CN108287123B - A visual testing device and method for CO2 fracturing fluid carrying sand under dynamic filtration - Google Patents

Abstract

The invention relates to a visualization device and a visualization method for measuring sand carrying performance of a CO2 fracturing fluid under a high-pressure dynamic fluid loss condition, and belongs to the technical field of devices for simulating fracturing reformation of oil and gas fields and evaluating the sand carrying performance of the fracturing fluid. The fracturing fluid monitoring system comprises a sand carrying measuring device and an image acquisition device, and is characterized by further comprising a fluid loss measuring device, wherein the visualization device is communicated through a connecting pipeline, and fracturing fluid circulates in the connecting pipeline; the sand-carrying measuring device comprises a visual inner cavity and is used for simulating a sand-carrying flowing process of fracturing fluid in a fracturing fracture; the fluid loss measuring device is communicated with the visual inner cavity and is used for simulating the influence of stratums with different permeability in the fractured fracture on the fluid loss process; the image acquisition device is used for acquiring the sand-carrying flowing form of the fracturing fluid and analyzing data. The invention can simulate the change of the fluid loss performance of the fracturing fluid under the influence of different permeability of the stratum rock matrix when the fracturing fluid enters the stratum rock matrix through the wall surface of the fracture along the flowing direction of the fracturing fluid in the actual fracturing process.

Description

A visual testing device and method for CO2 fracturing fluid carrying sand under dynamic filtration

technical field

The invention relates to a visual testing device and method for sand-carrying of CO2 fracturing fluid under dynamic filtration, belonging to the technical field of devices for simulating fracturing reformation of oil and gas fields and evaluating the sand-carrying performance of fracturing fluid.

Background technique

With the large-scale development of oil and gas reservoirs, fracturing technology has become an important technical means for the stimulation and development of oil and gas reservoirs. During the fracturing process, the fracturing fluid is mainly used to carry the proppant into the fractures. Proppant fracture channels with high conductivity. By simulating the actual fracturing process and measuring the filtration performance and sand-carrying performance of the sand-carrying fluid, the appropriate fracturing fluid can be selected during the actual fracturing process to ensure the fracturing effect. In the actual fracturing process, in the fracture, along the flow direction of the fracturing fluid, the fracturing fluid will enter the formation rock matrix through the fracture wall, and the permeability of the formation rock matrix will affect the filtration process of the fracturing fluid, that is, fracturing. Fluid loss is a dynamic process. The change of fluid loss will further affect the sand-carrying performance of fracturing fluid. Therefore, when the fracturing fluid flows in the fracture, it is affected by the permeability of the surrounding formation, and the filtration performance changes, which in turn affects the sand-carrying performance of the fracturing fluid.

Liquid CO2 dry fracturing refers to the stimulation technology that uses pure liquid CO2 as fracturing fluid to fracturing oil and gas reservoirs. Compared with water-based fracturing fluid, CO2 fracturing has unique advantages: no residue, good compatibility, and reduced pollution; CO2 has strong fluidity and can enter the micro-fractures in the reservoir to better communicate with the reservoir; After fracturing, the gas in the formation expands to speed up the flowback; at the same time, CO2 is easily soluble in crude oil, reducing the viscosity of crude oil, which is conducive to improving the recovery of crude oil. The above performance of liquid CO2 dry fracturing is of great significance to the fracturing stimulation effect and ultimate recovery of unconventional tight oil and gas formations, especially sensitive formations, and has good application prospects. However, there are also some technical difficulties in the application of liquid CO2 dry fracturing. The viscosity of liquid CO2 is extremely low, generally 0.02-0.16mPa·s, and its physical properties such as viscosity, density, surface tension are closely related to temperature and pressure, and the sand-carrying ability is poor during the fracturing process. At the same time, due to the low viscosity, the filtration loss is large.

Therefore, it is necessary to measure the fluid loss performance and sand-carrying performance of liquid CO2 after changing its viscosity under high-pressure dynamic fluid-loss conditions. However, the existing fracturing fluid sand-carrying measurement device has a simple structure and a single function, and cannot be used in formations with different permeability. The sand-carrying ability of fracturing fluid was tested under the condition of filtration loss.

Chinese patent document CN206002508U discloses "A device for evaluating the sand-carrying effect of fracturing fluid", which is a device for evaluating the sand-carrying effect of fracturing fluid in a large-scale circuit system. However, this patented technology is only aimed at common conventional fracturing fluids, with limited pressure resistance, and is not suitable for evaluating the sand-carrying capacity of liquid CO2 fracturing fluids under high pressure; the device does not take into account that the sand-carrying fluid will flow to the surrounding formations during the fracturing process. Fluid loss and sand-carrying performance will be affected by dynamic fluid loss, which cannot simulate the real conditions in fracturing construction.

SUMMARY OF THE INVENTION

Aiming at the deficiencies of the prior art, the present invention provides a visual testing device for CO ₂ fracturing fluid carrying sand under dynamic filtration;

The present invention also provides the above-mentioned measurement method of the visualization device for measuring the sand-carrying performance of the _CO2 fracturing fluid under the condition of high-pressure dynamic filtration.

The invention realizes that, under the condition of dynamic filtration, to evaluate the sand-carrying performance and filtration performance of liquid _CO2 fracturing fluid or conventional single-phase fracturing fluid, both the formation permeability in the same fracture along the flow direction of the sand-carrying fluid can be simulated. The influence of the change of , on the sand-carrying performance, can also simulate the sand-carrying performance in formation fractures with different permeability, and measure its filtration performance at the same time.

The technical scheme of the present invention is as follows:

A visual test device for _CO2 fracturing fluid carrying sand under dynamic filtration, comprising a sand carrying measurement device and an image acquisition device, characterized in that the visualization device further comprises a filtration measurement device, and the visualization device is communicated through a connecting pipeline , the fracturing fluid circulates in the connecting pipeline;

The sand-carrying measurement device includes a visual inner cavity, which is used to simulate the sand-carrying flow process of the fracturing fluid in the fracturing fracture;

The fluid loss measurement device communicates with the visualized inner cavity, and the number of the fluid loss measurement device is multiple groups, each group of the fluid loss measurement device includes a core holder and a core, and the core is arranged in the core holder. In the holder, the fluid loss measurement device is used to simulate the influence of different permeability formations on the fluid loss process in the fracturing fracture;

The image acquisition device is arranged on the upper part of the visualized inner cavity, and includes a computer and a camera, and is used for collecting the flow pattern of fracturing fluid carrying sand and data analysis. The image acquisition device is in the prior art, well known to those skilled in the industry, and does not belong to the protection scope of the present invention.

The advantage of the design here is that the sand-carrying measurement device simulates the sand-carrying flow process of the fracturing fluid in the fracturing fracture, and the fluid loss measurement device simulates the influence of different permeability formations on the fluid loss process in the fracturing fracture. The image acquisition device It is used to collect the flow pattern and data analysis of fracturing fluid carrying sand; realize the full reduction of dynamic filtration loss of fracturing fluid in fractures, and provide the most realistic environment for measuring fracturing fluid.

In another aspect of the present disclosure, the sand-carrying measuring device further includes a first valve, a circulating pump, a first pressure sensor, and a sand feeder sequentially arranged on the sand-carrying liquid injection pipe, and sequentially arranged on the sand-carrying liquid discharge pipe The second back pressure valve and the fourth valve, the sand-carrying liquid injection pipe and the sand-carrying liquid discharge pipe are respectively connected to the front side wall and the rear side wall of the visual cavity;

Each group of the fluid loss measuring devices includes a second valve, a core holder, a first back pressure valve, a third valve, and a mass flow meter connected in sequence, and the core holder is provided with a plurality of temperature sensors and pressure sensor;

The left and right sides of the visualization cavity are provided with transparent plates, and the transparent plates are provided with openings; the fluid loss measurement device is connected to the visualization cavity through the connecting pipeline through the opening, and the fracturing fluid in the cavity can be visualized Enter the core through the opening to simulate the process of fracturing fluid filtration into the formation.

The advantage of the design here is that the present invention utilizes the circulating pump to push the flow of the liquid CO ₂ sand-carrying liquid, adds proppant through the sanding tank, and the sand-carrying liquid circulates inside the visual cavity, and is filtered out through the opening on the visual cavity. The fracturing fluid flows into the core holder, and the fracturing fluid flows through the core and is discharged. An image acquisition device is installed outside the inner cavity of the visual window opposite to the transparent plate. The image acquisition device records the flow pattern of liquid CO ₂ carrying sand, Collect, store and analyze the sand-carrying parameters of the fracturing fluid, monitor the height of the sand bank formed by proppant settlement and the critical settlement velocity, and further evaluate the sand-carrying capacity of the liquid CO2 fracturing fluid in the simulated fracture.

In another aspect of the disclosure of the present invention, a first filter screen is provided on the outlet end of the visualization inner cavity on the sand-carrying liquid discharge pipe.

The advantage of the design here lies in the function of the first filter screen: First, when the farthest distance of the proppant particle migration is greater than the maximum length of the fracture, the proppant is filtered and accumulated at the end of the fracture to study the fracturing of different systems. Under the fluid carrying, the proppant is placed on the fracture end face changes; the second is to filter out the particles in the fracturing fluid, so as not to damage the back pressure valve.

In another aspect of the disclosure, a plurality of uniform and equal-area areas are arranged vertically in the inner cavity of the viewing window, and each area is provided with an opening corresponding to the transparent plate, and the filter loss measuring device is connected through the opening.

In another aspect of the disclosure, there are 6 uniform and equal-area areas in the vertical direction of the viewing window, numbered A, B, C, D, E, F, and each area is equidistantly arranged on the transparent plate. There are 4 openings, and the upper part of each area is correspondingly connected to a group of filter loss measurement devices through the 4 openings, which are numbered a, b, c, d, e, and f respectively.

The advantage of the design here is that there are 6 uniform areas of equal area, each area is connected to a set of filtration measurement devices, and the core with appropriate permeability is selected and installed in the core holder to restore the fracturing fluid in the actual mining process. Flow in fracturing fractures, and filtrate enters formations with different permeability, which affects the amount of fracturing fluid filtrate.

In another aspect of the disclosure, the core holder is provided with 4 pressure sensors and 4 temperature sensors at equal intervals.

In another aspect of the disclosure, the bottom of the visualized inner cavity and the bottom of the core holder are provided with a sand discharge hole, and a plugging device is provided on the sand discharge hole.

The advantage of the design here is that the flange blocking device is selected, and the sand discharge hole is blocked with a flange blocking device during the measurement process. After the measurement, the flange blocking device is opened to discharge the internal residual material.

In another aspect of the disclosure, the sand-carrying liquid injection pipe is arranged on the top of the front side wall of the visualization cavity, and the sand-carrying liquid discharge pipe is arranged on the top of the rear side wall of the visualization cavity .

According to another aspect of the disclosure, the visualized inner cavity has a length of 500-700 mm, a height of 70-90 mm, and a width of 1-3 mm. Simulates actual crack size.

In another aspect of the disclosure, the sand-carrying liquid injection pipe and the sand-carrying liquid discharge pipe belong to the connecting pipeline; the connecting pipeline is a stainless steel pipeline with an inner diameter of 3-6 mm.

Another aspect disclosed by the present invention, the core is square, the length of the core is 200-400mm, the height is 10-30mm, the width is 10-30mm, and the permeability of the core is 1×10 ^-3 μm ² - 1 μm ² .

In another aspect of the disclosure, the transparent plate is a quartz glass plate.

Another aspect of the disclosure, the pressure resistance of the transparent plate is 20-30MPa.

As described above, the method for the visualization device for measuring the sand-carrying performance of the _CO fracturing fluid under the condition of high-pressure dynamic fluid loss includes the following steps:

Assemble the device according to the experimental requirements, choose to install the core holder and the core; test the pressure resistance of the visual cavity, no puncture and no leakage is qualified; the fracturing fluid flows with sand, and the image acquisition device is turned on to record the liquid CO ₂ carrying through the transparent plate. Sand fluid flow morphology process; fluid loss measurement under dynamic fluid loss conditions; fluid loss data processing.

Another aspect disclosed by the present invention, the method of filtering out data processing in the filtering out data processing is:

的关系曲线，所述滤液体积Q为经过每组滤失测量装置得到的滤液体积，t为该组滤失装置Q对应的测量时间；5-1) Draw the filtration characteristic curve: draw the filtrate volume Q and

The relationship curve of , the filtrate volume Q is the filtrate volume obtained through each group of filtration loss measuring devices, and t is the measurement time corresponding to this group of filtration loss devices Q;

5-2) Obtain the filter loss coefficient: Fit the straight line segment in the stable stage of the filter loss characteristic curve to obtain the slope s of the straight line segment, and derive the calculation formula of the filter loss coefficient according to the Darcy equation:

；A为岩心端面面积，cm²。The C is the fracturing fluid filtration coefficient,

; A is the core end face area, cm ² .

Another aspect disclosed in the present invention, the method of testing the pressure resistance of the visual lumen, and the method of not puncturing and not leaking is qualified as follows: closing the fourth valve at the outlet end of the visual lumen, closing the second valve on all the fluid loss measuring devices, High-pressure clean water is introduced into the visualized inner cavity, and the maximum construction pressure is maintained for 30-40 minutes. If the visualized inner cavity is not punctured or leaked, the pressure test is qualified, and the maximum construction pressure is the highest pressure resistance value.

In another aspect of the disclosure, the fracturing fluid flows with sand, and the method of opening the image acquisition device to record the flow pattern process of the sand-carrying fluid of liquid CO ₂ through a transparent plate includes: opening the fourth valve at the outlet end of the visualized inner cavity, opening all the The second valve on the fluid loss measurement device, adjust the overflow pressure of the second back pressure valve according to the experimental requirements to ensure that the _CO2 is in a liquid state; connect one end of the sand-carrying liquid injection pipe to the _CO2 storage tank, and connect the test support The flow rate of the fracturing fluid is adjusted by loading the agent into the sand feeder; the image acquisition device is turned on to record the flow pattern of the liquid CO ₂ -carrying sand fluid through a transparent plate.

In another aspect of the disclosure, the method for measuring fluid loss under dynamic fluid loss conditions includes: liquid CO ₂ flows to the core holder through the connecting pipeline at the opening of the visualized inner cavity, and the liquid CO ₂ fracturing fluid passes through the core, along the The core flows out in the length direction and flows through the first back pressure valve and mass flowmeter. The pressure sensor and temperature sensor measure the temperature and pressure of the core during the circulation process. The data of the mass flowmeter and the temperature and pressure data of the core are collected and stored by the computer.

Beneficial effects of the present invention:

1. During the simulation of the actual fracturing process in the present invention, along the flow direction of the fracturing fluid, the fracturing fluid enters the formation rock matrix through the fracture wall surface, and is affected by the different permeability of the formation rock matrix, and the filtration performance of the fracturing fluid changes.

2. The present invention has the characteristics of simple operation, strong safety and high efficiency. It can consider the formation permeability, simulate the sand-carrying performance of liquid _CO2 fracturing fluid under the condition of filtration, and can synchronize the sand-carrying experiment and the filtration experiment. Carry out, strong operability.

3. The quartz glass plate used in the present invention constitutes a visualization window that can withstand the impact of solid particles, simulate on-site construction pressure conditions, and evaluate the sand-carrying performance of liquid _CO2 fracturing fluid under high pressure, and has the characteristics of pressure resistance and wear resistance.

4. The data of the temperature sensor, the pressure sensor and the mass flow meter used in the present invention are all collected and analyzed by the computer, and have the characteristics of accurate collection and high precision.

Description of drawings

Fig. 1 is the overall structure schematic diagram of the present invention;

FIG. 2 is a schematic view of the visualized lumen structure of the present invention;

Figure 3 is the fluid loss curve of liquid _CO2 under different permeability formations after thickening.

In Figure 1-3, 1. Sand-carrying liquid injection pipe; 2. First valve; 3. Circulating pump; 4. First pressure sensor; 5. Sand filler; 6. Visual cavity; 7. Second valve; 8. Core holder; 9. Pressure sensor; 10. Temperature sensor; 11. Core; 12. The first back pressure valve; 13. The third valve; 14. Mass flow meter; 15. One-way valve; 16. The first 1. Filter screen; 17. Second back pressure valve; 18. Fourth valve; 19. Sand-carrying liquid discharge pipe; 20. Fixing bolt; 21. Quartz glass plate; 22. Second filter screen; 23. Connecting pipeline; 24 , blocking equipment;

Detailed ways

The present invention will be described in detail below with reference to the embodiments and the accompanying drawings, but is not limited thereto.

As shown in Figure 1-3.

Example 1

A visual testing device for _CO2 fracturing fluid carrying sand under dynamic filtration, comprising a sand carrying measurement device and an image acquisition device, characterized in that the visualization device further comprises a filtration measurement device, and the visualization device is communicated through a connecting pipeline , the fracturing fluid circulates in the connecting pipeline;

The sand-carrying measuring device includes a visualized inner cavity 6, which is used to simulate the sand-carrying flow process of the fracturing fluid in the fracturing fracture;

The fluid loss measuring device communicates with the visualized inner cavity 6, and the number of the fluid loss measuring devices is 6 groups. Each group of the fluid loss measuring devices includes a core holder 8 and a core 11. In the core holder 8, the fluid loss measurement device is used to simulate the influence of different permeability formations on the fluid loss process in the fracturing fracture;

The image acquisition device is arranged on the upper part of the visualization inner cavity 6, and includes a computer and a camera, and is used for collecting the flow pattern of fracturing fluid carrying sand and data analysis. The image acquisition device is in the prior art, well known to those skilled in the industry, and does not belong to the protection scope of the present invention.

Example 2

As described in Example 1, a visual testing device for CO ₂ fracturing fluid sand-carrying under dynamic filtration, the difference is that the sand-carrying measuring device further includes a first valve 2 sequentially arranged on the sand-carrying fluid injection pipe 1 , circulating pump 3, first pressure sensor 4, sand feeder 5, second back pressure valve 17, fourth valve 18 sequentially arranged on the sand-carrying liquid discharge pipe 19, the sand-carrying liquid injection pipe 1 and the The sand-carrying liquid discharge pipes 19 are respectively connected to the front side wall and the rear side wall of the visualized inner cavity 6;

Each group of the fluid loss measuring devices includes a second valve 7 , a core holder 8 , a first back pressure valve 12 , a third valve 13 , and a mass flow meter 14 connected in sequence. The core holder 8 is provided with 4 temperature sensors 10, pressure sensors 9;

The left and right sides of the visualization cavity are provided with transparent plates, and the transparent plates are provided with openings; the fluid loss measurement device is connected to the visualization cavity 6 through the connecting pipeline 23 through the openings, and the fluid in the visualization cavity 6 is connected. The fracturing fluid enters the core 11 through the opening, and is used to simulate the process of the fracturing fluid filtering out into the formation.

Example 3

A visual test device for CO ₂ fracturing fluid sand-carrying under dynamic filtration described in Example 2, the difference is that the sand-carrying fluid discharge pipe 19 is provided with a first Filter 16.

Example 4

A visual test device for _CO2 fracturing fluid carrying sand under dynamic filtration described in Example 1, the difference is that there are 6 uniform and equal-area areas in the vertical direction in the inner cavity of the visual window, numbered as A, B, C, D, E, F, each area corresponds to the transparent plate with 4 openings at equal distances, and the upper part of each area is connected to a group of filter loss measurement devices through the openings, numbered a, b, c, d, e, f.

Example 5

As described in Example 1, a visual test device for sand-carrying CO ₂ fracturing fluid under dynamic filtration, the difference is that the bottom of the visual cavity 6 and the bottom of the core holder 8 are provided with sand discharge holes, A plugging device is arranged on the sand discharge hole.

Example 6

A visual test device for CO ₂ fracturing fluid sand-carrying under dynamic filtration loss as described in Example 2, the difference is that the sand-carrying fluid injection pipe 1 is arranged on the top of the front side wall of the visualized inner cavity 6 , the sand-carrying liquid discharge pipe 19 is arranged on the top of the rear side wall of the visualized inner cavity 6 .

Example 7

As described in Example 1, a visual test device for CO ₂ fracturing fluid carrying sand under dynamic filtration, the difference is that the length of the visual cavity 6 is 500-700mm; the height is 70-90mm; the width is 1- 3mm. Simulates actual crack size.

Example 8

A visual test device for _CO2 fracturing fluid sand-carrying under dynamic filtration as described in Example 2, the difference is that the sand-carrying fluid injection pipe 1 and the sand-carrying fluid discharge pipe 19 belong to the connecting pipeline 23 ; The connecting pipeline 23 is a stainless steel pipeline with an inner diameter of 3-6mm.

Example 9

As described in Example 1, a visual test device for _CO2 fracturing fluid carrying sand under dynamic filtration, the difference is that the core 11 is square, the length of the core 11 is 200-400mm, and the height is 10-30mm , the width is 10-30mm, and the permeability of the core 11 is 1×10 ^-3 μm ² -1 μm ² .

Example 10

As described in Example 2, a visual test device for CO ₂ fracturing fluid carrying sand under dynamic filtration, the difference is that the transparent plate is a quartz glass plate.

Example 11

As described in Example 2, a visual test device for CO ₂ fracturing fluid carrying sand under dynamic filtration, the difference is that the pressure resistance of the transparent plate is 20-30 MPa.

Example 12

As described above, the measurement method of the visualization device for measuring the sand-carrying performance of the _CO fracturing fluid under the condition of high-pressure dynamic filtration includes the following steps: assembling the device according to the experimental requirements, selecting and installing the core holder 8 and the core 11; testing the visualized inner cavity 6 The pressure resistance, no puncture and no leakage is qualified; the fracturing fluid flows with sand, and the image acquisition device is turned on to record the flow pattern process of the liquid CO ₂ -carrying sand through the transparent plate; fluid loss measurement under dynamic fluid loss conditions; fluid loss data processing .

Example 13

A measurement method of a visualization device for measuring the sand-carrying performance of _CO fracturing fluid under high-pressure dynamic fluid loss conditions as described in Example 12, the difference lies in that the method for processing the fluid loss data is:

的关系曲线，所述滤液体积Q为经过每组滤失测量装置得到的滤液体积，t为该组滤失装置Q对应的测量时间；5-1) Draw the filtration characteristic curve: draw the filtrate volume Q and

The relationship curve of , the filtrate volume Q is the filtrate volume obtained through each group of filtration loss measuring devices, and t is the measurement time corresponding to this group of filtration loss devices Q;

5-2) Obtain the filter loss coefficient: Fit the straight line segment in the stable stage of the filter loss characteristic curve to obtain the slope s of the straight line segment, and derive the calculation formula of the filter loss coefficient according to the Darcy equation:

；A为岩心端面面积，cm²。The C is the fracturing fluid filtration coefficient,

; A is the core end face area, cm ² .

Example 14

As described in Example 12, a measurement method of a visualization device for measuring the sand-carrying performance of _CO fracturing fluid under the condition of high-pressure dynamic filtration, the difference is that the test visualizes the pressure resistance of the inner cavity 6, and no puncture or leakage is The qualified method is: close the fourth valve 18 at the outlet end of the visual cavity 6, close the second valve 7 on all the fluid loss measurement devices, pass high-pressure clean water into the visual cavity 6, and maintain the maximum construction pressure for 30-40min. , the visible inner cavity 6 is not punctured or leaked to be qualified for the pressure test, and the maximum construction pressure is the maximum pressure resistance value.

Example 15

A measurement method of a visualization device for measuring the sand-carrying performance of _CO fracturing fluid under high-pressure dynamic filtration conditions as described in Example 12, the difference is that the fracturing fluid flows with sand-carrying, and the image acquisition device is turned on to pass through the transparent plate. The method of photographing and recording the flow pattern process of the liquid CO ₂ sand-carrying liquid includes: opening the fourth valve 18 at the outlet end of the visual cavity 6, opening the second valve 7 on all fluid loss measuring devices, and adjusting the second back pressure valve 17 according to the experimental requirements. to ensure that the CO ₂ is in a liquid state; inject the sand-carrying fluid into one end of the pipe 1 and connect it to the CO ₂ storage tank, put the test proppant into the sand filler 5, and adjust the flow rate of the fracturing fluid; start the image acquisition The device records the flow pattern process of liquid CO ₂ sand-carrying liquid through a transparent plate.

Example 16

A measurement method of a visualization device for measuring the sand-carrying performance of _CO2 fracturing fluid under high-pressure dynamic filtration conditions as described in Example 12, the difference lies in that the method for filtration measurement under dynamic filtration conditions includes: liquid CO _2. Flow to the core holder 8 through the connecting pipeline 23 at the opening of the visual cavity 6, the liquid _CO2 fracturing fluid passes through the core 11, flows out along the length of the core 11, and flows through the first back pressure valve 12 and the mass flow meter 14 , the pressure sensor 9 and the temperature sensor 10 measure the temperature and pressure of the core 11 during the circulation process, and the data of the mass flow meter 14 and the temperature and pressure data of the core 11 are collected and stored by the computer.

Example 17

A visualization device for measuring the sand-carrying performance of CO _{2 fracturing fluid under the condition of high-pressure dynamic filtration described in Examples 1-11 and a method for measuring high-pressure dynamic filtration of CO 2 fracturing} fluid described in Examples 12-16 The measurement method of the visualization device for the sand-carrying performance under the loss condition, the difference is that the proppant particle size is selected to be 0.18-0.25mm, and the permeable particles are placed in a and f, b and e, c and d in the core holder, respectively Artificial cores with the rate of 0.32×10 ^-3 μm ² , 0.55×10 ^-3 μm ² and 1.15×10 ^-3 μm ² .

Choose a thickener to mix liquid _CO2 fracturing fluid, inject it into the visualization device, and test its sand-carrying effect, as shown in Table 1:

As shown in Table 1, under the conditions of 20 °C and 10 MPa, the liquid _CO2 fracturing fluid containing the thickener type TNJ-1 and the concentration of 1% was introduced into the sand-carrying fluid injection pipe. In the process of sand-carrying performance, the balance data collected by the computer calculates the critical settling velocity, the critical velocity from static to "tumble flow", the critical velocity from "tumble flow" to "jump migration", and the critical suspension velocity.

As shown in Table 2, under the conditions of 20°C and 10MPa, the liquid _CO2 fracturing fluid containing thickener type TNJ-1 with a concentration of 1% was introduced into the sand-carrying fluid injection pipe, and different permeability rates were recorded. Core filter loss measurement device, processing to obtain the corresponding slope and filter loss coefficient.

Claims (10)

1. CO under dynamic filtration₂The fracturing fluid sand-carrying visual testing device comprises a sand-carrying measuring device and an image acquisition device, and is characterized by further comprising a fluid loss measuring device, wherein the visual testing device is communicated through a connecting pipeline, and fracturing fluid circulates in the connecting pipeline;

the sand-carrying measuring device comprises a visual inner cavity and is used for simulating a sand-carrying flowing process of fracturing fluid in a fracturing fracture;

the fluid loss measuring devices are communicated with the visual inner cavity, the number of the fluid loss measuring devices is multiple, each group of the fluid loss measuring devices comprises a rock core holder and a rock core, the rock core is arranged in the rock core holder, and the fluid loss measuring devices are used for simulating the influence of different permeability strata in a fracturing fracture on a fluid loss process;

the image acquisition device is arranged on the upper part of the visual inner cavity, comprises a computer and a camera and is used for acquiring the sand-carrying flowing form of the fracturing fluid and analyzing data.

2. CO under kinetic fluid loss according to claim 1₂The fracturing fluid sand-carrying visual testing device is characterized by further comprising a first valve, a circulating pump, a first pressure sensor and a sand feeder which are sequentially arranged on a sand-carrying fluid injection pipe, a second back-pressure valve and a fourth valve which are sequentially arranged on a sand-carrying fluid discharge pipe, wherein the sand-carrying fluid injection pipe and the sand-carrying fluid discharge pipe are respectively connected to the front side wall and the rear side wall of the visual inner cavity;

each group of the fluid loss measuring devices comprises a second valve, a rock core holder, a first back pressure valve, a third valve and a mass flowmeter which are sequentially connected, wherein a plurality of temperature sensors and pressure sensors are arranged on the rock core holder;

transparent plates are arranged on the left side and the right side of the visual inner cavity, and openings are formed in the transparent plates; the fluid loss measuring device penetrates through the opening through a connecting pipeline to be connected with the visual inner cavity, and fracturing fluid in the visual inner cavity enters the rock core through the opening and is used for simulating the process that the fracturing fluid is filtered and enters the stratum.

3. CO under kinetic fluid loss according to claim 2₂The fracturing fluid sand-carrying visual testing device is characterized in that a first filter screen is arranged at the outlet end of the visual inner cavity on a sand-carrying fluid discharge pipe.

4. CO under kinetic fluid loss according to claim 2₂The fracturing fluid sand-carrying visual testing device is characterized in that a plurality of uniform regions with equal areas are arranged in the vertical direction of the visual inner cavity, each region is provided with an opening corresponding to the transparent plate, and the openings are connected with a fluid loss measuring device.

5. CO under kinetic fluid loss according to claim 2₂Fracturing fluid sand-carrying visual testThe device, its characterized in that, visual inner chamber vertical direction is provided with 6 even equal area's region, and every region corresponds on the transparent plate equidistance and sets up 4 the opening, through 1 group of filtration measuring device are connected to the opening.

6. CO under kinetic fluid loss according to claim 2₂The fracturing fluid sand-carrying visual testing device is characterized in that 4 pressure sensors and 4 temperature sensors are arranged on the rock core holder at equal intervals.

7. CO under kinetic fluid loss according to claim 1₂The fracturing fluid sand-carrying visual testing device is characterized in that sand discharge holes are formed in the bottom of the visual inner cavity and the bottom of the rock core holder, and plugging equipment is arranged on the sand discharge holes.

8. CO under kinetic fluid loss according to claim 2₂The fracturing fluid sand-carrying visual testing device is characterized in that the sand-carrying fluid injection pipe is arranged at the top of the front side wall of the visual inner cavity, the sand-carrying fluid discharge pipe is arranged at the top of the rear side wall of the visual inner cavity, the length of the visual inner cavity is 500-700mm, the height is 70-90mm, the width is 1-3mm, the sand-carrying fluid injection pipe and the sand-carrying fluid discharge pipe belong to the connecting pipeline, the connecting pipeline is a stainless steel pipeline with the inner diameter of 3-6mm, the rock core is square, the length of the rock core is 200-400mm, the height is 10-30mm, the width is 10-30mm, and the permeability of the rock core is 1 × 10^-3μm²- 1 μm²(ii) a The transparent plate is a quartz glass plate; the transparent plate has a withstand voltage of 20-30 MPa.

9. CO under kinetic fluid loss according to any of claims 1 to 8₂The measuring method of the fracturing fluid sand-carrying visual testing device comprises the following steps: assembling the device according to the experimental requirements, and selecting and installing a rock core holder and a rock core; testing the pressure resistance of the visual inner cavity, and determining that the pressure resistance is qualified without puncture and leakage; fracturing fluid flows with sand and is openedStarting the image acquisition device to shoot and record liquid CO through the transparent plate₂A sand carrying fluid flowing form process; measuring fluid loss under dynamic fluid loss conditions; and (4) processing the fluid loss data.

10. The underfiltration CO of claim 9₂The measurement method of the fracturing fluid sand-carrying visual testing device comprises the following steps:

5-1) plotting the fluid loss characteristic: plotting the filtrate volume Q and

the filtrate volume Q is the filtrate volume obtained by each group of fluid loss measurement devices, and t is the measurement time corresponding to the group of fluid loss devices Q;

5-2) obtaining the fluid loss coefficient: and fitting a straight-line segment of a stable stage of the fluid loss characteristic curve to obtain a slope s of the straight-line segment, and deducing a fluid loss coefficient calculation formula according to the Darcy equation:

(1)

c is the loss of fracturing fluid coefficient,

(ii) a A is the area of the end face of the core in cm²；

The method for testing the pressure resistance of the visual inner cavity without puncture and leakage is qualified as follows: closing a fourth valve at the outlet end of the visual inner cavity, closing second valves on all the fluid loss measuring devices, introducing high-pressure clean water into the visual inner cavity, keeping the highest construction pressure for 30-40min, and judging that the visual inner cavity is qualified in pressure test without puncture and leakage, wherein the highest construction pressure is the highest pressure-resistant value;

the fracturing fluid flows with sand, the image acquisition device is started to shoot and record liquid CO through the transparent plate₂The method for the process of the flowing form of the sand carrying fluid comprises the following steps: opening the fourth valve at the outlet end of the visualization lumen, opening the second valves on all fluid loss measuring devicesThe valve is used for adjusting the overflowing pressure of the second back-pressure valve according to the experiment requirement to ensure CO₂In a liquid state; injecting the sand-carrying liquid into one end of the pipe and CO₂Connecting the storage tanks, filling the proppant for the test into a sand feeder, and adjusting the flow rate of the fracturing fluid; opening the image acquisition device to shoot and record liquid CO through the transparent plate₂A sand carrying fluid flowing form process;

the method of fluid loss measurement under dynamic fluid loss conditions comprises: liquid CO₂The liquid CO flows to the core holder through the connecting pipeline at the opening of the visual inner cavity₂The fracturing fluid flows out along the length direction of the rock core through the rock core, flows through the first back pressure valve and the mass flow meter, the temperature and the pressure of the rock core in the flowing process are measured by the pressure sensor and the temperature sensor, and the data of the mass flow meter and the temperature and pressure data of the rock core are collected and stored by the computer.

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