One-dimensional online core displacement experiment method for simulating pressure driving process

Abstract

The invention provides a one-dimensional on-line core displacement experiment method for simulating a pressure driving process, which comprises the following steps of: 1, screening a core, and measuring the mechanical property of the core; 2, assembling a new rock core model by using a gasket, and putting the new rock core model into a rock core clamping system; 3, connecting an experimental device, and injecting a pressure flooding liquid with a certain pressure into the rock core model by using a displacement pump; step 4, pressure flooding experiments of different contrasts are carried out, and the crack expansion condition of each small section of the rock core is monitored; and 5, performing CT scanning on the damaged rock sample, and determining the internal crack form and spatial distribution of the rock sample. According to the one-dimensional online core displacement experiment method for simulating the pressure driving process, the complex structure in the core and seepage dialysis parameters can be actually measured, the size of a crack can be observed and recorded, and the problem that the simulation experiment in the pressure driving process lacks an accurate method is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas exploitation experimental research, and particularly to a one-dimensional on-line core displacement experiment method for simulating the pressure drive process. Background Art

[0002] Pressure drive refers to achieving near-wellbore fracture formation by continuously injecting high-pressure fluid into the reservoir, thereby expanding the seepage area, improving the water injection capacity of low-permeability reservoirs, and quickly replenishing the formation capacity. However, currently, there is a lack of effective experimental research instruments and methods for accurately measuring relevant parameters in the flow field. Therefore, it is necessary to invent a low-cost experimental method that can perform batch screening work.

[0003] In previous pressure drive research:

[0004] (1) A method for characterizing non-Darcy flow in low-permeability reservoirs, patent number CN202111507971.1: provides a method that can reflect the rheological changes caused by the interaction between fluid and rock, providing new ideas for subsequent large-scale reservoir simulation. The optimal parameter combination is obtained by fitting the measured values. It is impossible to monitor the complex fracture morphology inside the core in real time online.

[0005] (2) A multi-physical-field coupled microscopic seepage experiment device and method, patent number CN201910451146.0: discloses an experimental device composed of components such as a computer, an injection pump, an optical microscope, a laser emitter, and a liquid / gas bag. It solves the problem that previous microscopic seepage experiments could only observe the flow but not obtain the fluid velocity during the seepage process. The device is too complex to complete batch screening work.

[0006] (3) A multi-phase seepage experiment system for rock mass rough fractures based on 3D printing technology, patent number CN202210258127.8: This experimental system can test the full-domain seepage velocity field in natural fractures of rock masses, obtain seepage velocity fields, pressure differences at the inlet and outlet of the model, two-phase boundary structures during the displacement process, and characteristic data of gas-liquid-liquid multi-phase flow interfaces. It can accurately control various parameters during the experiment and has visualization to realize real-time measurement of various fluid parameters. It is impossible to achieve low cost and a large amount of screening work.

[0007] (4) A resetable layered and segmented pressure drive water injection string and method, patent number CN202211286125.6: This invention is applicable to layered and segmented pressure drive water injection in oilfield injection wells, can meet the needs of formation layered and segmented water injection, the injection string can be reused, improving the qualification rate of water injection intervals and saving operation costs. It is impossible to conduct small-scale seepage experiments to measure the required relevant parameters.

[0008] The above existing technologies are quite different from the present invention and fail to solve the technical problems of batch obtaining of core parameters and distribution of pressure-driven fractures. Therefore, we have invented a new one-dimensional on-line core displacement experiment method for simulating the pressure-driven process. Summary of the Invention

[0009] The object of the present invention is to provide a one-dimensional on-line core displacement experiment method for simulating the pressure-driven process, which can not only truly measure the parameters of the complex structure and seepage dialysis inside the core, but also observe and record the size of the fractures.

[0010] The object of the present invention can be achieved by the following technical measures: A one-dimensional on-line core displacement experiment method for simulating the pressure-driven process, which includes:

[0011] Step 1: Screen the core and measure the mechanical properties of the core.

[0012] Step 2: Assemble a new core model using gaskets and place it in the core holding system.

[0013] Step 3: Connect the experimental device and use a displacement pump to inject a pressure-driven fluid into the core model at a certain pressure.

[0014] Step 4: Conduct pressure-driven experiments with different controls and monitor the crack propagation of each small section of the core.

[0015] Step 5: CT scan the damaged rock samples to determine the internal crack morphology and spatial distribution of the rock samples.

[0016] The object of the present invention can also be achieved by the following technical measures:

[0017] In Step 1, in order to ensure the appearance of cracks in the core, it is necessary to weaken the thickness of the core and divide the core into small sections; through experimental data measurement, reducing the thickness of the core can achieve fracturing.

[0018] In Step 1, it is necessary to compress the core thickness to between 45 mm and 48 mm, and the diameter is 45.5 mm.

[0019] In Step 2, the size of the gasket is designed as: the thickness is 10 mm, the inner diameter is 25.5 mm, and the outer diameter is 45.5 mm; it is convenient to remove each section of the core and draw relevant conclusions by observing the cracks of each section of the core.

[0020] In Step 3, when connecting the experimental device, connect two displacement pumps to one end of two intermediate containers, the other end of the two intermediate containers is connected to one end of the core holder, the other end of the core holder is respectively connected to the oil-water separator and the back pressure pump, and the confining pressure pump is connected to the core holder.

[0021] In Step 3, prepare a colored displacement fluid with appropriate viscosity, and use a displacement pump to inject the displacement fluid into the core model at a certain pressure. Set the displacement speed to 0.008 mL / min for easy observation of the flow of the displacement fluid.

[0022] In Step 4, according to the experimental data, fractures occur within the injection pressure range of 20 - 35 MPa, which is convenient for controlling the pressure borne by the rock sample. A pressure sensor is used to record the pressure changes in real time.

[0023] In Step 4, test the differences in the sizes of the opened fractures of the same type of core with the same displacement fluid at different pressures to investigate the influence of pressure on fracture propagation. Disassemble the composed core into small segments and monitor the fracture propagation of each small segment of the core.

[0024] In Step 4, test the differences in the sizes of the opened fractures of different types of cores with the same displacement fluid at the same pressure to investigate the influence of core type on fracture propagation. Disassemble the composed core into small segments and monitor the fracture propagation of each small segment of the core.

[0025] In Step 4, test the differences in the sizes of the opened fractures of the same type of core with different displacement fluids at the same pressure to investigate the influence of the displacement fluid on fracture propagation. Disassemble the composed core into small segments and monitor the fracture propagation of each small segment of the core.

[0026] This one-dimensional online core displacement experiment method for simulating the displacement process further includes, after Step 2, first conducting uniaxial compression experiments and triaxial stress experiments on the target core model to obtain relevant mechanical property parameters such as the elastic modulus and Poisson's ratio of the core.

[0027] The object of the present invention can also be achieved by the following technical measures: a one-dimensional online core displacement experiment system for simulating the displacement process, which uses the one-dimensional online core displacement experiment method for simulating the displacement process to measure the parameters of the complex structure and seepage dialysis inside the core and observe and record the size of the fractures.

[0028] In the one-dimensional online core displacement experiment method for simulating the displacement process in the present invention, by shortening the size of the one-dimensional core, reducing the thickness, and shortening the distance, in-situ fracturing of the fluid is achieved, which is convenient for carrying out large-scale screening experimental work. The present invention can not only truly measure the parameters of the complex structure and seepage dialysis inside the core, but also observe and record the size of the fractures, solving the problem of the lack of accurate methods in the simulation experiment of the displacement process. Compared with the prior art, the present invention has the following beneficial effects:

[0029] (1) Using the experimental models of each small segment of the core, a method for screening a large number of cores as required to provide batch experiments can be provided.

[0030] (2) The influence of different pressures on crack propagation can be investigated, and the results of seepage dialysis can be obtained by comparing the sizes of the cracks. Description of the Drawings

[0031] Figure 1 It is a structural diagram of the experimental device adopted in a specific embodiment of the present invention;

[0032] Figure 2 It is an example diagram of the core model in a specific embodiment of the present invention;

[0033] Figure 3 It is an example diagram of the sandstone core model in a specific embodiment of the present invention;

[0034] Figure 4 It is a schematic diagram of observing cracks in the dissected experimental sample in a specific embodiment of the present invention;

[0035] Figure 5 It is a flowchart of a specific embodiment of the one-dimensional on-line core displacement experiment method for simulating the pressure drive process of the present invention. Detailed Embodiments

[0036] It should be noted that the following detailed description is exemplary and is intended to provide further illustration of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0037] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular forms are also intended to include the plural forms. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they specify the presence of features, steps, operations, and / or combinations thereof.

[0038] As Figure 5 shown, Figure 5 It is a flowchart of the one-dimensional on-line core displacement experiment method for simulating the pressure drive process of the present invention. The key lies in reducing the size, thickness and distance of the core, assembling a new core with gaskets to achieve in-situ fracturing of the fluid. The one-dimensional on-line core displacement experiment method for simulating the pressure drive process includes:

[0039] Step 1, screening the core and measuring the mechanical properties of the core.

[0040] With reference to and based on the dual - medium model, in the dual - medium model, it is assumed that pores exist in the matrix rock blocks and are homogeneous. The fracture direction is consistent with the direction of the main permeability, the fracture width is constant, the fracture network can be uniformly distributed or non - uniformly distributed, and it develops discretely in three - dimensional space. The flow capacity is characterized by the geometric mean permeability:

[0041]

[0042] where: \(K_t\) is the geometric mean permeability (\(\mu m\)) 2 ; \(K\) matinx is the matrix permeability (\(\mu m\)) 2 ; \(K\) f is the fracture network permeability (\(\mu m\)) 2 .

[0043] Therefore, in order to ensure the appearance of fractures in the core, the thickness of the core needs to be weakened, and the core is divided into small segments. According to the experimental data, reducing the thickness of the core can achieve fracturing, and gaskets are used to connect each small core segment to form the required core. The core thickness needs to be compressed to between 45 mm and 48 mm, and the diameter is 45.5 mm.

[0044] Step 2: Assemble a new core using gaskets and place it in the core - holding system.

[0045] Connect the gaskets to form a new core. According to the research in a method for preparing long cores based on the cementation method, the size of the gasket can be designed as: thickness 10 mm, inner diameter 25.5 mm, and outer diameter 45.5 mm. This is convenient for removing each core segment and drawing relevant conclusions by observing the cracks in each core segment.

[0046] Step 3: Equipment connection. Assemble the experimental instruments as Figure 1 shown. When connecting the experimental device, connect two displacement pumps to one end of two intermediate containers, the other ends of the two intermediate containers are connected to one end of the core - holder, the other end of the core - holder is respectively connected to the oil - water separator and the back - pressure pump, and the confining - pressure pump is connected to the core - holder.

[0047] Configure a colored displacement fluid with appropriate viscosity, use the displacement pump to inject the displacement fluid at a certain pressure into the core model, and set the displacement speed to 0.008 mL / min for easy observation of the flow of the displacement fluid.

[0048] Step 4: Conduct displacement experiments with different controls and monitor the crack propagation in each small core segment.

[0049] According to the experimental data, fractures occur in the range of injection pressure from 20 - 35 MPa, which is convenient for controlling the pressure borne by the rock sample, and a pressure sensor is used to record the pressure change in real - time.

[0050] When observing that the sizes of the opened fractures of the same type of core are different under the same displacement fluid at different pressures to investigate the influence of pressure on fracture propagation, the composed core is disassembled into small segments, and the fracture propagation of each small segment of the core is monitored.

[0051] When observing that the sizes of the opened fractures of different types of cores are different under the same displacement fluid at the same pressure to investigate the influence of pressure on fracture propagation, the composed core is disassembled into small segments, and the fracture propagation of each small segment of the core is monitored.

[0052] When observing that the sizes of the opened fractures of the same type of core are different under different displacement fluids at the same pressure to investigate the influence of pressure on fracture propagation, the composed core is disassembled into small segments, and the fracture propagation of each small segment of the core is monitored.

[0053] Step 5: CT scan the damaged rock samples to determine the internal fracture morphology and spatial distribution of the rock samples. After different control experiments are completed, static CT scans are performed on the damaged rock samples to determine the internal fracture morphology and spatial distribution of the rock samples.

[0054] The experimental steps are as follows:

[0055] 1. Preparation stage:

[0056] For the target core, prepare different types of cores to be screened, connect the cores with gaskets to form a new core. First, conduct uniaxial compression experiments and triaxial stress experiments on the target core to obtain relevant mechanical property parameters such as the elastic modulus and Poisson's ratio of the core.

[0057] 2. Assemble the experimental instruments as Figure 1 shown. Configure a displacement fluid with an appropriate viscosity and color, and the displacement speed is 0.008 mL / min to facilitate the observation of the flow of the displacement fluid.

[0058] 3. Reduce the thickness of the core model, and the thickness is set to an order of magnitude between 45 mm and 48 mm. Connect the cores with gaskets with a thickness of 10 mm, an inner diameter of 25.5 mm, and an outer diameter of 45.5 mm in the manner shown to form a new core, and place the assembled core at Figure 2 the model holder in Figure 1 .

[0059] 4. Turn on the pump, inject the displacement fluid into the core experimental model, record the pressure change with a pressure gauge, disassemble the gaskets after the experiment, and perform static CT scans on the damaged rock samples to determine the internal fracture morphology and spatial distribution of the rock samples.

[0060] 5. Replace different cores, and repeat the above experiments with the same pressure and displacement fluid to observe the influence of pressure on fracture propagation.

[0061] 6. Replace with different pressures and repeat the above experiments using the same core and pressure-driven fluid to observe the influence of pressure on fracture propagation.

[0062] 7. Replace with different pressure-driven fluids and repeat the above experiments using the same core and pressure to observe the influence of pressure on fracture propagation.

[0063] This experimental method can not only truly measure the complex structure inside the core and the parameters of seepage and dialysis, but also observe and record the influence of pressure on fracture size.

[0064] The following are several specific embodiments of applying the present invention

[0065] Embodiment 1

[0066] In a specific Embodiment 1 of applying the present invention, a one-dimensional on-line core displacement experimental method for simulating the pressure-driven process in sandstone is designed. The purpose is to change the pressure-driven fluid used and batch-record the morphological changes in the dynamic fracture propagation process simultaneously. The steps include:

[0067] Preparation stage: Design the core for the experiment, and divide the thickness of the sandstone core into 3 small sections of 50 mm for use as experimental samples.

[0068] Connect the experimental samples with gaskets having a thickness of 10 mm, an inner diameter of 25.5 mm, and an outer diameter of 45.5 mm to form a new core, and assemble the core used in the experiment in the manner of Figure 3 . Figure 3 Wherein: 1. A 46-mm-thick core; 2. A 10-mm-thick gasket.

[0069] Assemble the experimental apparatus as shown in Figure 1 , and place the assembled sandstone core model 3 at the core holder.

[0070] Open the piston pump, inject the pressure-driven fluid into the core experimental model, record the pressure change with a pressure gauge, the displacement speed is 0.008 mL / min, control the pressure borne by the sandstone core at about 30 MPa, and let the seeped-out liquid flow to the liquid storage bottle.

[0071] After the experiment, conduct a static CT scan on the damaged rock sample to determine the internal fracture morphology and spatial distribution of the rock sample.

[0072] This experiment measures the pressure data when fractures occur in the sandstone through a pressure detector, uses static CT scanning and analysis to determine the internal fracture morphology size and spatial distribution of the rock sample, and calculates to obtain a water saturation between 35% and 50%.

[0073] Embodiment 2

[0074] In a specific embodiment 2 of applying the present invention, a one-dimensional on-line core displacement experiment method for simulating the pressure drive process in shale is designed. The purpose is to change the pressure magnitude and batch-record and simultaneously record the morphological changes in the dynamic fracture propagation process. The method includes the following steps:

[0075] Preparation stage: Design the core for the experiment. Select the shale of the Longmaxi Formation in the Silurian System. Divide the thickness of the shale core into 4 small sections of 45 mm each for use as experimental samples. Use gaskets with a thickness of 10 mm, an inner diameter of 25.5 mm, and an outer diameter of 45.5 mm to connect them to form a new core. Assemble the core used in the experiment in the following Figure 2 way. Figure 2 In the figure: 1. Core with a thickness of 45 mm; 2. Gasket with a thickness of 10 mm.

[0076] Assemble the experimental instruments as shown in Figure 1 the figure, and place the assembled core model 2 at the core holder.

[0077] Open the pump, inject the pressure drive fluid into the core experimental model, and the pressure gauge records the pressure change. Make the displacement speed 0.008 mL / min, and control the pressure borne by the shale core at about 30 MPa.

[0078] During the experiment, observe the relevant changes of the rock sample model in real time.

[0079] After the experiment, perform a static CT scan on the damaged rock sample, and then dissect the rock sample to determine the internal fracture morphology and spatial distribution of the rock sample. Figure 4 The fractures observed for the dissected specimen are, from left to right: at the leftmost end, cracking along the natural bedding plane forms an obvious main fracture, and fracturing forms an intersecting fracture network at any angle; in the middle and at the rightmost end, the main fracture parallel to the bedding and the secondary fracture perpendicular to the bedding after fracturing penetrate through to form an intersecting network fracture.

[0080] This experiment measures the pressure data when fractures are generated in the shale through a pressure detector, uses static CT scanning and dissection to determine the internal fracture morphology size and spatial distribution of the rock sample, and calculates that the oil displacement efficiency ranges from about 40%.

[0081] Example 3

[0082] In a specific embodiment 3 of applying the present invention, a one-dimensional on-line core displacement experiment method for simulating the pressure drive process in carbonate rock is designed. The purpose is to change the pressure magnitude and batch-record and simultaneously record the morphological changes in the dynamic fracture propagation process. The method includes the following steps:

[0083] Preparation stage: Design the core for the experiment. Divide the thickness of the carbonate rock core into 4 small segments of 45 mm each to be used as experimental samples. Use gaskets with a thickness of 10 mm, an inner diameter of 25.5 mm, and an outer diameter of 45.5 mm to connect them to form a new core. Assemble the core used in the experiment in the manner of Figure 2 . Figure 2 In it: 1. Core with a thickness of 45 mm; 2. Gasket with a thickness of 10 mm.

[0084] Assemble the experimental instruments as shown in Figure 1 . Place the assembled core model 2 at the core holder.

[0085] Open the pump and inject the pressure displacement fluid into the core experimental model. The pressure gauge records the pressure change. Keep the displacement speed at 0.008 mL / min and control the pressure on the carbonate rock core at about 30 MPa.

[0086] After the experiment, conduct a static CT scan on the damaged rock sample to determine the internal crack morphology and spatial distribution of the rock sample.

[0087] This experiment measures the pressure data when cracks occur in the carbonate rock through a pressure detector, and uses static CT scanning and analysis to determine the internal crack morphology size and spatial distribution of the rock sample.

[0088] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

[0089] Except for the technical features described in the specification, the rest are the known technologies of those skilled in the art.

Claims

1. One-dimensional on-line core displacement experiment method for simulating the pressure drive process, characterized in that, The one-dimensional on-line core displacement experiment method for simulating the pressure drive process includes: Step 1: Screen the core and measure the mechanical properties of the core. Step 2: Assemble a new core model with gaskets and place it in the core clamping system. Step 3: Connect the experimental device and use a displacement pump to inject a pressure-driven fluid into the core model at a certain pressure. Step 4: Conduct pressure drive experiments with different controls and monitor the crack propagation of each small section of the core. Step 5: CT scan the damaged rock sample to determine the internal crack morphology and spatial distribution of the rock sample.

2. The one-dimensional on-line core displacement experiment method for simulating the pressure drive process according to claim 1, characterized in that, In Step 1, in order to ensure cracks appear in the core, it is necessary to weaken the thickness of the core and divide the core into small sections. According to the experimental data, reducing the thickness of the core can achieve fracturing.

3. The one-dimensional on-line core displacement experiment method for simulating the pressure drive process according to claim 2, characterized in that, In Step 1, the thickness of the core needs to be compressed to between 45 mm and 48 mm, and the diameter is 45.5 mm.

4. The one-dimensional on-line core displacement experiment method for simulating the pressure drive process according to claim 1, characterized in that, In Step 2, the size of the gasket can be designed as: the thickness is 10 mm, the inner diameter is 25.5 mm, and the outer diameter is 45.5 mm. This is convenient for removing each section of the core and drawing relevant conclusions by observing the cracks in each section of the core.

5. The one-dimensional on-line core displacement experiment method for simulating the pressure drive process according to claim 1, characterized in that, In Step 3, when connecting the experimental device, connect two displacement pumps to one end of two intermediate containers, the other end of the two intermediate containers is connected to one end of the core holder, the other end of the core holder is respectively connected to the oil-water separator and the back pressure pump, and the confining pressure pump is connected to the core holder.

6. The one-dimensional on-line core displacement experiment method for simulating the pressure drive process according to claim 1, characterized in that, In Step 3, configure a pressure-driven fluid with appropriate viscosity and color, use a displacement pump to inject a pressure-driven fluid into the core model at a certain pressure, and set the displacement speed to 0.008 mL / min for easy observation of the flow of the pressure-driven fluid.

7. The one-dimensional on-line core displacement experiment method for simulating the pressure drive process according to claim 1, characterized in that, In Step 4, according to the experimental data, rupture occurs in the range of injection pressure from 20 to 35 MPa, which is convenient for controlling the pressure borne by the rock sample, and a pressure sensor is used to record the pressure change in real time.

8. The one-dimensional on-line core displacement experiment method for simulating the pressure drive process according to claim 1, characterized in that, In Step 4, test the difference in the crack opening size of the same type of core by the same pressure-driven fluid under different pressures, investigate the influence of pressure on crack propagation, disassemble the composed core into small sections, and monitor the crack propagation of each small section of the core.

9. The one-dimensional on-line core displacement experiment method for simulating the pressure drive process according to claim 1, characterized in that, In Step 4, test the difference in the crack opening size of different types of cores by the same pressure-driven fluid under the same pressure, investigate the influence of core type on crack propagation, disassemble the composed core into small sections, and monitor the crack propagation of each small section of the core.

10. The one-dimensional on-line core displacement experiment method for simulating the pressure drive process according to claim 1, characterized in that, In Step 4, test the difference in the crack opening size of the same type of core by different pressure-driven fluids under the same pressure, investigate the influence of the pressure-driven fluid on crack propagation, disassemble the composed core into small sections, and monitor the crack propagation of each small section of the core.

11. The one-dimensional on-line core displacement experiment method for simulating the pressure drive process according to claim 1, the one-dimensional on-line core displacement experiment method for simulating the pressure drive process further includes, after step 2, first conducting a uniaxial compression experiment and a triaxial stress experiment on the target core model to obtain relevant mechanical property parameters such as the elastic modulus and Poisson's ratio of the core.

12. One-dimensional on-line core displacement experiment system for simulating the pressure drive process, characterized in that, The one-dimensional on-line core displacement experiment system for simulating the pressure drive process uses the one-dimensional on-line core displacement experiment method described in any one of claims 1-11 to measure the complex structure and seepage and dialysis parameters inside the core, and observe and record the crack size.

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