CN107476796B - Experimental device and method for simulating backflow of fracturing fluid to control proppant backflow - Google Patents

Abstract

The invention discloses an experimental device and method for simulating fracturing fluid flowback to control proppant reflux, including a stirring tank, a screw pump, a visual sand spreading device, a waste liquid tank, a nitrogen bottle, a gas source distributor, and a fracturing fluid stirring tank , a fracturing fluid pipe, a fracturing pump; the mixing tank, the screw pump, the visual sand spreading device, and the waste liquid tank are sequentially connected through pipelines, and a flow meter is arranged between the visual sand spreading device and the waste liquid tank; The nitrogen cylinder, the gas source distributor, and the visual sand spreading device are sequentially connected through pipelines, and the fracturing fluid mixing tank, fracturing pump, and fracturing fluid pipe are connected in sequence, and the fracturing fluid pipe is provided with a liquid outlet. The liquid outlet is connected with the visual sand spreading device through pipelines. The present invention uses the gas source distributor and its pipeline system to simulate the process of formation gas filtration, and simulates the flowback of fracturing fluid and the process of formation fluid filtration to fractures through the injection pipeline of the liquid circulation system, so as to be consistent with the actual pressure on site. The fission flowback process coincides.

Description

An experimental device and method for simulating fracturing fluid flowback to control proppant flowback

technical field

The invention belongs to the technical field of hydraulic fracturing, in particular to an experimental device and method for simulating flowback of fracturing fluid and controlling proppant backflow.

Background technique

According to the movement characteristics of the proppant in the fracture during the fracturing fluid flowback during the fracturing process, a mathematical model was established to simulate the flowback process of the fracturing fluid in the fracture to control the proppant backflow. Through the simulation calculation, it is found that the flowback velocity of fracturing fluid and the filtration loss of formation fluid have a great influence on the return volume of proppant and the distribution shape of proppant in the fracture. With the increase of fracturing fluid flowback velocity, the proppant backflow rate increases gradually, but the increase rate gradually slows down; the distribution of proppant in fractures gradually increases with the increase of fracturing fluid flowback velocity. get better. The calculation results show that in order to obtain a better distribution of proppant in fractures, the flowback velocity of fracturing fluid should be increased as much as possible within the scope of construction conditions, which can not only improve the distribution of proppant in fractures, but also reduce the impact of fracturing fluid on fractures. ground damage.

Contents of the invention

The present invention mainly solves the deficiencies in the prior art, and provides an experimental device and method for controlling proppant backflow by simulating fracturing fluid flowback that can match on-site construction.

The technical solution adopted by the present invention to solve the above technical problems is: an experimental device for simulating fracturing fluid flowback to control proppant backflow, including a stirring tank, a screw pump, a visual sand spreading device, a waste liquid tank, a nitrogen bottle, and a gas source Distributors, fracturing fluid mixing tanks, fracturing fluid pipes, fracturing pumps;

The stirring tank, the screw pump, the visualized sand spreading device, and the waste liquid tank are sequentially connected through pipelines, and a flow meter is arranged between the visualized sand spreading device and the waste liquid tank;

The nitrogen cylinder, gas source distributor, and visual sand spreading device are connected through pipelines in sequence,

The fracturing fluid mixing tank, fracturing pump, and fracturing fluid pipe are connected in sequence, and the fracturing liquid pipe is provided with a liquid outlet, and the liquid outlet is connected to the visual sand spreading device through a pipeline.

Further, the visual sand laying device includes a shaft, a first outer frame, a second outer frame, a first plexiglass plate, a second plexiglass plate, a Y-shaped silicone ring, and a sensitive spring; the first outer frame 1. The second outer frame is connected to each other, the wellbore is installed at the junction of the first outer frame and the second outer frame, and the first organic glass plate and the second organic glass plate are installed on the first outer frame and the second outer frame through a Y-shaped silicone ring. Between the second outer frames, the first plexiglass plate is fixed inside the first outer frame, and the second plexiglass plate is connected to the inner side of the second outer frame through a sensitive spring.

Further, the first outer frame and the second outer frame are connected by bolts.

Further, one end of the fracturing fluid pipe is connected to a fracturing pump, and the other end is connected to a fracturing fluid stirring tank.

An experimental method for simulating flowback of fracturing fluid to control proppant flowback, comprising the following steps:

S100. Optimizing the fracturing fluid system according to the geological data, and configuring the fracturing fluid;

S200. Check the cleanliness of each device, and adjust the valves on the gas source distributor and the fracturing fluid pipe to the closed state, zero the flow meter and the pressure gauge on the gas source distributor, and open the connection between the screw pump and the mixing tank. between valves;

S300, put the fracturing fluid configured in step S100 into the mixing tank and stir evenly, inject the fracturing fluid into the visual sand spreading device through the screw pump, and the fracturing fluid enters between the first plexiglass plate and the second plexiglass plate After being in the crack, the second plexiglass plate moves outward under the push of pressure, and the sensitive spring shrinks at the same time, and a tiny crack is formed between the first plexiglass plate and the second plexiglass plate. This process is the crack formation stage;

S400. Uniformly mix the fracturing fluid and proppant in the stirring tank, and the formed sand-carrying fluid is also pumped into the crack between the first organic glass plate and the second organic glass plate through the screw pump, and the crack is further opened , the sensitive spring further shrinks, and the proppant begins to lay in the fracture. Under the combined action of the pressure between the first organic glass plate and the second organic glass plate and the sensitive spring, the fracture is in a state of dynamic expansion or closure. The proppant is dynamically placed in the crack, and the waste liquid during the proppant laying process is discharged into the waste liquid tank, the experimental phenomenon is observed, and the experimental data is recorded;

S500. After the mixing tank is completely pumped into the visible sand-spreading device, the proppant is laid in the visible sand-spreading device. At this time, continue to pump the pre-prepared post-placement fluid to replace the remaining proppant in the wellbore to the second stage. Go to the crack between the first plexiglass plate and the second plexiglass plate, after the post fluid is completely pumped in, close the screw pump, the mixing tank and the valve between them, open the valve on the fracturing fluid pipe, and calibrate the zero flow gauge and the pressure gauge on the air source distributor;

S600. According to the principle of equal Reynolds number, the on-site flowback displacement is converted into the simulated displacement in the laboratory, and the fracturing fluid prepared in the fracturing fluid mixing tank is pumped into the first plexiglass plate and the second plexiglass plate through the fracturing pump. In the cracks between the plates, the backflow of proppant can be observed, and the shape of the proppant laid in the fracture changes. Observe the change of the proppant laying shape in the fracture, and record the outflow of proppant at the perforation port and the drainage port. , record the experimental data;

S700. Open the upper valve of the air source distributor, calibrate the zero pressure gauge, open the valve of the nitrogen cylinder, and nitrogen enters the crack between the first plexiglass plate and the second plexiglass plate. In the same flow, observe the migration of proppant in the fracture network, record the outflow of proppant in the liquid outlet on the end face of the perforation and the experimental data;

S800, then switch the fracturing fluid stirring tank to clean water, and pump the clean water into the crack between the first plexiglass plate and the second plexiglass plate, after a period of time, the formation fluid will leak into the fracture, observe Experimental phenomenon and record experimental data;

S900. Turn off the fracturing pump, and close the nitrogen cylinder, the gas source distributor, and the valves on the fracturing liquid pipe, discharge the remaining gas, and complete the experimental operation;

S1000, remove the gas source distributor and fracturing fluid pipe, install the device cleaning system, and clean the experimental device;

S1100. According to the converted experimental simulation displacement, change the displacement of the fracturing fluid flowback, repeat the experimental steps of S100-S1000, and record the experimental data. When the proppant return flow is the least, it corresponds to the optimal flowback of the fracturing fluid Displacement, to draw the experimental conclusion.

Further, in the step S600, according to the reading of the pressure gauge, the pressure and flow rate of nitrogen are controlled by adjusting the opening of the valve.

The beneficial effects of the present invention are: compared with the prior art, the present invention considers the flowback of fracturing fluid, and designs a gas source distributor, a fracturing fluid circulation system, a liquid (fracturing fluid, formation water) filtration system, The gas filtration system controls the air pressure by adjusting the opening of the nitrogen cylinder, uses the gas source distributor and its pipeline system to simulate the state of formation gas filtration, and simulates the fracturing fluid flowback and flowback through the liquid circulation system injection pipeline. Formation fluid filtration conditions, so as to achieve more matching with the actual construction on site, through a visual proppant dynamic laying sand control device considering fracturing fluid flowback of the present invention, the proppant sanding experimental data obtained from the field construction and oil and gas The evaluation of stimulation effects has important reference value; the fractures during on-site construction are in a state of dynamic closure/expansion; the existing visual sanding devices have fixed fracture widths, and when the fracturing fluid enters the main fractures, the fracture width The pressure keeps rising, but the width of the main fracture is fixed, which is inconsistent with the actual characteristics of the formation fracture network in the actual fracturing project. During fracturing, the width of the fracture depends on the closure pressure of the fracture and the pressure formed by the fracturing fluid in the fracture. The size and seam width are dynamically changed.

Description of drawings

Fig. 1 is a structural representation of the present invention;

Fig. 2 is the structural representation of visualization sand laying device in the embodiment;

Figure 3 is a schematic diagram of the connection of the Y-shaped silicone ring.

As shown in the figure: 1-well shaft, 2-first outer frame, 3-second outer frame, 4-first plexiglass plate, 5-second plexiglass plate, 6-Y-shaped silicone ring, 7-sensitive Spring, 14-stirring tank, 15-screw pump, 16-visual sand spreading device, 17-flow meter, 18-waste liquid tank, 19-nitrogen bottle, 20-air source distributor, 21-fracturing fluid stirring tank, 22-fracturing liquid pipe, 23-fracturing pump.

Detailed ways

The technical solution of the present invention will be described in detail below through the embodiments and in conjunction with the accompanying drawings.

As shown in Figures 1, 2, and 3, an experimental device for simulating fracturing fluid flowback to control proppant reflux of the present invention includes a stirring tank 14, a screw pump 15, a visual sanding device 16, a waste liquid tank 18, a nitrogen gas Bottle 19, gas source distributor 20, fracturing fluid mixing tank 21, fracturing fluid pipe 22, fracturing pump 23; the mixing tank 14, screw pump 15, visual sanding device 16, and waste liquid tank 18 pass through the pipeline in sequence connection, the visual sanding device 16 and the waste liquid tank 18 are provided with a flow meter 17, which is the proppant laying part; the nitrogen cylinder 19, the gas source distributor 20, and the visual sanding device 16 pass through in sequence Pipeline connection, this part is the simulated gas fracture fluid loss part, the fracturing fluid stirring tank 21, fracturing pump 23, and fracturing fluid pipe 22 are connected in sequence, and the fracturing fluid pipe 22 is provided with a liquid outlet, so The above-mentioned liquid outlet is connected with the visualized sand-laying device 16 through a pipeline, and this part is the simulated fluid loss part of the fracture. The present invention considers the flowback of fracturing fluid, and designs a gas source distributor, a fracturing fluid circulation system, a liquid (fracturing fluid, formation water) filtration system, and a gas filtration system. By adjusting the opening of the nitrogen cylinder 19 To control the air pressure, use the gas source distributor 20 and its pipeline system to simulate the state of formation gas filtration, and inject the pipeline through the liquid circulation system to simulate the flowback of fracturing fluid and formation fluid filtration, so as to achieve a more realistic on-site The construction is matched, and the proppant sanding experimental data obtained by a visual proppant dynamic laying sand control device considering fracturing fluid flowback of the present invention has important reference value for on-site construction and evaluation of oil and gas stimulation and transformation effects.

The specific embodiment of the visual sanding device 16 is that the visual sanding device 16 includes a shaft 1, a first outer frame 2, a second outer frame 3, a first plexiglass plate 4, a second plexiglass plate 5, and a Y Zigzag silicone ring 6, sensitive spring 7; the first outer frame 2 and the second outer frame 3 are connected to each other, the shaft 1 is installed at the junction of the first outer frame 2 and the second outer frame 3, and the first outer frame 2 and the second outer frame 3 are connected. The plexiglass plate 4 and the second plexiglass plate 5 are installed between the first outer frame 2 and the second outer frame 3 through the Y-shaped silicone ring 6, that is, the Y-shaped upper part of the Y-shaped silicone ring 6 is the inner ring, and the lower The half part is the outer ring, the first outer frame 2 and the second outer frame 3 clamp the outer ring of the Y-shaped silicone ring 6 in parallel and fix it, and the first plexiglass plate 4 and the second plexiglass plate 5 are fixed in parallel on the Y-shaped On the inner ring of the silicone ring 6, the first plexiglass plate 4 is fixed on the inside of the first outer frame 2, and the second plexiglass plate 5 is connected to the inner side of the second outer frame 3 by a sensitive spring 7, so that the second The plexiglass plate 5 can drive the second plexiglass plate 5 to move through the compression and stretching of the sensitive spring 7, and the distance between the first plexiglass plate 4 and the second plexiglass plate 5 can be changed to change the slit width. Wherein, the wellbore 1 is provided with 9 perforation ports, and the first outer frame 2 is provided with a plurality of discharge ports, cleaning ports, liquid outlets and the like.

In the above structure, the elasticity of the Y-shaped silicone ring 6 is used to realize the process between the first plexiglass plate 4 and the second plexiglass plate 5 from the initial closed state to the process of gradually opening under the impact of fluid pressure. At this time, the sensitive spring 7 is gradually compressed, and when the pressure in the slit decreases, due to the elasticity of the sensitive spring 7, the spring stretches, and the slit width decreases with the pressure in the slit decreasing. This design can simulate the initial closure of the formation fractures, the opening of the fractures due to the sand-carrying fluid, the narrowing of the fracture width caused by the decrease of the fracture pressure during fluid drainage, and finally the process of proppant laying.

In order to facilitate disassembly, a preferred embodiment is that the first outer frame 2 and the second outer frame 3 are connected by bolts. In order to avoid leakage and ensure the tightness of the device, a sealing gasket is arranged between the first outer frame 2 and the second outer frame 3 .

The preferred embodiment is that one end of the fracturing fluid pipe 22 is connected to the fracturing pump 23, and the other end is connected to the fracturing fluid stirring tank 21, which can achieve the purpose of liquid circulation.

When using the above-mentioned experimental device for controlling proppant reflux by fracturing fluid flowback to conduct experiments, the experimental method for simulating fracturing fluid flowback to control proppant reflux includes the following steps:

S100. Optimizing the fracturing fluid system according to the geological data, and configuring the fracturing fluid;

S200. Check the cleanliness of each device, adjust the valves on the gas source distributor 20 and the fracturing fluid pipe 22 to the closed state, zero the pressure gauge on the flow meter 17 and the gas source distributor 20, and turn on the screw pump 15 and the valve between the mixing tank 14;

S300, put the fracturing fluid configured in step S100 into the mixing tank 14 and stir evenly, inject the fracturing fluid into the visual sand spreading device 16 through the screw pump 15, and the fracturing fluid enters the first organic glass plate 4, the second organic glass After the crack between the glass plates 5, the second plexiglass plate 5 moves outward under the push of the pressure, and the sensitive spring 7 shrinks at the same time, a tiny crack is formed between the first plexiglass plate 4 and the second plexiglass plate 5, This process is the crack formation stage;

S400, uniformly mix the fracturing fluid and proppant in the stirring tank 14, and pump the formed sand-carrying fluid into the crack between the first plexiglass plate 4 and the second plexiglass plate 5 through the screw pump 15, and The crack is further opened, and the sensitive spring 7 is further contracted, and the proppant begins to lay in the crack. Under the joint action of the pressure between the first organic glass plate 4 and the second organic glass plate 5 and the sensitive spring 7, the crack In the state of dynamic expansion or closure, the proppant is dynamically laid in the fracture, and the waste liquid during the proppant laying process is discharged into the waste liquid tank 18, the experimental phenomenon is observed, and the experimental data is recorded;

S500. After the stirring tank 14 is completely pumped into the visible sand-laying device 16, the proppant is laid in the visible sand-laying device 16. At this time, continue to pump in the post-placement liquid prepared in advance to remove the proppant remaining in the wellbore 1. Displacing the agent into the crack between the first plexiglass plate 4 and the second plexiglass plate 5, after the post liquid is completely pumped in, close the screw pump 15, the stirring tank 14 and the valve between them, and open the fracturing fluid The valve on the pipe 22, the pressure gauge on the zero calibration flow meter 17 and the air source distributor 20;

S600. According to the principle of equal Reynolds number, convert the on-site flowback displacement into the simulated displacement in the laboratory, and pump the fracturing fluid prepared in the fracturing fluid mixing tank 21 into the first plexiglass plate 4 and the second through the fracturing pump 23 In the crack between the two plexiglass plates 5, it can be observed that the proppant reflows, and the shape of the proppant laid in the crack changes. Propant outflow, record experimental data;

S700, open the upper valve of the air source distributor 20, calibrate the zero pressure gauge, open the valve of the nitrogen cylinder 19, nitrogen enters the crack between the first plexiglass plate 4 and the second plexiglass plate 5, at this time, the gas in the slit network, Liquid and solid three-phase flow, observe the migration of proppant in the fracture network, record the outflow of proppant in the liquid outlet on the end face of the perforation and the experimental data;

S800, then switch the fracturing fluid stirring tank 21 to clean water, and pump the clean water into the cracks between the first plexiglass plate 4 and the second plexiglass plate 5, after a period of time, the formation fluid will leak into the cracks process, observe the experimental phenomena and record the experimental data;

S900. Turn off the fracturing pump 23, and close the nitrogen cylinder 19, the gas source distributor 20, and the valves on the fracturing liquid pipe 22, discharge the remaining gas, and complete the experimental operation;

S1000, remove the gas source distributor 20 and the fracturing fluid pipe 22, install the device cleaning system, and clean the experimental device;

S1100. According to the converted experimental simulation displacement, change the displacement of the fracturing fluid flowback, repeat the experimental steps of S100-S1000, and record the experimental data. When the proppant return flow is the least, it corresponds to the optimal flowback of the fracturing fluid Displacement, to draw the experimental conclusion.

Among them, the preferred embodiment is that in the step S600, according to the reading of the pressure gauge, the pressure and flow rate of nitrogen are controlled by adjusting the opening of the valve.

The experimental device and method for simulating flowback of fracturing fluid to control proppant flowback of the present invention is aimed at solving the influence of flowback of fracturing fluid on the form of laid proppant in the late stage of actual fracturing construction. The invention is optimized and improved on the basis of the existing visual fracturing fluid flowback device. By redesigning the fracturing fluid circulation system and nitrogen injection system, the flow process closest to the actual working conditions on site is simulated. The applicable new device is consistent with the process of fracture formation, fracture extension, proppant placement, fracture closure, fracturing fluid flowback, and gas-liquid flow during actual fracturing construction, and matches the actual fracture environment variables, realizing the experimental environment and Optimization of the construction environment. By using non-toxic and non-polluting nitrogen instead of natural gas, the gas-liquid injection into the pipe string is used to simulate the filtration process of formation fluid and fracturing fluid into the fracture network. It truly simulates the actual situation on site, and the experimental data has more reference value, which has an important guiding role in on-site fracturing construction.

The above description does not limit the present invention in any form. Although the present invention has been disclosed above through the embodiments, it is not used to limit the present invention. When the technical content disclosed above can be used to make some changes or be modified into equivalent embodiments with equivalent changes, any simple modifications made to the above embodiments according to the technical essence of the present invention, Equivalent changes and modifications still fall within the scope of the technical solution of the present invention.

Claims (2)

1. The experimental method of simulating the flowback of fracturing fluid to realize the control of proppant backflow is characterized in that it comprises the following steps: S100. Optimizing the fracturing fluid system according to the geological data, and configuring the fracturing fluid; S200. Check the cleanliness of each device, and adjust each valve on the gas source distributor (20) and fracturing fluid pipe (22) to the closed state, and zero the flow meter (17) and gas source distributor (20) Open the pressure gauge on the screw pump (15) and the valve between the mixing tank (14); S300. Put the fracturing fluid prepared in step S100 into the stirring tank (14) and stir evenly, inject the fracturing fluid into the visual sanding device (16) through the screw pump (15), and the fracturing fluid enters the first plexiglass After the plate (4) and the second plexiglass plate (5) are in the crack, the second plexiglass plate (5) translates outward under the push of pressure, and the sensitive spring (7) shrinks at the same time, and the first plexiglass plate (4), tiny cracks are formed between the second plexiglass plates (5), and this process is the crack formation stage; S400. Uniformly mix the fracturing fluid and proppant in the stirring tank (14), and the formed sand-carrying fluid is also pumped into the first plexiglass plate (4) and the second plexiglass plate (5) through the screw pump (15) ), the cracks are further opened, and the sensitive spring (7) is further shrunk, and the proppant begins to lay in the cracks, and the first plexiglass plate (4), the second plexiglass plate (5) Under the joint action of the pressure between them and the sensitive spring (7), the fracture is in a dynamic expansion or closure state, proppant is dynamically laid in the fracture, and the waste liquid during the proppant laying process is discharged into the waste liquid tank (18) Inside, observe the experimental phenomena and record the experimental data; S500. After the mixing tank (14) is completely pumped into the visible sand-laying device (16), the proppant is laid in the visible sand-laying device (16). The remaining proppant in the wellbore (1) is displaced into the crack between the first plexiglass plate (4) and the second plexiglass plate (5). Agitate the tank (14) and the valve between them, open the valve on the fracturing fluid pipe (22), zero the pressure gauge on the flow meter (17) and the gas source distributor (20); S600. According to the principle of equal Reynolds numbers, the on-site flowback displacement is converted into the simulated displacement in the laboratory, and the fracturing fluid prepared in the fracturing fluid mixing tank (21) is pumped into the first plexiglass through the fracturing pump (23). In the crack between the plate (4) and the second plexiglass plate (5), it can be observed that the proppant reflows, and the shape of the proppant laid in the crack changes. Observe the change of the proppant laying shape in the crack, record The outflow of proppant at the perforation port and drain port, and record the experimental data; S700. Open the upper valve of the gas source distributor (20), zero the pressure gauge, open the valve of the nitrogen cylinder (19), and nitrogen gas enters the crack between the first plexiglass plate (4) and the second plexiglass plate (5). , at this time, gas, liquid and solid flow in the fracture network, observe the migration of proppant in the fracture network, record the outflow of proppant in the liquid outlet on the end face of the perforation and the experimental data; S800, then switch the fracturing fluid stirring tank (21) to clean water, and pump the clean water into the cracks between the first plexiglass plate (4) and the second plexiglass plate (5), after a period of time, the formation The process of fluid leakage into the fracture, observe the experimental phenomenon and record the experimental data; S900. Close the fracturing pump (23), and close the valves on the nitrogen cylinder (19), the gas source distributor (20), and the fracturing liquid pipe (22), discharge the remaining gas, and complete the experimental operation; S1000, remove the gas source distributor (20) and the fracturing fluid pipe (22), install the device cleaning system, and clean the experimental device; S1100. According to the converted experimental simulation displacement, change the displacement of the fracturing fluid flowback, repeat the experimental steps of S100-S1000, and record the experimental data. When the proppant return flow is the least, it corresponds to the optimal flowback of the fracturing fluid Displacement, to draw the experimental conclusion. 2. The simulated fracturing fluid flowback according to claim 1 is characterized in that in the step S700, according to the reading of the pressure gauge, the flow of nitrogen is controlled by adjusting the opening of the valve. air pressure and flow.

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