An apparatus and method for simulating the response of a phase change formation during CO2 injection

Abstract

The application provides a simulation device and method for phase change stratum response in a CO2 injection process, wherein the simulation device comprises a placing container and a sealing sleeve for sleeving outside a rock sample, a cavity is arranged in the placing container, a hollow spiral elbow pipe through which oil flows is arranged in the cavity, inlet and outlet ends of the hollow spiral elbow pipe are connected with temperature adjusting assemblies through an oil inlet pipe and an oil outlet pipe respectively, and the temperature adjusting assemblies are electrically connected with a controller; the cavity is connected with a supercritical CO2 injection system, an injection end of the supercritical CO2 injection system extends into a reserved vertical hole of the rock sample; the cavity is also connected with a confining pressure loading system, and the confining pressure loading system is electrically connected with the controller; an upper cover for compacting the rock sample is detachably connected with an opening at an upper end of the placing container; and an acoustic emission probe electrically connected with the controller is also arranged in the cavity. The application can simulate the stratum response in a real CO2 phase change process, realize the control of the CO2 phase change process in any way, and determine the optimal storage parameter of the supercritical CO2 storage.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of CO2 geological storage geotechnical engineering, in particular to a simulation device and method for the response of phase change strata in the CO2 injection process. BACKGROUND

[0002] In the process of CO2 geological storage, supercritical CO2 is injected into a saline aquifer through a CO2 injection well for storage. This method has been widely used for CO2 saline aquifer storage in various parts of the world. However, current CO2 saline aquifer storage has no economic benefits, and the implementation cost of CO2 saline aquifer storage is huge. Unless there is a subsidy or related tax reduction policy, enterprises will not quickly recommend it. With the continuous development of oil and gas exploration, early oil and gas production wells are close to exhaustion, and these exhausted oil and gas wells can be used as CO2 injection wells to store CO2. According to field measurement data, the bottom hole pressure of these exhausted oil and gas wells is reduced by 30% to 90% compared to the formation pressure before oil and gas exploration, and the degree of reduction depends on the formation characteristics. Therefore, in the process of storing supercritical CO2 in these exhausted oil and gas reservoirs, due to the low bottom hole pressure of the exhausted oil and gas reservoirs, supercritical CO2 will rapidly phase change when the pressure decreases, changing from a supercritical state to a liquid or gaseous state, instantaneously increasing in volume and generating a large pressure, which affects the stability of the CO2 injection well and the surrounding rock strata. The degree of response of the rock strata determines the selection of injection strategies. Currently, the damage and impact of phase change on the formation during CO2 injection are mainly based on numerical simulation, but there is a lack of experimental devices to simulate the response of the formation during the real CO2 phase change process. The present application is based on this background to study the response of the formation during the phase change of CO2 injection, in order to optimize the optimal injection strategy. SUMMARY

[0003] The present application aims to at least solve one of the above technical problems in the related art to some extent. To this end, the present application provides a simulation device for the response of phase change strata in the CO2 injection process, which can simulate the response of the formation during the real CO2 phase change process and can realize the control of CO2 phase change process in any way. The response of the formation during different CO2 phase change processes is obtained, and the optimal storage parameters for supercritical CO2 storage are determined, providing data support for the storage of supercritical CO2 in oil and gas wells.

[0004] The present application also provides a method for simulating experiments using the above device.

[0005] The simulation device for the response of a phase change formation in a CO2 injection process according to the first aspect of the embodiment of the present application comprises a placing container and a sealing sleeve for sleeving outside a rock sample, a cavity for placing the rock sample is arranged in the placing container, a hollow spiral bent pipe for surrounding outside the rock sample is arranged in the cavity, oil flows through the hollow spiral bent pipe, the inlet and outlet ends of the hollow spiral bent pipe are respectively connected with a temperature adjusting assembly for temperature rising and falling through an oil inlet pipe and an oil outlet pipe, an inlet temperature sensor is arranged on the oil inlet pipe, the inlet temperature sensor is electrically connected with a controller, an outlet temperature sensor is arranged on the oil outlet pipe, and the outlet temperature sensor and the temperature adjusting assembly are both electrically connected with the controller; the cavity is connected with a supercritical CO2 injection system, the injection end of the supercritical CO2 injection system extends into a reserved vertical hole of the rock sample; the cavity is also connected with a confining pressure loading system, and the confining pressure loading system is electrically connected with the controller; an upper cover for compacting the rock sample is detachably connected at the open upper end of the placing container; and an acoustic emission probe electrically connected with the controller is also arranged in the cavity.

[0006] The simulation device for the response of a phase change formation in a CO2 injection process according to the embodiment of the application has at least the following technical effects: 1. By using a rock with a reserved vertical hole as a sample, the reserved vertical hole is equivalent to an oil and gas well in the process of simulation experiment, and a supercritical CO2 injection system is started to inject the rock sample through the reserved vertical hole, which more truly restores the supercritical CO2 injection into the underground rock formation through the oil and gas well in the actual project, more truly reproduces the formation response in the phase change process of the CO2 injection into the oil and gas well, and ensures the precision of the experiment. 2. By providing a confining pressure loading system in communication with the cavity and a hollow spiral bent pipe surrounding the outside of the rock sample, and the hollow spiral bent pipe is cyclically communicated with a temperature adjusting assembly, before the experiment, the confining pressure loading system is used to load hydraulic oil into the cavity to the confining pressure of the rock sample to reach a set value, and then the oil in the hollow spiral bent pipe is pumped out for heating and recirculation back to the hollow spiral bent pipe to exchange heat with the rock sample, so that the internal temperature of the rock sample reaches a set value; in the process of the experiment, after a certain amount of supercritical CO2 is injected into the reserved vertical hole through the supercritical CO2 injection system, according to the CO2 phase change to be simulated, the CO2 phase change process of any path can be selected (either the way of keeping the cavity confining pressure unchanged and cooling the rock sample through the temperature adjusting assembly or the way of keeping the temperature of the rock sample unchanged and reducing the cavity confining pressure through the confining pressure loading system or the way of cooling and depressurizing at the same time), the formation response in the CO2 phase change process is obtained, the optimal storage parameter of the supercritical CO2 storage is determined, and data support is provided for the supercritical CO2 injection into the oil and gas well for storage. 3. In the process of the experiment, the temperature adjusting assembly can be controlled by the controller to control the cooling speed or the confining pressure loading system can be controlled by the controller to control the depressurization speed, so that the CO2 phase change rate of any path can be controlled, and then the formation response in the phase change process near and far from the oil and gas well can be simulated. 4. In the process of the experiment, a pair of acoustic emission probes can be arranged at the upper and lower ends of the rock sample, and four pairs of acoustic emission probes can be arranged on the outer wall of the rock sample in the circumferential direction; thus, the data of the acoustic emission probes can be monitored in real time in the phase change process of the CO2 injection into the oil and gas well, the wave velocity information of the compression wave (P wave) and the shear wave (S wave) can be obtained, these wave velocities are used to calculate the dynamic elastic constants of the rock, such as Poisson's ratio, Young's modulus (E), bulk modulus (K) and shear modulus (G), the generation and expansion of the microcracks in the rock material under the load in the phase change process can be continuously and real-timely monitored, and the damage position can be located. 5. By sleeving a sealing sleeve on the rock sample, the sealing sleeve tightly seals the rock sample to prevent the mutual communication of the rock sample and the liquid in the cavity.

[0007] According to some embodiments of the present application, the supercritical CO2 injection system comprises a supercritical CO2 storage tank, an outlet of the supercritical CO2 storage tank is communicated with an injection pipe through an injection pump, an end of the injection pipe away from the injection pump extends into a pre-prepared vertical hole of a rock sample; a first valve, a back pressure valve and a first pressure sensor are sequentially arranged on a side of the injection pipe away from the injection pump; a second valve and a second pressure sensor are sequentially arranged on a side of the first pressure sensor away from the back pressure valve, the first pressure sensor and the second pressure sensor are both used for monitoring the CO2 pressure in the pre-prepared vertical hole of the rock sample.

[0008] According to some embodiments of the present application, an end of the back pressure valve towards the first pressure sensor is sequentially provided with a buffer container and a third valve.

[0009] According to some embodiments of the present application, an end of the third valve away from the buffer container is sequentially provided with a third pressure sensor, a pre-heater and a fourth valve.

[0010] According to some embodiments of the present application, the confining pressure loading system comprises a confining pressure loading pump electrically connected with the controller, an outlet end of the confining pressure loading pump is communicated with the cavity through a first pipe, an oil pressure delivery valve is arranged on the first pipe.

[0011] According to some embodiments of the present application, a middle of an inner bottom wall of the cavity is provided with a base for bearing the rock sample, a first through hole is vertically penetrated in the base, the first through hole is communicated with a pore pressure loading system, the pore pressure loading system comprises a interstitial pressure loading pump, an outlet end of the interstitial pressure loading pump is communicated with the first through hole through a second pipe, a water pressure switch valve and an interstitial water pressure sensor are sequentially arranged on the second pipe in a direction away from the interstitial pressure loading pump.

[0012] According to some embodiments of the present application, the temperature adjusting assembly comprises a heating tank and a cooling tank, a heating resistor is arranged in the heating tank, the heating resistor is electrically connected with the controller, an outlet of the heating tank is provided with a first delivery pump electrically connected with the controller; a cooling coil and a cooling fan blowing towards the cooling coil are arranged in the cooling tank, the cooling fan is electrically connected with the controller, an outlet of the cooling tank is provided with a second delivery pump electrically connected with the controller.

[0013] According to some embodiments of the present application, a second through hole is vertically penetrated in the upper cover, a third temperature monitoring sensor for monitoring the temperature in the cavity is inserted into the second through hole, the third temperature monitoring sensor is electrically connected with the controller.

[0014] According to some embodiments of the present application, the left and right sides of the placement container are symmetrically provided with screw rods, the upper cover is provided with third through holes corresponding to the positions of the screw rods, and the screw rods are threadedly connected with fastening nuts during installation, and the fastening nuts press the upper cover.

[0015] According to the second aspect of the present application, a method for simulating experiments by using the device of any of the above embodiments is provided, which comprises the following steps: Step A: preparing a rock sample, selecting a rock type according to the water content and saturation of the formation to be simulated before the experiment, processing the rock of the determined type into the required size, and opening a reserved vertical hole in the middle of the upper end of the rock to obtain the rock sample;

[0016] Step B: CT scanning the rock sample before the experiment to obtain the internal structure image of the rock sample;

[0017] Step C: sleeving the sealing sleeve outside the rock sample, and then putting the rock sample through the hollow spiral bend pipe into the cavity of the placement container;

[0018] Step D: assembling the device, connecting the acoustic emission probe with the rock sample, then connecting the upper cover at the upper end of the placement container, fixing the rock sample while sealing the cavity, connecting the injection end of the supercritical CO2 injection system with the cavity and extending into the reserved vertical hole of the rock sample, and testing the air tightness of the experimental device;

[0019] Step E: loading the inside of the cavity to the bearing confining pressure of the rock sample to a set value through the confining pressure loading system according to the formation pressure to be simulated, heating the oil through the temperature adjusting assembly and delivering the oil into the hollow spiral bend pipe to exchange heat with the rock sample, so that the internal temperature of the rock sample reaches a set value, and injecting supercritical CO2 into the reserved vertical hole of the rock sample through the supercritical CO2 injection system until the pressure in the reserved vertical hole is equal to the bearing confining pressure of the rock sample according to the formation temperature to be simulated;

[0020] Step F: starting the simulation of the CO2 phase change process, setting the phase change path according to the required simulation of the CO2 phase change, monitoring the pressure change in the reserved vertical hole of the rock sample in the phase change process, and monitoring the wave velocity information of the compression wave (P wave) and shear wave (S wave) emitted by the rock sample in the process of stress deformation and fracture through the acoustic emission probe;

[0021] Step G: experimental analysis, gradually cooling the device to room temperature after the reaction is completed, taking out the rock sample to perform CT scanning, observing the influence of the phase change on the rock structure, and comparing with the internal structure image of the rock sample obtained in the step B to quantitatively evaluate the response characteristics of the formation in the phase change process.

[0022] According to the method for simulating experiment of the embodiment of the present application, at least the following technical effects are achieved: 1. By using the rock with the reserved vertical hole as the sample, the reserved vertical hole is equivalent to the oil and gas well in the process of simulating experiment, the supercritical CO2 injection system is started to inject the supercritical CO2 into the rock sample through the reserved vertical hole, the supercritical CO2 injection into the underground rock layer through the oil and gas well in the actual project is more truly restored, the stratum response condition of the phase change process of CO2 injection into the oil and gas well is more truly reproduced, so that the optimal injection strategy is selected. 2. In the process of the experiment, after a certain amount of supercritical CO2 is injected into the reserved vertical hole through the supercritical CO2 injection system, according to the CO2 phase change condition to be simulated, the CO2 phase change process of any path can be selected, the stratum response condition of the CO2 phase change process of different paths is obtained, the optimal storage strategy of the supercritical CO2 storage is determined, and data support is provided for the supercritical CO2 injection into the oil and gas well for storage. 3. In the process of the experiment, the cooling speed of the temperature adjusting assembly or the pressure reducing speed of the confining pressure loading system can be controlled through the controller, so that the CO2 phase change rate of any path can be controlled, and then the stratum response condition of the phase change process of CO2 injection into the near end and the far end of the oil and gas well is simulated. 4. In the process of the experiment, the data of the acoustic emission probe can be monitored in real time in the phase change process of CO2 injection into the oil and gas well, the wave speed information of the compression wave (P wave) and the shear wave (S wave) can be obtained, the wave speed is used to calculate the dynamic elastic constants of the rock, such as Poisson's ratio, Young's modulus (E), bulk modulus (K) and shear modulus (G), the generation and expansion of the microcracks in the rock material under the load in the phase change process can be continuously and real-timely monitored, and the damage position is located.

[0023] Additional aspects and advantages of the present application will be made apparent from the following description. BRIEF DESCRIPTION OF DRAWINGS

[0024] The present application will be further described below in conjunction with the drawings and embodiments, in which:

[0025] Figure 1 The structure schematic diagram of the embodiment of the present application is shown in the figure;

[0026] Figure 2 The structure schematic diagram of the temperature adjusting assembly in the embodiment of the present application is shown in the figure;

[0027] Figure 3 The CO2 phase state change schematic diagram is shown in the figure.

[0028] Reference signs:

[0029] 100 placing container, 110 sealing sleeve, 120 cavity, 130 upper cover, 140 acoustic emission probe, 150 base, 160 screw rod, 170 fastening nut;

[0030] 210 hollow coil pipe, 220 oil inlet pipe, 221 inlet temperature sensor, 230 oil outlet pipe, 231 outlet temperature sensor, 240 temperature regulating assembly, 241 heating tank, 242 cooling tank, 243 first delivery pump, 244 second delivery pump, 250 third temperature monitoring sensor;

[0031] 300 rock sample, 310 pre-reserved vertical hole;

[0032] 410 injection pump, 420 injection pipe, 430 first valve, 440 back pressure valve, 450 first pressure sensor, 461 second valve, 462 second pressure sensor, 471 buffer container, 472 third valve, 481 third pressure sensor, 482 pre-heater, 483 fourth valve;

[0033] 510 confining pressure loading pump, 520 first pipe, 530 oil pressure delivery valve;

[0034] 610 interstitial pressure loading pump, 620 second pipe, 630 water pressure on-off valve, 640 interstitial water pressure sensor. DETAILED DESCRIPTION

[0035] This part will describe the specific embodiments of the present application in detail, the preferred embodiments of the present application are shown in the drawings, the role of the drawings is to supplement the description of the text part with graphics, so that people can intuitively and visually understand each technical feature and the overall technical scheme of the present application, but it cannot be understood as a limitation on the protection scope of the present application.

[0036] In the description of the present application, it should be understood that the orientation description, such as "up", "down", "front", "back", "left", "right" and the like, indicates the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, therefore it cannot be understood as a limitation on the present application.

[0037] In the description of the present application, if "first", "second" and the like are described, they are only used for the purpose of distinguishing technical features, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated or the sequence of technical features indicated.

[0038] In the description of the present application, unless otherwise explicitly limited, the words such as setting, installing, connecting and the like should be understood in a broad sense, and the person skilled in the art can reasonably determine the specific meaning of the above words in the present application in combination with the specific content of the technical scheme.

[0039] Reference Figure 1As shown, the simulation device for phase change formation response in CO2 injection provided by the embodiment of the first aspect of the application comprises a placing container 100 and a sealing sleeve 110 for sleeving outside a rock sample 300, the placing container 100 is internally provided with a cavity 120 for placing the rock sample 300, the cavity 120 is internally provided with a hollow spiral bent pipe 210 for surrounding outside the rock sample 300, oil flows through the hollow spiral bent pipe 210, the inlet and outlet ends of the hollow spiral bent pipe 210 are respectively communicated with a temperature adjusting assembly 240 for temperature rising and falling through an oil inlet pipe 220 and an oil outlet pipe 230, the temperature adjusting assembly 240 is electrically connected with a controller, the oil inlet pipe 220 is provided with an inlet temperature sensor 221, the oil outlet pipe 230 is provided with an outlet temperature sensor 231, the outlet temperature sensor 231 and the inlet temperature sensor 221 are both electrically connected with the controller; the cavity 120 is communicated with a supercritical CO2 injection system, the injection end of the supercritical CO2 injection system extends into a reserved vertical hole 310 of the rock sample 300; the cavity 120 is also communicated with a confining pressure loading system, the confining pressure loading system is electrically connected with the controller; the upper end opening of the placing container 100 is detachably connected with an upper cover 130 for pressing the rock sample 300; the cavity 120 is also provided with an acoustic emission probe 140 electrically connected with the controller. It can be understood that the controller is internally provided with a data acquisition system, and the controller is specifically selected as a computer.

[0040] Compared with the prior art, the embodiment of the application firstly adopts a rock with a reserved vertical hole 310 as a sample, in the process of simulation experiment, the reserved vertical hole 310 plays a role in simulating an oil and gas well, the supercritical CO2 injection system is started to inject the rock sample 300 through the reserved vertical hole 310, which more truly restores the situation that the supercritical CO2 is injected into the underground rock layer through the oil and gas well for storage in the actual engineering, more truly reproduces the situation that the formation response in the phase change process of the CO2 injection oil and gas well, and ensures the precision of the experiment, so as to select the optimal injection strategy. Secondly, the confining pressure loading system communicated with the cavity 120 and the hollow spiral bent pipe 210 surrounding outside the rock sample 300 are arranged, and the hollow spiral bent pipe 210 is circularly communicated with the temperature adjusting assembly 240, before the experiment, the confining pressure loading system is used to load hydraulic oil into the cavity 120 until the bearing confining pressure of the rock sample 300 reaches a set value, then the oil in the hollow spiral bent pipe 210 is pumped out, heated and recirculated back to the hollow spiral bent pipe 210 to exchange heat with the rock sample 300, so that the internal temperature of the rock sample 300 reaches a set value; in the engineering of the experiment, after a certain amount of supercritical CO2 is injected into the reserved vertical hole 310 through the supercritical CO2 injection system, according to the required CO2 phase change situation, such as Figure 3As shown, the CO2 phase change process of any path can be selected (both the way of keeping the confining pressure of the cavity 120 unchanged and cooling the rock sample 300 through the temperature adjusting assembly 240 or the way of keeping the temperature of the rock sample 300 unchanged and reducing the confining pressure of the cavity 120 through the confining pressure loading system or the way of cooling and decompressing at the same time), the formation response conditions of different CO2 phase change processes are obtained, the optimal storage parameters of supercritical CO2 storage are determined, and data support is provided for the injection of supercritical CO2 into the oil and gas well for storage. Moreover, in the process of the experiment, the cooling speed of the temperature adjusting assembly 240 or the decompression speed of the confining pressure loading system can be controlled through the controller, so that the phase change rate of CO2 in any path can be controlled, and then the phase change process of the formation near and far from the injection of CO2 into the oil and gas well is simulated. At the same time, in the process of the experiment, a pair of acoustic emission probes 140 can be arranged at the upper and lower ends of the rock sample 300, and four pairs of acoustic emission probes 140 can be arranged on the outer wall of the rock sample 300 in the circumferential direction; thus, the data of the acoustic emission probes 140 in the phase change process of CO2 injected into the oil and gas well can be monitored in real time, the wave speed information of compression waves (P waves) and shear waves (S waves) can be obtained, these wave speeds are used to calculate the dynamic elastic constants of rocks, such as Poisson's ratio, Young's modulus (E), bulk modulus (K) and shear modulus (G), the generation and expansion of microcracks in the rock material under the action of load in the CO2 phase change process can be continuously and real-timely monitored, and the location of the damage can be located. The rock sample 300 is tightly sleeved and sealed by the sealing sleeve 110, so as to prevent the mutual communication between the rock sample 300 and the liquid in the cavity 120. In addition, the inlet temperature sensor 221 is arranged on the oil inlet pipe 220, and the outlet temperature sensor 231 is arranged on the oil outlet pipe 230, so that when the rock sample 300 is heated, the temperature adjusting assembly 240 and the hollow spiral bent pipe 210 cooperate to heat the rock sample 300 to the temperature value monitored by the outlet temperature sensor 231 equal to the temperature value monitored by the inlet temperature sensor 221, at which time the internal temperature of the rock sample 300 reaches the set value. The temperature value monitored by the outlet temperature sensor 231 and the temperature value monitored by the inlet temperature sensor 221 can be observed in real time through the display screen on the computer, so that whether the internal temperature of the rock sample 300 reaches the set value can be determined more accurately.

[0041] Specifically, in order to avoid heat loss in the cavity 120, a heat preservation layer is arranged outside the container 100 to improve the accuracy of the experiment.

[0042] Specifically, considering the acidity of CO2 and the high-temperature environment of the experiment, the rock container is made of Hastelloy alloy material which is resistant to high temperature and high pressure and anticorrosion.

[0043] As Figure 1As shown, preferably, the supercritical CO2 injection system comprises a supercritical CO2 storage tank, an outlet of the supercritical CO2 storage tank is communicated with an injection pipe 420 through an injection pump 410, an end of the injection pipe 420 away from the injection pump 410 extends into the pre-reserved vertical hole 310 of the rock sample 300; a first valve 430, a back pressure valve 440 and a first pressure sensor 450 are sequentially arranged on a side of the injection pipe 420 away from the injection pump 410; a second valve 461 and a second pressure sensor 462 are sequentially arranged on a side of the first pressure sensor 450 away from the back pressure valve 440, and the first pressure sensor 450 and the second pressure sensor 462 are both used for monitoring the CO2 pressure in the pre-reserved vertical hole 310 of the rock sample 300. The CO2 pressure in the pre-reserved vertical hole 310 can be monitored in real time through the first pressure sensor 450 and the second pressure sensor 462, and feedback to the computer, and when the CO2 pressure in the pre-reserved vertical hole 310 is equal to the confining pressure of the rock sample 300, the injection of CO2 into the pre-reserved vertical hole 310 can be stopped, so that the CO2 pressure in the pre-reserved vertical hole 310 is equal to the confining pressure of the rock sample 300, and the accuracy of the experiment is improved; the CO2 pressure value in the pre-reserved vertical hole 310 can also be monitored in real time through the first pressure sensor 450, so as to adjust the pressure value of the back pressure valve 440, so that it is lower than the reading value of the first pressure sensor 450 and higher than the pressure value of the injection pump 410, so that the supercritical CO2 injection system injects CO2 with a set pressure into the pre-reserved vertical hole 310 in a gradient increasing manner; at the same time, after the CO2 pressure in the pre-reserved vertical hole 310 reaches the set value, the first valve 430, the second valve 461 and the injection pump 410 are closed, and the second pressure sensor 462 can continue to monitor the CO2 pressure in the pre-reserved vertical hole 310, so that the change of the pressure in the pre-reserved vertical hole 310 in the phase transition process can be observed through the second pressure sensor 462.

[0044] Further preferably, in order to more truly simulate the process of supercritical CO2 injection into an oil and gas well, a buffer container 471 and a third valve 472 are sequentially arranged on an end of the back pressure valve 440 towards the first pressure sensor 450. The buffer container 471 can buffer the supercritical CO2, so as to more truly simulate the process of supercritical CO2 injection into an oil and gas well. It can be understood that, in order to smoothly inject the supercritical CO2 in the buffer container 471 into the pre-reserved vertical hole 310, the CO2 pressure in the buffer container 471 is greater than the CO2 pressure in the pre-reserved vertical hole 310.

[0045] Further preferably, the third valve 472 is sequentially provided with a third pressure sensor 481, a pre-heater 482 and a fourth valve 483 at one end away from the buffer container 471. The CO2 pressure in the buffer container 471 can be monitored in real time through the third pressure sensor 481; at the same time, the CO2 to be injected into the reserved vertical hole 310 is pre-heated to be substantially equal to the internal temperature of the rock sample 300 through the pre-heater 482, which can prevent the temperature change of the rock sample 300 caused by the injection of cold CO2 into the reserved vertical hole 310.

[0046] Preferably, the confining pressure loading system comprises a confining pressure loading pump 510 electrically connected to the controller, and an outlet end of the confining pressure loading pump 510 is communicated with the cavity 120 through a first pipe 520, and an oil pressure delivery valve 530 is arranged on the first pipe 520. Before injecting supercritical CO2 into the reserved vertical hole 310, the oil pressure delivery valve 530 is opened and the confining pressure loading pump 510 is started to load hydraulic oil into the cavity 120 until the confining pressure borne by the rock sample 300 reaches a set value; during the process of simulating the phase change of CO2, the confining pressure borne by the rock sample 300 can be lowered to make the CO2 phase change by adjusting the loading pressure of the confining pressure loading pump 510. By controlling the descending gradient of the loading pressure of the confining pressure loading pump 510, the phase change rate of CO2 can be adjusted, and then the situation of the formation response during the phase change process of CO2 injection into the near wellbore and the far wellbore of the oil and gas well can be simulated.

[0047] Preferably, a base 150 for bearing the rock sample 300 is arranged in the middle of the inner bottom wall of the cavity 120, a first through hole is vertically arranged in the base 150, and a pore pressure loading system electrically connected to the controller is communicated with the first through hole, the pore pressure loading system comprises a interstitial pressure loading pump 610, an outlet end of the interstitial pressure loading pump 610 is communicated with the first through hole through a second pipe 620, and a water pressure switch valve 630 and an interstitial water pressure sensor 640 are sequentially arranged on the second pipe 620 in a direction away from the interstitial pressure loading pump 610. When the rock sample 300 is a dry sample and does not meet the water content of the formation to be simulated, the water pressure switch valve 630 can be opened and the interstitial pressure loading pump 610 can be started to inject ion-free water into the rock sample 300 until the interstitial water pressure in the rock sample 300 reaches a set value (the water content of the rock sample 300 is substantially the same as the water content of the formation to be simulated) monitored by the interstitial water pressure sensor 640, so as to ensure the accuracy of the experiment. The water pressure switch valve 630 and the interstitial pressure loading pump 610 are closed during the experiment, and the pore water pressure change of the rock sample 300 during the CO2 phase change process is monitored by the interstitial water pressure sensor 640.

[0048] As Figure 2As shown, preferably, the temperature adjusting assembly 240 comprises a heating tank 241 and a cooling tank 242, the heating tank 241 is provided with a heating resistor, the heating resistor is electrically connected to the controller, the outlet of the heating tank 241 is provided with a first delivery pump 243 electrically connected to the controller; the cooling tank 242 is provided with a cooling coil and a cooling fan blowing to the cooling coil, the cooling fan is electrically connected to the controller, the outlet of the cooling tank 242 is provided with a second delivery pump 244 electrically connected to the controller. After the confining pressure loading system loads the confining pressure to the bearing confining pressure of the rock sample 300 to reach the set value, before injecting supercritical CO2 into the pre-reserved vertical hole 310, the first delivery pump 243 is started to pump the oil in the hollow spiral coil 210 into the heating tank 241 for heating and recycling back to the hollow spiral coil 210 for heat exchange with the rock sample 300, so that the internal temperature of the rock sample 300 rises to the set value; during the process of simulating CO2 phase change, the second delivery pump 244 is started to pump the oil in the hollow spiral coil 210 into the cooling tank 242 for cooling and recycling back to the hollow spiral coil 210 for heat exchange with the rock sample 300, so that the internal temperature of the rock sample 300 drops, thereby causing the phase change of CO2; by controlling the power of the cooling fan, the phase change rate of CO2 can be adjusted, and then the formation response in the process of simulating the phase change of CO2 injected into the near wellbore and the far wellbore of the oil and gas well can be simulated.

[0049] Preferably, the upper cover 130 is provided with a second through hole penetrating in the up-down direction, a third temperature monitoring sensor 250 for monitoring the temperature in the cavity 120 is inserted into the second through hole, and the third temperature monitoring sensor 250 is electrically connected to the controller. The temperature in the cavity 120 is monitored in real time by the third temperature monitoring sensor 250, and when the temperature values monitored by the third temperature monitoring sensor 250, the outlet temperature sensor 231 and the inlet temperature sensor 221 are equal, it indicates that the internal temperature of the rock sample 300 and the temperature in the cavity 120 both reach the set value, the internal temperature of the rock sample 300 reaching the set value is more accurately determined, and the accuracy of the experiment is further improved.

[0050] Preferably, the left and right sides of the placing container 100 are symmetrically provided with screw rods 160, the upper cover 130 is provided with a third through hole corresponding to the positions of the screw rods 160, and during installation, the upper cover 130 is covered on the upper end opening of the placing container 100 through the screw rods 160, and then the fastening nuts 170 are tightened on the screw rods 160, the fastening nuts 170 press the upper cover 130, so that the upper cover 130 can seal the upper end opening of the placing container 100 and fix the rock sample 300 at the same time.

[0051] Reference Figures 1 to 3As shown, according to the method for simulating experiments by using the device of the first aspect of the present application, the method of the second aspect of the present application comprises the following steps: Step A: making a rock sample 300, before the experiment, selecting the rock type according to the water content and saturation of the formation to be simulated, processing the rock of the determined type into a cylinder with a diameter of 100 mm and a height of 150 mm, and setting a reserved vertical hole 310 with a diameter of 5 mm in the middle of the upper end of the cylinder to obtain the rock sample 300, and the depth of the reserved vertical hole 310 is selected to be 1 / 3 to 1 / 2 of the height of the rock sample 300.

[0052] Step B: CT scanning the rock sample 300 before the experiment to obtain the internal structure image of the rock sample 300;

[0053] Step C: The sealing sleeve 110 is sleeved outside the rock sample 300, and then the rock sample 300 is put into the cavity 120 of the placing container 100 through the hollow spiral bend pipe 210;

[0054] Step D: device assembly, select six pairs of acoustic emission probes 140, wherein one pair of acoustic emission probes 140 is arranged at the upper and lower ends of the rock sample 300, and four pairs of acoustic emission probes 140 are arranged on the outer sidewall of the rock sample 300 in the circumferential direction, install the third temperature monitoring sensor 250 in the cavity 120, cover the upper cover 130 on the upper end opening of the placing container 100 through the screw rod 160, tighten the fastening nut 170 to seal the upper end opening of the placing container 100 while fixing the rock sample 300, extend the injection end of the supercritical CO2 injection system through the upper cover 130 into the reserved vertical hole 310 of the rock sample 300; test the air tightness of the experimental device;

[0055] Step E: According to the simulated formation pressure, the confining pressure required to be borne by the rock sample 300 is 50 MPa, the confining pressure loading system is opened, the loading pressure is set to 50 MPa, and the hydraulic oil is started to be loaded into the cavity 120 to the rock sample 300 until the confining pressure borne by the cavity 120 reaches 50 MPa; according to the simulated formation temperature, the internal temperature of the rock sample 300 is 40°C, the temperature adjusting assembly 240 is opened, the loading temperature is set to 40°C, the oil is heated by the temperature adjusting assembly 240 and delivered into the hollow spiral pipe 210 to exchange heat with the rock sample 300 until the temperature values monitored by the outlet temperature sensor 231 and the inlet temperature sensor 221 are equal and kept at 40°C, which indicates that the internal temperature of the rock sample 300 and the temperature of the cavity 120 both reach 40°C; since the prepared rock sample 300 contains a certain amount of water (unsaturated), the pore pressure loading system does not need to be started to inject a certain amount of pore water (ion-free water) into the rock sample 300, at this time the water pressure switch valve 630 is kept closed; if a dry sample is placed, a certain amount of pore water can be injected through the interstitial pressure loading pump 610, the pore water loading system can be set to load pressure or measure the volume of water entering or flowing out, and if the mass of the dry sample is known, the water content of the rock sample 300 after injection can be estimated; after the internal temperature and the confining pressure borne by the rock sample 300 are stable, the supercritical CO2 injection system is started to inject supercritical CO2 into the reserved vertical hole 310 of the rock sample 300; specifically, the CO2 injection is first injected by the injection pump 410, a certain amount of CO2 is injected to adjust the CO2 pressure in the buffer container 471 through the back pressure valve 440, considering that the CO2 is injected into the reserved vertical hole 310, at this time the CO2 pressure in the buffer container 47124 is greater than the CO2 pressure in the reserved vertical hole 310, at this time the third valve 472 is opened, and the CO2 pressure in the buffer container 471 is monitored in real time through the third pressure sensor 481, at this time the CO2 is room temperature, and placing cold CO2 into the reserved vertical hole 310 will cause the temperature change of the rock sample 300, therefore before injection, the CO2 passes through a pre-heater 482 to heat the CO2 in the pipeline to a temperature close to the internal temperature of the rock sample 300, at this time the fourth valve 483 and the second valve 461 are opened, the CO2 is smoothly injected into the reserved vertical hole 310, the CO2 pressure in the reserved vertical hole 310 is monitored in real time through the second pressure sensor 462, the above steps are repeated until the reading of the second pressure sensor 462 is consistent with the confining pressure, the CO2 injection is stopped, and the injection pump 410 and the valves are closed, at this time the CO2 in the entire rock sample 300 and the reserved vertical hole 310 reaches the same temperature and pressure. It can be understood that before the CO2 is injected into the reserved vertical hole 310, the injection pipe 420 can be vacuumed.

[0056] Step F: Start the simulation of CO2 phase change process, CO2 phase change diagram as follows Figure 3 As shown in the right upper corner of the point for the experimental state (temperature of 40 ℃, confining pressure of 50 Mpa), from Figure 3 It can be seen that the CO2 phase change process includes from supercritical state to gaseous state or from supercritical state to liquid state, if the above phase change process occurs, the temperature needs to be reduced and the pressure needs to be reduced, the device can realize any path, such as keeping the pressure unchanged, that is, keeping the confining pressure loading system unchanged, the temperature reduction process, adjusting the temperature adjusting assembly 240, such as Figure 3 Path 1 shown in FIG. 1; such as keeping the temperature unchanged, that is, keeping the temperature adjusting assembly 240 unchanged, the pressure reduction process, adjusting the confining pressure loading system, such as Figure 3 Path 4 shown in FIG. 1; can reduce the pressure at the same time, that is, adjust the confining pressure loading system and the temperature adjusting assembly 240 at the same time, such as Figure 3 Path 2 or 3 shown in FIG. 1; according to the required simulation of CO2 phase change, one of the phase change paths is selected, and the temperature or pressure is adjusted to achieve the purpose of sharp phase change or gradual phase change, and then the simulation of CO2 injection into the near and far end of the oil and gas well is realized. During the CO2 phase change process, the volume of CO2 can rapidly increase, the pressure near the vertical hole 310 can rapidly increase, and the rock acoustic emission is the phenomenon that the rock emits acoustic waves or ultrasonic waves in the process of stress deformation and fracture. Real-time monitoring of the data of the six acoustic emission probes 140 can obtain the wave velocity information of the compression wave (P wave) and the shear wave (S wave). These wave velocities are used to calculate the dynamic elastic constants of the rock, such as Poisson's ratio, Young's modulus (E), bulk modulus (K) and shear modulus (G); the generation and expansion of microcracks in the rock material under the action of load during the phase change process can be continuously and real-timely monitored, and the location of the damage position can be located. The reading of the gap water pressure sensor 640 can obtain the change of the pore water pressure of the rock sample 300 during the phase change process

[0057] Step G: Experimental analysis, after the reaction is completed, the confining pressure is adjusted to zero, the device is gradually cooled to room temperature, the device is disassembled, the rock sample 300 is taken out, and CT scanning is performed, the influence of the phase change on the rock structure is observed, and the internal structure image of the rock sample 300 obtained in step B is compared, and the response characteristics of the formation during the phase change process are quantitatively evaluated.

[0058] Compared with the prior art, the method of the embodiment of the present application adopts the rock with the reserved vertical hole 310 as the sample, in the process of carrying out the simulation experiment, the reserved vertical hole 310 can simulate the oil and gas well in the actual engineering, the supercritical CO2 injection system is started to inject the rock sample 300 through the reserved vertical hole 310, which more truly restores the supercritical CO2 injection through the oil and gas well into the underground rock layer for storage in the actual engineering, more truly reproduces the formation response of the phase change process at the CO2 injection oil and gas well, so as to select the optimal injection strategy. In the process of carrying out the experiment, after a certain amount of supercritical CO2 is injected into the reserved vertical hole 310 through the supercritical CO2 injection system, according to the CO2 phase change condition to be simulated, the CO2 phase change process of any path can be selected, the formation response of the CO2 phase change process is obtained, through comparison and analysis, the optimal storage strategy of the supercritical CO2 storage is determined, which provides data support for the supercritical CO2 injection into the oil and gas well for storage. At the same time in the process of the experiment, the cooling speed of the temperature adjusting assembly 240 or the pressure reducing speed of the confining pressure loading system can be controlled through the controller, so that the CO2 phase change rate of any path can be controlled, and then the formation response of the phase change process near and far from the CO2 injection oil and gas well can be simulated. The data of the acoustic emission probe 140 can also be monitored in real time during the phase change process at the CO2 injection oil and gas well, the wave velocity information of the compression wave (P wave) and the shear wave (S wave) is obtained, these wave velocities are used to calculate the dynamic elastic constants of the rock, such as Poisson's ratio, Young's modulus (E), bulk modulus (K) and shear modulus (G), the generation and expansion of the microcracks in the rock material under the load in the phase change process can be continuously and real-timely monitored, and the damage position is located, the formation response of the phase change process at the CO2 injection oil and gas well is more truly reproduced, so as to select the optimal injection strategy.

[0059] The above is only the preferred embodiment of the present application, and is not used to limit the present application, any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method of simulating an experiment, characterized by, The application discloses a simulation device for phase change stratum response in a CO2 injection process, which comprises a placing container and a sealing sleeve for sleeving outside a rock sample, a cavity for placing the rock sample is arranged in the placing container, a hollow spiral bending pipe for surrounding outside of the rock sample is arranged in the cavity, oil flows through the hollow spiral bending pipe, inlet and outlet ends of the hollow spiral bending pipe are communicated with a temperature adjusting assembly for temperature rising and falling through an oil inlet pipe and an oil outlet pipe respectively, an inlet temperature sensor is arranged on the oil inlet pipe, the inlet temperature sensor is electrically connected with a controller, an outlet temperature sensor is arranged on the oil outlet pipe, and the outlet temperature sensor and the temperature adjusting assembly are electrically connected with the controller; the cavity is communicated with a supercritical CO2 injection system, an injection end of the supercritical CO2 injection system extends into a reserved vertical hole of the rock sample; the cavity is also communicated with a confining pressure loading system, and the confining pressure loading system is electrically connected with the controller; an upper end opening of the placing container is detachably connected with an upper cover for pressing the rock sample; an acoustic emission probe electrically connected with the controller is also arranged in the cavity. The method comprises the following steps: Step A: preparing a rock sample, selecting a rock type according to water content and saturation of a stratum to be simulated before experiment, processing the rock of the determined type into a required size, and opening a reserved vertical hole in the middle of the upper end of the rock to obtain the rock sample; Step B: performing CT scanning on the rock sample before experiment to obtain an internal structure image of the rock sample; Step C: sleeving the sealing sleeve outside the rock sample, and then placing the rock sample through the hollow spiral bending pipe into the cavity of the placing container; Step D: assembling the device, connecting the acoustic emission probe with the rock sample, then connecting the upper cover to the upper end of the placing container, fixing the rock sample and sealing the cavity at the same time, communicating the injection end of the supercritical CO2 injection system with the cavity and extending into the reserved vertical hole of the rock sample, and testing air tightness of the experimental device; Step E: starting to load the inside of the cavity to the confining pressure of the rock sample to reach a set value through the confining pressure loading system according to stratum pressure to be simulated, heating the oil through the temperature adjusting assembly and conveying the oil into the hollow spiral bending pipe to exchange heat with the rock sample so that the internal temperature of the rock sample reaches a set value according to stratum temperature to be simulated, and injecting supercritical CO2 into the reserved vertical hole of the rock sample through the supercritical CO2 injection system so that the pressure in the reserved vertical hole is equal to the confining pressure of the rock sample; Step F: starting to simulate the CO2 phase change process, setting a phase change path according to the CO2 phase change to be simulated, monitoring pressure change in the reserved vertical hole of the rock sample in the phase change process, and monitoring wave velocity information of compression waves and shear waves emitted by the rock sample in the stress deformation and fracture process through the acoustic emission probe. Step G: experimental analysis, after the reaction is completed, the device is gradually cooled to room temperature, the rock sample is taken out for CT scanning, the influence of phase change on the structure of the rock is observed, and the internal structure image of the rock sample obtained in step B is compared, and the response characteristics of the formation in the phase change process are quantitatively evaluated; The phase change path includes keeping the cavity confining pressure unchanged, cooling the rock sample through the temperature adjusting assembly, or keeping the temperature of the rock sample unchanged, reducing the cavity confining pressure through the confining pressure loading system, or cooling and depressurizing at the same time.

2. The method of simulating an experiment of claim 1, wherein, The supercritical CO2 injection system comprises a supercritical CO2 storage tank, an injection pump is connected to the outlet of the supercritical CO2 storage tank through an injection pipe, one end of the injection pipe away from the injection pump extends into the reserved vertical hole of the rock sample, a first valve, a back pressure valve and a first pressure sensor are arranged on the side of the injection pipe away from the injection pump in sequence, a second valve and a second pressure sensor are arranged on the side of the first pressure sensor away from the back pressure valve in sequence, and the first pressure sensor and the second pressure sensor are used to monitor the CO2 pressure in the reserved vertical hole of the rock sample.

3. A method of simulating an experiment according to claim 2, wherein, The end of the back pressure valve towards the first pressure sensor is sequentially provided with a buffer container and a third valve.

4. The method of simulating an experiment of claim 3, wherein, The end of the third valve away from the buffer container is sequentially provided with a third pressure sensor, a pre-heater and a fourth valve.

5. The method of simulating an experiment of claim 1, wherein, The confining pressure loading system comprises a confining pressure loading pump electrically connected to the controller, and the outlet end of the confining pressure loading pump is connected to the cavity through a first pipe, and an oil pressure delivery valve is arranged on the first pipe.

6. The method of simulating an experiment of claim 1, wherein, A base for bearing the rock sample is arranged in the middle of the inner bottom wall of the cavity, a first through hole vertically penetrating the base is connected to a pore pressure loading system, and the pore pressure loading system comprises a gap pressure loading pump, the outlet end of the gap pressure loading pump is connected to the first through hole through a second pipe, and a water pressure on-off valve and a gap water pressure sensor are arranged on the second pipe in sequence away from the gap pressure loading pump.

7. The method of simulating an experiment of claim 1, wherein, The temperature adjusting assembly comprises a heating tank and a cooling tank, a heating resistor is arranged in the heating tank, the heating resistor is electrically connected to the controller, and the outlet of the heating tank is provided with a first delivery pump electrically connected to the controller; a cooling elbow and a cooling fan blowing towards the cooling elbow are arranged in the cooling tank, the cooling fan is electrically connected to the controller, and the outlet of the cooling tank is provided with a second delivery pump electrically connected to the controller.

8. The method of simulating an experiment of claim 1, wherein, A second through hole penetrating the upper cover in the up-down direction is inserted with a third temperature monitoring sensor for monitoring the temperature in the cavity, and the third temperature monitoring sensor is electrically connected to the controller.

9. The method of simulating an experiment of claim 1, wherein, Screws are symmetrically arranged on the left and right sides of the placing container, third through holes corresponding to the screws are arranged on the upper cover, when installed, fastening nuts are threadedly connected to the screws, and the fastening nuts press the upper cover.

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