Fracturing string capable of reducing nitrogen foam fracturing friction and fracturing method thereof

Abstract

The fracturing string capable of reducing the nitrogen foam fracturing friction resistance comprises a casing pipe, a safety connector, a hydraulic anchor and a packer are arranged in the casing pipe, the safety connector, the hydraulic anchor and the packer are sequentially connected through a tool string, the end, away from the hydraulic anchor, of the packer is connected with a horn mouth through the tool string, and the end, away from the hydraulic anchor, of the packer is connected with the horn mouth through the tool string. A sleeve head is arranged at the end opening, close to the safety connector, of the sleeve, and the other end of the tool string penetrates through the sleeve head. The invention further discloses a fracturing method, and the fracturing tubular column capable of reducing the fracturing friction resistance of the nitrogen foam and the fracturing method of the fracturing tubular column solve the problems that in the fracturing process in the prior art, the friction resistance is large, and the pressure borne by a casing head is insufficient.

Description

Technical Field

[0001] The invention belongs to the technical field of tight gas exploitation, relates to a fracturing pipe column for reducing friction resistance of nitrogen foam fracturing, and also relates to a fracturing method. Background Art

[0002] In addition to the characteristics of "low permeability, low pressure, and low abundance" of tight gas reservoirs, the complex pore throat structure, small pore throat radius, and large pore throat ratio of the reservoir have caused serious reservoir pore water lock problems. At the same time, the ability to return the reservoir's own energy is poor and slow, and the fracturing fluid retained in the formation causes great damage to the formation; this block is dry and water-scarce due to geographical reasons. The use of nitrogen foam fracturing to improve the return capacity of the fracturing fluid can effectively solve the problems of fracturing fluid loss and damage caused by retained formations in the transformation of low-pressure and low-permeability oil and gas reservoirs. Combined with the previous layer conversion or repeated transformation of old wells, due to the problem of insufficient pressure on the casing head of the old well production casing, the friction resistance of the nitrogen foam fracturing construction is large, the wellhead pressure is high, the scale of fracturing is limited, and the fracturing transformation effect is affected. Summary of the invention

[0003] The first purpose of the present invention is to provide a fracturing string that reduces the friction resistance of nitrogen foam fracturing, thereby solving the problems of large friction resistance and insufficient pressure bearing of the casing head during the fracturing process in the prior art.

[0004] A second object of the present invention is to provide a method for fracturing using a fracturing string that reduces nitrogen foam fracturing friction.

[0005] The first technical solution adopted by the present invention is a fracturing string for reducing friction resistance of nitrogen foam fracturing, including a casing, a safety joint, a hydraulic anchor and a packer are arranged in the casing, the safety joint, the hydraulic anchor and the packer are connected in sequence through a tool string, one end of the packer away from the hydraulic anchor is connected with a bell mouth through the tool string, a casing head is arranged at the end of the casing close to the safety joint, and the other end of the tool string passes through the casing head.

[0006] The first technical solution of the present invention is also characterized in that: The tubing string includes multiple tubings, one end of each of which passes through the casing head, and the safety joint, hydraulic anchor and packer are connected in sequence through the multiple tubings, and the multiple tubings are commonly connected to the bellmouth.

[0007] The number of oil pipes is 4 or 5, the length of the multiple oil pipes is 40-50m, and the diameters of the multiple oil pipes are 73mm or 89mm.

[0008] A plurality of reservoir perforations are provided on the casing wall near the bell mouth.

[0009] The second technical solution adopted by the present invention is a fracturing method, which uses a fracturing string that reduces the friction resistance of nitrogen foam fracturing, and the specific steps are as follows: S1, preparing fracturing fluid by continuous mixing; S2, adopts the combined injection method of tubing and casing, injects the fracturing fluid into the tubing by pressure, and the fracturing fluid flows through the tubing in sequence through the hydraulic anchor, the packer and the bell mouth, and finally flows out into the casing through the bell mouth. The fracturing fluid enters the reservoir through the casing and the reservoir perforations to complete the fracturing.

[0010] The second technical solution of the present invention is also characterized in that: The pH value of the water used to prepare the fracturing fluid in S1 is 6.5-7.5, and the content of mechanical impurities is not more than 0.2%.

[0011] When the pressure in S2 exceeds 35Mpa, the annulus begins to increase the balance pressure, and the pressure difference between the tubing and the casing is controlled to be no more than 45Mpa.

[0012] The increased balance pressure shall not exceed 25Mpa.

[0013] The packer's pressure resistance is no less than 70Mpa.

[0014] Compared with the prior art, the present invention has the following beneficial effects: (1) The fracturing string and fracturing method for reducing friction of nitrogen foam fracturing of the present invention are suitable for depleted or underpressure wells, water-sensitive formations, and low-permeability gas wells. Nitrogen foam fracturing technology is used to increase reservoir energy. The combined injection method of tubing + casing is used, and a 40-50m tubing is used for injection at the wellhead. The fluid flows through the bell mouth and is then injected into the casing. The fracturing method can increase the displacement, reduce the amount of fluid entering the well, reduce reservoir damage, increase the flowback rate, and increase gas production.

[0015] (2) The fracturing string and fracturing method for reducing friction during nitrogen foam fracturing of the present invention effectively reduce friction during fracturing construction by 20-30 MPa, and the pump pressure during nitrogen foam fracturing construction of 73 mm oil pipe is reduced by 20%-28%. Safety risks during fracturing construction are reduced.

[0016] (3) The fracturing string and fracturing method for reducing friction of nitrogen foam fracturing of the present invention have a foam mass of sand-carrying liquid of 65-80%, and the amount of sand added is increased by 3.2% compared with nitrogen foam fracturing of oil pipes, and the maximum sand ratio is increased from 69.8% to 84%.

[0017] (4) The fracturing string and fracturing method for reducing friction of nitrogen foam fracturing of the present invention have high liquid efficiency, less liquid volume entering the ground, and the liquid volume per cubic meter of sand is 10m3 / s compared with 10m3 / s for conventional fracturing. 3 Reduced to 4m 3, low reservoir damage. And the liquid nitrogen ratio reaches 105%, which is much higher than the 7.6% liquid nitrogen ratio of conventional hydraulic fracturing. Increase reservoir energy and increase the return rate to more than 90%. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the structure of a fracturing string for reducing frictional resistance of nitrogen foam fracturing according to the present invention.

[0019] In the figure, 1. tool string, 2. casing head, 3. safety joint, 4. hydraulic anchor, 5. packer, 6. bell mouth, 7. casing, 8. reservoir perforation, 9. artificial bottom hole. DETAILED DESCRIPTION

[0020] The present invention will be further explained below in conjunction with the accompanying drawings and specific embodiments.

[0021] The present invention provides a fracturing column for reducing the friction resistance of nitrogen foam fracturing, such as Figure 1 As shown, it includes a casing 7, in which a safety joint 3, a hydraulic anchor 4 and a packer 5 are arranged, the safety joint 3, the hydraulic anchor 4 and the packer 5 are connected in sequence through a tool string 1, one end of the packer 5 away from the hydraulic anchor 4 is connected with a bell mouth 6 through the tool string 1, a casing head 2 is arranged at the end of the casing 7 close to the safety joint 3, and the other end of the tool string 1 penetrates the casing head 2; the tool string 1 includes a plurality of oil pipes, one end of the plurality of oil pipes all penetrates the casing head 2, the safety joint 3, the hydraulic anchor 4 and the packer 5 are connected in sequence through the plurality of oil pipes, and the plurality of oil pipes are connected to the bell mouth 6 together; the number of oil pipes is 4-5, the length of the plurality of oil pipes is 40-50m, and the diameters of the plurality of oil pipes are all 73mm or 89mm; a plurality of reservoir perforations 8 are opened on the pipe wall of the casing 7 close to the bell mouth 6, and the bottom of the casing 7 is an artificial well bottom 9.

[0022] Among them, the hydraulic anchor 4 is used to fix the oil pipe and the packer 5 during the fracturing construction. The packer 5 can isolate the pressure transmission during the fracturing construction to protect the old well casing from the condition where the fracturing casing head cannot withstand the pressure required by the construction. At the same time, after the packer 5 is sealed and pressurized, its rubber expands and forms a sealing state with the inner wall of the casing 7.

[0023] The present invention also provides a method for fracturing using a fracturing string that reduces nitrogen foam fracturing friction, the specific steps of which are as follows: S1, preparing fracturing fluid by continuous mixing; Among them, the water quality pH value of the fracturing fluid is 6.5-7.5, and the content of mechanical impurities is not more than 0.2%.

[0024] S2, adopts the combined injection method of oil pipe and casing 7, injects the fracturing fluid into the oil pipe by pressure, and the fracturing fluid flows through the hydraulic anchor 4, the packer 5 and the bell mouth 6 in sequence through the oil pipe, and finally flows out into the casing 7 through the bell mouth 6, and the fracturing fluid enters the reservoir perforation 8 through the casing 7, and enters the reservoir through the reservoir perforation 8 to complete the fracturing.

[0025] During the construction process, the fracturing fluid flows from the tool string 1 into the casing 7, and the inner diameter becomes larger. This combined injection method achieves a significant reduction in friction resistance.

[0026] When the pressure exceeds 35 MPa, the balance pressure begins to increase, and the pressure difference between the oil pipe and the casing 7 is controlled to be no more than 45 MPa, and the increased balance pressure is no more than 25 MPa, while ensuring that the pressure resistance of the packer 5 is no less than 70 MPa.

[0027] Example 1 This embodiment provides a fracturing string for reducing friction of nitrogen foam fracturing, such as Figure 1 As shown, it includes a casing 7, in which a safety joint 3, a hydraulic anchor 4 and a packer 5 are arranged. The safety joint 3, the hydraulic anchor 4 and the packer 5 are connected in sequence through a tool string 1. The end of the packer 5 away from the hydraulic anchor 4 is connected with a bell mouth 6 through the tool string 1. A casing head 2 is arranged at the end of the casing 7 close to the safety joint 3, and the other end of the tool string 1 passes through the casing head 2.

[0028] Example 2 This embodiment provides a fracturing string for reducing friction of nitrogen foam fracturing, such as Figure 1 As shown, it includes a casing 7, in which a safety joint 3, a hydraulic anchor 4 and a packer 5 are arranged, and the safety joint 3, the hydraulic anchor 4 and the packer 5 are sequentially connected through a tool string 1, and the end of the packer 5 away from the hydraulic anchor 4 is connected to a bell mouth 6 through the tool string 1, and a casing head 2 is arranged at the end of the casing 7 close to the safety joint 3, and the other end of the tool string 1 penetrates the casing head 2. The tool string 1 includes 5 oil pipes with a length of 50m, and the diameter of the 5 oil pipes is 73mm, and one end of the 5 oil pipes penetrates the casing head 2, and the safety joint 3, the hydraulic anchor 4 and the packer 5 are sequentially connected through the 5 oil pipes, and the 5 oil pipes are connected to the bell mouth 6 together.

[0029] Example 3 This embodiment provides a fracturing string for reducing friction of nitrogen foam fracturing, such as Figure 1As shown, it includes a casing 7, in which a safety joint 3, a hydraulic anchor 4 and a packer 5 are arranged. The safety joint 3, the hydraulic anchor 4 and the packer 5 are connected in sequence through a tool string 1. The end of the packer 5 away from the hydraulic anchor 4 is connected to a bell mouth 6 through the tool string 1. The end of the casing 7 close to the safety joint 3 is provided with a casing head 2, and the other end of the tool string 1 penetrates the casing head 2. The tool string 1 includes 5 oil pipes with a length of 50m, and the diameter of the 5 oil pipes is 73mm. One end of the 5 oil pipes penetrates the casing head 2, and the safety joint 3, the hydraulic anchor 4 and the packer 5 are connected in sequence through the 5 oil pipes, and the 5 oil pipes are connected to the bell mouth 6 together. A number of reservoir perforations 8 are opened on the pipe wall of the casing 7 close to the bell mouth 6, and the bottom of the casing 7 is an artificial well bottom 9.

[0030] Example 4 This embodiment provides a fracturing string for reducing friction of nitrogen foam fracturing, such as Figure 1 As shown, it includes a casing 7, in which a safety joint 3, a hydraulic anchor 4 and a packer 5 are arranged. The safety joint 3, the hydraulic anchor 4 and the packer 5 are connected in sequence through a tool string 1, and one end of the packer 5 away from the hydraulic anchor 4 is connected with a bell mouth 6 through the tool string 1. A casing head 2 is arranged at the end of the casing 7 close to the safety joint 3, and the other end of the tool string 1 passes through the casing head 2; the tool string 1 includes 5 oil pipes with a length of 50m, and the diameter of the 5 oil pipes is 89mm, one end of the 5 oil pipes passes through the casing head 2, the safety joint 3, the hydraulic anchor 5 and the packer 5 are connected in sequence through 4 oil pipes, and the 5 oil pipes are connected to the bell mouth 6 together, a plurality of reservoir perforations 8 are opened on the pipe wall of the casing 7 close to the bell mouth 6, and the bottom of the casing 7 is an artificial well bottom 9.

[0031] Example 5 This embodiment provides a fracturing string for reducing friction of nitrogen foam fracturing, such as Figure 1 As shown, it includes a casing 7, in which a safety joint 3, a hydraulic anchor 4 and a packer 5 are arranged. The safety joint 3, the hydraulic anchor 4 and the packer 5 are connected in sequence through a tool string 1, and one end of the packer 5 away from the hydraulic anchor 4 is connected with a bell mouth 6 through the tool string 1. A casing head 2 is arranged at the end of the casing 7 close to the safety joint 3, and the other end of the tool string 1 passes through the casing head 2; the tool string 1 includes 4 oil pipes with a length of 40m, and the diameter of the 4 oil pipes is 89mm, one end of the 4 oil pipes passes through the casing head 2, the safety joint 3, the hydraulic anchor 4 and the packer 5 are connected in sequence through the 4 oil pipes, and the 4 oil pipes are connected to the bell mouth 6 together, a plurality of reservoir perforations 8 are opened on the pipe wall of the casing 7 close to the bell mouth 6, and the bottom of the casing 7 is an artificial well bottom 9.

[0032] Example 6 This embodiment provides a fracturing string for reducing friction of nitrogen foam fracturing, such as Figure 1As shown, it includes a casing 7, in which a safety joint 3, a hydraulic anchor 4 and a packer 5 are arranged, the safety joint 3, the hydraulic anchor 4 and the packer 5 are connected in sequence through a tool string 1, one end of the packer 5 away from the hydraulic anchor 4 is connected with a bell mouth 6 through the tool string 1, a casing head 2 is arranged at the end of the casing 7 close to the safety joint 3, and the other end of the tool string 1 passes through the casing head 2; the tool string 1 includes 4 oil pipes with a length of 40m, and the diameter of the 4 oil pipes is 73mm, one end of the 4 oil pipes passes through the casing head 2, the safety joint 3, the hydraulic anchor 4 and the packer 5 are connected in sequence through the 4 oil pipes, and the 4 oil pipes are connected to the bell mouth 6 together, a plurality of reservoir perforations 8 are opened on the pipe wall of the casing 7 close to the bell mouth 6, and the bottom of the casing 7 is an artificial well bottom 9.

[0033] Example 7 This embodiment provides a fracturing string for reducing friction of nitrogen foam fracturing, such as Figure 1 As shown, it includes a casing 7, in which a safety joint 3, a hydraulic anchor 4 and a packer 5 are arranged, the safety joint 3, the hydraulic anchor 4 and the packer 5 are connected in sequence through a tool string 1, one end of the packer 5 away from the hydraulic anchor 4 is connected with a bell mouth 6 through the tool string 1, a casing head 2 is arranged at the end of the casing 7 close to the safety joint 3, and the other end of the tool string 1 passes through the casing head 2; the tool string 1 includes 4 oil pipes with a length of 50m, and the diameter of the 4 oil pipes is 73mm, one end of the 4 oil pipes passes through the casing head 2, the safety joint 3, the hydraulic anchor 4 and the packer 5 are connected in sequence through the 4 oil pipes, and the 4 oil pipes are commonly connected to the bell mouth 6, a plurality of reservoir perforations 8 are opened on the pipe wall of the casing 7 close to the bell mouth 6, and the bottom of the casing 7 is an artificial well bottom 9.

[0034] Example 8 This embodiment provides a fracturing string for reducing friction of nitrogen foam fracturing, such as Figure 1 As shown, it includes a casing 7, in which a safety joint 3, a hydraulic anchor 4 and a packer 5 are arranged, the safety joint 3, the hydraulic anchor 4 and the packer 5 are connected in sequence through a tool string 1, one end of the packer 5 away from the hydraulic anchor 4 is connected with a bell mouth 6 through the tool string 1, a casing head 2 is arranged at the end of the casing 7 close to the safety joint 3, and the other end of the tool string 1 passes through the casing head 2; the tool string 1 includes 4 oil pipes with a length of 50m, and the diameter of the 4 oil pipes is 89mm, one end of the 4 oil pipes passes through the casing head 2, the safety joint 3, the hydraulic anchor 4 and the packer 5 are connected in sequence through the 4 oil pipes, and the 4 oil pipes are connected to the bell mouth 6 together, a plurality of reservoir perforations 8 are opened on the pipe wall of the casing 7 close to the bell mouth 6, and the bottom of the casing 7 is an artificial well bottom 9.

[0035] Example 9 This embodiment provides a fracturing method, using the fracturing string for reducing nitrogen foam fracturing friction provided in the above embodiment, and the specific steps are as follows: S1, preparing fracturing fluid by continuous mixing; Among them, the water quality pH value of the fracturing fluid is 6.5-7.5, and the content of mechanical impurities is not more than 0.2%.

[0036] S2, adopts the combined injection method of oil pipe and casing 7, injects fracturing fluid into the oil pipe by pressure, and the fracturing fluid flows through the hydraulic anchor 4, the packer 5 and the bell mouth 6 in sequence through the oil pipe, and finally flows out into the casing 7 through the bell mouth 6, and the fracturing fluid enters the reservoir through the casing 7 and the reservoir perforation 8 to complete the fracturing.

[0037] When the pressure exceeds 35 MPa, the balance pressure begins to increase, and the pressure difference between the oil pipe and the casing 7 is controlled to be no more than 45 MPa, and the increased balance pressure is no more than 25 MPa, while ensuring that the pressure resistance of the packer 5 is no less than 70 MPa.

[0038] Example 10 This embodiment adopts the fracturing string and fracturing method for reducing nitrogen foam fracturing friction provided in Embodiment 3 and Embodiment 9, which are specifically as follows: Select an old well to transfer layers and apply nitrogen foam fracturing, the layer is Shanxi Group 2 3 The depth of reservoir perforation is 3172m. Five 50m oil pipes are used, and the outer diameter of the oil pipe is 73mm. The 50m oil pipe + casing 7 combination injection method is used. At the beginning of the construction, the packer 5 is first sealed, and the fracturing fluid with a foam mass of 70% is added, which is equivalent to a bottom hole displacement of about 5.0m 3 / min. During the sand adding stage, the ground sand concentration is 12.0 PPA and the liquid volume per cubic meter of sand is 4m 3 / min, the proportion of liquid nitrogen reaches 105%, the construction pressure is stable during sand adding, the sand adding amount is completed according to the design requirements, and the construction pressure is 37.7-47.0MPa.

[0039] After the gas test as required, the return rate was 93%, the static pressure was 23.27MPa, and the stable gas production in 12 hours was 4.5×104m3 under the conditions of wellhead oil pressure of 11.3MPa and ф20.9mm orifice plate. 3 / d, the calculated unimpeded flow rate is 8.7×104m 3 / d.

[0040] Comparative Example 1 Select an old well to transfer layers and apply nitrogen foam fracturing, the layer is Shanxi Group 2 3 The perforation section corresponds to a depth of 3210m. The outer diameter of the applied tubing is 89mm. The injection is done using a 3210m tubing. The surface sand concentration is 2.9PPA, which is equivalent to a bottom hole displacement of about 3m 3 / min, construction pressure 57-68MPa, construction displacement is relatively low, and construction pressure is relatively high.

[0041] Select a gas well and apply conventional clean fracturing fluid, located in Shanxi Group 2 3 The perforation section corresponds to a depth of 2973m. Fracturing is carried out by injecting 73mm tubing, with a displacement of 3m 3 / min, construction pressure 57-70MPa, liquid volume per cubic meter of sand 10m 3 / min, liquid nitrogen ratio 7.6%.

[0042] It can be seen that the multiple oil pipes + casing 7 fracturing combination injection provided by the present invention can effectively reduce the friction resistance of the pipe column and achieve good gas production. After comparison, it can be seen that the fracturing method provided by the present invention significantly reduces the friction resistance of the pipe column, reduces the construction pump pressure by 20%-28%, increases the displacement relatively, and makes the reservoir transformation more sufficient, while reducing the construction safety risk.

[0043] The fracturing string and fracturing method for reducing nitrogen foam fracturing friction provided by the present invention are mainly suitable for layer transfer or repeated fracturing of old wells. At present, the existing technology adopts the fracturing method of oil pipe injection or the method of direct casing injection, and the method of casing injection of sand-carrying fluid makes the cracks generated in the formation longer. In view of the fact that the pressure bearing of the casing head of the old well cannot meet the set requirements, the present invention proposes the method of using multiple oil pipes and casings for combined injection, so as to protect the casing head and increase the injection and displacement of the fracturing pump.

Claims

1. A fracturing string for reducing friction in nitrogen foam fracturing, characterized in that: The invention comprises a casing (7), wherein a safety joint (3), a hydraulic anchor (4) and a packer (5) are arranged inside the casing (7), wherein the safety joint (3), the hydraulic anchor (4) and the packer (5) are connected in sequence through a tool string (1), wherein one end of the packer (5) away from the hydraulic anchor (4) is connected to a bell mouth (6) through the tool string (1), and a casing head (2) is arranged at a port of the casing (7) close to the safety joint (3), and the other end of the tool string (1) passes through the casing head (2).

2. The fracturing string for reducing friction of nitrogen foam fracturing according to claim 1, characterized in that: The tool string (1) comprises a plurality of oil pipes, one end of each of the plurality of oil pipes passes through a casing head (2), the safety joint (3), the hydraulic anchor (4) and the packer (5) are connected in sequence through the plurality of oil pipes, and the plurality of oil pipes are connected together to a bellmouth (6).

3. The fracturing string for reducing friction of nitrogen foam fracturing according to claim 2, characterized in that: The number of the oil pipes is 4 or 5, the length of the plurality of oil pipes is 40-50m, and the diameters of the plurality of oil pipes are 73mm or 89mm.

4. The fracturing string for reducing friction of nitrogen foam fracturing according to claim 3, characterized in that: A plurality of reservoir perforations (8) are provided on the wall of the casing (7) near the bell mouth (6).

5. A fracturing method, characterized in that: The fracturing string for reducing nitrogen foam fracturing friction as claimed in claim 4 is used, and the specific steps are as follows: S1, preparing fracturing fluid by continuous mixing; S2, adopting a combined injection method of the oil pipe and the casing (7), the fracturing fluid is injected into the oil pipe by pressure, the fracturing fluid flows through the oil pipe in sequence through the hydraulic anchor (4), the packer (5) and the bell mouth (6), and finally flows out into the casing (7) through the bell mouth (6), and the fracturing fluid enters the reservoir through the casing (7) and the reservoir perforation (8), thereby completing the fracturing.

6. The fracturing method according to claim 5, characterized in that: The pH value of the water used to prepare the fracturing fluid in S1 is 6.5-7.5, and the content of mechanical impurities is not more than 0.2%.

7. The fracturing method according to claim 5, characterized in that: When the pressure in S2 exceeds 35 MPa, the balance pressure starts to be increased to control the pressure difference between the oil pipe and the casing (7) to be no greater than 45 MPa.

8. The fracturing method according to claim 7, characterized in that: The increased balance pressure is no greater than 25 MPa.

9. The fracturing method according to claim 5, characterized in that: The packer has a pressure resistance of not less than 70 MPa.

Images