural core columns are subjected to fluid saturation treatment, pore structures, cracks and crude oil distribution conditions are obtained, the multiple natural core columns are placed around a horizontal well model pipe column by a circle at equal angles, and a horizontal well model pipe column is formed; the actual rock is placed between the natural core columns as an interlayer; s2, performing external pouring on the natural core column containing the interlayer by using cement and quartz sand, wherein the proportions of the cement and the quartz sand are different in pairs; s3, fracturing, flowback and displacement are carried out; and S4, obtaining the pore structure, the crack and the crude oil distribution condition again, and obtaining the pore structure change, the crack distribution change and the final crude oil distribution condition of the natural core column. The method can effectively describe the fracture distribution pattern and the transformation effect before and after fracturing; the influence of longitudinal heterogeneity on crack propagation and transformation volume is researched; conditions are created for determining remaining oil distribution research under different development modes, fracturing scales and parameters.

Description

Technical Field

[0001] The invention relates to the technical field of fracturing and transformation of low-permeability, ultra-low-permeability and tight oil reservoirs, and in particular to a combined fracturing and displacement simulation experimental method and device for heterogeneous reservoirs. Background Art

[0002] With the gradual deepening of exploration and development of conventional oil and gas reservoirs at home and abroad, it is becoming increasingly difficult to increase reserves and production. Unconventional tight oil reservoirs have become an important strategic successor resource. Although the reserves of tight reservoirs are considerable, compared with conventional oil reservoirs, the physical properties of tight reservoirs are relatively poor. The crude oil production of conventional development methods is very low or even zero. Mine development practice has proved that fracturing transformation is a mature process measure for efficient production of single wells and effective development of such reservoirs.

[0003] Under hydraulic fracturing conditions, the interaction mechanisms and expansion and penetration patterns between rock mass structural surfaces of different scales and strengths and hydraulic fractures are often quite different. Since the strength of the natural structural surface of the rock mass is usually much smaller than the strength of the rock skeleton itself, under the influence of factors such as increased differential stress caused by hydraulic fracturing and reservoir heterogeneity defects, the reservoir rock mass usually not only undergoes tension-shear failure of small-scale cracks, but also complex mechanical behaviors such as tension, shear, slip and dislocation of large-scale structural surfaces such as joints and faults. If natural fractures of different densities develop in the reservoir, complex mechanical behaviors such as splitting and direction conversion will occur when hydraulic fractures encounter natural fractures, which is also the main factor controlling the formation of complex networks.

[0004] For example, patent document CN 115639083 A provides a mine-level true triaxial hydraulic fracturing simulation experiment method and device, which includes preparing experimental rock samples according to the mechanical characteristics and lithological characteristics of the reservoir rock in the target block; placing a simulated wellbore inside the experimental rock sample, simulating perforation holes on the peripheral wall of the simulated wellbore, and simulating perforation channels corresponding to the perforation holes of the simulated wellbore inside the experimental rock sample; placing the experimental rock sample in an ultra-large true triaxial stress loading system for a fracturing simulation experiment; after the experiment, taking out the experimental rock sample, and combining the experimental data monitored during the fracturing simulation experiment, analyzing the experimental rock sample fracturing simulation experiment results. The experimental rock samples used in the simulation device of this scheme are collected from the target block, which are single and sporadic, and have great differences from the mechanical characteristics of the dense rock to be simulated, and cannot feedback the full-scale fluid occurrence conditions.

[0005] After large-scale fracturing, the tight reservoir forms a complex fracture network. The original single medium reservoir becomes a dual medium reservoir with coexistence of fractures and matrix. It is difficult to directly observe and measure the parameters and structural characteristics of different types of pores and fracture spaces. In addition, the microscopic distribution of residual oil in the core after fracturing is very critical to the optimization of fracturing parameters. In order to obtain the above parameters and structural characteristics, the core thin section microscopic model, online CT scanning and nuclear magnetic resonance technology are currently mainly used to study the fluid seepage characteristics, residual oil distribution characteristics and pore structure characteristics in the core. The core thin section microscopic model belongs to a one-dimensional simulation, and it is difficult to quantitatively characterize the residual oil as a whole. On the one hand, online CT scanning can obtain the fracture distribution and pore characteristic parameters, and can also provide an intuitive residual oil distribution image, but the accuracy of the scanning result is closely related to the image processing and resolution, and the subjective influence is serious. It is impossible to quantitatively analyze the residual oil distribution in pore throats of different pore sizes. Therefore, it is usually combined with the nuclear magnetic resonance method on this basis to reflect the full-scale fluid occurrence status and analyze the micro-scale crude oil production characteristics and residual oil distribution characteristics before and after real core fracturing.

[0006] Based on this, the inventors of the present application realized that there is still room for further improvement in the technical solutions of the current simulation devices in terms of simulating multi-scale fracturing of reservoirs and intuitively obtaining parameters and structural characteristics of different types of pores and fracture spaces.

[0007] Therefore, a simulation device is designed to simulate the multi-scale fracturing of the reservoir, to study the distribution and expansion laws of cracks in the natural core of the reservoir before and after fracturing, as well as the micro-scale crude oil utilization characteristics and residual oil distribution characteristics before and after fracturing, and to further study the design rationality of the well shut-in and flowback system after fracturing and the displacement process, which is of great significance to the transformation and effective development of tight oil reservoirs. Summary of the invention

[0008] In order to solve the existing technical problems, the present invention proposes a combined fracturing and displacement simulation experimental method and device for heterogeneous reservoirs, which simulates the distribution law of artificial fractures under different reservoir physical properties and rock mechanics conditions, obtains the pore structure and microscopic distribution state of natural core columns before and after fracturing through CT scanning technology, calculates the crude oil utilization of pores of different sizes after fracturing using nuclear magnetic resonance signals, and reveals the residual microscopic displacement and occurrence mechanism of different pore structures of reservoir transformation oil reservoirs.

[0009] According to one aspect of the present invention, a combined fracturing and displacement simulation experimental method for a heterogeneous reservoir is provided, which comprises the following steps:

[0010] S1. Perform fluid saturation treatment on the natural core column and obtain the pore structure, fractures and crude oil distribution of the natural core column. Place several natural core columns around the horizontal well model string at equal angles, and place the actual rock as an interlayer between the natural core columns;

[0011] S2. Use cement and quartz sand to externally cast the natural core column containing the interlayer, forming three sample layers in the vertical direction, and the ratio of cement and quartz sand between the sample layers is different, so as to form a three-dimensional casting combination model of heterogeneous reservoir rock mass;

[0012] S3, performing fracturing, flowback and displacement on the three-dimensional casting combination model;

[0013] S4. The pore structure, fractures and crude oil distribution of the natural core column are obtained again, thereby obtaining the changes in the pore structure, fracture distribution and final distribution of crude oil of the natural core column before and after fracturing.

[0014] According to one embodiment of the present invention, in step S1 / S4, obtaining the pore structure, fractures and crude oil distribution of the natural core column includes:

[0015] NMR T2 spectrum sampling and CT scanning were performed to obtain the pore structure, fractures and crude oil distribution of natural core columns.

[0016] According to one embodiment of the present invention, in step S2, cement and quartz sand are used to externally cast the natural core column containing the interlayer to form three sample layers in the vertical direction, including:

[0017] The horizontal well model string is centered and vertically penetrates the three sample layers.

[0018] According to one embodiment of the present invention, the length of the horizontal well model pipe string is less than the length of the natural core column and the height of the three-dimensional casting combination model.

[0019] According to one embodiment of the present invention, in step S4, the pore structure, fractures and crude oil distribution of the natural core column are obtained again, including:

[0020] Observe the expansion morphology of hydraulic fractures generated by fracturing in a three-dimensional casting combination model.

[0021] According to one embodiment of the present invention, in step S3, fracturing, flowback and displacement are performed on the three-dimensional casting assembly model, including:

[0022] The three-dimensional casting assembly model is fractured using a fracturing fluid containing a fluorescent dye.

[0023] According to one embodiment of the present invention, the length of the natural core column is the same as the height of the three-dimensional casting assembly model and penetrates each layer of the sample layer in the vertical direction.

[0024] According to one embodiment of the present invention, in step S1, the fluid saturation treatment of the natural core column includes:

[0025] subjecting the natural core column to saturated water treatment;

[0026] The natural core column is saturated with crude oil.

[0027] According to one embodiment of the present invention, the natural core column is a standard 2.5 cm core, and the drilling direction is perpendicular to the original size core, and the bedding is parallel to the ground.

[0028] According to one embodiment of the present invention, in step S3, fracturing, flowback and displacement are performed on the three-dimensional casting assembly model, including:

[0029] Fluid is pumped into the three-dimensional casting assembly model through the horizontal well model pipe string, and natural core flowback fluid is made to flow into the horizontal well model pipe string.

[0030] According to one embodiment of the present invention, in step S1, before the natural core column is subjected to fluid saturation treatment, the following steps are included:

[0031] The natural core column was cleaned and dried, and then placed in a core holder. After adding a confining pressure of 2 to 3 MPa, the core was vacuumed for 12 hours.

[0032] According to one embodiment of the present invention, step S1 further includes:

[0033] The horizontal well model string is perforated by simulating perforation holes.

[0034] According to one embodiment of the present invention, a pressure sensor is disposed on the inner wall of the horizontal well model string, and a velocity sensor is disposed at the wellhead.

[0035] According to one embodiment of the present invention, in step S3, fracturing, flowback and displacement are performed on the three-dimensional casting assembly model, including:

[0036] During the fracturing process, the pressure in the horizontal well model string is monitored by a pressure sensor, and the well pressure is changed through the fracturing control system, different return speeds are set, and real-time monitoring is performed using a speed sensor.

[0037] According to one embodiment of the present invention, the horizontal well model pipe string is spaced apart from the bottom of the three-dimensional casting assembly model.

[0038] According to an embodiment of the present invention, the medium used for displacement includes one or more of gas, water, foam, chemical agent and different medium slugs.

[0039] According to another aspect of the present invention, a combined fracturing and displacement simulation experimental device for heterogeneous reservoirs is provided, which comprises:

[0040] A three-dimensional casting combination model, wherein the three-dimensional casting combination model is composed of three sample layers with different cement and quartz sand ratios, and a fluid-saturated natural core column and a horizontal well model pipe column penetrating the three sample layers;

[0041] A liquid metering system, wherein the liquid metering system is connected to the three-dimensional casting assembly model through a mixed liquid pipeline;

[0042] A fracturing control system, wherein the fracturing control system is connected to the three-dimensional casting assembly model through a fracturing fluid pipeline;

[0043] A displacement system, wherein the displacement system is connected to the three-dimensional casting assembly model through a displacement pipeline;

[0044] The confining pressure system is connected to the three-dimensional casting combination model through a confining pressure pipeline.

[0045] According to one embodiment of the present invention, the length of the natural core column is the same as the height of the three-dimensional casting combination model, and the horizontal well model pipe string is spaced apart from the bottom of the three-dimensional casting combination model.

[0046] According to one embodiment of the present invention, a pressure sensor is disposed on the inner wall of the horizontal well model string, and a velocity sensor is disposed at the wellhead.

[0047] According to one embodiment of the present invention, the natural core column is a standard 2.5 cm core, and the drilling direction is perpendicular to the original size core, and the bedding is parallel to the ground.

[0048] Due to the adoption of the above technical solution, the present invention has the following advantages compared with the prior art:

[0049] 1. The present invention is used for large-scale physical simulation experiments of tight oil. A three-dimensional rock model similar to the mechanical characteristics of tight rock is produced. At the same time, a cylindrical natural core column is set in the core to simulate the crack initiation process during tight oil fracturing. The crack distribution morphology and effective transformation effect in the three-dimensional casting combination model and the natural core column after fracturing are described, and the crack initiation mechanism is revealed.

[0050] 2. The present invention is used to simulate the influence of reservoirs with different mechanical strengths and physical properties on the initiation and extension of fractures, quantify the influence of longitudinal heterogeneity on the transformation volume, and evaluate the adaptability of fracturing technology and fracturing parameters.

[0051] 3. The present invention combines CT scanning with nuclear magnetic resonance analysis to further quantify the pore space parameters and fluid occurrence state before and after fracturing and before and after displacement, quantitatively express the remaining oil state under different fracturing parameters, flowback, displacement parameters and systems, and optimize fracturing parameters, flowback systems and displacement parameters. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] In order to more clearly illustrate the technical solution of the embodiment of the present invention, the drawings required for use in the embodiment will be briefly introduced below. Obviously, the drawings described below are only some implementation cases of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0053] Figure 1 A schematic flow chart of a combined fracturing and displacement simulation experimental method for heterogeneous reservoirs according to the present invention is shown;

[0054] Figure 2 A schematic diagram of a combined fracturing and displacement simulation device for a heterogeneous reservoir according to the present invention is shown;

[0055] Figure 3 A top view of a three-dimensional casting combination model of a heterogeneous reservoir combined fracturing and displacement simulation device according to the present invention is shown.

[0056] The reference numerals in the figures are described as follows:

[0057] 1-three-dimensional casting combination model; 101-single-layer casting model; 102-horizontal well model string; 103-natural core column; 104-velocity sensor; 105-pressure sensor; 106-rock interlayer; 107-first casting sample layer; 108-second casting sample layer; 109-third casting sample layer; 2-fracturing control system; 201-fracturing fluid pipeline; 202-fracturing fluid one-way flow valve; 3-liquid metering system; 301-mixed liquid pipeline; 4-displacement system; 401-displacement pipeline; 402-displacement one-way flow valve; 5-confining pressure system; 501-confining pressure pipeline; 6-microcomputer control system; 601-signal transmission line. DETAILED DESCRIPTION

[0058] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the embodiments of the present invention are further described in detail below in combination with specific embodiments and with reference to the accompanying drawings.

[0059] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0060] like Figure 1As shown, the present invention provides a combined fracturing and displacement simulation experimental method for heterogeneous reservoirs. Figure 1 A schematic flow chart of an exemplary simulation test method according to the present invention is shown, which may specifically include the following steps:

[0061] S1. Perform fluid saturation treatment on the natural core column 103 and obtain the pore structure, fractures and crude oil distribution of the natural core column 103. Place several (for example, three) natural core columns 103 at equal angles around the horizontal well model string 102, and place the actual rock as an interlayer between the natural core columns 103.

[0062] S2, externally pouring the natural core column 103 containing the interlayer with cement and quartz sand to form three sample layers in the vertical direction, with the ratio of cement and quartz sand between the sample layers being different to form a three-dimensional pouring combination model 1 of the heterogeneous reservoir rock mass;

[0063] S3, performing fracturing, flowback and displacement on the three-dimensional casting assembly model 1;

[0064] S4. The pore structure, cracks and crude oil distribution of the natural core column 103 are obtained again, thereby obtaining the changes in the pore structure, crack distribution and final distribution of crude oil of the natural core column 103 before and after fracturing.

[0065] In some embodiments, in step S1, before adding the natural core column 103 to the three-dimensional casting combination model 1, the natural core column 103 needs to be cleaned and dried and then placed in a core holder. After adding a confining pressure of 2 to 3 MPa, the core is vacuumed for 12 hours, and then fully saturated with simulated formation water, and simulated oil is injected to reach saturated oil to obtain the required crude oil saturation, and then the core is sampled by nuclear magnetic resonance T2 spectrum. Based on the collected T2 spectrum, the distribution of the initial saturated crude oil of the natural core column 103 can be determined. At the same time, through CT scanning, the crack distribution and pore characteristics of the natural core column 103 before fracturing can be obtained.

[0066] In some embodiments of step S1, the step further includes: drilling holes by simulating perforation holes on the horizontal well model string 102. Specifically, four sections are drilled at equal distances along the axial direction of the horizontal well model string 102, and six holes are drilled at equal angles in each section, for a total of 24 holes, for simulating perforation holes.

[0067] In some embodiments, the outer radius of the horizontal well model tubing string 102 is 53.97 mm, the inner radius is 30.34 mm, and the length is 500 mm. At the same time, a pressure sensor 105 is placed on the inner wall of the horizontal well model tubing string 102, and a speed sensor 104 is placed at the wellhead. The pressure sensor 105 and the speed sensor 104 are used to monitor changes in pressure and speed, respectively.

[0068] In step S1, a plurality of natural core columns 103 are placed at equal angles around the horizontal well model string 102. The specific operation is as follows: the horizontal well model string 102 is placed vertically in the middle, and the natural core columns 103 are divided into a plurality of natural core columns 103, which are placed at equal angles around the horizontal well model string 102 at a distance of 100 mm from the horizontal well model string 102.

[0069] The length of the horizontal well model string is less than the length of the natural core column and the height of the three-dimensional model. In some embodiments, the outer radius of the natural core column 103 used is 100 mm, the inner radius is 30 mm, and the height is 600 mm.

[0070] According to some embodiments, the horizontal well model string 102 is spaced apart from the bottom of the three-dimensional casting assembly model 1. Specifically, the bottom of the horizontal well model string 102 is higher than the bottom of the model by, for example, 50 mm.

[0071] In step S1, an actual rock is selected and cut into two pieces as a rock interlayer (ie, actual rock) 106 by a saw blade cutter, and the size after cutting is 600 mm×600 mm×10 mm.

[0072] After the placement is completed, the three-dimensional casting assembly model 1 is a cube with a size of 600mm×600mm×600mm.

[0073] In step S2, cement and quartz sand are used to externally cast the natural core column 103 containing the interlayer. In order to achieve heterogeneity, a layered casting method is adopted during casting, and three sample layers are formed in the vertical direction, thereby completing the production of the model.

[0074] The model includes a three-dimensional stratum, that is, the three-dimensional casting combination model 1 is divided into three layers, namely the first casting sample layer 107, the second casting sample layer 108 and the third casting sample layer 109. The three-dimensional casting combination model 1 also includes a horizontal well model string 102 and a natural core column 103. The horizontal well model string 102 and the natural core column 103 both run through the three-layer model, so that the model simulation results are closer to the actual stratum conditions.

[0075] The rock mechanical properties of the selected block rock, such as elastic modulus, Poisson's ratio, compressive strength and squeeze strength, were measured. On the one hand, an artificial model close to the actual block rock mechanical properties was made by mixing cement, quartz sand and water; on the other hand, the permeability of the three-layer sample was made heterogeneous by different ratios of cement and quartz sand between the sample layers, which made the entire sample heterogeneous and resulted in strength stratification.

[0076] The configuration methods of cement and quartz sand with different proportions are as follows:

[0077] The first casting sample layer 107: The volume ratio of cement, quartz sand and water in the sample is 5:4:1. The cement used is composite silicate cement with a strength grade of PC 32.5; the mass fraction of SiO2 is >96%, mainly fine sand with a particle size (d) of 0.08-0.50 mm; the casting sample size is 600mm×600mm×200mm, and the porosity, permeability, tensile strength and compressive strength of the sample are controlled by the consolidation temperature, so that the mechanical properties of the cast sample are close to the mechanical properties of the dense rock to be simulated. After the sample solidifies, the rock interlayer 106 is placed on the surface of the first casting sample layer 107. Then, the second casting sample layer 108 is cast on the basis of the first casting sample layer 107.

[0078] The second casting sample layer 108: mainly changes the volume ratio of cement, quartz sand and water, and secondly changes the particle size of quartz sand, so as to change the mechanical characteristics such as tensile strength, compressive strength and elastic modulus and the permeability of the second casting sample layer 108. After it solidifies, the rock interlayer 106 is placed on the surface of the second casting sample layer 108.

[0079] The third cast sample layer 109: Finally, based on the second cast sample layer 108, the volume ratio of cement, quartz sand and water and the particle size of quartz sand are changed again. The changed volume ratio and particle size are different from those of the first cast sample layer 107 and the second cast sample layer 108, thereby forming the third cast sample layer 109. Finally, the entire sample has dual heterogeneity of rock mechanical properties and permeability, and a significant stratification phenomenon occurs.

[0080] In step S3, the three-dimensional cast assembly model 1 is subjected to fracturing, flowback and displacement, including fracturing the three-dimensional cast assembly model 1 with a fracturing fluid containing a fluorescent dye, so as to observe the expansion morphology of the hydraulic fracture after the fracturing is completed.

[0081] In step S3 , fluid is pumped into the three-dimensional casting assembly model 1 through the horizontal well model string 102 , and natural core flowback fluid also flows into the horizontal well model string 102 .

[0082] Step S3 also includes connecting the first cast sample layer 107 to the confining pressure system 5 and ensuring the boundary sealing before performing fracturing, flowback and displacement.

[0083] The pressure fluid control system is accessed, the fracturing source pipeline is connected, the displacement is controlled by the microcomputer system, and the pressure-time curve is monitored in real time. When the fracturing fluid is observed to overflow from the edge of the three-dimensional casting assembly model 1, the injection of the fracturing fluid is stopped through the control program.

[0084] After the fracturing is completed, it is in the depressurization and flowback stage. The pressure in the horizontal well model string 102 is continuously monitored by the pressure sensor 105. The internal pressure of the horizontal well model string 102 is changed through the fracturing control system 2 to set different flowback speeds. The speed sensor 104 is used for monitoring, and the functional relationship between the well pressure and the flowback speed is established. Then, the influence of the flowback speed on the crude oil recovery degree is analyzed. CT scanning is used to monitor the influence of the speed change of the entire flowback process on the distribution morphology of the fractures. The changes in the seepage field and the crude oil saturation field after fracturing are calculated by measuring the signal through the nuclear magnetic resonance T2 spectrum.

[0085] In step S3, after the flowback is completed, the displacement system 4 is turned on, the displacement speed and the pressure in the horizontal well model string 102 are monitored by the microcomputer system, the volume of the produced crude oil is calculated by the liquid metering system 3, and finally the displacement effect is evaluated.

[0086] In some embodiments, the displacement medium may be one or more of gas, water, foam, chemical agent, and slugs of different media.

[0087] In step S4, the three-dimensional cast composite model 1 is opened along the hydraulic fractures opened by the pressure, and the natural core column 103 is taken out. After taking out, the extension morphology of the hydraulic fractures generated by the fracturing of the three-dimensional cast composite model 1 itself is first observed through the traces of fluorescent dyes, and the influence of the differences in different mechanical properties on the crack opening characteristics is observed; then the fractured core column is placed in a clamp, and T2 spectrum sampling is performed. Through the nuclear magnetic resonance signal, the volume fractions of different pore types in the core are calculated, and the crude oil utilization of pores of different sizes after the displacement process is calculated.

[0088] In step S4, the natural core column 103 is CT scanned by CT scanning technology to observe the spatial distribution morphology of the fracturing cracks, the pore structure and the crude oil distribution inside the core after fracturing, so as to obtain the pore structure of the natural core column 103 after displacement, the change of the crack distribution and the final distribution of the crude oil.

[0089] like Figure 2-3 As shown, the present invention also provides a combined fracturing and displacement simulation device for heterogeneous reservoirs, which comprises:

[0090] A three-dimensional casting assembly model 1, wherein the three-dimensional casting assembly model 1 is composed of three sample layers with different cement and quartz sand ratios, and a fluid-saturated natural core column 103 and a horizontal well model pipe column 102 that penetrate the three sample layers. The three-dimensional casting assembly model 1 is also provided with a velocity sensor 104 and a pressure sensor 105;

[0091] A liquid metering system 3, wherein the liquid metering system 3 is fixedly connected to the three-dimensional casting assembly model 1 through a mixed liquid pipeline 301;

[0092] A fracturing control system 2, wherein the fracturing control system 2 is fixedly connected to the three-dimensional casting assembly model 1 through a fracturing fluid pipeline 201, and a fracturing fluid one-way flow valve 202 is also provided on the fracturing fluid pipeline 201;

[0093] A displacement system 4, wherein the displacement system 4 is fixedly connected to the three-dimensional casting assembly model 1 through a displacement pipeline 401, and a displacement one-way flow valve 402 is also provided on the displacement pipeline 401;

[0094] A confining pressure system 5, wherein the confining pressure system 5 is fixedly connected to the three-dimensional casting assembly model 1 through a confining pressure pipeline 501; and

[0095] The microcomputer control system 6 is communicatively connected with the liquid metering system 3 , the fracturing control system 2 , the displacement system 4 , and the confining pressure system 5 via a signal transmission line 601 .

[0096] The length of the natural core column 103 is the same as the height of the three-dimensional casting combination model 1, and the horizontal well model pipe string 102 is spaced apart from the bottom of the three-dimensional casting combination model 1. Specifically, the bottom of the horizontal well model pipe string 102 is 50 mm higher than the bottom of the model.

[0097] The inner wall of the horizontal well model string 102 is provided with a pressure sensor, and the wellhead is provided with a velocity sensor. The pressure sensor 105 and the velocity sensor 104 are used to monitor the changes of pressure and velocity respectively.

[0098] The natural core column used in the device is a standard 2.5 cm core, and the drilling direction is perpendicular to the original size core, and the bedding is parallel to the ground.

[0099] In a combined fracturing and displacement simulation experimental method and device for heterogeneous reservoirs according to an embodiment of the present invention, based on the existing technology, the fracturing simulation experiment considering multiple factors such as reservoir, fluid, and development method is improved for oil reservoirs implementing reservoir transformation. The improved simulation experimental method and device can effectively describe the distribution morphology of cracks and the transformation effect before and after fracturing; study the influence of longitudinal heterogeneity on crack expansion and transformation volume; and create conditions for determining the distribution of residual oil under different development methods and fracturing scales and parameters.

[0100] A person skilled in the art should understand that the discussion of any of the above embodiments is only exemplary and is not intended to imply that the scope of the disclosure of the embodiments of the present invention (including the claims) is limited to these examples; under the concept of the embodiments of the present invention, the technical features in the above embodiments or different embodiments can also be combined, and there are many other changes in different aspects of the embodiments of the present invention as above, which are not provided in detail for the sake of simplicity. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the embodiments of the present invention should be included in the protection scope of the embodiments of the present invention.

Claims

1. A combined fracturing and displacement simulation experimental method for heterogeneous reservoirs, characterized in that: The following steps are involved: S1. Perform fluid saturation treatment on the natural core column and obtain the pore structure, fractures and crude oil distribution of the natural core column. Place several natural core columns around the horizontal well model string at equal angles, and place the actual rock as an interlayer between the natural core columns; S2. Use cement and quartz sand to externally cast the natural core column containing the interlayer, forming three sample layers in the vertical direction, and the ratio of cement and quartz sand between the sample layers is different, so as to form a three-dimensional casting combination model of heterogeneous reservoir rock mass; S3, performing fracturing, flowback and displacement on the three-dimensional casting combination model; S4. The pore structure, fractures and crude oil distribution of the natural core column are obtained again, thereby obtaining the changes in the pore structure, fracture distribution and final distribution of crude oil of the natural core column before and after fracturing.

2. The combined fracturing and displacement simulation experimental method for heterogeneous reservoirs according to claim 1, characterized in that: In step S1 / S4, the pore structure, fractures and crude oil distribution of the natural core column are obtained, including: NMR T2 spectrum sampling and CT scanning were performed to obtain the pore structure, fractures and crude oil distribution of natural core columns.

3. The combined fracturing and displacement simulation experimental method for heterogeneous reservoirs according to claim 1, characterized in that: In step S2, cement and quartz sand are used to externally cast the natural core column containing the interlayer to form three sample layers in the vertical direction, including: The horizontal well model string is centered and vertically penetrates the three sample layers.

4. The combined fracturing and displacement simulation experimental method for heterogeneous reservoirs according to claim 1, characterized in that: The length of the horizontal well model pipe string is less than the length of the natural core column and the height of the three-dimensional casting combined model.

5. The combined fracturing and displacement simulation experimental method for heterogeneous reservoirs according to claim 1, characterized in that: In step S4, the pore structure, fractures and crude oil distribution of the natural core column are obtained again, including: Observe the expansion morphology of hydraulic fractures generated by fracturing in a three-dimensional casting combination model.

6. The combined fracturing and displacement simulation experimental method for heterogeneous reservoirs according to claim 1, characterized in that: In step S3, the three-dimensional casting assembly model is subjected to fracturing, flowback and displacement, including: The three-dimensional casting assembly model is fractured using a fracturing fluid containing a fluorescent dye.

7. The combined fracturing and displacement simulation experimental method for heterogeneous reservoirs according to claim 1, characterized in that: The length of the natural core column is the same as the height of the three-dimensional casting assembly model and penetrates each layer of the sample layer in the vertical direction.

8. The combined fracturing and displacement simulation experimental method for heterogeneous reservoirs according to claim 1, characterized in that: In step S1, the fluid saturation treatment of the natural core column includes: subjecting the natural core column to saturated water treatment; The natural core column is saturated with crude oil.

9. The combined fracturing and displacement simulation experimental method for heterogeneous reservoirs according to claim 1, characterized in that: The natural core column is a standard 2.5 cm core, and the drilling direction is perpendicular to the original size core, and the bedding is parallel to the ground.

10. The combined fracturing and displacement simulation experimental method for heterogeneous reservoirs according to claim 1, characterized in that: In step S3, the three-dimensional casting assembly model is subjected to fracturing, flowback and displacement, including: Fluid is pumped into the three-dimensional casting assembly model through the horizontal well model pipe string, and natural core flowback fluid is made to flow into the horizontal well model pipe string.

11. The combined fracturing and displacement simulation experimental method for heterogeneous reservoirs according to claim 1, characterized in that: In step S1, before the natural core column is subjected to fluid saturation treatment, the following steps are included: The natural core column was cleaned and dried, and then placed in a core holder. After adding a confining pressure of 2 to 3 MPa, the core was vacuumed for 12 hours.

12. The combined fracturing and displacement simulation experimental method for heterogeneous reservoirs according to claim 1, characterized in that: Step S1 also includes: The horizontal well model string is perforated by simulating perforation holes.

13. The combined fracturing and displacement simulation experimental method for heterogeneous reservoirs according to claim 1, characterized in that: The inner wall of the horizontal well model pipe string is provided with a pressure sensor, and the wellhead is provided with a velocity sensor.

14. The combined fracturing and displacement simulation experimental method for heterogeneous reservoirs according to claim 13, characterized in that: In step S3, the three-dimensional casting assembly model is subjected to fracturing, flowback and displacement, including: During the fracturing process, the pressure in the horizontal well model string is monitored by a pressure sensor, and the well pressure is changed through the fracturing control system, different return speeds are set, and real-time monitoring is performed using a speed sensor.

15. The combined fracturing and displacement simulation experimental method for heterogeneous reservoirs according to claim 1, characterized in that: The horizontal well model pipe string is spaced apart from the bottom of the three-dimensional casting combination model.

16. The combined fracturing and displacement simulation experimental method for heterogeneous reservoirs according to claim 1, characterized in that: The medium used for displacement includes one or more of gas, water, foam, chemical agent and different medium slugs.

17. A combined fracturing and displacement simulation experimental device for heterogeneous reservoirs, characterized in that: include: A three-dimensional casting combination model, wherein the three-dimensional casting combination model is composed of three sample layers with different cement and quartz sand ratios, and a fluid-saturated natural core column and a horizontal well model pipe column penetrating the three sample layers; A liquid metering system, wherein the liquid metering system is connected to the three-dimensional casting assembly model through a mixed liquid pipeline; A fracturing control system, wherein the fracturing control system is connected to the three-dimensional casting assembly model through a fracturing fluid pipeline; A displacement system, wherein the displacement system is connected to the three-dimensional casting assembly model through a displacement pipeline; The confining pressure system is connected to the three-dimensional casting combination model through a confining pressure pipeline.

18. The combined fracturing and displacement simulation experimental device for heterogeneous reservoirs according to claim 17, characterized in that: The length of the natural core column is the same as the height of the three-dimensional casting combination model, and the horizontal well model pipe column is spaced apart from the bottom of the three-dimensional casting combination model.

19. The combined fracturing and displacement simulation experimental device for heterogeneous reservoirs according to claim 17, characterized in that: The inner wall of the horizontal well model pipe string is provided with a pressure sensor, and the wellhead is provided with a velocity sensor.

20. The combined fracturing and displacement simulation experimental device for heterogeneous reservoirs according to claim 17, characterized in that: The natural core column is a standard 2.5 cm core, and the drilling direction is perpendicular to the original size core, and the bedding is parallel to the ground.

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