Formation device of nitrogen foam fracturing fluid for oil and gas well and wellhead fracturing method

Abstract

The application discloses a nitrogen foam fracturing fluid forming device for oil and gas wells, a sand mixing vehicle is respectively connected with a water-based fracturing fluid tank, a fracturing sand tank, a crosslinking agent tank, a foaming agent tank and a high-pressure manifold, the output end of the high-pressure manifold is connected with a foam generator, and the foam generator is respectively connected with a wellhead and a nitrogen pipeline. The fracturing method is as follows: the water-based fracturing fluid, the fracturing sand and the crosslinking agent are simultaneously added into the sand mixing vehicle along the pipeline, high-speed stirring is carried out to form sand mixing liquid; the foaming agent is added into the sand mixing liquid to form sand mixing liquid containing the foaming agent; the sand mixing liquid containing the foaming agent is introduced into the foam generator through the high-pressure manifold along the pipeline, nitrogen is introduced into the nitrogen pipeline through a nitrogen inlet along the pipeline at the same time, low-density high-quality foam sand mixing liquid is formed; and finally, the low-density high-quality foam sand mixing liquid is introduced into the wellhead along the pipeline. The application realizes the reform purposes of neutral fracturing fluid, small liquid amount, high sand ratio, energy increase, easy flowback, filtration loss reduction, liquid control and sand increase.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of reservoir reconstruction, and particularly relates to a nitrogen foam fracturing fluid forming device for oil and gas wells. BACKGROUND

[0002] The conventional wellhead fracturing is accompanied by a small amount of injected liquid nitrogen, high friction, and uneven gas-liquid stirring. The foaming agent is added into the base fluid in advance. The conventional fracturing sand mixing truck has a relatively large stirring tank volume (for example, 1.5-2.0 m 3 ), and a small stirring speed (for example, about 100 revolutions per minute), which cannot achieve the liquid control and sand increasing target. Carbon dioxide energy increasing fracturing can supplement the formation energy, but the supercritical carbon dioxide cannot be fully and uniformly stirred with the water-based fracturing fluid. Field tests show that the carbon dioxide mixed with the water-based fracturing fluid does not improve the sand carrying performance. The carbon dioxide is weakly acidic, and has high requirements for the corrosion resistance of the oil and gas well pipe string. The carbon dioxide may also react with calcium ions in the reservoir to form new blockages, and part of the carbon dioxide not stored in the reservoir is released into the air to cause pollution.

[0003] Therefore, in view of the difficulties in the reconstruction of the tight detritus sandstone reservoir with high clay mineral content, large water sensitivity damage, and low energy of the depleted or under-pressured old oil and gas well, a new way of liquid control and sand increasing energy fracturing with less liquid and high sand concentration needs to be sought. SUMMARY

[0004] The application aims to provide a nitrogen foam fracturing fluid forming device for oil and gas wells, which solves the problem of large water sensitivity damage of the existing technology to the reservoir when the base fracturing fluid enters the ground.

[0005] Another object of the application is to provide a wellhead fracturing method.

[0006] The technical scheme adopted by the application is that the nitrogen foam fracturing fluid forming device for oil and gas wells comprises a sand mixing truck 5, the sand mixing truck 5 is connected with a water-based fracturing fluid tank 1, a fracturing sand tank 2, and a crosslinking agent tank 3 through pipelines respectively, a lower interface is formed on the lower side of the sand mixing truck 5, the lower interface is connected with a foaming agent tank 4 through a pipeline, the sand mixing truck 5 is also connected with a high-pressure manifold 6 input end, a foam generator 7 is connected with the high-pressure manifold 6 output end, the foam generator 7 is connected with a wellhead 8 through a pipeline, and two nitrogen liquid tanks 19 are also connected with the foam generator 7 through pipelines.

[0007] The application also has the following characteristics:

[0008] The foam generator enhancer 7 comprises a center spherical ball 14 with a cavity in the center, and the center spherical ball 14 is respectively communicated with a fracturing sand slurry input port 9 and a fracturing sand slurry output port 10, the fracturing sand slurry input port 9 is communicated with the high-pressure manifold 6 through a pipeline, the fracturing sand slurry output port 10 is communicated with the wellhead 8 through a pipeline, the center spherical ball 14 is respectively communicated with a first nitrogen inlet pipe 11 and a second nitrogen inlet pipe 12 through a foaming spring sheet 13, and the first nitrogen inlet pipe 11 and the second nitrogen inlet pipe 12 are respectively communicated with two nitrogen liquid tanks 19 through pipelines;

[0009] The fracturing sand slurry input port 9 and the fracturing sand slurry output port 10 are symmetrically arranged, and the first nitrogen inlet pipe 11 and the second nitrogen inlet pipe 12 are symmetrically arranged.

[0010] The foaming spring sheet 13 comprises a spring pipe 18, the spring pipe 18 is internally provided with a mesh 15, the mesh 15 is respectively connected with the inner wall of the spring pipe 18 through springs 16 on both sides, and the inner and outer diameters of the spring pipe 18 are equal to the inner and outer diameters of the first nitrogen inlet pipe 11 and the second nitrogen inlet pipe 12.

[0011] The mesh 15 is uniformly provided with a plurality of round holes 17.

[0012] Another technical scheme adopted by the present application is a wellhead fracturing method of an oil production well, and the specific steps are as follows:

[0013] Firstly, a water-based fracturing fluid, fracturing sand and a crosslinking agent are simultaneously added into a sand mixing vehicle along a pipeline, and a sand slurry is formed through high-speed stirring;

[0014] Then, a foaming agent is added into the sand slurry to form a sand slurry containing the foaming agent;

[0015] Then, the sand slurry containing the foaming agent is introduced into the foam generator enhancer along the pipeline through the high-pressure manifold, and nitrogen is introduced into the nitrogen gas through the first nitrogen inlet pipe and the second nitrogen inlet pipe along the pipeline to form a low-density high-quality foam sand slurry;

[0016] Finally, the low-density high-quality foam sand slurry is introduced into the wellhead along the pipeline.

[0017] The present application is characterized in that the stirring speed is greater than or equal to 1200 revolutions per minute.

[0018] The present application has the following beneficial effects:

[0019] 1. The present application designs a nitrogen foam fracturing process, and a foaming agent with excellent compatibility is optimized and pumped into the downstream outlet of the sand mixing vehicle, so that it is better mixed with the sand slurry, and the foam is more delicate;

[0020] 2. The present application enhances the mixing of nitrogen and water-based fracturing fluid by designing a foam generator, which forms a nitrogen foam mixture phase, and solves the problem of breaking laminar flow state to make nitrogen flow and water-based fracturing fluid fully mixed to form a foam phase under the condition of low pump displacement;

[0021] 3. The present application solves the problem of small liquid phase and high displacement sand concentration during foam fracturing construction by using a high-speed sand mixing truck;

[0022] 4. The nitrogen foam fracturing fluid has good sand carrying performance, thereby reducing the amount of liquid into the ground and reducing the water-based fracturing fluid into the reservoir water sensitivity damage; supplementing the energy of low-pressure tight reservoirs and improving the flowback efficiency; the nitrogen foam fracturing fluid system is neutral, the sand carrying performance does not rely on cross-linking, the amount of cross-linking agent into the ground is reduced, the residual glue damage is low, compared with conventional fracturing, the present application realizes the purpose of neutral fracturing fluid, less liquid amount, high sand ratio, energy increase, easy flowback, filtration loss reduction, liquid control and sand improvement. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is a structural schematic diagram of the nitrogen foam fracturing device of the present application;

[0024] Figure 2 is a structural schematic diagram of the foam generator of the present application;

[0025] Figure 3 is a structural schematic diagram of the foaming spring leaf of the present application.

[0026] In the figure, 1. water-based fracturing fluid tank, 2. fracturing sand tank, 3. cross-linking agent tank, 4. foaming agent tank, 5. sand mixing truck, 6. high-pressure manifold, 7. foam generator, 8. wellhead, 9. fracturing sand mixing liquid input port, 10. fracturing sand mixing liquid output port, 11. first nitrogen inlet pipe, 12. second nitrogen inlet pipe, 13. foaming spring leaf, 14. center ball, 15. mesh, 16. spring, 17. circular hole, 18. spring pipe, 19. nitrogen liquid tank. DETAILED DESCRIPTION

[0027] The present application will be described in detail below in combination with the drawings and specific embodiments.

[0028] The oil and gas well nitrogen foam fracturing fluid forming device, as shown in Figure 1 Fig. 1, comprises a sand mixing truck 5, which is connected with a water-based fracturing fluid tank 1, a fracturing sand tank 2, a cross-linking agent tank 3, a foaming agent tank 4 and a high-pressure manifold 6 through pipelines respectively, and when in use, the water-based fracturing fluid, the fracturing sand and the cross-linking agent are mixed into the sand mixing truck 5 for high-speed stirring to form a sand mixing liquid, wherein the stirring tank has a smaller volume than the conventional volume (0.2m 3 3), the stirring speed is ≥1200 revolutions per minute, and the highest sand concentration requirement during sand adding stage can be achieved at 1800kg / m 3 3.

[0029] Further, the foaming agent tank 4 is located at the lower end interface of the sand mixing vehicle 5, which mainly makes the foaming agent input from the lower end of the sand mixing vehicle 5 to be mixed with the sand mixing liquid, so that the foam is more delicate. The foaming agent used in the application belongs to anionic surfactant, is compatible with the liquid system, has stable rheological properties, good compatibility with guar gum liquid system, an applicable temperature range of less than 125 DEG C, a foaming rate of more than 70%, a foam half-life period of 75-80 minutes, and a surface tension slightly lower than that of conventional surface active agents, and has good performance. The output end of the high-pressure manifold 6 is communicated with a foam generation enhancer 7. The foam generation enhancer 7 is respectively communicated with a well head 8 and a nitrogen pipeline.

[0030] Further, as shown in Figure 2 , the foam generation enhancer 7 includes a center sphere 14, the center sphere 14 is provided with a cavity in the center, and the center sphere 14 is respectively communicated with a fracturing sand mixing liquid input port 9 and a fracturing sand mixing liquid output port 10. The fracturing sand mixing liquid input port 9 and the fracturing sand mixing liquid output port 10 are symmetrically arranged. The fracturing sand mixing liquid input port 9 is communicated with the high-pressure manifold 6 through a pipeline. The fracturing sand mixing liquid output port 10 is communicated with the well head 8 through a pipeline. In use, the sand mixing liquid flows into the high-pressure manifold 6, the fracturing sand mixing liquid input port 9, the foam generation enhancer 7, the fracturing sand mixing liquid output port 10, and finally into the well head 8 in sequence along the pipeline through the sand mixing vehicle 5.

[0031] Further, the center sphere 14 is respectively communicated with a first nitrogen inlet pipe 11 and a second nitrogen inlet pipe 12 through a foaming spring sheet 13. The first nitrogen inlet pipe 11 and the second nitrogen inlet pipe 12 are symmetrically arranged. The nitrogen pipeline is respectively communicated with the first nitrogen inlet pipe 11 and the second nitrogen inlet pipe 12. As shown in Figure 3 , the foaming spring sheet 13 includes a spring tube 18. The spring tube 18 is provided with a mesh 15 inside. The two sides of the mesh 15 are respectively connected with the inner wall of the spring tube 18 through a plurality of springs 16. The inner and outer diameters of the spring tube 18 are equal to the inner and outer diameters of the first nitrogen inlet pipe 11 and the second nitrogen inlet pipe 12. A plurality of round holes 17 are uniformly arranged on the mesh 15. The diameter of the round hole 17 is smaller than the diameter of the fracturing sand particles. The nanoscale effect is better. In the working process, when the sand mixing liquid containing the foaming agent flows into the foam generation enhancer 7, the nitrogen is introduced into the nitrogen pipeline through the first nitrogen inlet and the second nitrogen inlet. By using the principle of opposite collision, the nitrogen gas introduced through the first nitrogen inlet pipe 11 and the second nitrogen inlet pipe 12 is driven to reciprocate in a certain amplitude range under the mutual impact, so as to scatter the nitrogen. The scattered nitrogen and the fracturing sand mixing liquid are fully mixed to form a low-density high-quality nitrogen foam mixed-phase sand mixing liquid. Even in the case of low pump injection displacement, high sand concentration sand carrying fracturing can also be realized.

[0032] The oil production wellhead fracturing method comprises the following specific steps:

[0033] Firstly, the water-based fracturing fluid, fracturing sand and crosslinking agent are simultaneously added into the sand mixing vehicle along the pipeline, and the sand mixing liquid is formed through high-speed stirring, wherein the stirring speed is ≥1200 revolutions per minute, so that the stirring and mixing can be better and faster;

[0034] Then, the foaming agent is added into the sand mixing liquid to form the sand mixing liquid containing the foaming agent. The foaming agent used in the present application belongs to an anionic surfactant, is compatible with the liquid system, has stable rheological properties, good compatibility with the guar gum liquid system, an applicable temperature range of less than 125℃, a foaming rate of more than 70%, a foam half-life period of 75-80 minutes, and a surface tension slightly lower than that of a conventional surfactant, and has good foaming performance;

[0035] Then, the sand mixing liquid containing the foaming agent is introduced into the foam generator along the pipeline through the high-pressure manifold, and nitrogen is introduced into the nitrogen gas along the pipeline through the first nitrogen inlet and the second nitrogen inlet. After the nitrogen is introduced, the nitrogen gas introduced through the first nitrogen inlet pipe 11 and the second nitrogen inlet pipe 12 is driven to reciprocate in a small amplitude range under the mutual impact, the nitrogen gas is dispersed, the dispersed nitrogen gas and the fracturing sand mixing liquid are fully mixed, and the low-density high-quality nitrogen foam mixed sand mixing liquid is formed. In this way, high-sand-concentration sand fracturing can be realized even under the condition of low pump injection displacement, and the low-density high-quality foam sand mixing liquid is formed;

[0036] Finally, the low-density high-quality foam sand mixing liquid is introduced into the wellhead along the pipeline for fracturing.

[0037] Example 1

[0038] The high-quality nitrogen foam fracturing reconstruction process is adopted, the average sand ratio is 33.3%, the average sand concentration is 576.6㎏ / m³, the highest sand concentration is 660㎏ / m³, the liquid displacement is 0.8-1.1m³ / min, the liquid nitrogen is 89m³ (design 91m³), the liquid nitrogen displacement is 850-950L / min, the total liquid volume into the ground is 103.4m³. After fracturing, the one-time jetting is performed, the oil drainage mode is adopted, the fire yellow length is 3-2m, the well is shut down for 2.5d to recover the oil pressure: 0↗18.1MPa, the casing pressure is 10.8↗11.2MPa, the final flowback rate is 58.3%, and the gas test obtains the open flow capacity of 12900m³ / d.

[0039] Compared with conventional crosslinking gel fracturing: the amount of liquid into the ground is greatly reduced (only 30%~40%), the well is added with 33 cubic meters of sand, and the fracturing fluid is only 110 cubic meters; the sand carrying performance does not rely on crosslinking, the total amount of gel powder into the ground is small, the residual gel damage is low, and the whole process is not crosslinked; the sand carrying relies on foam, and does not depend on viscosity, a large amount of gel breaker can be added, the post-fracturing gel breaking and cleaning are good, and the average gel breaker of the well is 0.6 kg / m³ of fracturing fluid.

[0040] Example 2

[0041] Construction parameters: the amount of liquid into the ground is 372.0 cubic meters, the amount of sand is 78.4 cubic meters, the maximum sand concentration on the ground is 1400 kg / m 3 , the construction discharge is 1.5~2.5 m 3 / min, the amount of liquid nitrogen is 255.5 cubic meters, the discharge is 900~1500 L / min, and the mass ratio of nitrogen foam is 60~65%.

[0042] Gas testing: the liquid discharge period is 11 days, which is 50% shorter than that of conventional fracturing process, the cumulative liquid discharge is 87 cubic meters, the flowback rate is 22.4%, the fire length is 6~7 m; the well is shut in for 24 h, and the casing pressure is 15.7↗21.6 MPa. The test is unblocked at 42.9×10 4 m 3 / d, and the transformation effect is remarkable.

[0043] Effect analysis: the volume of nitrogen gas under the formation condition of 85℃, 30 MPa is 1 / 218 of that under the standard condition, the actual total amount of injected liquid nitrogen of the well is 255.5m 3 , which is converted into 814m 3 underground volume. The volume expansion and pressure increase of nitrogen gas promote flowback, and the existence of gas reduces the density of the liquid column in the wellbore, thereby achieving energy increase and flowback assistance.

[0044] Compared with 7 conventional fracturing processes of the same well type in Suzhong block, the sand ratio of nitrogen foam fracturing is increased by 1.3 times, the maximum sand concentration is increased by 2.1 times, the total liquid into the well is reduced by 59%, the liquid discharge time is reduced by 38%, the gas testing yield is increased by 3 times, and the effect of less water fracturing is remarkable.

[0045] Example 3

[0046] The forming device of the nitrogen foam fracturing fluid for oil and gas wells comprises a sand mixing vehicle 5, a water-based fracturing fluid tank 1, a fracturing sand tank 2 and a crosslinking agent tank 3 which are communicated with the sand mixing vehicle 5 through pipelines respectively, a lower interface is formed on the lower side of the sand mixing vehicle 5, the lower interface is communicated with a foaming agent tank 4 through a pipeline, the sand mixing vehicle 5 is further connected with a high-pressure manifold 6 input end, the high-pressure manifold 6 output end is communicated with a foam generation enhancer 7, the foam generation enhancer 7 is communicated with a wellhead 8 through a pipeline, and the foam generation enhancer 7 is further communicated with two nitrogen liquid tanks 19 through pipelines,

[0047] The foam generator 7 includes a central sphere 14 with a cavity at its center. The central sphere 14 is connected to a fracturing sand-mixing fluid input port 9 and a fracturing sand-mixing fluid output port 10. The fracturing sand-mixing fluid input port 9 and the fracturing sand-mixing fluid output port 10 are symmetrically arranged. The fracturing sand-mixing fluid input port 9 is connected to the high-pressure manifold 6 through a pipe, and the fracturing sand-mixing fluid output port 10 is connected to the wellhead 8 through a pipe. The central sphere 14 is connected to a first nitrogen inlet pipe 11 and a second nitrogen inlet pipe 12 through a foaming spring 13. The first nitrogen inlet pipe 11 and the second nitrogen inlet pipe 12 are connected to two nitrogen liquid tanks 19 through pipes. The first nitrogen inlet pipe 11 and the second nitrogen inlet pipe 12 are symmetrically arranged.

[0048] Example 4

[0049] The specific steps of wellhead fracturing for oil wells are as follows:

[0050] First, water-based fracturing fluid, fracturing sand, and crosslinking agent are simultaneously added to the mixing truck along the pipeline. The mixture is then stirred at high speed to form a mixed sand solution. The stirring speed is ≥1200 rpm, which can achieve better and faster mixing.

[0051] Then, a foaming agent is added to the sand mixing liquid to form a sand mixing liquid containing a foaming agent. The foaming agent used in this invention is an anionic surfactant that is compatible with liquid systems, has stable rheological properties, good compatibility with guar gum systems, an applicable temperature range of less than 125°C, a foaming rate of more than 70%, a foam half-life of 75 to 80 minutes, and a surface tension of slightly lower than that of conventional surface actives, thus exhibiting good foaming performance.

[0052] The foaming agent-containing sand-mixing liquid is then introduced into the foam generator via a high-pressure manifold through a pipeline. At the same time, nitrogen gas is introduced through the pipeline from the first nitrogen inlet and the second nitrogen inlet. After the nitrogen gas is introduced, the nitrogen gas introduced through the first nitrogen inlet pipe 11 and the second nitrogen inlet pipe 12 impacts each other, causing the mesh 15 to reciprocate in a small amplitude range, which disperses the nitrogen gas and forms a low-density gas-liquid-solid mixed phase flow state. This allows the dispersed nitrogen gas and the fracturing sand-mixing liquid to be fully mixed, forming a low-density, high-quality nitrogen foam mixed-phase sand-mixing liquid. In this way, even with a low pumping discharge rate, high-concentration sand-carrying fracturing can be achieved, forming a low-density, high-quality foam mixed sand-mixing liquid.

[0053] Finally, the low-density, high-quality foamed sand mixture is piped into the wellhead for fracturing.

Claims

1. A wellhead fracturing method for oil production wells, characterized in that, The specific steps are as follows: First, water-based fracturing fluid, fracturing sand, and crosslinking agent are simultaneously added to the mixing truck along the pipeline, and a mixing solution is formed by high-speed stirring. Then, a foaming agent is added to the sand mixing solution to form a sand mixing solution containing the foaming agent; The foaming agent-containing sand mixture is then introduced into the foam generator through a high-pressure manifold along the pipeline. At the same time, nitrogen gas is introduced into the pipeline through the first nitrogen inlet pipe and the second nitrogen inlet pipe respectively to form a low-density, high-quality foam sand mixture. Finally, the low-density, high-quality foamed sand mixture is pumped into the wellhead along the pipeline; The wellhead fracturing method of the oil well is completed using a nitrogen foam fracturing fluid forming device for oil and gas wells. The nitrogen foam fracturing fluid forming device for oil and gas wells includes a sand mixing truck (5). The sand mixing truck (5) is connected to a water-based fracturing fluid tank (1), a fracturing sand tank (2), and a crosslinking agent tank (3) through pipelines. The sand mixing truck (5) has a lower interface on its lower side. The lower interface is connected to a foaming agent tank (4) through a pipeline. The sand mixing truck (5) is also connected to the input end of a high-pressure manifold (6). The output end of the high-pressure manifold (6) is connected to a foam generator (7). The foam generator (7) is connected to the wellhead (8) through a pipeline. The foam generator (7) is also connected to two nitrogen liquid tanks (19) through pipelines. The foam generator (7) includes a central sphere (14), which has a cavity in the center. The central sphere (14) is connected to a fracturing sand-mixing fluid input port (9) and a fracturing sand-mixing fluid output port (10). The fracturing sand-mixing fluid input port (9) is connected to the high-pressure manifold (6) through a pipe. The fracturing sand-mixing fluid output port (10) is connected to the wellhead (8) through a pipe. The central sphere (14) is connected to a first nitrogen inlet pipe (11) and a second nitrogen inlet pipe (12) through a foaming spring (13). The first nitrogen inlet pipe (11) and the second nitrogen inlet pipe (12) are connected to two nitrogen liquid tanks (19) through pipes. The fracturing sand mixing fluid input port (9) and the fracturing sand mixing fluid output port (10) are symmetrically arranged, and the first nitrogen inlet pipe (11) and the second nitrogen inlet pipe (12) are symmetrically arranged; The bubbling spring (13) includes a spring tube (18), and a mesh (15) is provided inside the spring tube (18). The mesh (15) is connected to the inner wall of the spring tube (18) by several springs (16) on both sides. The inner and outer diameters of the spring tube (18) are equal to the inner and outer diameters of the first nitrogen inlet pipe (11) and the second nitrogen inlet pipe (12). The mesh (15) has several round holes (17) evenly distributed on it.

2. The wellhead fracturing method for oil production wells according to claim 1, characterized in that, The mixer speed is ≥1200 rpm.

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