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

Abstract

According to the forming device of the nitrogen foam fracturing fluid for the oil and gas well, a fracturing blender truck is communicated with a water-based fracturing fluid tank, a fracturing sand tank, a cross-linking agent tank, a foaming agent tank and a high-pressure manifold, the output end of the high-pressure manifold is communicated with a foam generation intensifier, and the foam generation intensifier is communicated with a well mouth and a nitrogen pipeline. The fracturing method comprises the following steps: simultaneously adding the water-based fracturing fluid, the fracturing sand and the cross-linking agent into a fracturing blender truck along a pipeline, and stirring at a high speed to form a sand blending fluid; adding a foaming agent into the sand mixing liquid to form the sand mixing liquid containing the foaming agent; sand mixing liquid containing a foaming agent enters a foam generation intensifier through a high-pressure manifold along a pipeline, and meanwhile nitrogen is introduced into the foam generation intensifier through a nitrogen inlet along the pipeline, so that low-density and high-quality foam sand mixing liquid is formed; and finally, the low-density and high-quality foam sand mixing liquid is converged into a wellhead along a pipeline. According to the method, the transformation purposes of neutral fracturing fluid, small fluid amount, high sand ratio, energy increasing, easy flowback, filtration reduction, fluid control and sand increase are achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of reservoir transformation, and in particular relates to a device for forming nitrogen foam fracturing fluid for oil and gas wells. The invention also relates to a wellhead fracturing method. Background Art

[0002] Conventional wellhead fracturing is accompanied by a small amount of liquid nitrogen injection, high friction, uneven gas-liquid mixing, and the foaming agent is added to the base fluid in advance. The mixing tank volume of the conventional fracturing sand mixer is relatively large (for example, 1.5-2.0m3), and the agitator speed is low (for example, about 100 rpm), which cannot achieve the goal of controlling liquid and increasing sand. Although carbon dioxide energy fracturing can replenish formation energy, supercritical carbon dioxide cannot be fully mixed with water-based fracturing fluid. Field tests have shown that mixing carbon dioxide with water-based fracturing fluid does not improve sand carrying performance. Carbon dioxide is weakly acidic and has high corrosion resistance requirements for oil and gas well pipes. It is also possible to react with calcium ions in the reservoir to form new blockages. Some of the unburied carbon dioxide is released back into the air to cause pollution.

[0003] Therefore, in order to address the difficulties in fracturing such as the great water sensitivity of tight lithic sandstone reservoirs with high clay mineral content and the low energy of tight reservoirs in depleted or under-pressurized old oil and gas wells, it is necessary to seek new ways of fracturing with low liquid volume, high sand concentration, controlled liquid, increased sand and increased energy. Summary of the invention

[0004] The purpose of the present invention is to provide a device for forming nitrogen foam fracturing fluid for oil and gas wells, which solves the problem that the prior art base fracturing fluid has great damage to water-sensitive reservoirs when entering the ground.

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

[0006] The technical solution adopted by the present invention is a device for forming nitrogen foam fracturing fluid for oil and gas wells, comprising a sand mixing truck 5, which is connected to a water-based fracturing fluid tank 1, a fracturing sand tank 2 and a cross-linking agent tank 3 through pipelines, a lower interface is provided on the lower side of the sand mixing truck 5, and 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, and the output end of the high-pressure manifold 6 is connected to a foam generating enhancer 7, the foam generating enhancer 7 is connected to a wellhead 8 through a pipeline, and the foam generating enhancer 7 is also connected to two nitrogen liquid tanks 19 through pipelines.

[0007] The present invention is also characterized in that:

[0008] The foam generating enhancer 7 comprises a central sphere 14, a cavity is formed in the center of the central sphere 14, the central sphere 14 is respectively connected 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 is connected with the high pressure manifold 6 through a pipeline, the fracturing sand mixing liquid output port 10 is connected with the wellhead 8 through a pipeline, the central sphere 14 is respectively connected with a first nitrogen inlet pipe 11 and a second nitrogen inlet pipe 12 through a foaming reed 13, the first nitrogen inlet pipe 11 and the second nitrogen inlet pipe 12 are respectively connected with two nitrogen liquid tanks 19 through pipelines;

[0009] 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;

[0010] The foaming reed 13 includes a reed tube 18, a mesh 15 is provided inside the reed tube 18, and both sides of the mesh 15 are connected to the inner wall of the reed tube 18 through springs 16 respectively. The inner and outer diameters of the reed tube 18 are equal to the inner and outer diameters of the first nitrogen inlet pipe 11 and the second nitrogen inlet pipe 12;

[0011] A plurality of circular holes 17 are evenly formed on the mesh 15 .

[0012] Another technical solution adopted by the present invention is a wellhead fracturing method for an oil well, the specific steps of which are as follows:

[0013] First, water-based fracturing fluid, fracturing sand and cross-linking agent are added into the sand mixing truck along the pipeline at the same time, and the mixed sand liquid is formed through high-speed stirring;

[0014] Then, a foaming agent is added to the sand-mixing liquid to form a sand-mixing liquid containing the foaming agent;

[0015] Then, the sand-mixing liquid containing the foaming agent is passed through the pipeline through the high-pressure manifold into the foam generating intensifier, and nitrogen is introduced into the pipeline through the first nitrogen inlet pipe and the second nitrogen inlet pipe respectively to form a low-density and high-quality foam sand-mixing liquid;

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

[0017] The invention is also characterized in that the rotating speed of the stirrer is ≥1200 rpm.

[0018] The beneficial effects of the present invention are:

[0019] 1. The present invention designs a nitrogen foam fracturing process flow, optimizes the foaming agent with excellent compatibility, and is pumped into the downstream outlet of the sand mixing truck to make it better mixed with the sand mixing liquid and make the foam more delicate;

[0020] 2. The present invention enhances the mixing of nitrogen and water-based fracturing fluid to form a nitrogen foam mixed phase by designing a foam generation enhancer, thereby solving the problem of breaking the laminar flow state even when the pumping displacement is low, so that the nitrogen flow and the water-based fracturing fluid are fully mixed to form a foam phase;

[0021] 3. The present invention solves the problem of small liquid phase, high displacement and concentrated sand during foam fracturing construction by adopting a high-speed sand mixer;

[0022] 4. The nitrogen foam fracturing fluid of the present invention has good sand-carrying performance, thereby reducing the amount of liquid entering the ground, reducing the damage of water-based fracturing fluid entering the ground to water-sensitive reservoirs; replenishing the energy of low-pressure dense 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 entering the ground is reduced, and the residual glue damage is low. Compared with conventional fracturing, the present invention achieves the purposes of neutral fracturing fluid, low liquid volume and high sand ratio, energy enhancement, easy flowback and reduced filter loss, and liquid control and sand enhancement transformation. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the structure of the nitrogen foam fracturing device of the present invention;

[0024] Figure 2 It is a schematic diagram of the structure of the foam generation enhancer of the present invention;

[0025] Figure 3 It is a schematic diagram of the structure of the foaming reed of the present invention.

[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 generation enhancer, 8. injection and production well, 9. fracturing sand mixing fluid input port, 10. fracturing sand mixing fluid output port, 11. first nitrogen inlet pipe, 12. second nitrogen inlet pipe, 13. bubbling reed, 14. center sphere, 15. mesh, 16. spring, 17. round hole, 18. reed tube, 19. nitrogen liquid tank. DETAILED DESCRIPTION

[0027] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0028] A device for forming nitrogen foam fracturing fluid for oil and gas wells, such as Figure 1 As shown, the sand mixing vehicle 5 is provided, and the sand mixing vehicle 5 is connected to the water-based fracturing fluid tank 1, the fracturing sand tank 2, the cross-linking agent tank 3, the foaming agent tank 4 and the high-pressure manifold 6 through pipelines. When in use, the water-based fracturing fluid, the fracturing sand and the cross-linking agent are combined into the sand mixing vehicle 5 and stirred at high speed to form a sand mixing liquid. The volume of the mixing tank is smaller than the conventional volume (0.2m 3 The stirrer speed is ≥1200 rpm, and the maximum sand concentration in the sand adding stage is 1800 kg / m 3 Mixing requirements;

[0029] Furthermore, the foaming agent tank 4 is located at the lower end interface of the sand mixing vehicle 5. This design is mainly to allow the foaming agent to be input from the lower end of the sand mixing vehicle 5 and merged with the sand mixing liquid to make the foam more delicate. The foaming agent used in the present invention is an anionic surfactant, compatible with the liquid system, stable rheological properties, good compatibility with the guar gum liquid system, applicable temperature range is less than 125°C, foaming rate is more than 70%, foam half-life period is 75 to 80 minutes, the surface tension of the foaming agent is slightly lower than the conventional surfactant, and has better performance. The output end of the high-pressure manifold 6 is connected to a foam generation enhancer 7, and the foam generation enhancer 7 is respectively connected to a wellhead 8 and a nitrogen pipeline.

[0030] Further, such as Figure 2 As shown, the foam generating enhancer 7 includes a central sphere 14, a cavity is opened in the center of the central sphere 14, and the central sphere 14 is respectively connected 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 connected with the high-pressure manifold 6 through a pipeline, and the fracturing sand mixing liquid output port 10 is connected with the wellhead 8 through a pipeline. When in use, the sand mixing liquid flows along the pipeline through the sand mixing vehicle 5 in sequence into the high-pressure manifold 6, the fracturing sand mixing liquid input port 9, the foam generating enhancer 7, and the fracturing sand mixing liquid output port 10, and finally flows into the wellhead 8;

[0031] Furthermore, the central ball 14 is connected to the first nitrogen inlet pipe 11 and the second nitrogen inlet pipe 12 through the foaming reed 13, the first nitrogen inlet pipe 11 and the second nitrogen inlet pipe 12 are symmetrically arranged, and the nitrogen pipeline is connected to the first nitrogen inlet pipe 11 and the second nitrogen inlet pipe 12, respectively. Figure 3 As shown, the foaming reed 13 includes a reed tube 18, a mesh 15 is arranged inside the reed tube 18, and the two sides of the mesh 15 are connected to the inner wall of the reed tube 18 through a plurality of springs 16, and the inner and outer diameters of the reed 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 circular holes 17 are evenly opened on the mesh 15, and the diameter of the circular holes 17 is smaller than the diameter of the fracturing sand particles, and the nanometer effect is better. During the working process, when the mixed sand liquid containing the foaming agent flows into the foam generating enhancer 7, the nitrogen is respectively Nitrogen is introduced from the first nitrogen inlet and the second nitrogen inlet. By utilizing the counteraction principle, the nitrogen gas injected through the first nitrogen inlet pipe 11 and the second nitrogen inlet pipe 12 drives the mesh 15 to reciprocate in a small amplitude within a certain amplitude range under the mutual impact, thereby breaking up the nitrogen and forming a low-density gas-liquid-solid mixed phase flow state, so that the broken up nitrogen and the fracturing sand-mixing fluid are fully mixed to form a low-density, high-quality nitrogen foam mixed phase sand-mixing fluid, so that high-sand and high-concentration sand-carrying fracturing can be achieved even under the condition of low pumping displacement.

[0032] The specific steps of the wellhead fracturing method of oil wells are as follows:

[0033] First, water-based fracturing fluid, fracturing sand and cross-linking agent are added to the sand mixing truck along the pipeline at the same time, and the mixed sand is formed by high-speed stirring, wherein the stirring speed of the stirrer is ≥1200 rpm, which can achieve better and faster stirring and mixing;

[0034] Then, a foaming agent is added to the sand mixing liquid to form a sand mixing liquid containing the foaming agent. The foaming agent used in the present invention is an anionic surfactant, which 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° C., a foaming rate of more than 70%, a foam half-life period of 75 to 80 minutes, and a surface tension of the foaming agent is slightly lower than that of a conventional surfactant, and has good foaming performance;

[0035] Then, the sand-mixing liquid containing the foaming agent is passed through the pipeline through the high-pressure manifold into the foam generating intensifier, and nitrogen is introduced into the pipeline from the first nitrogen inlet and the second nitrogen inlet respectively. After the nitrogen is introduced, the nitrogen gas injected through the first nitrogen inlet pipe 11 and the second nitrogen inlet pipe 12 drives the mesh 15 to reciprocate in a small amplitude within a certain amplitude range under the mutual impact of the counteraction principle, thereby breaking up the nitrogen and forming a low-density gas-liquid-solid mixed phase flow state, so that the broken nitrogen and the fracturing sand-mixing liquid are fully mixed to form a low-density high-quality nitrogen foam mixed phase sand-mixing liquid, so that even under the condition of low pumping displacement, high-sand concentrated sand fracturing can be achieved to form a low-density high-quality foam sand-mixing liquid;

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

[0037] Example 1

[0038] High-quality nitrogen foam fracturing technology is used, with an average sand ratio of 33.3% and an average sand concentration of 576.6 kg / m 3 , the highest sand concentration is 660 kg / m 3 , liquid displacement 0.8~1.1m 3 / min, liquid nitrogen 89m 3 (Design 91m 3 ), liquid nitrogen displacement 850~950L / min, total liquid volume entering the ground 103.4m 3 After the pressure was released, the well was blown through once, and the oil was released and the liquid was discharged. The fire yellow length was 3 to 2m. After shutting in the well for 2.5 days, the oil pressure was restored: 0↗18.1MPa, the casing pressure was 10.8↗11.2MPa, the final return flow rate was 58.3%, and the unobstructed flow rate obtained by the gas test was 12,900 cubic meters / day.

[0039] Compared with conventional cross-linked rubber fracturing: the amount of fluid entering the ground is greatly reduced (only 30% to 40%), 33 cubic meters of sand is added to the well, and only 110 cubic meters of fracturing fluid are used; the sand carrying performance does not rely on cross-linking, the total amount of rubber powder entering the ground is small, the residual rubber damage is low, and there is no cross-linking throughout the process; the sand carrying depends on foam, not viscosity, and a large amount of capsule breaker can be added. The broken gel is cleaned well after fracturing, and the average capsule breaker in the well is 0.6kg / m 3 Fracturing fluid.

[0040] Example 2

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

[0042] Gas test results: the drainage cycle was 11 days, which was 50% shorter than that of conventional fracturing technology. The cumulative drainage was 87 cubic meters, the return rate was 22.4%, and the fire length was 6 to 7 meters. The well was shut in for 24 hours, and the casing pressure was 15.7 to 21.6 MPa. The test was unobstructed 42.9×10 4 m 3 / d, the transformation effect is remarkable.

[0043] Effect analysis: Under the conditions of 85℃ and 30MPa, the volume of nitrogen is 1 / 218 of that under standard conditions. The total amount of liquid nitrogen actually injected into this well is 255.5m 3 , which is converted into an underground volume of 814m 3 The volume expansion and pressurization of nitrogen promotes flowback, and the presence of gas reduces the density of the wellbore liquid column, achieving energy enhancement and drainage assistance.

[0044] Compared with the conventional fracturing technology of the same type in 7 wells in the Suzhong block, the sand ratio of nitrogen foam fracturing increased by 1.3 times, the maximum sand concentration increased by 2.1 times, the total liquid entering the well was reduced by 59%, the time for drainage was reduced by 38%, the test gas production increased by 3 times, and the effect of low-water fracturing was significant.

[0045] Example 3

[0046] The device for forming nitrogen foam fracturing fluid for oil and gas wells comprises a sand mixing truck 5, which is respectively connected to a water-based fracturing fluid tank 1, a fracturing sand tank 2 and a cross-linking agent tank 3 through pipelines. A lower interface is provided at the lower side of the sand mixing truck 5, which is connected to a foaming agent tank 4 through a pipeline. The sand mixing truck 5 is also connected to an input end of a high-pressure manifold 6, and an output end of the high-pressure manifold 6 is connected to a foam generating enhancer 7, which is connected to a wellhead 8 through a pipeline, and the foam generating enhancer 7 is also connected to two nitrogen liquid tanks 19 through pipelines.

[0047] Among them, the foam generating enhancer 7 includes a central sphere 14, a cavity is opened in the center of the central sphere 14, the central sphere 14 is respectively connected 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 connected to the high-pressure manifold 6 through a pipeline, and the fracturing sand mixing liquid output port 10 is connected to the wellhead 8 through a pipeline, the central sphere 14 is respectively connected with a first nitrogen inlet pipe 11 and a second nitrogen inlet pipe 12 through a foaming reed 13, the first nitrogen inlet pipe 11 and the second nitrogen inlet pipe 12 are respectively connected to two nitrogen liquid tanks 19 through pipelines, and the first nitrogen inlet pipe 11 and the second nitrogen inlet pipe 12 are symmetrically arranged.

[0048] Example 4

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

[0050] First, water-based fracturing fluid, fracturing sand and cross-linking agent are added to the sand mixing truck along the pipeline at the same time, and the mixed sand is formed by high-speed stirring, wherein the stirring speed of the stirrer is ≥1200 rpm, which can achieve better and faster stirring and mixing;

[0051] Then, a foaming agent is added to the sand mixing liquid to form a sand mixing liquid containing the foaming agent. The foaming agent used in the present invention is an anionic surfactant, which 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° C., a foaming rate of more than 70%, a foam half-life period of 75 to 80 minutes, and a surface tension of the foaming agent is slightly lower than that of a conventional surfactant, and has good foaming performance;

[0052] Then, the sand-mixing liquid containing the foaming agent is passed through the pipeline through the high-pressure manifold into the foam generating intensifier, and nitrogen is introduced into the pipeline from the first nitrogen inlet and the second nitrogen inlet respectively. After the nitrogen is introduced, the nitrogen gas injected through the first nitrogen inlet pipe 11 and the second nitrogen inlet pipe 12 drives the mesh 15 to reciprocate in a small amplitude within a certain amplitude range under the mutual impact of the counteraction principle, thereby breaking up the nitrogen and forming a low-density gas-liquid-solid mixed phase flow state, so that the broken nitrogen and the fracturing sand-mixing liquid are fully mixed to form a low-density high-quality nitrogen foam mixed phase sand-mixing liquid, so that even under the condition of low pumping displacement, high-sand concentrated sand fracturing can be achieved to form a low-density high-quality foam sand-mixing liquid;

[0053] Finally, the low-density, high-quality foam-mixed sand fluid is introduced into the wellhead along the pipeline for fracturing.

Claims

1. A device for forming nitrogen foam fracturing fluid for oil and gas wells, characterized in that: The invention comprises a sand mixing vehicle (5), wherein the sand mixing vehicle (5) is connected to a water-based fracturing fluid tank (1), a fracturing sand tank (2) and a cross-linking agent tank (3) through pipelines, respectively; a lower interface is provided on the lower side of the sand mixing vehicle (5), and the lower interface is connected to a foaming agent tank (4) through a pipeline; the sand mixing vehicle (5) is also connected to an input end of a high-pressure manifold (6), and an output end of the high-pressure manifold (6) is connected to a foam generating intensifier (7); the foam generating intensifier (7) is connected to a wellhead (8) through a pipeline, and the foam generating intensifier (7) is also connected to two nitrogen liquid tanks (19) through pipelines.

2. The device for forming nitrogen foam fracturing fluid for oil and gas wells according to claim 1, characterized in that: The foam generating intensifier (7) comprises a central sphere (14), a cavity is formed at the center of the central sphere (14), the central sphere (14) is respectively connected to 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) is connected to a high-pressure manifold (6) through a pipeline, the fracturing sand mixing liquid output port (10) is connected to a wellhead (8) through a pipeline, the central sphere (14) is respectively connected to a first nitrogen inlet pipe (11) and a second nitrogen inlet pipe (12) through a foaming reed (13), the first nitrogen inlet pipe (11) and the second nitrogen inlet pipe (12) are respectively connected to two nitrogen liquid tanks (19) through pipelines.

3. The device for forming nitrogen foam fracturing fluid for oil and gas wells according to claim 2, characterized in that: 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.

4. The device for forming nitrogen foam fracturing fluid for oil and gas wells according to claim 2, characterized in that: The foaming reed (13) comprises a reed tube (18), a mesh sheet (15) is arranged inside the reed tube (18), two sides of the mesh sheet (15) are connected to the inner wall of the reed tube (18) through a plurality of springs (16), and the inner and outer diameters of the reed tube (18) are equal to the inner and outer diameters of the first nitrogen inlet pipe (11) and the second nitrogen inlet pipe (12).

5. The device for forming nitrogen foam fracturing fluid for oil and gas wells according to claim 4, characterized in that: The mesh (15) is evenly provided with a plurality of circular holes (17).

6. A method for fracturing an oil well head, characterized in that: The specific steps are as follows: First, water-based fracturing fluid, fracturing sand and cross-linking agent are added into the sand mixing truck along the pipeline at the same time, and the mixed sand liquid is formed through high-speed stirring; Then, a foaming agent is added to the sand-mixing liquid to form a sand-mixing liquid containing the foaming agent; Then, the sand-mixing liquid containing the foaming agent is passed through the pipeline through the high-pressure manifold into the foam generating intensifier, and nitrogen is introduced into the pipeline through the first nitrogen inlet pipe and the second nitrogen inlet pipe respectively to form a low-density and high-quality foam sand-mixing liquid; Finally, the low-density high-quality foam sand-mixing fluid is introduced into the wellhead along the pipeline.

7. The oil wellhead fracturing method according to claim 6, characterized in that: The stirring speed is ≥1200 rpm.

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