Simulated experimental device and method for fracturing well carbon dioxide gas drive induced fracture

Abstract

This invention provides a simulation experimental apparatus and method for carbon dioxide gas-driven induced fracture in fractured wells. The experimental rock sample is located within a true triaxial stress loading system. A carbon dioxide injection well and multiple gas concentration monitoring wells are positioned downwards from the top center. Hydraulic fractures of predetermined orientation and length are locally incorporated into the injection well casing. The true triaxial stress loading system applies pressure in three directions to the space outside the experimental rock sample. The carbon dioxide injection system injects carbon dioxide into the experimental rock sample. A gas concentration detection system collects changes in carbon dioxide gas concentration in the monitoring wells during the carbon dioxide gas drive process. An acoustic emission monitoring system detects the fracture information and fracture propagation process of the experimental rock sample. This simulation experimental apparatus and method for carbon dioxide gas-driven induced fracture in fractured wells is convenient to operate and highly practical, providing a reliable research tool for studying the mechanism of carbon dioxide gas-driven induced fracture in fractured wells.

Description

Technical Field

[0001] This invention relates to the field of reservoir development technology, and in particular to a simulation experimental device and method for carbon dioxide gas drive-induced fracturing in fractured wells. Background Technology

[0002] In CCUS (Carbon Capture, Utilization, and Storage) technology, captured CO2 is safely stored by liquefying and injecting it into the microscopic pores of common deep underground rocks. This achieves rapid and large-scale reduction of greenhouse gas emissions while increasing crude oil production and improving economic efficiency. In the later stages of development of hydraulically fractured wells in low-permeability reservoirs, CO2 injection can be used to transform the development method and solve the development problem of "injection failure and production failure."

[0003] When injecting carbon dioxide (SCCO) into a fractured well for oil displacement, the impact of SCCO injection on fracture propagation needs to be carefully considered. Under formation pressure, SCCO transforms from its liquid state upon injection into a supercritical state (SC-CO2). Compared to liquid CO2, supercritical SC-CO2 has a density closer to that of a liquid, a viscosity closer to that of a gas, and a greater diffusion coefficient. Supercritical SC-CO2 has a lower rock-breaking threshold pressure, making it easier to form a dense fracture network in the fracture zone. This disrupts the original structure of the hydraulically fractured well, making it more prone to fingering during oil displacement. This causes SCCO to prematurely break through the reservoir and escape along microfractures, leading to reduced well production and well leakage.

[0004] Current research on CO2 gas drive in low-permeability reservoirs at home and abroad mainly focuses on the CO2 miscible injection mechanism and CO2 drive to improve oil recovery. There is a lack of simulation experimental devices and methods for evaluating reservoir fracture induced by liquid carbon dioxide and supercritical carbon dioxide gas drive in hydraulically fractured wells.

[0005] Chinese patent application CN201810291699.X discloses an apparatus and method for simulating carbon dioxide dry fracturing, comprising: a liquid CO2 preparation module for preparing liquid CO2; a liquid CO2 pumping module connected to the liquid CO2 preparation module for pumping liquid CO2; a CO2 heating module connected to the liquid CO2 pumping module for regulating the temperature of the liquid CO2; a pseudo-triaxial loading module including a pseudo-triaxial loading frame, an axial pressure pump, a confining pressure pump, and a core holding sleeve, the core holding sleeve being mounted on a loading base for holding the core, and the confining pressure pump and axial pressure pump for applying pressure to the core; a core heating module located outside the confining pressure sleeve for heating the core; and the liquid CO2 pumping module and CO2 heating module being connected to the fluid injection end at the loading base. Using the apparatus and method for simulating carbon dioxide dry fracturing provided by this invention, optimal injection parameters affecting fracture morphology can be obtained.

[0006] Chinese patent application CN201610972423.9 discloses a supercritical carbon dioxide fracturing simulation experimental device, characterized by a pressure chamber, a vacuum saturation system, and a carbon dioxide phase conversion system. The pressure chamber comprises a sealed cavity, flat jacks, and heating rods. The sealed cavity consists of an upper cover plate, a confining cylinder, and a pressure chamber base, sealed by a sealing ring. Four flat jacks are evenly distributed on the side wall of the confining cylinder, with one flat jack fixed to the upper cover plate and the pressure chamber base respectively. The heating rod is fixed to the pressure chamber base. The vacuum saturation system includes a vacuum pump and a saturation liquid station. The carbon dioxide phase conversion system includes a carbon dioxide gas source, a cooling device, and an injection pump, which cools and liquefies the carbon dioxide before pressurizing and heating it to convert it to a supercritical state. This invention conducts supercritical carbon dioxide fracturing simulation experiments on rocks and artificial specimens under saturated pore pressure conditions, real-time monitoring of parameters such as injection pressure, temperature, and displacement of the fracturing fluid during the fracturing process, and obtaining the fracture propagation law. It serves as an experimental platform for studying the mechanism of supercritical carbon dioxide fracturing.

[0007] Chinese patent application CN201810755321.0 discloses a method for visualizing supercritical carbon dioxide fracturing physical simulation experiments. The method includes: preparing a rock sample; drilling a central hole in the rock sample and creating pre-fabricated fractures; attaching a PVC film and a lower PVC film to the surface of the rock sample for curing; fixing the cured rock sample in the confining pressure chamber of a visual two-dimensional hydraulic fracture simulation experimental device; applying a set triaxial confining pressure and pore pressure to the rock sample; activating a high-speed camera; injecting supercritical carbon dioxide fracturing fluid into the central hole; continuously recording the injection pressure and surface image information of the rock sample until the end of the experiment; sequentially removing the injection pressure, pore pressure, and triaxial confining pressure; removing the rock sample; and cutting the rock sample to observe the internal hydraulic fractures. This method can obtain images of the entire process of artificial fracture initiation and propagation during supercritical carbon dioxide fracturing, as well as the distribution patterns of parameters such as stress, strain, and pore pressure on the surface of the rock sample.

[0008] Chinese patent application CN202010514034.8 relates to a device for continuous phase change carbon dioxide flooding, fracturing, and proppant migration, which simultaneously simulates the process of carbon dioxide flooding, fracturing, and proppant migration. The phases are distinguished before carbon dioxide injection, and three visualized carbon dioxide chambers form a carbon dioxide phase change system. The supercritical, liquid, and gaseous carbon dioxide stored in the chambers can be observed in real time under different temperature and pressure conditions, as well as the phase change process. This allows for the study of subtle phase changes of carbon dioxide and the impact of these states on the flooding, fracturing, and proppant migration processes.

[0009] The above-mentioned existing technologies are all quite different from the present invention and have failed to solve the technical problem we want to solve. Therefore, we have invented a new simulation experimental device and method for carbon dioxide gas drive-induced fracture in fractured wells. Summary of the Invention

[0010] The purpose of this invention is to provide a convenient and practical simulation experimental device and method for carbon dioxide gas drive-induced fracturing in fractured wells.

[0011] The objective of this invention can be achieved through the following technical measures: a simulation experimental device for evaluating carbon dioxide gas-driven fracture in fractured wells. This simulation experimental device includes an experimental rock sample, a true triaxial stress loading system, a carbon dioxide injection system, an acoustic emission monitoring system, and a gas concentration detection system. The experimental rock sample is located within the true triaxial stress loading system. A carbon dioxide injection well and multiple gas concentration monitoring wells are positioned downwards from the top center. Hydraulic fractures of predetermined orientation and length are locally arranged in the injection well. The true triaxial stress loading system applies pressure in three directions to the space outside the experimental rock sample. The carbon dioxide injection system injects carbon dioxide into the experimental rock sample. The gas concentration detection system collects data on the changes in carbon dioxide gas concentration in the monitoring wells during the carbon dioxide gas drive process. The acoustic emission monitoring system detects the fracture information and fracture propagation process of the experimental rock sample.

[0012] The objective of this invention can also be achieved through the following technical measures:

[0013] The simulation experimental device for carbon dioxide gas drive-induced fracturing in fractured wells also includes a temperature loading control system, which simulates and records the thermal conditions of the experimental rock sample during carbon dioxide injection.

[0014] The temperature loading control system includes a heating resistance wire, a thermocouple temperature sensor, and a temperature acquisition and control instrument. The heating resistance wire is connected to the temperature acquisition and control instrument and heats the experimental rock sample. The probe of the thermocouple temperature sensor is set on the inner wall of the well barrel of the experimental rock sample and connected to the temperature acquisition and control instrument to collect the temperature of the experimental rock sample near the well barrel wall and transmit the temperature information to the temperature acquisition and control instrument. The temperature acquisition and control instrument displays the temperature information. When the temperature near the well barrel wall reaches the set temperature value, the heating resistance wire is de-energized through the temperature acquisition instrument.

[0015] The temperature measurement range of this thermocouple temperature sensor is -50℃ to 500℃.

[0016] The experimental rock sample was prepared by casting with cement mortar, and its external dimensions are 300mm×300mm×300mm. A vertical center hole with a diameter of 10mm and a length of 200mm is opened in the center of the top surface of the experimental rock sample, which is used to simulate the carbon dioxide injection well. Multiple vertical center holes with a diameter of 10mm and a length of 200mm are set around the experimental rock sample, which are used to simulate gas concentration monitoring wells to monitor the changes in carbon dioxide concentration in the well group during the experiment.

[0017] Multiple gas concentration monitoring wells are located at the orientation of the pre-fabricated fracture extension line, the vertical orientation of the fracture, and the orientation at a preset angle to the fracture.

[0018] The true triaxial stress loading system comprises a multi-channel hydraulic servo controller, a hydraulic injection pipeline, a high-pressure bearing cylinder, a high-pressure cylinder top cover, a hydraulic side top plate, a hydraulic bottom top plate, a rigid upper top plate, and a rigid side pad. The experimental rock sample is located in the high-pressure bearing cylinder, and the rigid pad is located between the experimental rock sample and the hydraulic side top plate to fix the horizontal position of the experimental rock sample. The hydraulic side top plate and the hydraulic bottom top plate are used to apply true triaxial stress loads to the side and bottom surfaces of the experimental rock sample. The rigid upper top plate is located between the experimental rock sample and the high-pressure cylinder top cover to fix the vertical position of the experimental rock sample. The hydraulic side top plate and the hydraulic bottom top plate are connected to the multi-channel hydraulic servo controller through the hydraulic injection pipeline. The multi-channel hydraulic servo controller is used to set and control the triaxial stress load.

[0019] The acoustic emission monitoring system includes an acoustic emission probe, an acoustic emission signal line, a signal amplifier, and an acoustic emission instrument. The acoustic emission probe is set on two opposite horizontal sides of the experimental rock sample to monitor the acoustic emission ringing rate and energy rate of the experimental rock sample corresponding to the carbon dioxide injection parameters. The acoustic emission probe is connected to the signal amplifier through the acoustic emission signal line. The signal amplifier amplifies the acoustic emission signal and then connects to the acoustic emission instrument through the acoustic emission signal line. The acoustic emission instrument processes and interprets the amplified acoustic emission signal, locates the spatial position of the fracture point, and analyzes the fracture event and fracture propagation law of the experimental rock sample.

[0020] The gas concentration detection system consists of a concentration detection probe and a concentration detector. The gas concentration detection probe is placed in the monitoring well and connected to the concentration detector via a signal line. The concentration detector dynamically records the changes in carbon dioxide concentration in different monitoring wells. Combined with the analysis of the fracture time and fracture propagation law of the experimental rock sample by the acoustic emission instrument, the system analyzes the variation law of carbon dioxide gas-driven fracture and gas channeling in different directions of the fractured well.

[0021] The carbon dioxide injection system includes a carbon dioxide cylinder, a cryogenic bath, a booster pump, a cooling tracing pipe, a carbon dioxide preheating system, and a safety valve. The carbon dioxide cylinder provides experimental carbon dioxide gas and is connected to the cryogenic bath via the cooling tracing pipe. By controlling the temperature of the cryogenic bath, the temperature of the carbon dioxide injection system pipeline is regulated. The cryogenic bath is connected to the booster pump via the cooling tracing pipe. The booster pump controls and increases the pressure within the pipeline, causing the carbon dioxide flowing from the carbon dioxide cylinder to change from a gaseous state to a liquid state, simulating the effects of injecting carbon dioxide in different phases. The booster pump is connected to the carbon dioxide preheating system via the cooling tracing pipe to control the temperature of the carbon dioxide before injection, achieving the transformation of carbon dioxide from a liquid state to a supercritical state. The carbon dioxide preheating system is connected to the safety valve, which controls the discharge rate of the injected carbon dioxide.

[0022] The objective of this invention can also be achieved through the following technical measures: a simulation experimental method for liquid carbon dioxide gas-driven induced fracture in fractured wells, wherein the simulation experimental method employs a simulation experimental device for carbon dioxide gas-driven induced fracture in fractured wells, comprising:

[0023] Step 1: Activate the true triaxial stress loading system and apply constant pressure to the three directions of the space outside the experimental rock sample.

[0024] Step 2: Turn on the carbon dioxide injection system and inject liquid carbon dioxide into the experimental rock sample;

[0025] Step 3: Activate the acoustic emission monitoring system to collect rock sample fracture signals during liquid carbon dioxide injection;

[0026] Step 4: Turn on the gas concentration detection system to collect data on changes in carbon dioxide concentration in the monitoring well during the liquid carbon dioxide injection process;

[0027] Step 5: Change the injection parameters until the carbon dioxide concentration in the monitoring well reaches a critical value, then stop the experiment.

[0028] The objective of this invention can also be achieved through the following technical measures: a simulation experimental method for supercritical carbon dioxide gas-driven induced fracture in fractured wells, wherein the simulation experimental method employs a simulation experimental device for carbon dioxide gas-driven induced fracture in fractured wells, comprising:

[0029] Step 1: Activate the true triaxial stress loading system and apply constant pressure to the three directions of the space outside the experimental rock sample.

[0030] Step 2: Turn on the temperature loading control system to heat the experimental rock sample and collect the temperature of the experimental rock sample near the well wall. When the temperature reaches the set temperature, turn off the temperature acquisition and control instrument.

[0031] Step 3: Turn on the carbon dioxide injection system and inject liquid carbon dioxide into the experimental rock sample;

[0032] Step 4: Convert liquid carbon dioxide into a supercritical state and inject it using a carbon dioxide injection system;

[0033] Step 5: Turn on the acoustic emission monitoring system to collect rock sample fracture signals during supercritical carbon dioxide injection;

[0034] Step 6: Turn on the gas concentration detection system to collect data on changes in carbon dioxide concentration in the monitoring well during the liquid carbon dioxide injection process;

[0035] Step 7: Change the injection parameters until the carbon dioxide concentration in the monitoring well reaches a critical value, then stop the experiment.

[0036] The objective of this invention can also be achieved through the following technical measures: The simulation experiment method for supercritical carbon dioxide gas drive-induced fracture in fractured wells further includes, after step 7, taking out the experimental rock sample, cutting the sample along the local area of ​​the wellbore and the area where the acoustic emission signal is obvious during the loading experiment, and observing the fracture change characteristics near the wellbore and at typical fracture locations.

[0037] This invention presents a simulation experimental device and method for carbon dioxide gas drive-induced fracture in fractured wells. Considering downhole load environments such as in-situ stress and reservoir temperature, it comprehensively monitors the impact of carbon dioxide gas drive on the fracture characteristics of experimental well groups from two aspects: acoustic emission fracture signals and carbon dioxide concentration detection. This is of great significance for improving the development effect of carbon dioxide drive and realizing the scientific management of carbon dioxide-driven reservoirs. The beneficial effects of this invention are: it uses a true triaxial stress loading system to realistically simulate the in-situ stress state of actual reservoirs; it uses a temperature loading control system to simulate the actual shallow and deep reservoir temperatures; it controls the changes in the injected phase state of liquid and supercritical carbon dioxide through a carbon dioxide injection system; it uses acoustic emission monitoring to analyze the characteristics of reservoir fracture and fracture propagation under the combined effects of in-situ stress load, reservoir temperature, carbon dioxide injection parameters, and injected phase state; and it uses a carbon dioxide gas concentration detection device to analyze the changes in carbon dioxide concentration along different orientations of hydraulic fractures, analyzing the relationship between reservoir fracture and carbon dioxide gas channeling. This experimental device is easy to operate and highly practical, providing a reliable research tool for studying the mechanism of carbon dioxide gas drive-induced reservoir fracture in fractured wells. Attached Figure Description

[0038] Figure 1 This is a structural diagram of the simulation experimental device for carbon dioxide gas drive-induced fracturing in fractured wells according to the present invention;

[0039] Figure 2 This is a schematic diagram showing the location distribution of the injection wells and inspection wells in an experimental sample according to a specific embodiment of the present invention.

[0040] The components include: 1. High-pressure cylinder top cover; 2. High-pressure bearing cylinder; 3. Rigid upper top plate; 4. Acoustic emission probe; 5. Hydraulic side top plate; 6. Rigid pad; 7. Thermocouple sensor; 8. Pre-fabricated crack; 9. Concentration detection probe; 10. Resistance wire; 11. Hydraulic bottom top plate; 12. Experimental rock sample; 13. Injection well; 14. Monitoring well; 15. Carbon dioxide cylinder; 16. Cryogenic bath; 17. Cooling pipe; 18. Booster pump; 19. Carbon dioxide preheating system; 20. Safety valve. Detailed Implementation

[0041] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0042] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments of the present invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, and / or combinations thereof.

[0043] The present invention provides a simulation experimental device for carbon dioxide gas-driven induced fracturing in fractured wells, comprising an experimental rock sample, a true triaxial stress loading system, a temperature loading control system, an acoustic emission monitoring system, a gas concentration detection system, and a carbon dioxide injection system. The experimental rock sample is cast in cement mortar, with a carbon dioxide injection well and multiple gas concentration monitoring wells positioned downwards from the center of the top surface. Hydraulic fractures of predetermined orientation and length are locally incorporated into the injection well casing. The true triaxial stress loading system applies pressure in three directions to the space outside the experimental rock sample. The temperature loading control system includes a heating resistance wire, thermocouple temperature sensors, and temperature acquisition and control instruments to simulate and record the thermal conditions of the rock sample during carbon dioxide injection. The acoustic emission monitoring system detects the fracturing information and fracture propagation process of the experimental rock sample. The gas concentration detection system collects data on changes in carbon dioxide gas concentration in the monitoring wells during the carbon dioxide gas drive process. The carbon dioxide injection system controls the injection phase and injection parameter changes of carbon dioxide during the injection process. This invention can realistically simulate the coupling effect of carbon dioxide injection in different phases with reservoir temperature, geostress, and hydraulic fractures, evaluate the reservoir fracturing induced by carbon dioxide gas drive in fractured wells and the gas channeling at different locations in the well group. It is easy to operate and highly practical, providing a reliable research method for studying the mechanism of reservoir fracturing induced by carbon dioxide gas drive in fractured wells.

[0044] The following are several specific embodiments of the application of the present invention.

[0045] Example 1

[0046] In a specific embodiment 1 of the present invention, the simulation experimental device for carbon dioxide gas-driven fracture in a fracturing well comprises an experimental rock sample, a true triaxial stress loading system, a temperature loading control system, an acoustic emission monitoring system, a gas concentration detection system, and a carbon dioxide injection system. The experimental rock sample is cast in cement mortar, with a carbon dioxide injection well and multiple gas concentration monitoring wells positioned downwards from the center of the top surface. The true triaxial stress loading system applies pressure in three directions to the space outside the experimental rock sample. The temperature loading control system includes heating resistance wires, thermocouple temperature sensors, and temperature acquisition and control instruments to simulate and record the thermal conditions of the rock sample during carbon dioxide injection. The acoustic emission monitoring system detects the fracture information and fracture propagation process of the experimental rock sample. The gas concentration detection system collects data on changes in carbon dioxide gas concentration in the monitoring wells during the carbon dioxide gas drive process. The carbon dioxide injection system controls the injected phase and injection parameters during the injection process.

[0047] Furthermore, the experimental rock sample was prepared by casting with cement mortar, and its external dimensions were 300mm×300mm×300mm. A vertical central hole with a diameter of 10mm and a length of 200mm was drilled at the center of the top surface of the experimental rock sample, serving as a simulation of a carbon dioxide injection well. Multiple vertical central holes with a diameter of 10mm and a length of 200mm were set around the rock sample to monitor changes in carbon dioxide concentration in the well group during the experiment. During the casting process, a thermocouple temperature sensor was pre-embedded in the experimental rock sample at a designed position, and the sensor probe data cable was led out. A steel pipe with pre-fabricated channels was inserted into the pre-fabricated central hole, a concentration detection probe was placed in the carbon dioxide concentration monitoring well, and the data cable was led out. An injection pipeline connector was reserved in the carbon dioxide injection well.

[0048] Furthermore, during the preparation of the experimental rock sample by pouring cement mortar, pre-fabricated cracks of predetermined angle and length to the stress loading direction are pre-set on both sides of the injection well. The monitoring wells are located at the orientation of the pre-fabricated crack extension line, the vertical orientation of the crack, and the orientation at a predetermined angle to the crack.

[0049] Furthermore, the true triaxial stress loading system consists of a multi-channel hydraulic servo controller, a hydraulic injection pipeline, a high-pressure bearing cylinder, a high-pressure cylinder top cover, a hydraulic side top plate, a hydraulic bottom top plate, a rigid upper top plate, and a rigid pad plate. The pressure control range is 0-70 MPa, and it is used to load triaxial geostress loads onto experimental rock samples.

[0050] Furthermore, the temperature loading control system comprises a heating resistance wire, a thermocouple temperature sensor, and a temperature acquisition and control instrument. The heating resistance wire is connected to the temperature acquisition and control instrument via an insulated wire; the thermocouple temperature sensor has a temperature measurement range of -50℃ to 500℃, and its probe is installed on the inner wall of the experimental rock sample wellbore, connected to the temperature acquisition and control instrument via a data line; the temperature acquisition and control instrument is used to display and control the temperature of the experimental rock sample near the wellbore wall.

[0051] Furthermore, the acoustic emission monitoring system consists of an acoustic emission probe, an acoustic emission signal line, and an acoustic emission instrument. The acoustic emission probe is set on two opposite horizontal sides of the experimental rock sample to detect the acoustic emission ringing rate and energy rate of the experimental rock sample corresponding to the carbon dioxide injection parameters, locate the spatial position of the fracture point, and analyze the fracture event and crack propagation law of the experimental rock sample.

[0052] Furthermore, the gas concentration detection system consists of a concentration detection probe, a signal line, and a concentration detector. The gas concentration detection probe is placed in the monitoring well and connected to the concentration detector via the signal line.

[0053] Furthermore, the carbon dioxide injection system comprises a carbon dioxide cylinder, a cryogenic bath, a booster pump, a cooling tracing pipe, a carbon dioxide preheating system, safety valves, and connecting pipelines. The injection pressure of carbon dioxide is controlled by increasing the pump, and the injection flow rate is controlled by the safety valves. The carbon dioxide flowing from the cylinder is converted from a gaseous state to a liquid state by controlling the cryogenic bath, simulating the effects of liquid carbon dioxide injection. Furthermore, the liquid carbon dioxide can be kept warm by the cooling tracing pipe, and the injected carbon dioxide is converted from a liquid state to a supercritical state by controlling the booster pump and the carbon dioxide preheating system, simulating the effects of supercritical carbon dioxide injection.

[0054] Example 2

[0055] In a specific embodiment 2 of the present invention, an experimental method for evaluating reservoir fracturing induced by carbon dioxide gas drive in fractured wells includes the following steps:

[0056] a. Fix the prepared experimental rock sample inside the high-pressure cylinder, then place the hydraulic side top plate and the rigid side top plate against the corresponding horizontal sides of the experimental rock sample; connect the carbon dioxide injection pipeline to the injection well; install four acoustic emission probes on the two opposite horizontal sides of the experimental rock sample; lead out the heating resistance wire, thermocouple data line, acoustic emission signal line, and carbon dioxide concentration detection line; place the rigid top plate on top of the experimental rock sample, seal the high-pressure cylinder, and complete the installation of the experimental equipment;

[0057] b. The study investigated the effect of carbon dioxide injection in shallow reservoirs on fracture characteristics; a multi-channel hydraulic servo was activated to apply constant pressure in three directions to the space outside the experimental rock sample, and the pressure was set according to the geostress load conditions of the shallow and intermediate reservoirs.

[0058] c. Open the carbon dioxide cylinder, control the outlet pressure of the carbon dioxide cylinder through the pressure regulating valve, open the pipeline control valve, and control the low temperature bath to convert the carbon dioxide flowing out of the cylinder from a gaseous state to a liquid state, and inject the liquid carbon dioxide into the injection well.

[0059] d. Turn on the acoustic emission instrument to collect and store the acoustic emission signals around the pre-fabricated cracks during the liquid carbon dioxide injection process, and locate the rupture signal using the acoustic emission instrument;

[0060] e. Turn on the carbon dioxide concentration detection device, record the changes in carbon dioxide concentration in the monitoring well at different locations during the experiment, compare it with the location of the rupture signal recorded by acoustic emission, and analyze the gas expansion path during the carbon dioxide flooding process;

[0061] f. Turn on the carbon dioxide booster pump to increase the pressure of liquid carbon dioxide in the pipeline to the supercritical carbon dioxide pressure condition; control the temperature of the carbon dioxide preheating system to raise the temperature of liquid carbon dioxide in the pipeline to the supercritical carbon dioxide temperature condition; open the pipeline control valve to inject supercritical carbon dioxide into the injection wellbore; repeat processes d and e, collect and store the acoustic emission signals around the pre-fabricated fractures during the supercritical carbon dioxide injection process, record the gas concentration changes of monitoring wells at different locations of supercritical carbon dioxide injection, and analyze the impact of supercritical carbon dioxide injection on the fracture morphology and gas drive path of the fracturing fractures.

[0062] g. Investigate the effect of carbon dioxide injection on fracture characteristics in deep high-temperature reservoirs; turn on the temperature acquisition and control instrument and heat the high-pressure cylinder through the heating resistance wire; collect the temperature of the test point inside the sample through the temperature acquisition and control instrument, and disconnect the power supply of the heating resistance wire when the sample temperature reaches the preset temperature; increase the load of the multi-channel hydraulic servo to the deep reservoir geostress load condition.

[0063] h. Repeat step f above to evaluate the carbon dioxide gas drive-induced reservoir fracture in deep high-temperature reservoir fractured wells.

[0064] i. After the experiment is completed, take out the experimental rock sample, cut the sample along the local area of ​​the wellbore and the area where the acoustic emission signal was obvious during the loading experiment, and observe the crack change characteristics near the wellbore and at typical fracture locations.

[0065] Example 3

[0066] In a specific embodiment 3 of the present invention, such as Figure 1As shown, the present invention provides a simulation experimental device for carbon dioxide gas drive-induced fracture in fractured wells, comprising an experimental rock sample, a true triaxial stress loading system, a temperature loading control system, an acoustic emission monitoring system, a gas concentration detection system, and a carbon dioxide injection system.

[0067] like Figure 1 As shown: Experimental rock sample 12 is cast with cement mortar, and a carbon dioxide injection well 13 and multiple gas concentration monitoring wells 14 are set from the center of the top surface downwards. Experimental rock sample 12 is cast from cement sandstone according to the change ratio of reservoir rock mechanical strength, and its external dimensions are 300mm×300mm×300mm. A vertical center hole with a diameter of 10mm and a length of 200mm is opened in the center of the top surface of experimental rock sample 12, which is used to simulate the carbon dioxide drive injection well. Multiple vertical center holes with a diameter of 10mm and a length of 200mm are set around the rock sample to simulate inspection wells and monitor the changes in carbon dioxide concentration at different positions of the well group during the experiment. During the casting process, thermocouple temperature sensors 7 are pre-embedded in the experimental rock sample 12 at the designed position, and the sensor probe data line is led out. A steel pipe with pre-made channels is inserted into the pre-made center hole, the carbon dioxide concentration monitoring well is inserted with a concentration detection probe 9, and the data line is led out. The carbon dioxide injection well is reserved with an injection pipeline joint.

[0068] like Figure 2 As shown, during the preparation of the experimental rock sample by pouring cement mortar, a pre-fabricated crack 8 is pre-set at the injection well shaft at a specified angle to the stress loading direction. Among them, inspection wells a and f are arranged perpendicular to the crack direction, inspection wells c and d are arranged along the crack orientation, and inspection wells b and e are at a specified angle to the crack.

[0069] like Figure 1 As shown, the true triaxial stress loading system consists of a multi-channel hydraulic servo controller, a hydraulic injection pipeline, a high-pressure bearing cylinder 2, a high-pressure cylinder top cover 1, a hydraulic side top plate 5, a hydraulic bottom top plate 11, a rigid upper top plate 3, and a rigid pad 6. The pressure control range is 0–70 MPa, and it is used to load triaxial geostress onto experimental rock samples. The multi-channel hydraulic servo controller, with a pressure control range of 0–70 MPa, can apply pressure in three directions to the space outside the experimental rock sample, simulating the triaxial geostress state within a well depth of 0–3000 m in oil reservoirs.

[0070] like Figure 1As shown, the temperature loading control system consists of a heating resistance wire 10, a thermocouple temperature sensor 7, and a temperature acquisition and control instrument. The heating resistance wire 10 is connected to the temperature acquisition and control instrument via an insulated wire. The thermocouple temperature sensor 7 has a temperature measurement range of -50℃ to 500℃. The probe of the thermocouple temperature sensor 7 is installed on the inner wall of the wellbore of the experimental rock sample 12 and is connected to the temperature acquisition and control instrument via a data line. The temperature acquisition and control instrument is used to display and control the temperature near the wellbore wall of the experimental rock sample. When the temperature near the wellbore wall reaches the set temperature value, the temperature acquisition and control instrument is powered off.

[0071] like Figure 1 As shown, the acoustic emission monitoring system consists of an acoustic emission probe 4, an acoustic emission signal line, and an acoustic emission instrument. The acoustic emission probe 4 is set on two opposite horizontal sides of the experimental rock sample 12 to detect the acoustic emission ringing rate and energy rate of the experimental rock sample corresponding to the carbon dioxide injection parameters, locate the spatial position of the fracture point, and analyze the fracture event and crack propagation law of the experimental rock sample.

[0072] like Figure 1 As shown, the gas concentration detection system consists of a concentration detection probe 9, a signal line, and a concentration detector. The gas concentration detection probe 9 is placed in the monitoring well 14 and is connected to the concentration detector through the signal line.

[0073] like Figure 1 As shown, the carbon dioxide injection system consists of a carbon dioxide cylinder 15, a cryogenic bath 16, a booster pump 18, a cooling tracing pipe 17, a carbon dioxide preheating system 19, a safety valve 20, and connecting pipelines. When the valve of the carbon dioxide cylinder 15 is opened, gaseous carbon dioxide flows into the cryogenic bath 16 and is cooled into liquid carbon dioxide. The liquid carbon dioxide is then injected into the rock sample through the cooling tracing pipe 17 and the injection pipeline. Furthermore, the booster pump 18 and the carbon dioxide preheating system 19 can be opened to convert the liquid carbon dioxide into supercritical carbon dioxide for injection.

[0074] In operation, the prepared experimental rock sample is first fixedly installed at the center of the bottom of the high-pressure cylinder; four acoustic emission probes are placed on the two opposite horizontal sides of the experimental rock sample; insulated heating tube wires, thermocouple wires, acoustic emission signal lines, and carbon dioxide concentration detection signal lines are introduced; the high-pressure cylinder is sealed with a top cover; and the carbon dioxide injection pipeline is connected to complete the installation of the experimental equipment.

[0075] When conducting an evaluation experiment on reservoir fracturing induced by liquid carbon dioxide gas drive in a fractured well, the multi-channel hydraulic servo is first activated to apply constant pressure in three directions to the space outside the experimental rock sample. Then, the carbon dioxide cylinder valve is opened, the cryogenic bath switch is turned on, and liquid carbon dioxide is injected into the experimental rock sample. The acoustic emission monitoring system is turned on to collect the rock sample fracturing signal during the liquid carbon dioxide injection process. The carbon dioxide concentration detection instrument is turned on to collect the change in carbon dioxide concentration in the monitoring well during the liquid carbon dioxide injection process. The injection parameters are varied until the change in carbon dioxide concentration in the monitoring well reaches a critical value, at which point the experiment is stopped.

[0076] When conducting an evaluation experiment on reservoir fracturing induced by supercritical carbon dioxide gas drive in fractured wells, the multi-channel hydraulic servo is first activated to apply constant pressure in three directions to the space outside the experimental rock sample. The thermal resistance switch in the temperature loading control system is then turned on to heat the high-pressure cylinder. The temperature is controlled by a local thermocouple injected into the wellbore. When the set temperature is reached, the temperature acquisition controller is disconnected. Next, the carbon dioxide cylinder valve and the cryogenic bath switch are opened to cool the gaseous carbon dioxide in the cylinder into a liquid state. The booster pump and carbon dioxide preheating system are then activated to convert the liquid carbon dioxide into a supercritical state for injection. The acoustic emission monitoring system is activated to collect rock sample fracturing signals during supercritical carbon dioxide injection. The carbon dioxide concentration detection instrument is activated to collect changes in the monitoring well's carbon dioxide concentration during liquid carbon dioxide injection. Injection parameters are varied until the monitoring well's carbon dioxide concentration reaches a critical value, at which point the experiment is stopped.

[0077] Take out the experimental rock sample, cut the sample along the local area of ​​the wellbore and the area with obvious acoustic emission signals during the loading test, and observe the crack change characteristics near the wellbore and at typical fracture locations.

[0078] Finally, it should be noted that the above description is merely a preferred embodiment of the present invention and is not intended 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 make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

[0079] Except for the technical features described in the specification, all other technologies are known to those skilled in the art.

Claims

1. A simulation experimental device for carbon dioxide gas-driven induced fracture in fractured wells, characterized in that... The system includes an experimental rock sample, a true triaxial stress loading system, a carbon dioxide injection system, an acoustic emission monitoring system, and a gas concentration detection system. The experimental rock sample is located in the true triaxial stress loading system. A carbon dioxide injection well and multiple gas concentration monitoring wells are set from the top center downwards. Hydraulic fractures of predetermined orientation and length are set locally in the injection well. The true triaxial stress loading system applies pressure to the space outside the experimental rock sample in three directions. The carbon dioxide injection system injects carbon dioxide into the experimental rock sample. The gas concentration detection system collects the changes in carbon dioxide gas concentration in the monitoring wells during the carbon dioxide gas drive process. The acoustic emission monitoring system detects the fracture information and fracture propagation process of the experimental rock sample. Multiple gas concentration monitoring wells are located at the orientation of the pre-fabricated fracture extension line, the vertical orientation of the fracture, and the orientation at a preset angle to the fracture, respectively. The acoustic emission monitoring system includes an acoustic emission probe, an acoustic emission signal line, a signal amplifier, and an acoustic emission instrument. The acoustic emission probe is set on two opposite horizontal sides of the experimental rock sample to monitor the acoustic emission ringing rate and energy rate of the experimental rock sample corresponding to the carbon dioxide injection parameters. The acoustic emission probe is connected to the signal amplifier through the acoustic emission signal line. The signal amplifier amplifies the acoustic emission signal and then connects to the acoustic emission instrument through the acoustic emission signal line. The acoustic emission instrument processes and interprets the amplified acoustic emission signal, locates the spatial position of the fracture point, and analyzes the fracture event and fracture propagation law of the experimental rock sample. The gas concentration detection system includes a concentration detection probe and a concentration detector. The concentration detection probe is placed in the monitoring well and connected to the concentration detector via a signal line. The concentration detector dynamically records the changes in carbon dioxide concentration in different monitoring wells. Combined with the analysis of the fracture time and fracture propagation law of the experimental rock sample by the acoustic emission instrument, the system analyzes the variation law of carbon dioxide gas-driven fracture and gas channeling in different directions along the fractured well.

2. The experimental apparatus for simulating fracturing well carbon dioxide gas drive induced fracture according to claim 1, characterized in that, The simulation experimental device for carbon dioxide gas drive-induced fracturing in fractured wells also includes a temperature loading control system, which simulates and records the thermal conditions of the experimental rock sample during carbon dioxide injection.

3. The experimental apparatus for simulating fracturing of a well by carbon dioxide gas flooding according to claim 2, wherein The temperature loading control system includes a heating resistance wire, a thermocouple temperature sensor, and a temperature acquisition and control instrument. The heating resistance wire is connected to the temperature acquisition and control instrument and heats the experimental rock sample. The probe of the thermocouple temperature sensor is set on the inner wall of the well barrel of the experimental rock sample and connected to the temperature acquisition and control instrument to collect the temperature of the experimental rock sample near the well barrel wall and transmit the temperature information to the temperature acquisition and control instrument. The temperature acquisition and control instrument displays the temperature information. When the temperature near the well barrel wall reaches the set temperature value, the heating resistance wire is de-energized through the temperature acquisition instrument.

4. The experimental apparatus for simulating fracturing of a well by carbon dioxide gas flooding according to claim 3, wherein The temperature measurement range of this thermocouple temperature sensor is -50℃ to 500℃.

5. The experimental apparatus for simulating fracturing of a well by carbon dioxide gas flooding according to claim 1, wherein, The experimental rock sample was prepared by casting with cement mortar, and its external dimensions are 300mm×300mm×300mm. A vertical center hole with a diameter of 10mm and a length of 200mm is opened in the center of the top surface of the experimental rock sample, which is used to simulate the carbon dioxide injection well. Multiple vertical center holes with a diameter of 10mm and a length of 200mm are set around the experimental rock sample, which are used to simulate gas concentration monitoring wells to monitor the changes in carbon dioxide concentration in the well group during the experiment.

6. The experimental apparatus for simulating fracturing of a well by carbon dioxide gas flooding according to claim 1, wherein, The true triaxial stress loading system includes a multi-channel hydraulic servo controller, a hydraulic injection pipeline, a high-pressure bearing cylinder, a high-pressure cylinder top cover, a hydraulic side top plate, a hydraulic bottom top plate, a rigid upper top plate, and a rigid pad. The experimental rock sample is located in the high-pressure bearing cylinder, and the rigid pad is located between the experimental rock sample and the hydraulic side top plate to fix the horizontal position of the experimental rock sample. The hydraulic side top plate and the hydraulic bottom top plate are used to apply true triaxial stress loads to the side and bottom surfaces of the experimental rock sample. The rigid upper top plate is located between the experimental rock sample and the high-pressure cylinder top cover to fix the vertical position of the experimental rock sample. The hydraulic side top plate and the hydraulic bottom top plate are connected to the multi-channel hydraulic servo controller through the hydraulic injection pipeline. The multi-channel hydraulic servo controller is used to set and control the triaxial stress load.

7. The simulation experimental apparatus for carbon dioxide gas-driven induced fracturing in fractured wells according to claim 1, characterized in that, The carbon dioxide injection system includes a carbon dioxide cylinder, a cryogenic bath, a booster pump, a cooling tracing pipe, a carbon dioxide preheating system, and a safety valve. The carbon dioxide cylinder provides experimental carbon dioxide gas and is connected to the cryogenic bath via the cooling tracing pipe. By controlling the temperature of the cryogenic bath, the temperature of the carbon dioxide injection system pipeline is regulated. The cryogenic bath is connected to the booster pump via the cooling tracing pipe. The booster pump controls and increases the pressure within the pipeline, causing the carbon dioxide flowing from the carbon dioxide cylinder to change from a gaseous state to a liquid state, simulating the effects of injecting carbon dioxide in different phases. The booster pump is connected to the carbon dioxide preheating system via the cooling tracing pipe to control the temperature of the carbon dioxide before injection, achieving the transformation of carbon dioxide from a liquid state to a supercritical state. The carbon dioxide preheating system is connected to the safety valve, which controls the discharge rate of the injected carbon dioxide.

8. A method of simulating the fracturing of a well by liquid carbon dioxide gas flooding, characterized in that, The simulation experiment method for fracturing wells induced by liquid carbon dioxide gas drive employs the simulation experiment device for fracturing wells induced by carbon dioxide gas drive as described in claim 1, comprising: Step 1: Activate the true triaxial stress loading system and apply constant pressure to the three directions of the space outside the experimental rock sample. Step 2: Turn on the carbon dioxide injection system and inject liquid carbon dioxide into the experimental rock sample; Step 3: Activate the acoustic emission monitoring system to collect rock sample fracture signals during liquid carbon dioxide injection; Step 4: Turn on the gas concentration detection system to collect data on changes in carbon dioxide concentration in the monitoring well during the liquid carbon dioxide injection process; Step 5: Change the injection parameters until the carbon dioxide concentration in the monitoring well reaches a critical value, then stop the experiment.

9. A method of simulating experiments of supercritical carbon dioxide gas drive induced fracture in fracturing wells, characterized in that, The simulation experiment method for supercritical carbon dioxide gas-driven induced fracture in fractured wells uses the simulation experiment device for carbon dioxide gas-driven induced fracture in fractured wells as described in claim 1, including: Step 1: Activate the true triaxial stress loading system and apply constant pressure to the three directions of the space outside the experimental rock sample. Step 2: Turn on the temperature loading control system to heat the experimental rock sample and collect the temperature of the experimental rock sample near the well wall. When the temperature reaches the set temperature, turn off the temperature acquisition and control instrument. Step 3: Turn on the carbon dioxide injection system and inject liquid carbon dioxide into the experimental rock sample; Step 4: Convert liquid carbon dioxide into a supercritical state and inject it using a carbon dioxide injection system; Step 5: Turn on the acoustic emission monitoring system to collect rock sample fracture signals during supercritical carbon dioxide injection; Step 6: Turn on the gas concentration detection system to collect data on changes in carbon dioxide concentration in the monitoring well during the liquid carbon dioxide injection process; Step 7: Change the injection parameters until the carbon dioxide concentration in the monitoring well reaches a critical value, then stop the experiment.

10. The method of claim 9, wherein the supercritical carbon dioxide gas drive induced fracture simulation experiment of a fractured well is characterized by, The simulation experiment method for supercritical carbon dioxide gas drive-induced fracture in fractured wells also includes, after step 7, taking out the experimental rock sample, cutting the sample along the local area of ​​the wellbore and the area with obvious acoustic emission signals during the loading experiment, and observing the fracture change characteristics near the wellbore and at typical fracture locations.

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