Water injection reservoir large well section multi-layer mechanical water finding and chemical water plugging integrated pipe column

Abstract

The application discloses a water injection reservoir large well section multilayer mechanical water finding and chemical water plugging integrated pipe column, which can realize separate layer mining, separate layer plugging, and makes the production potential of the oil well maximized; the pipe column comprises a suspension device, a pumping unit, a casing, a plurality of packers, a plurality of electric valves, a plurality of multifunctional check valves and a tubing; the pumping unit and the tubing are connected with the suspension device, and the pumping unit is arranged in the tubing; the tubing comprises a plurality of tubing sections; the plurality of packers are connected with corresponding tubing sections; each two adjacent packers and the packer at the bottom end and the well bottom are taken as one oil production unit; each oil production unit is provided with an electric valve and a multifunctional check valve.

Description

Technical Field

[0001] This invention belongs to the field of water shut-off in oil wells and relates to a water-finding and shut-off process for reducing water cut in oil wells and improving the development effect of water-injected oil reservoirs, specifically involving a multi-layer mechanical water-finding and chemical water shut-off integrated tubing string for large well sections in water-injected oil reservoirs. Background Technology

[0002] The Shuguang Oilfield's water-injected reservoirs have entered a "high-water-cut" development stage, with prominent horizontal and vertical contradictions, severe local water flooding and water channeling, and a significant problem of high water cut in the production wells. Statistics show that there are currently 165 oil wells in the water-injected reservoirs with a water cut exceeding 85%, producing 5465 tons of fluid and 269 tons of oil per day, with a water cut of 95.1%. These high-water-cut wells account for 21% of all light oil wells in operation, 76.4% of total fluid production, and 31.8% of total oil production. Currently used conventional mechanical water shut-off tubing cannot achieve the purpose of changing layers with a single tubing run. Mechanical water shut-off with multiple tubing runs is costly and has a short effective period. In terms of water shut-off, mechanical water shut-off can only achieve isolation within the wellbore. Moreover, due to the long water injection reservoir sections and multiple water-producing layers in Shuguang Oilfield, it is far from sufficient in terms of accuracy and sealing strength. Chemical water shut-off can only adopt a general water shut-off process at present. It is difficult to identify the water-producing layers, has poor targeting, and has poor water shut-off effect. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention provides an integrated multi-layer mechanical water-finding and chemical water-plugging tubing string for large well sections in water-injected oil reservoirs, forming a water-plugging process suitable for water-injected oil reservoirs, improving water-plugging effect and reducing the cost of measures.

[0004] The technical solution adopted by this invention to solve its technical problem is: an integrated tubing string for multi-layer mechanical water finding and chemical water shut-off in a large well section of a water-injection oil reservoir, comprising: a suspension device, a pump, casing, several packers, several electric valves, several multi-functional check valves, and tubing. The tubing extends into the casing, and an annular space is formed between the tubing and the casing. The pump is connected to the bottom end of the suspension device, and the tubing is connected to the outer wall of the suspension device and fitted onto the outside of the pump. The tubing includes several tubing sections, and several packers are connected to the outer walls of the corresponding tubing sections. Each pair of adjacent packers and the bottom of the well serve as an oil production unit. Each oil production unit is equipped with an electric valve and a multi-functional check valve.

[0005] Furthermore, the tubing comprises at least three tubing segments.

[0006] Furthermore, the suspension device includes a joint, a coupling, a screen tube, and a central tube; the outer wall of the top of the central tube is connected to the inner wall of the bottom of the joint, the outer wall of the bottom of the joint is connected to the inner wall of the top of the coupling, the inner wall of the bottom of the coupling is connected to the outer wall of the top of the screen tube, the diameter of the screen tube is larger than the diameter of the central tube, and the screen tube is fitted onto the outside of the central tube; the bottom of the central tube is connected to an oil pump, and the bottom of the screen tube is connected to the uppermost oil pipe section.

[0007] Furthermore, the packer includes packer a, packer b, and packer c, which are respectively fitted onto the outer walls of three tubing sections from top to bottom. An electric valve a and a multi-functional check valve a are connected to the tubing between packer a and packer b. The electric valve a is directly connected to the multi-functional check valve a, or connected to the multi-functional check valve a through several tubing sections. An electric valve b and a multi-functional check valve b are connected to the tubing between packer b and packer c. The electric valve b is directly connected to the multi-functional check valve b, or connected to the multi-functional check valve b through several tubing sections. An electric valve c and a multi-functional check valve c are connected to the tubing between packer c and the bottom of the well. The electric valve c is directly connected to the multi-functional check valve c, or connected to the multi-functional check valve c through several tubing sections.

[0008] Furthermore, the electric valve includes a valve body a, a motor a, a piston a, and an inlet / outlet port; the valve body a is hollow inside, and its side wall has an inlet / outlet port that can connect its internal and external spaces; a motor a is fitted outside the valve body a, and a piston a is provided between the motor a and the valve body a; the piston a is driven by the motor a and can slide vertically along the outer wall of the valve body a to block or open the inlet / outlet port.

[0009] Furthermore, the multifunctional single-flow valve includes a valve body b, a valve seat, a valve cover, a valve ball, and an inlet channel; the valve body b is hollow inside, with a protruding part protruding outward in its middle section, and an L-shaped inlet channel that can connect its internal and external spaces is opened in the protruding part. The axial part of the inlet channel is provided with a valve cover and a valve seat. A through hole is opened in the middle of the valve seat, and several channels are opened on the valve cover. A valve ball is provided between the valve seat and the valve cover, and the diameter of the valve ball is larger than the diameter of the through hole.

[0010] Furthermore, the valve seat is located at the inlet port and is connected to the axial portion of the inlet channel via threads.

[0011] Furthermore, the multi-functional single-flow valve also includes a motor b and a piston b. The outer wall of the valve body b is fitted with a motor b and a piston b driven by the motor b. The piston b is located above the axial portion of the inlet channel and corresponds to the axial portion of the inlet channel, so as to move vertically under the drive of the motor b to block or open the inlet channel.

[0012] The beneficial effects of this invention include: the multi-layer mechanical water-finding and chemical water-plugging integrated tubing string provided by this invention for large well sections of water-injected oil reservoirs forms a multi-layer water-finding and water-plugging process for large well sections of water-injected oil reservoirs, which can achieve targeted treatment of high water-cut layers and realize layered development and layered chemical plugging of more than 3 layers. After the application of this tubing string, the overall water cut of the oil well can be effectively reduced and the crude oil production can be increased. This invention is particularly suitable for oil wells in water-injected development of light oil reservoirs, effectively ensuring the utilization of reserves in water-producing wells, helping to solve the problem of inefficient and ineffective water circulation, improving the overall development effect of water-injected oil reservoirs, and at the same time, this water-finding and water-plugging tubing string can also effectively reduce costs and has broad application prospects. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the overall structure of the present invention;

[0014] Figure 2 This is a schematic diagram of the suspension device structure of the present invention;

[0015] Figure 3 This is a schematic diagram of the multifunctional single-flow valve structure of the present invention;

[0016] Figure 4 This is a schematic diagram of the electric valve structure of the present invention;

[0017] Figure 5 yes Figure 4 The diagram showing the changing states.

[0018] The following are the annotations in the attached diagram: 1. Suspension device; 1-1. Connector; 1-2. Coupling; 1-3. Screen pipe; 1-4. Central pipe; 2. Oil pump; 4. Casing; 5. Packer a; 6. Electric valve a; 6-1. Valve body a; 6-2. Motor a; 6-3. Piston a; 6-4. Inlet / outlet; 7. Multifunctional check valve a; 7-1. Valve body b; 7-2. Motor b; 7-3. Piston b; 7-4. Valve seat; 7-5. Valve cover; 7-6. Valve ball; 7-7. Inlet channel; 8. Packer b; 9. Electric valve b; 10. Multifunctional check valve b; 11. Packer c; 12. Electric valve c; 13. Multifunctional check valve c; 14. Plug; 15. Oil pipe. Detailed Implementation

[0019] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] In the description of this invention, it should be noted that the terms "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or component referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used only to distinguish components and should not be construed as indicating or implying relative importance.

[0021] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0022] Example 1

[0023] The existing method of separating chemical water shut-off and oil production into two separate tubing runs affects the production rate of oil wells. Furthermore, the operation inevitably causes environmental pollution. This embodiment provides an integrated tubing string for multi-layer mechanical water finding and chemical water shut-off in a large section of a water-injection reservoir. This allows for layered production and layered water shut-off, maximizing the production potential of the oil well. The tubing includes: a suspension device 1, a pumping unit 2, casing 4, several packers, several electric valves, several multi-functional check valves, and tubing 15.

[0024] The oil pump 2 is located inside the oil pipe 15, which extends into the casing 4, and an annular space is formed between the oil pipe 15 and the casing 4. In this embodiment, the oil pipe 15 includes a first oil pipe segment, a second oil pipe segment, a third oil pipe segment, a fourth oil pipe segment, a fifth oil pipe segment, a sixth oil pipe segment, and a tail oil pipe segment.

[0025] The suspension device 1 includes a connector 1-1, a coupling 1-2, a screen tube 1-3, and a central tube 1-4.

[0026] The top of the connector 1-1 is used to connect to the upper oil pipe. The top outer wall of the central pipe 1-4 is connected to the bottom inner wall of the connector 1-1. The bottom outer wall of the connector 1-1 is connected to the top inner wall of the coupling 1-2. The bottom inner wall of the coupling 1-2 is connected to the top outer wall of the screen pipe 1-3. The diameter of the screen pipe 1-3 is larger than the diameter of the central pipe 1-4, and the screen pipe 1-3 is fitted on the outside of the central pipe 1-4.

[0027] The bottom of the central pipe 1-4 is connected to the oil pump 2, and the bottom of the screen pipe 1-3 is connected to the first oil pipe section.

[0028] Electric valves include electric valves a6, b9, and c12 with the same structure; multi-functional check valves include multi-functional check valves a7, b10, and c13 with the same structure.

[0029] The bottom of the first oil pipe section is connected to electric valve a6. The bottom of electric valve a6 is connected to the second oil pipe section. The bottom of the second oil pipe section is connected to multi-functional check valve a7. The bottom of multi-functional check valve a7 is connected to the third oil pipe section. The bottom of the third oil pipe section is connected to electric valve b9. The bottom of electric valve b9 is connected to the fourth oil pipe section. The bottom of the fourth oil pipe section is connected to multi-functional check valve b10. The bottom of multi-functional check valve b10 is connected to the fifth oil pipe section. The bottom of the fifth oil pipe section is connected to electric valve c12. The bottom of electric valve c12 is connected to the sixth oil pipe section. The bottom of the sixth oil pipe section is connected to multi-functional check valve c13. The bottom of multi-functional check valve c13 is connected to the tail oil pipe section. The end of the tail oil pipe section is connected to plug 14.

[0030] The packers include packer a5, packer b8, and packer c11;

[0031] Packer a5 is fitted onto the outer wall of the first tubing section via threads, packer b8 is fitted onto the outer wall of the third tubing section via threads, and packer c11 is fitted onto the outer wall of the fifth tubing section via threads.

[0032] The first oil production unit is located between packer a5 and packer b8, the second oil production unit is located between packer b8 and packer c11, and the third oil production unit is located between packer c11 and the bottom of the well.

[0033] Taking electric valve A6 as an example, its structure is explained as follows:

[0034] The electric valve a6 includes a valve body a6-1, a motor a6-2, a piston a6-3, and inlet / outlet ports 6-4.

[0035] The valve body a6-1 is hollow inside, and its side wall has an inlet / outlet port 6-4 that can connect its internal and external spaces. A motor a6-2 is installed on the outside of the valve body a6-1. A piston a6-3 is provided between the motor a6-2 and the valve body a6-1. The piston a6-3 is driven by the motor a6-2 and can slide vertically along the outer wall of the valve body a6-1 to block or open the inlet / outlet port 6-4.

[0036] Taking the multi-functional single-flow valve a7 as an example, its structure is explained as follows:

[0037] The multi-functional single-flow valve a7 includes a valve body b7-1, a motor b7-2, a piston b7-3, a valve seat 7-4, a valve cover 7-5, a valve ball 7-6, and an inlet channel 7-7.

[0038] The valve body b7-1 is hollow inside, with a protruding part protruding outward in its middle section. An L-shaped liquid inlet channel 7-7 is provided in the protruding part to connect the internal and external spaces. The axial part of the liquid inlet channel 7-7 is provided with a valve cover 7-5 and a valve seat 7-4. The valve seat 7-4 is located at the port of the liquid inlet channel 7-7 and is connected to the axial part of the liquid inlet channel 7-7 by threads. A through hole is provided in the middle of the valve seat 7-4. Several channels are provided on the valve cover 7-5. A valve ball 7-6 is provided between the valve seat 7-4 and the valve cover 7-5. The diameter of the valve ball 7-6 is larger than the diameter of the through hole. A motor b7-2 and a piston b7-3 driven by the motor b7-2 are installed on the outer wall of the valve body b7-1. The piston b7-3 is located above the port of the axial part of the liquid inlet channel 7-7 and corresponds to the axial part of the liquid inlet channel 7-7, so as to move vertically under the drive of the motor b7-2 to block or open the liquid inlet channel 7-7.

[0039] During operation, after the tubing is lowered to the designed position inside casing 4, packers a5, b8, and c11 are set. If the pressure inside the tubing is greater than the pressure of one of the oil production units, the valve ball 7-6 of the multi-functional check valve corresponding to that oil production unit will block the valve seat 7-4 under pressure, i.e., the inlet channel 7-7 of the multi-functional check valve is blocked. If the pressure inside the tubing is less than the pressure of the oil production unit, the valve ball 7-6 of the multi-functional check valve corresponding to that oil production unit will move away from the through hole of the valve ball 7-6 under pressure, i.e., the inlet channel 7-7 of the multi-functional check valve is opened.

[0040] The pressure inside the tubing depends on the reservoir pressure corresponding to the first, second, and third oil production units. The reservoir with the highest pressure is extracted first, and when the pressures of the corresponding reservoirs are equal, the three oil production units extract the reservoirs together.

[0041] When well washing is required, well washing fluid is injected through the annular space between tubing 15 and casing 4. The well washing fluid enters the tubing 15 through screen pipe 1-3 and then enters the lower part of pumping pump 2. At this time, because the pressure inside the tubing string is greater than the pressure of the three production units, the fluid inlet channels of the three production units are blocked. The well washing fluid enters pumping pump 2 from the bottom and rises further to the surface to complete a flushing process until the cleanliness of the returned well washing fluid meets the requirements.

[0042] When it is necessary to test the production status of three oil production units separately, two of the following valves—multifunctional check valves a7, b10, and c13—are closed via ground control, leaving only one open. Specifically, the pistons b7-3 of the two multifunctional check valves are driven by the corresponding motor b7-2 to move downwards and block the valve seats 7-4, thereby blocking the fluid inlet channel 7-7. The multifunctional check valves a7, b10, and c13 are then opened alternately to complete the testing.

[0043] When chemical water shut-off is decided based on test results, the multi-functional check valve corresponding to the oil production unit that is not chemically shut off is closed, and the electric valve corresponding to the oil production unit that is chemically shut off is opened. For example, when chemical shut-off is performed on the first oil production unit, multi-functional check valves B10 and C13, as well as the outlet of pump 2, need to be closed. Electric valve A6 is opened, meaning piston A6-3 moves upward under the drive of the corresponding motor A6-2, opening the inlet / outlet ports 6-4. At this time, chemical plugging agent is injected into the annular space of the casing and tubing. When the injected chemical plugging agent reaches the designed amount, cleaning fluid is injected into the annular space of the casing and tubing for tubing cleaning. When the returned fluid reaches the cleanliness requirement, cleaning is stopped. Multi-functional check valves A7, B10, and C13 are then opened for oil production.

[0044] Based on the above implementation plan, it is possible to achieve layered mining and layered plugging of more than three layers, with an effective period longer than conventional water plugging. It is suitable for oil wells in water injection development of light oil reservoirs, effectively ensuring the utilization of reserves in water-producing wells, helping to solve the problem of inefficient and ineffective water circulation, and improving the overall development effect of water-injected reservoirs. At the same time, this water plugging string can also effectively reduce costs and has broad application prospects.

[0045] Example 2

[0046] The difference between this embodiment and Embodiment 1 is that:

[0047] The tubing 15 includes a first tubing section, a second tubing section, a third tubing section, and a tail tubing section; packers a5, b8, and c11 are respectively connected to the outer walls of the first tubing section, the second tubing section, and the third tubing section;

[0048] The bottom of the first oil pipe section is connected to electric valve a6. The bottom of electric valve a6 is connected to multi-functional check valve a7. The bottom of multi-functional check valve a7 is connected to the second oil pipe section. The bottom of the second oil pipe section is connected to electric valve b9. The bottom of electric valve b9 is connected to multi-functional check valve b10. The bottom of multi-functional check valve b10 is connected to the third oil pipe section. The bottom of the third oil pipe section is connected to electric valve c12. The bottom of electric valve c12 is connected to multi-functional check valve c13. The bottom of multi-functional check valve c13 is connected to the tail oil pipe section. The end of the tail oil pipe section is connected to plug 14.

[0049] Example 3

[0050] The difference between this embodiment and Embodiment 2 is as follows:

[0051] Oil pipe 15 includes a first oil pipe section, a second oil pipe section, and a third oil pipe section;

[0052] The bottom of the first oil pipe section is connected to electric valve a6. The bottom of electric valve a6 is connected to multi-functional check valve a7. The bottom of multi-functional check valve a7 is connected to the second oil pipe section. The bottom of the second oil pipe section is connected to electric valve b9. The bottom of electric valve b9 is connected to multi-functional check valve b10. The bottom of multi-functional check valve b10 is connected to the third oil pipe section. The bottom of the third oil pipe section is connected to electric valve c12. The bottom of electric valve c12 is connected to multi-functional check valve c13. The bottom of multi-functional check valve c13 is connected to plug 14.

[0053] Example 4

[0054] The difference between this embodiment and Embodiment 1 is that:

[0055] Oil pipe 15 includes a first oil pipe segment, a second oil pipe segment, a third oil pipe segment, a fourth oil pipe segment, a fifth oil pipe segment, and a sixth oil pipe segment;

[0056] The bottom of the first oil pipe section is connected to electric valve a6. The bottom of electric valve a6 is connected to the second oil pipe section. The bottom of the second oil pipe section is connected to multi-functional check valve a7. The bottom of multi-functional check valve a7 is connected to the third oil pipe section. The bottom of the third oil pipe section is connected to electric valve b9. The bottom of electric valve b9 is connected to the fourth oil pipe section. The bottom of the fourth oil pipe section is connected to multi-functional check valve b10. The bottom of multi-functional check valve b10 is connected to the fifth oil pipe section. The bottom of the fifth oil pipe section is connected to electric valve c12. The bottom of electric valve c12 is connected to the sixth oil pipe section. The bottom of the sixth oil pipe section is connected to multi-functional check valve c13. The bottom of multi-functional check valve c13 is connected to plug 14.

[0057] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A multi-layer integrated tubing string for mechanical water finding and chemical water shut-off in a large well section of a water-injected oil reservoir, characterized in that, include: The equipment includes a suspension device (1), a pump (2), a casing (4), several packers, several electric valves, several multi-functional check valves, and tubing (15). The tubing (15) extends into the casing (4), and an annular space is formed between the tubing (15) and the casing (4). The pump (2) is connected to the bottom of the suspension device (1), and the tubing (15) is connected to the outer wall of the suspension device (1) and fitted onto the outside of the pump (2). The tubing (15) includes several tubing sections, and several packers are connected to the outer wall of the corresponding tubing sections. Each pair of adjacent packers and the bottom packer and the bottom of the well are respectively used as an oil production unit. Each oil production unit is equipped with an electric valve and a multi-functional check valve. The oil pipe (15) comprises at least three oil pipe segments; The suspension device (1) includes a connector (1-1), a coupling (1-2), a screen pipe (1-3), and a central pipe (1-4); the top outer wall of the central pipe (1-4) is connected to the bottom inner wall of the connector (1-1), the bottom outer wall of the connector (1-1) is connected to the top inner wall of the coupling (1-2), the bottom inner wall of the coupling (1-2) is connected to the top outer wall of the screen pipe (1-3), the diameter of the screen pipe (1-3) is larger than the diameter of the central pipe (1-4), and the screen pipe (1-3) is fitted on the outside of the central pipe (1-4); the bottom of the central pipe (1-4) is connected to the oil pump (2), and the bottom of the screen pipe (1-3) is connected to the uppermost oil pipe section; The packer includes packer a (5), packer b (8), and packer c (11), which are respectively fitted onto the outer walls of three tubing sections from top to bottom. An electric valve a (6) and a multi-functional check valve a (7) are connected to the tubing between packer a (5) and packer b (8). The electric valve a (6) is directly connected to the multi-functional check valve a (7), or connected to the multi-functional check valve a (7) through several tubing sections. The tubing between packer b (8) and packer c (11) is connected to... There is an electric valve b (9) and a multi-functional check valve b (10). The electric valve b (9) is directly connected to the multi-functional check valve b (10), or is connected to the multi-functional check valve b (10) through several tubing sections. The packer c (11) and the bottom of the well are connected to an electric valve c (12) and a multi-functional check valve c (13). The electric valve c (12) is directly connected to the multi-functional check valve c (13), or is connected to the multi-functional check valve c (13) through several tubing sections. The multi-functional single-flow valve includes a valve body b (7-1), a valve seat (7-4), a valve cover (7-5), a valve ball (7-6), and an inlet channel (7-7). The valve body b (7-1) is hollow inside, with a protruding part protruding outward in its middle section. An L-shaped inlet channel (7-7) is provided in the protruding part to connect its internal and external spaces. The axial part of the inlet channel (7-7) is provided with a valve cover (7-5) and a valve seat (7-4). A through hole is provided in the middle of the valve seat (7-4). Several channels are provided on the valve cover (7-5). A valve ball (7-6) is provided between the valve seat (7-4) and the valve cover (7-5). The diameter of the valve ball (7-6) is larger than the diameter of the through hole.

2. The integrated multi-layer mechanical water-finding and chemical water-plugging tubing string for large well sections of water-injected oil reservoirs according to claim 1, characterized in that, The electric valve includes a valve body a (6-1), a motor a (6-2), a piston a (6-3), and an inlet / outlet port (6-4). The valve body a (6-1) is hollow inside, and its side wall has an inlet / outlet port (6-4) that can connect its internal and external spaces. The motor a (6-2) is fitted outside the valve body a (6-1). The piston a (6-3) is provided between the motor a (6-2) and the valve body a (6-1). The piston a (6-3) is driven by the motor a (6-2) and can slide vertically along the outer wall of the valve body a (6-1) to block or open the inlet / outlet port (6-4).

3. The integrated multi-layer mechanical water-finding and chemical water-plugging tubing string for large well sections of water-injected oil reservoirs according to claim 1, characterized in that, The valve seat (7-4) is located at the port of the liquid inlet channel (7-7) and is connected to the axial portion of the liquid inlet channel (7-7) by means of threads.

4. The integrated multi-layer mechanical water-finding and chemical water-plugging tubing string for large well sections of water-injected oil reservoirs according to claim 1, characterized in that, The multi-functional single-flow valve also includes a motor b (7-2) and a piston b (7-3). The outer wall of the valve body b (7-1) is fitted with a motor b (7-2) and a piston b (7-3) driven by the motor b (7-2). The piston b (7-3) is located above the axial portion of the inlet channel (7-7) and corresponds to the axial portion of the inlet channel (7-7) so that it can move vertically under the drive of the motor b (7-2) to block or open the inlet channel (7-7).

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