Device and method for evaluating dynamic filtration performance of CO2-based fracturing fluid under high-temperature and high-pressure conditions

Abstract

The invention discloses a device and a method for evaluating the dynamic filtration performance of CO2-based fracturing fluid under high-temperature and high-pressure conditions. The evaluation device comprises a pressurizing system, a heating system, a circulating system, a core clamping system and a metering system which are connected in sequence. The process that CO2-based fracturing fluid is filtered from a crack to a stratum is simulated through the rock core clamping system, rock cores can be placed at the two ends of the simulated crack, and the filtration process of the CO2-based fracturing fluid under the conditions of different crack widths and crack wall surface roughness can be simulated by changing the positions of the rock cores at the two ends and the rock core end surface roughness.

Description

Technical Field

[0001] The present invention relates to the technical field of unconventional oil and gas production enhancement, and more specifically to a device and method for evaluating the dynamic filtration performance of a CO2-based fracturing fluid under high temperature and high pressure conditions. Background Art

[0002] CO2-based fracturing fluids include liquid CO2 fracturing fluids, supercritical CO2 fracturing fluids, CO2 foam fracturing fluids and other special fracturing fluids. CO2-based fracturing fluids have many advantages such as less formation damage, low residue content, and easy backflow after fracturing. However, the high filtration loss characteristics of CO2-based fracturing fluids limit the promotion and application of CO2-based fracturing fluids. Under the condition of a certain amount of injected fluid, the greater the filtration loss, the smaller the crack width and effective length will be, resulting in low effective utilization of fracturing fluids, which directly affects the post-fracturing production capacity. Therefore, determining the filtration loss coefficient of CO2-based fracturing fluids is a key parameter for achieving efficient construction of CO2-based fracturing.

[0003] The fracturing fluid loss surface in the fracture is two symmetrical fracture walls, but the current CO2 fracturing fluid dynamic loss instruments all use a single loss surface, and are unable to adjust parameters such as the loss wall roughness and fracture width, which is quite different from the fracturing fluid loss in the actual fracturing process. Summary of the invention

[0004] In view of this, the present invention provides a device and method for evaluating the dynamic filtration performance of CO2-based fracturing fluid under high temperature and high pressure conditions.

[0005] In order to achieve the above object, the present invention adopts the following technical solution:

[0006] A dynamic filtration performance evaluation device for CO2-based fracturing fluid under high temperature and high pressure conditions, comprising a pressurizing system, a heating system, a circulation system, a core clamping system and a metering system connected in sequence;

[0007] Wherein, the pressurization system includes a CO2 gas cylinder, a booster pump, a pressure gauge, a buffer tank, and a pressure regulating valve;

[0008] The CO2 gas cylinder, booster pump, buffer tank and pressure regulating valve are connected in sequence;

[0009] The pressure gauges are provided with two, which are respectively provided on the outlet pipeline of the CO2 cylinder and the outlet pipeline of the booster pump; the CO2 cylinder is connected to the booster pump and stores the CO2 in a buffer tank after pressurization; the buffer tank can be used to store liquid CO2 and can also be used to mix liquid CO2 with additives; the pressure regulating valve is connected to the buffer tank and can be used to control the fluid pressure at the inlet end of the core holder;

[0010] The heating system includes a constant temperature oven, a preheating coil, and a temperature sensor;

[0011] The preheating coil and the pressure regulating valve are both arranged inside the constant temperature oven, and the preheating coil is connected to the pressure regulating valve; the temperature sensor is arranged on the top of one side of the constant temperature oven; the oven is used to ensure that the core clamp system is at the formation temperature; the preheating coil is used to ensure that the low-temperature CO2 can achieve sufficient heat exchange after entering the oven, ensuring that the CO2 is in a supercritical state;

[0012] The circulation system includes a simulated fracture, a circulation pump, and a mass flow meter; the simulated fracture, the circulation pump, the mass flow meter, and the preheating coil together form a high-pressure circulation loop for simulating the state of fracturing fluid flowing in the fracture;

[0013] The core clamping system is used to simulate the process of supercritical CO2 fracturing fluid filtering out of the fracture into the formation. Cores can be placed at both ends of the simulated fracture. The core positions at both ends and the roughness of the core end surfaces can be changed to simulate the filtering out process of supercritical CO2 fracturing fluid under different fracture widths and fracture wall roughness conditions.

[0014] The core holding system comprises a core, b core, a core holder, an inlet pressure sensor, and an outlet pressure sensor. The simulated fracture is perpendicular to the core holder. The cores a and b are placed horizontally in the core holder. One end of the cores a and b is connected to the simulated fracture. After the CO2-based fracturing fluid enters the simulated fracture, shear is formed on the core end face to simulate the process of CO2-based fracturing fluid filtering through the fracture wall to the formation rock matrix.

[0015] The inlet pressure sensor is arranged on the pipeline between the preheating coil and the simulated fracture; the inlet pressure sensor and the outlet pressure sensor are used to calculate the pressure difference during the filtration process of the CO2-based fracturing fluid;

[0016] The metering system includes a buffered back-pressure valve, a conical flask, a beaker, an electronic balance, and an electronic computer connected in sequence; two outlets of the core holder converge into an outlet pipeline, which is connected to the buffered back-pressure valve through the outlet pipeline, and the outlet pressure sensor is placed on the pipeline between the core holder and the buffered back-pressure valve;

[0017] The metering system is connected to the outlet of the core support system to collect the gaseous CO2 filtrate and measure the mass of water with the same volume as the gaseous CO2 filtrate by the water displacement method, and then convert the volume of CO2 filtrate at different times.

[0018] Preferably, the positions of the core a and the core b are adjusted to change the width of the simulated fracture, thereby simulating the filtration process of the CO2-based fracturing fluid under different fracture width conditions;

[0019] By changing the roughness of the end faces of the core a and the core b connected to the simulated fracture, the filtration process of the CO2-based fracturing fluid under different fracture wall roughness conditions is simulated.

[0020] Preferably, the core holder is 280 mm long; the cores a and b are 50 mm long and 25 mm in diameter.

[0021] Another object of the present invention is to provide an evaluation method for a dynamic filtration performance evaluation device of a CO2-based fracturing fluid under high temperature and high pressure conditions, using the above-mentioned evaluation device, including: under the sealing conditions required for evaluation; ensuring that the CO2 in the core holder and the preheating tube is fully heated to the set temperature; simulating the dynamic filtration process of the CO2-based fracturing fluid under different seam widths and filtration wall roughness conditions, and collecting experimental data.

[0022] The specific steps include:

[0023] Step 1: Select the target formation core, split a fracture surface perpendicular to the core axis in the middle of the long core, and change the roughness of the core end surface according to the experimental requirements;

[0024] Step 2: Place core a and core b into the core holder, and change the positions of core a and core b according to experimental requirements;

[0025] Step 3: Heat the ambient temperature to the set temperature through the constant temperature oven of the heating system, wait for the core in the core holder to heat up to the target temperature, and set the confining pressure of the core holder;

[0026] Step 4: Use a booster pump to pump the gas in the CO2 cylinder into the buffer tank to ensure that the gas pressure in the buffer tank is higher than the set inlet pressure of the experiment;

[0027] Step 5: Adjust the pressure regulating valve to limit the gas pressure to the set inlet pressure, turn on the circulation pump, and adjust the buffer back pressure valve after the filtrate flow rate stabilizes;

[0028] Step 6: Change the back pressure, circulation pump frequency, core permeability, simulated fracture width, and filtration wall roughness according to the experimental requirements, and record the CO2-based fracturing fluid temperature T, fracturing fluid pressure p, fracturing fluid flow rate u, filtration pressure difference Δp, and time t under the above different conditions;

[0029] Step 7: Calculate the filtration volume Q of CO2-based fracturing fluid by converting the mass of water, and plot the filtration volume Q versus the square root of time. The relationship curve of

[0030] Step 8: Fit and calculate the filtration volume Q and the square root of time The relationship curve is obtained, and the slope of the straight line segment m is obtained to calculate the filtration loss rate and filtration loss coefficient:

[0031] The formula for calculating the filtration rate is:

[0032]

[0033] In the formula,

[0034] Q is the filtration volume of CO2-based fracturing fluid, cm 3 / s;

[0035] r is the core radius, cm;

[0036] v is the filtration velocity, cm / s;

[0037] The formula for calculating the filtration coefficient is:

[0038]

[0039] In the formula,

[0040] A is the cross-sectional area of ​​the core, cm 2

[0041] C is the filtration coefficient,

[0042] It can be seen from the above technical solution that compared with the prior art, the present invention has the following beneficial effects:

[0043] 1. The temperature and pressure of the experimental device can be adjusted to meet the temperature and pressure conditions for carbon dioxide to reach a liquid or supercritical state, and can also achieve the temperature and pressure environment required by different types of CO2 foam fracturing fluids;

[0044] 2. The experimental device can more realistically characterize the filtration process of CO2-based fracturing fluid under different temperature, pressure and phase conditions, and can more accurately study the filtration law of CO2-based fracturing fluid under different temperature and pressure conditions;

[0045] 3. The experimental device can adjust different core holder confining pressures and holder outlet back pressures, which can better study the filtration law of CO2-based fracturing fluid under different formation pressures and different filtration pressure differences;

[0046] 4. The experimental device can pre-saturate the core with CH4 to more realistically characterize the filtration law of CO2-based fracturing fluid in a reservoir filled with natural gas;

[0047] 5. The double-loss wall design of the experimental device can more accurately describe the loss process of CO2-based fracturing fluid in the reservoir, and can also simulate the loss process under conditions of different loss wall roughness and different fracture widths. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0049] Figure 1 It is a structural diagram of the device of the present invention;

[0050] Among them, in the figure:

[0051] 1. CO2 gas cylinder; 2. Pressure gauge; 3. Booster pump; 4. Buffer tank; 5. Constant temperature oven; 6. Pressure regulating valve; 7. Preheating coil; 8. Core holder; 9. Circulation pump; 10. Buffered back pressure valve; 11. Conical flask; 12. Beaker; 13. Electronic balance; 14. Inlet pressure sensor; 15. Outlet pressure sensor; 16. Temperature sensor; 17. Simulated fracture; 18. Mass flow meter; 19. Electronic computer; 20. a core; 21. b core. DETAILED DESCRIPTION

[0052] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0053] Example 1

[0054] See also Figure 1 , This embodiment provides a device for evaluating the dynamic filtration performance of CO2-based fracturing fluid under high temperature and high pressure conditions, including a pressurizing system, a heating system, a circulation system, a core clamping system and a metering system connected in sequence;

[0055] The pressurizing system includes a CO2 gas cylinder 1, a booster pump 3, a pressure gauge 2, a buffer tank 4, and a pressure regulating valve 6;

[0056] The CO2 gas cylinder 1, the booster pump 3, the buffer tank 4 and the pressure regulating valve 6 are connected in sequence;

[0057] There are two pressure gauges 2, which are respectively arranged on the outlet pipeline of the CO2 gas cylinder 1 and the outlet pipeline of the booster pump 3;

[0058] The heating system includes a constant temperature oven 5, a preheating coil 7, and a temperature sensor 16;

[0059] The preheating coil 7 and the pressure regulating valve 6 are both arranged inside the constant temperature oven 5, and the preheating coil 7 is connected to the pressure regulating valve 6; the temperature sensor 16 is arranged on the top of one side inside the constant temperature oven 5;

[0060] The circulation system includes a simulated crack 17, a circulation pump 9, and a mass flow meter 18; the simulated crack 17, the circulation pump 9, the mass flow meter 18, and the preheating coil 7 together form a high-pressure circulation loop;

[0061] The core holding system includes a core 20, b core 21, a core holder 8, an inlet pressure sensor 14, and an outlet pressure sensor 15. The simulated fracture 17 is perpendicular to the core holder 8. The a core 20 and the b core 21 are placed horizontally in the core holder 8. One end of the a core 20 and the b core 21 are connected to the simulated fracture 17. After the CO2-based fracturing fluid enters the simulated fracture 17, shear is formed on the core end face to simulate the process of CO2-based fracturing fluid filtering through the fracture wall to the formation rock matrix.

[0062] The inlet pressure sensor 14 is arranged on the pipeline between the preheating coil 7 and the simulated fracture 17; the outlet pressure sensor 15 is respectively connected to the two outlets of the core holder 8;

[0063] The metering system comprises a buffer back pressure valve 10 , a conical flask 11 , a beaker 12 , an electronic balance 13 , and an electronic computer 19 which are connected in sequence; the buffer back pressure valve 10 is connected to the outlet of the core holder 8 .

[0064] The positions of the a core 20 and the b core 21 are adjusted to change the width of the simulated fracture 17, thereby simulating the filtration process of the CO2-based fracturing fluid under different fracture width conditions;

[0065] By changing the roughness of the end faces of core a 20 and core b 21 connected to the simulated fracture, the filtration process of CO2-based fracturing fluid under different fracture wall roughness conditions is simulated.

[0066] Example 2

[0067] This embodiment provides an evaluation method for a dynamic fluid loss performance evaluation device for CO2-based fracturing fluid under high temperature and high pressure conditions, using the above-mentioned evaluation device, specifically comprising the following steps:

[0068] Step 1: Select the target formation core, split a fracture surface perpendicular to the core axis in the middle of the long core, and change the roughness of the core end surface according to the experimental requirements;

[0069] Step 2: Load core a 20 and core b 21 into the core holder 8, and change the positions of core a 20 and core b 21 according to experimental requirements;

[0070] Step 3: The ambient temperature is heated to a set temperature by the constant temperature oven 5 of the heating system, the temperature of the core in the core holder 8 is waited to rise to the target temperature, and the confining pressure of the core holder 8 is set;

[0071] Step 4: The gas in the CO2 cylinder 1 is pumped into the buffer tank 4 through the booster pump 3 to ensure that the gas pressure in the buffer tank is higher than the set inlet pressure of the experiment;

[0072] Step 5: Adjust the pressure regulating valve 6 to limit the gas pressure to the set inlet pressure, turn on the circulation pump 9, and adjust the buffer back pressure valve 10 after the filtrate flow rate stabilizes;

[0073] Step 6: Change the back pressure, circulation pump frequency, core permeability, simulated fracture width, and filtration wall roughness according to the experimental requirements, and record the CO2-based fracturing fluid temperature T, fracturing fluid pressure p, fracturing fluid flow rate u, filtration pressure difference Δp, and time t under the above different conditions;

[0074] Step 7: Calculate the filtration volume Q of CO2-based fracturing fluid by converting the mass of water, and plot the filtration volume Q versus the square root of time. The relationship curve of

[0075] Step 8: Fit and calculate the filtration volume Q and the square root of time The relationship curve is obtained, and the slope of the straight line segment m is obtained to calculate the filtration loss rate and filtration loss coefficient:

[0076] The formula for calculating the filtration rate is:

[0077]

[0078] In the formula,

[0079] Q is the filtration volume of CO2-based fracturing fluid, cm 3 / s;

[0080] r is the core radius, cm;

[0081] v is the filtration velocity, cm / s;

[0082] The formula for calculating the filtration coefficient is:

[0083]

[0084] In the formula,

[0085] A is the cross-sectional area of ​​the core, cm 2

[0086] C is the filtration coefficient,

[0087] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0088] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A dynamic filtration performance evaluation device for CO2-based fracturing fluid under high temperature and high pressure conditions, characterized in that: The evaluation device comprises a pressurizing system, a heating system, a circulation system, a core clamping system and a metering system connected in sequence; Wherein, the pressurizing system includes a CO2 gas cylinder, a booster pump, a pressure gauge, a buffer tank, and a pressure regulating valve; The CO2 gas cylinder, booster pump, buffer tank and pressure regulating valve are connected in sequence; The pressure gauges are provided with two, which are respectively provided on the outlet pipeline of the CO2 gas cylinder and the outlet pipeline of the booster pump; The heating system includes a constant temperature oven, a preheating coil, and a temperature sensor; The preheating coil and the pressure regulating valve are both arranged inside the constant temperature oven, and the preheating coil is connected to the pressure regulating valve; the temperature sensor is arranged on the top of one side inside the constant temperature oven; The circulation system includes a simulated crack, a circulation pump, and a mass flow meter; the simulated crack, the circulation pump, the mass flow meter, and the preheating coil together form a high-pressure circulation loop; The core holding system comprises a core, b core, a core holder, an inlet pressure sensor, and an outlet pressure sensor. The simulated fracture is perpendicular to the core holder. The cores a and b are placed horizontally in the core holder. One end of the cores a and b is connected to the simulated fracture. After the CO2-based fracturing fluid enters the simulated fracture, shear is formed on the core end face to simulate the process of CO2-based fracturing fluid filtering through the fracture wall to the formation rock matrix. The inlet pressure sensor is arranged on the pipeline between the preheating coil and the simulated fracture; the outlet pressure sensor is respectively connected to the two outlets of the core holder; The metering system comprises a buffered back-pressure valve, a conical flask, a beaker, an electronic balance and an electronic computer which are connected in sequence; the buffered back-pressure valve is connected to the outlet of the core holder, and the outlet pressure sensor is arranged on the pipeline between the core holder and the buffered back-pressure valve.

2. The dynamic filtration performance evaluation device for CO2-based fracturing fluid under high temperature and high pressure conditions according to claim 1 is characterized in that: By adjusting the positions of the core a and the core b to change the width of the simulated fracture, the filtration process of the CO2-based fracturing fluid under different fracture width conditions is simulated; By changing the roughness of the end faces of the core a and the core b connected to the simulated fracture, the filtration process of the CO2-based fracturing fluid under different fracture wall roughness conditions is simulated.

3. The dynamic filtration performance evaluation device for CO2-based fracturing fluid under high temperature and high pressure conditions according to claim 2 is characterized in that: The core holder is 280 mm long; the cores a and b are 50 mm long and 25 mm in diameter.

4. An evaluation method for a dynamic filtration performance evaluation device of a CO2-based fracturing fluid under high temperature and high pressure conditions, characterized in that: The evaluation device described in claim 3 includes: under the sealing conditions required for evaluation; ensuring that the CO2 in the core holder and the preheating tube is fully heated to the set temperature; simulating the dynamic filtration process of the CO2-based fracturing fluid under different fracture widths and filtration wall roughness conditions, and collecting experimental data.

5. The evaluation method of a dynamic filtration performance evaluation device for CO2-based fracturing fluid under high temperature and high pressure conditions according to claim 4, characterized in that: The specific steps include: Step 1: Select the target formation core, split a fracture surface perpendicular to the core axis in the middle of the long core, and change the roughness of the core end surface according to the experimental requirements; Step 2: Place core a and core b into the core holder, and change the positions of core a and core b according to experimental requirements; Step 3: Heat the ambient temperature to the set temperature through the constant temperature oven of the heating system, wait for the core in the core holder to heat up to the target temperature, and set the confining pressure of the core holder; Step 4: Use a booster pump to pump the gas in the CO2 cylinder into the buffer tank to ensure that the gas pressure in the buffer tank is higher than the set inlet pressure of the experiment; Step 5: Adjust the pressure regulating valve to limit the gas pressure to the set inlet pressure, turn on the circulation pump, and adjust the buffer back pressure valve after the filtrate flow rate stabilizes; Step 6: Change the back pressure, circulation pump frequency, core permeability, simulated fracture width, and filtration wall roughness according to the experimental requirements, and record the CO2-based fracturing fluid temperature T, fracturing fluid pressure p, fracturing fluid flow rate u, filtration pressure difference Δp, and time t under the above different conditions; Step 7: Calculate the filtration volume Q of CO2-based fracturing fluid by converting the mass of water, and plot the filtration volume Q versus the square root of time. The relationship curve of Step 8: Fit and calculate the filtration volume Q and the square root of time The relationship curve is obtained, and the slope of the straight line segment m is obtained to calculate the filtration loss rate and filtration loss coefficient: The formula for calculating the filtration rate is: In the formula, Q is the filtration volume of CO2-based fracturing fluid, cm 3 / s; r is the core radius, cm; v is the filtration velocity, cm / s; The formula for calculating the filtration coefficient is: In the formula, A is the cross-sectional area of ​​the core, cm 2 C is the filtration coefficient,

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