Pressure balancing device

Abstract

The invention provides a pressure balancing device. The pressure balancing device comprises a balancing bin, a piston, balancing fluid and an overflow valve, wherein the piston and the balancing fluid are located in the balancing bin, and the overflow valve is arranged on the wall of the balancing bin. The piston divides the balance bin into a first cavity and a second cavity, the first cavity is filled with the balance fluid, a communicating hole is formed in the position, at the second cavity, of the wall of the balance bin, and the second cavity is communicated with the outside of the balance bin through the communicating hole. The overflow valve is located in the first cavity. The pressure balancing device has the advantages that the reliability and safety problems of the pressure balancing device in the high-temperature environment are solved, meanwhile, the maintainability of the pressure balancing device is improved, and an underground instrument can be suitable for the underground high-temperature complex environment.

Description

Technical Field

[0001] The invention relates to the technical field of geophysical well logging, and in particular to a pressure balancing device for downhole instruments. Background Art

[0002] At present, the pressure balance devices used in downhole logging instruments mainly include: piston type, bladder type, and bellows type.

[0003] Among them, the bladder type is, first of all, relatively fragile. When working in a complex underground environment, it is easy to cause physical damage to the bladder, resulting in failure of the pressure balance device. Secondly, the volume change is small and the pressure balance capacity is limited. Under high temperature conditions, the silicone oil in the balance chamber expands to a large volume, which exceeds the elastic deformation range of the bladder itself, causing the bladder itself to rupture and damage. Thirdly, when there are gases such as hydrogen sulfide underground, it will directly cause the bladder itself to deteriorate and change in nature, bulge, increase in brittleness and damage. The actual application process also proves that the bladder type pressure balance device has the worst reliability and is the most easily damaged, especially in complex well conditions such as high temperature and high pressure, and when there is no cable logging process, when the instrument slides against the well wall, rock debris can easily scratch the bladder body and damage it, resulting in construction failure.

[0004] Among them, the bellows type has a very thin wall, poor mechanical strength and is relatively fragile. When it encounters the squeezing of rock debris and the scratching and bumping of irregular well walls underground, it is easy to cause the weak pipe wall to rupture and mud to invade, causing the pressure balance device to fail and damaging the instrument insulation and internal components. The bellows type has a small volume change and limited pressure balance capacity, and is not suitable for use in high temperature environments.

[0005] At present, the commonly used piston pressure balance device can adapt to the construction of conventional temperature and pressure wellbore environment, but it is still found to have obvious disadvantages in high temperature and high pressure environment:

[0006] (1) The free stroke of the piston of the traditional piston pressure balance device is long and the volume is large. Especially as the operating temperature range of the instrument increases, the piston stroke must be designed to be long enough to balance the internal and external pressures of the instrument within the target temperature range and protect the normal operation of the instrument. This results in a significant increase in the length and weight of the instrument when designing a high-temperature instrument.

[0007] (2) The working conditions are harsh and the instrument must be used within the design temperature range. Otherwise, the working environment temperature of the instrument exceeds the design temperature range, and the internal silicone oil expansion volume exceeds the compensation capacity of the device, causing the internal pressure to rise sharply after the piston reaches full stroke. When the internal pressure is much higher than the external mud column pressure, the pressure balance device will fail, or even be seriously damaged or scrapped.

[0008] (3) The maintenance requirements are stringent. If the oil filling amount is not strictly in accordance with the design requirements, the balancing device will fail and damage the instrument;

[0009] (4) For instruments with weak mechanical strength of the casing, such as fiberglass, once the internal and external pressures are unbalanced due to reasons such as lax oil filling and piston sticking, it will lead to catastrophic consequences such as instrument damage and scrapping.

[0010] In short, the bladder type and bellows type have poor application scope and reliability due to their inherent weaknesses; the traditional piston type pressure balance device has a larger size when the applicable temperature range increases, which is contrary to the current trend of shorter and lighter instruments, and is not conducive to transportation and handling. At the same time, its maintenance is relatively complicated, and its intrinsic safety and reliability are poor under extreme conditions. Therefore, the above three balance devices are not suitable for use in high temperature and complex environments. Summary of the invention

[0011] The present invention provides a pressure balancing device, which solves the reliability and safety problems of the pressure balancing device in a high temperature environment and improves its maintainability, so that the downhole instrument can be suitable for the high temperature and complex environment underground.

[0012] A pressure balancing device of the present invention may include a balancing chamber, a piston and a balancing fluid located in the balancing chamber, and a relief valve arranged on the wall of the balancing chamber. The piston divides the balancing chamber into a first cavity and a second cavity, the balancing fluid is injected into the first cavity, a connecting hole is provided on the wall of the balancing chamber at the second cavity, and the connecting hole connects the second cavity with the outside of the balancing chamber; the relief valve is located in the first cavity, and the relief valve has a one-way conducting structure from the first cavity to the outside of the balancing chamber, and the relief valve can be opened under the action of the pressure difference between the first cavity and the outside of the balancing chamber.

[0013] In one embodiment, the balancing device may further include a balancing valve disposed on a wall of the balancing chamber and located in the first cavity, wherein the balancing valve has the same structure as the overflow valve and has an opposite conduction direction.

[0014] In one embodiment, the overflow valve may include a valve body, a sealing member and a first elastic member. The valve body is provided with an inner cavity which is axially penetrated, the inner diameter of a portion at one end of the inner cavity gradually changes along the axial direction and forms a sealing surface, the sealing member is provided at the sealing surface; the sealing member cooperates with the first elastic member provided in the inner cavity, and the first elastic member can make the sealing member fit tightly with the sealing surface.

[0015] In one embodiment, the sealing surface is located at the inlet end of the inner cavity, and the inner diameter of the inner cavity at the sealing surface gradually decreases from the inside to the outside along the axial direction of the inner cavity, and the sealing member is located in the inner cavity and is connected or abutted with one end of the first elastic member; or, the sealing surface is located at the outlet end of the inner cavity, and the inner diameter of the inner cavity at the sealing surface gradually increases from the inside to the outside along the axial direction of the inner cavity, the sealing member is located outside the inner cavity, and the inner cavity has a connecting rod with an end extending outside the outlet end and connected to the sealing member, and the connecting rod cooperates with the first elastic member.

[0016] In one embodiment, the relief valve may further include a pressure regulating member disposed in the inner cavity, the pressure regulating member being located at the other end of the first elastic member relative to the end where the sealing member is located. The pressure regulating member can move in the inner cavity along the deformation direction of the first elastic member to adjust the pre-deformation amount of the first elastic member, so as to adjust the magnitude of the acting force between the tightly fitted sealing member and the sealing surface.

[0017] In one embodiment, the outer diameter of the pressure regulating part matches the inner diameter of the inner cavity, and the outer peripheral surface of the pressure regulating part cooperates with the inner wall thread of the inner cavity, and the center of the pressure regulating part has a center hole connected to the inner cavity; or, the outer diameter of the pressure regulating part is smaller than the inner diameter of the inner cavity, and the pressure regulating part is sleeved on the connecting rod in the inner cavity and cooperates with the connecting rod thread.

[0018] In one embodiment, the balancing device may further include a second elastic member, two ends of which are respectively connected to the balancing chamber and the piston, and the second elastic member can enable the piston to move in the direction from the second cavity to the first cavity.

[0019] In one embodiment, the second elastic member is disposed in the first cavity, and the second elastic member is a tension spring; or, the second elastic member is disposed in the second cavity, and the second elastic member is a spring.

[0020] In one embodiment, the balancing fluid is silicone oil or hydraulic oil.

[0021] In one embodiment, the volume change ΔVc corresponding to the movement stroke of the piston in the balancing chamber and the volume change ΔV when the balancing fluid expands satisfy:

[0022] △Vc≥1.5~2△V

[0023] Among them, △V satisfies the relationship:

[0024] △V=α×V×△T

[0025] In the formula, α is the expansion coefficient of the balancing fluid, V is the volume of the balancing fluid at room temperature, and ΔT is the temperature difference between the room temperature and the maximum working temperature of the balancing fluid.

[0026] The pressure balancing device provided by the present invention has at least the following beneficial effects compared with the prior art:

[0027] (1) The pressure balancing device of the present invention can improve the reliability of the balancing device by arranging an overflow valve on the balancing chamber. At the same time, when adding the balancing fluid, it can be directly filled without leaving any travel space for the piston, so that the balancing device can have a smaller mechanical size and the maintenance work can be simpler and safer.

[0028] (2) The pressure balancing device of the present invention can prevent mechanical damage to the instrument by arranging a balancing valve on the balancing chamber, thereby minimizing the loss and improving the inherent safety of the balancing device.

[0029] (3) The pressure balancing device of the present invention is provided with a second elastic member so that the pressure of the balancing fluid in the first cavity is always kept slightly greater than the pressure of the external fluid, so that the external fluid does not flow from a low-pressure area to a high-pressure area, and each sealing link of the balancing chamber can be kept clean. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Hereinafter, the present invention will be described in more detail based on embodiments and with reference to the accompanying drawings.

[0031] Figure 1 is a structural schematic diagram of a pressure balancing device according to an embodiment of the present invention;

[0032] Figure 2 It is an enlarged structural schematic diagram of the overflow valve of the embodiment of the present invention installed on the balance tank;

[0033] Figure 3 is an enlarged structural schematic diagram of a balancing valve according to an embodiment of the present invention installed on a balancing tank;

[0034] Figure 4 is a structural schematic diagram of a relief valve according to an embodiment of the present invention;

[0035] Figure 5 is a structural schematic diagram of a balancing valve according to an embodiment of the present invention;

[0036] Figure 6 is another structural schematic diagram of the relief valve according to an embodiment of the present invention;

[0037] Figure 7 is another structural schematic diagram of a balancing valve according to an embodiment of the present invention;

[0038] Figure 8 2 is another structural schematic diagram of the pressure balancing device according to an embodiment of the present invention.

[0039] In the drawings, the same reference numerals are used for the same components. The drawings are not drawn to scale.

[0040] Reference numerals:

[0041] 1-Balance chamber, 2-Piston, 3-Balance fluid, 4-Overflow valve, 5-Balance valve, 6-Communication hole, 7-Valve body, 8-Seal, 9-First elastic member, 10-Pressure regulating member, 11-Seal ring, 12-Connecting rod, 13-Supporting part, 14-Second elastic member, 15-Seal member. DETAILED DESCRIPTION

[0042] The present invention will be further described below in conjunction with the accompanying drawings.

[0043] like Figure 1 , Figure 2 and Figure 8 As shown, the pressure balancing device of the present invention may include a balancing chamber 1, a piston 2 and a balancing fluid 3 located in the balancing chamber 1, and a relief valve 4 arranged on the wall of the balancing chamber 1. The piston 2 divides the balancing chamber 1 into a first cavity and a second cavity, the first cavity is injected with the balancing fluid 3, and a connecting hole 6 is opened on the wall of the balancing chamber 1 at the second cavity, and the connecting hole 6 connects the second cavity with the outside of the balancing chamber 1. The relief valve 4 is located in the first cavity, and the relief valve 4 has a unidirectional conductive structure from the first cavity to the outside of the balancing chamber 1, and the relief valve 4 can be opened under the action of the pressure difference between the first cavity and the outside of the balancing chamber 1.

[0044] Specifically, the balancing chamber 1 is the main body of the entire balancing device, and is also the mechanical carrier of other components of the entire balancing device, and has a certain ability to withstand internal and external fluid pressure. The connecting hole 6 connects the second cavity with the outside of the balancing chamber 1, so that the external fluid of the balancing chamber 1 can enter the second cavity and exert pressure on the piston 2. The volume of the balancing fluid 3 changes with temperature. The piston 2 is installed inside the balancing chamber 1, and can slide back and forth along the axis direction of the balancing chamber 1 with the volume change of the balancing fluid 3. On the one hand, it can isolate the external fluid flowing into the second cavity through the connecting hole 6 and the balancing fluid 3 in the first cavity; on the other hand, the volume of the first cavity of the balancing chamber 1 is changed by the movement of the piston 2 to compensate for the volume change of the balancing fluid 3 caused by thermal expansion and contraction. The overflow valve 4 is a one-way valve and is set with a first pressure difference threshold. When the pressure difference between the first cavity and the outside of the balancing chamber 1 acting on the overflow valve 4 exceeds the first pressure difference threshold, the overflow valve 4 is opened, and the balancing fluid 3 can flow out of the first cavity to reduce the pressure inside the first cavity. On the one hand, this can prevent the pressure inside the first cavity from being too high, which may cause the pressure balancing device to fail or even the instrument to be damaged or scrapped, thereby improving the reliability of the pressure balancing device; on the other hand, when filling the balancing fluid 3, it can be filled directly, avoiding the potential risks caused by the liquid level error when filling the balancing fluid 3, making maintenance work simpler and safer; on another hand, because when filling the balancing fluid 3, it can be filled directly without retaining the empty piston 2 stroke, its design length is smaller than that of the traditional balancing device, and it can have a smaller mechanical size.

[0045] It should be noted that if the temperature resistance of the materials of the various components of the instrument is not taken into consideration, the present invention has no upper temperature limit, while when the traditional balancing device exceeds its operating temperature range, it will cause balancing failure and even cause serious damage to the instrument.

[0046] like Figure 1 , Figure 3 and Figure 8 As shown, in one example, the balancing device further includes a balancing valve 5 disposed on the wall of the balancing chamber 1 and located in the first cavity. The balancing valve 5 has the same structure as the overflow valve 4 and has an opposite conduction direction.

[0047] Specifically, the balancing valve 5 is also a one-way valve and is set with a second pressure difference threshold. When the pressure difference between the outside of the balancing chamber 1 and the first cavity acting on the balancing valve 5 exceeds the second pressure difference threshold, the balancing valve 5 opens, and the external fluid can flow into the first cavity to increase the pressure inside the first cavity. In this way, even if an extreme accident occurs in which the balancing fluid 3 inside the first cavity is missing, the balancing valve 5 opens, and the external fluid enters the first cavity of the balancing chamber 1, which can protect the instrument from mechanical damage, minimize the loss, and improve the intrinsic safety of the balancing device.

[0048] It should be noted that the overflow valve 4 and the balancing valve 5 both work when the balancing chamber 1 cannot rely on the axial movement of the piston 2 to balance or reduce the pressure difference between the balancing fluid 3 in the first cavity and the external fluid. When the piston 2 of the balancing chamber 1 can work normally, the overflow valve 4 and the balancing valve 5 are both in a closed state. The overflow valve 4 can only be opened when the pressure of the balancing fluid 3 acting on the inlet end of the overflow valve 4 is greater than the pressure of the external fluid acting on the outlet end of the overflow valve 4, exceeding the first pressure difference threshold set by it, and the balancing fluid 3 flows out from the inside of the first cavity to the outside of the balancing chamber 1. In order to prevent the valve from being misoperated, the overflow valve 4 uses a one-way valve with a flow direction from the first cavity to the outside of the balancing chamber 1. The balancing valve 5 can only be opened when the pressure of the external fluid acting on the inlet end of the balancing valve 5 is greater than the pressure of the balancing fluid 3 acting on the outlet end of the balancing valve 5, exceeding the second pressure difference threshold set by it, and the external fluid flows from the outside of the balancing chamber 1 to the inside of the first cavity. In order to prevent the valve from being misoperated, the balancing valve 5 uses a one-way valve with a flow direction from the outside of the balancing chamber 1 to the first cavity. Therefore, the overflow valve 4 and the balance valve 5 can be one-way valves with the same structure, but their conduction directions are set oppositely during installation.

[0049] Specifically, in this embodiment, Figures 4 to 7 As shown, when the overflow valve 4 and the balancing valve 5 are connected to the balancing tank 1, sealing rings 11 are provided at the connection to ensure the sealing of the connection. The overflow valve 4 and the balancing valve 5 are connected to the balancing tank 1 in a fixed manner to ensure that they can withstand the internal and external pressures of the balancing tank 1.

[0050] like Figures 4 to 7 As shown, in one example, the overflow valve 4 and the balancing valve 5 both include a valve body 7, a sealing member 8 and a first elastic member 9. The valve body 7 is provided with an axially through inner cavity, the inner diameter of a portion at one end of the inner cavity gradually changes along the axial direction and forms a sealing surface, and the sealing member 8 is provided at the sealing surface; the sealing member 8 cooperates with the first elastic member 9 provided in the inner cavity, and the first elastic member 9 can make the sealing member 8 fit closely with the sealing surface.

[0051] Specifically, the inner cavity at the sealing surface is designed to have an inner diameter that gradually changes along the axial direction, so that the seal 8 and the sealing surface fit better and more tightly when the valve is in a closed state, and can prevent the mechanical stress between the seal 8 and the valve body 7 from being concentrated locally, thereby reducing mechanical damage during operation. The seal 8 and the sealing surface fit tightly under the action of the preload force of the first elastic member 9 to prevent the fluid from passing through, while maintaining a certain pressure difference at both ends of the valve body 7. The size of the preload force set by the first elastic member 9 corresponds to the pressure difference threshold for the opening of the overflow valve 4 and the balance valve 5.

[0052] like Figure 4 and Figure 5As shown, in this example, the sealing surface is located at the entrance end of the inner cavity, and the inner diameter of the inner cavity at the sealing surface gradually decreases from the inside to the outside along the axial direction of the inner cavity. The sealing member 8 is located in the inner cavity and is connected or abutted with one end of the first elastic member 9.

[0053] Specifically, the seal 8 is completely located in the inner cavity of the valve. At this time, the direction of the preload force of the first elastic member 9 on the seal 8 is from inside to outside along the axial direction of the inner cavity. Under the action of the preload force, the seal 8 can fit tightly with the sealing surface to close the valve. When the fluid pressure on the seal 8 at the inlet end is greater than the fluid pressure entering the inner cavity of the valve body 7 from the outlet end and the pressure difference between the two exceeds the preload force of the first elastic member 9, the seal 8 is pushed to separate from the sealing surface, and the fluid at its inlet end enters the inner cavity of the valve through the gap between the two, and then flows out from the outlet end. Figure 4 The relief valve 4 is shown in two states of opening and closing. Figure 5 The two states of the balance valve 5 set in this way are shown: open and closed.

[0054] like Figure 6 and Figure 7 As shown, in this embodiment, the sealing surface is located at the outlet end of the inner cavity, and the inner diameter of the inner cavity at the sealing surface gradually increases from the inside to the outside along the axial direction of the inner cavity. The sealing member 8 is located outside the inner cavity, and the inner cavity has a connecting rod 12 whose end extends outside the outlet end and is connected to the sealing member 8. The connecting rod 12 cooperates with the first elastic member 9.

[0055] Specifically, at this time, the direction of the preload force exerted on the seal 8 by the first elastic member 9 or the connection rod 12 in cooperation with the first elastic member 9 is from the outside to the inside along the axial direction of the inner cavity, and the seal 8 can be closely fitted with the sealing surface under the action of the preload force to close the valve. When the fluid pressure of the seal 8 entering the inner cavity of the valve body 7 from the inlet end is greater than the fluid pressure exerted on the seal 8 at the outlet end and the pressure difference between the two exceeds the preload force of the first elastic member 9, the seal 8 is pushed to separate from the sealing surface, and the fluid in its inner cavity flows out of the inner cavity of the valve through the gap between the two, that is, flows out from the outlet end. Figure 6 The relief valve 4 is shown in two states of opening and closing. Figure 7 The two states of the balance valve 5 set in this way are shown: open and closed.

[0056] Specifically, Figures 4 to 7 As shown, the seal 8 can be a spherical structure or a hemispherical structure, but when the seal 8 is a hemispherical structure, its hemispherical surface faces the sealing surface. Of course, the structure of the seal 8 of the present invention is not limited to this, as long as it can form a tight fit with the sealing surface.

[0057] like Figures 4 to 7As shown, in one example, the relief valve 4 and the balancing valve 5 further include a pressure regulating member 10 disposed in the inner cavity, the pressure regulating member 10 is located at the other end of the first elastic member 9 relative to the end where the sealing member 8 is located, and the pressure regulating member 10 can move in the inner cavity along the deformation direction of the first elastic member 9 to adjust the pre-deformation of the first elastic member 9 to adjust the magnitude of the force between the tightly fitting sealing member 8 and the sealing surface. Specifically, adjusting the pre-deformation of the first elastic member 9 is to determine the magnitude of its preload force, that is, to adjust the pressure difference threshold of the relief valve 4 and the balancing valve 5.

[0058] Specifically, the pressure regulating member 10 is an axially through hollow structure and has a threaded structure. The pressure regulating member 10 can adjust the size of the preload force of the first elastic member 9 to make the seal 8 fit tightly with the sealing surface through the threaded structure. The pressure regulating member 10 is installed in the axial position of the inner cavity of the valve through the threaded structure to adjust the size of the preload force of the first elastic member 9, that is, to adjust the pressure difference threshold value of the overflow valve 4 and the balance valve 5.

[0059] like Figure 4 and Figure 5 As shown, in this embodiment, the outer diameter of the pressure regulating member 10 matches the inner diameter of the inner cavity, and the outer peripheral surface of the pressure regulating member 10 matches the inner wall thread of the inner cavity, and the center of the pressure regulating member 10 has a center hole connected to the inner cavity. Specifically, the pressure regulating member 10 is connected to the valve body 7 through matching internal and external threads, and the pressure regulating member 10 can adjust the size of the preload force of the first elastic member 9 by the installation depth of the threaded connection set in the inner cavity. At this time, the center hole of the pressure regulating member 10 is to make the inner cavity of the valve communicate with the outside of the end where it is located.

[0060] It should be noted that the pressure regulating member 10 is arranged so that the matching sealing surface is located at the inlet end of the inner cavity, forming a Figure 4 The overflow valve 4 shown and Figure 5 In the balancing valve 5 shown, the pressure regulating member 10 cooperates with the first elastic member 9 to apply a force from inside to outside along the axial direction of the inner cavity to the sealing member 8. At this time, the first elastic member 9 is compressed, and the tighter the pressure regulating member 10 and the sealing member 8 compress the first elastic member 9, the greater the preload force acting on the sealing member 8, that is, the greater the pressure difference threshold; otherwise, the smaller it is.

[0061] like Figure 6 and Figure 7As shown, in this embodiment, the outer diameter of the pressure regulating member 10 is smaller than the inner diameter of the inner cavity, and the pressure regulating member 10 is sleeved on the connecting rod 12 in the inner cavity and threadedly matched with the connecting rod 12. Specifically, the sealing member 8 is connected to the connecting rod 12 with external threads, and the pressure regulating member 10 has a central hole, and the central hole has an internal thread matching the external thread of the connecting rod 12. A support portion 13 located in the inner cavity and connected to the inner wall of the valve body is provided between the sealing member 8 and the pressure regulating member 10, and the support portion 13 is sleeved outside the connecting rod 12, and the first elastic member 9 is sleeved outside the connecting rod 12 and the two ends are connected to the support portion 13 and the pressure regulating member 10 respectively. The central hole of the pressure regulating member 10 is for setting the internal thread, so that the pressure regulating member 10 can be movably connected with the connecting rod 12 through matching internal and external threads, and at this time, the pressure regulating member 10 is not connected to the valve body 7. The pressure regulating member 10 is threadedly connected to the installation position set on the connecting rod 12 to adjust the size of the preload force of the first elastic member 9.

[0062] It should be noted that the pressure regulating member 10 is arranged so that the matching sealing surface is located at the outlet end of the inner cavity, forming a Figure 6 The overflow valve 4 shown and Figure 7 In the balancing valve 5 shown, the support part 13 can cooperate with the pressure regulating part 10 and the first elastic part 9 to apply a force from the outside to the inside along the axial direction of the inner cavity to the sealing part 8 through the connecting rod 12. At this time, the first elastic part 9 is compressed, and the tighter the pressure regulating part 10 and the support part 13 compress the first elastic part 9, the greater the pre-tightening force of the first elastic part 9, and the greater the force acting on the pressure regulating part 10. At this time, the pressure regulating part 10 is fixedly connected to the connecting rod 12 and the sealing part 8, so the force acting on the sealing part 8 is also greater, that is, the pressure difference threshold is greater; otherwise, it is smaller.

[0063] It should also be noted that the structures of the overflow valve 4 and the balance valve 5 of the present invention are not limited to this, and other methods are also acceptable as long as the seal 8 is closely fitted to the sealing surface through the cooperation of the pressure regulating member 10 and the first elastic member 9. For example, when the sealing surface is located at the outlet end of the inner cavity, the seal 8 is set to a hemispherical structure and the hemispherical surface of the seal 8 faces the sealing surface (such as Figure 6 and Figure 7 As shown), the pressure regulating member 10 can also be provided with a structure having a central hole and a threaded outer surface (as shown Figure 4 and Figure 5 As shown), the pressure regulating member 10 is movably connected to the valve body 7 through a thread, but at this time the first elastic member 9 is not compressed by the pressure regulating member 10 and the sealing member 8, but stretched, and the corresponding pre-tightening force is a tensile force.

[0064] like Figure 1 and Figure 8As shown, in one example, the balancing device includes a second elastic member 14, both ends of which are respectively connected to the balancing chamber 1 and the piston 2, and the second elastic member 14 can enable the piston 2 to move in the direction from the second cavity to the first cavity.

[0065] Specifically, the two ends of the elastic member are connected to the piston 2 and the balancing chamber 1 respectively. When the piston 2 is in a balanced state, the pressure of the balancing fluid 3 in the first cavity on the piston 2 is equal to the sum of the pressure of the external fluid in the second cavity on the piston 2 and the preload force of the second elastic member 14. In this way, on the one hand, the preload force of the second elastic member 14 can offset the friction between the piston 2 and the inner wall of the balancing chamber 1 when the volume of the balancing fluid 3 in the first cavity decreases; on the other hand, when the piston 2 is in a balanced state, the preload force formed by the second elastic member 14 is used to establish a certain pressure difference between the balancing fluid 3 in the first cavity and the external fluid, so that the pressure of the balancing fluid 3 acting on the inner surface of the piston 2 is always slightly greater than the pressure of the external fluid acting on the outer end surface of the piston 2, and the piston 2 can move back and forth with the volume change of the balancing fluid 3.

[0066] It should be noted that the second elastic member 14 is provided so that the pressure of the balancing fluid 3 in the first cavity is always kept slightly greater than the pressure of the external fluid, and an underpressure balance design is formed between the two. In this way, in the dynamic seal of the piston 2 and other static seals, since the pressure of the balancing fluid 3 in the first cavity is always kept greater than the pressure of the external fluid, the external fluid will not flow from a low pressure to a high pressure area. Even if a certain degree of intrusion occurs, it is the balancing fluid 3 in the first cavity that intrudes outward. In this way, each sealing link can be kept clean, and the pressure balancing device is also made more stable to prevent damage to the instrument.

[0067] In an example, Figure 1 As shown, the second elastic member 14 is disposed in the first cavity, and the second elastic member 14 is a tension spring; or Figure 8 As shown, the second elastic member 14 is disposed in the second cavity, and the second elastic member 14 is a spring.

[0068] Specifically, the second elastic member 14 is mainly provided to have a force to move the piston 2 in the direction from the second cavity to the first cavity, so that the pressure of the balancing fluid 3 in the first cavity is always slightly greater than the pressure of the external fluid. Then, the second elastic member 14 provided in the first cavity should apply a pulling force to the piston 2, and the second elastic member 14 provided in the second cavity should apply an elastic force to the piston 2. Of course, the second elastic member 14 of the present invention is not limited to a tension spring or a spring, and other elastic members that can achieve the above functions can be used.

[0069] In one example, the balancing fluid 3 is silicone oil or hydraulic oil. The balancing fluid 3 is mainly used as a pressure transmission medium for the balancing device, and at the same time provides an insulating medium for the electrical components inside the first cavity. Of course, according to the design requirements of the balancing device of the specific instrument, the balancing fluid 3 can also be other suitable fluids.

[0070] It should be noted that in the present invention, if the second elastic member 14 is not provided, it will affect the return of the piston 2 during maintenance in a ground environment, which requires certain other auxiliary measures to help the piston 2 return. The connecting hole 6 of the present invention can be designed with a suitable shape and number according to the specific structure of the instrument, as long as the external fluid can be connected to the outer end surface of the piston 2. When the second elastic member 14 is provided in the first cavity, the piston 2 can be fixedly provided with a corresponding Figure 1 The blocking member 15 shown can prevent the piston 2 from moving to the end of the balancing chamber 1 to seal the connecting hole 6, thereby causing the balancing device to fail.

[0071] In order to better understand the above embodiments of the present invention, Figure 1 The operation process of the balancing device underground is further explained.

[0072] The operation process of the balance device underground includes but is not limited to the following:

[0073] (1) Before the balancing device is lowered into the well, the balancing fluid 3 is filled to the full oil level, and the piston 2 reaches the outermost end, that is, the rightmost end of the stroke. At this time, the inner cavity of the balancing chamber 1 is filled with the maximum amount of balancing fluid 3.

[0074] (2) After the instrument is lowered into the well, as the borehole ambient temperature increases, the balancing fluid 3 will expand, causing the internal pressure of the first cavity to increase. At this time, the piston 2 has reached the rightmost end, and the volume change of the balancing fluid 3 cannot be compensated by the piston 2 continuing to move to the right to expand the volume of the first cavity of the balancing chamber 1. When the pressure of the balancing fluid 3 acting on the relief valve 4 is greater than the pressure of the external fluid (such as the mud column) acting on the outer end surface of the relief valve 4 and the pressure difference between the two exceeds the first pressure difference threshold set by the relief valve 4, the relief valve 4 opens, and the balancing fluid 3 inside the first cavity leaks out until the pressure difference between the inside and outside of the relief valve 4 is less than or equal to the set first pressure difference threshold. At the same time, due to the presence of the second elastic member 14, a certain small pressure difference is always maintained between the balancing fluid 3 and the external fluid, and the pressure of the balancing fluid 3 is slightly greater than the pressure of the external fluid.

[0075] (3) When an extreme accident occurs in which the amount of the internal balancing fluid 3 of the first cavity is seriously insufficient, the piston 2 moves to the innermost end of the stroke and can no longer move to the left to reduce the volume of the first cavity of the balancing chamber 1, so as to compensate for the volume change of the balancing fluid 3 and reduce the pressure difference between the first cavity and the outside of the balancing chamber 1. The pressure of the balancing fluid 3 decreases. When the pressure of the balancing fluid 3 acting on the inner end surface of the balancing valve 5 is less than the pressure of the external fluid acting on the outer end surface of the balancing valve 5 and the pressure difference between the two exceeds the second pressure difference threshold set by the balancing valve 5, the balancing valve 5 opens, and the external fluid enters the first cavity of the balancing chamber 1 through the balancing valve 5 until the pressure difference between the inside and outside of the balancing chamber 1 is less than or equal to the second pressure difference threshold set by the balancing valve 5, and then the balancing valve 5 closes, which can protect the internal mechanical structure and components of the instrument from damage to the greatest extent.

[0076] In order to better understand the present invention, the design requirements of the balancing device are further explained below.

[0077] (1) Piston stroke design

[0078] The stroke design of the piston must ensure that it can balance the internal and external pressures under the temperature range and environmental conditions used by the instrument. Although the present invention is designed with a balancing valve, this is only a means of protecting the instrument under extreme circumstances. During the entire logging data collection process, the instrument is first lowered from the wellhead to the target layer or the bottom of the well, and then lifted from the bottom of the well. As the instrument is lowered or lifted in the wellbore, the wellbore temperature and pressure gradually change with depth, and generally no sudden changes in temperature and pressure occur. The balancing valve is generally in a closed state, and the balancing valve will only open when the internal pressure of the first cavity of the balancing chamber is less than the external pressure. Therefore, when designing the balancing device, quantitative calculations must be performed to ensure that the piston has sufficient stroke and will not easily cause the balancing valve to open.

[0079] In order to make the balancing device safer, the volume change that the piston can compensate must be greater than the volume change of the balancing fluid inside the instrument at the highest operating temperature. In view of this premise, we must reasonably design the compensation volume of the piston and determine the stroke of the piston according to the amount of balancing fluid injected.

[0080] Assume that the total volume of the internal space of the first cavity of the balancing chamber is V, that is, the total volume of the injected balancing fluid.

[0081] The change in the expansion volume of the equilibrium fluid is:

[0082] △V=α×V×△T--------------(1)

[0083] Where: α is the equilibrium fluid expansion coefficient,

[0084] V is the equilibrium fluid volume,

[0085] △T is the temperature difference, the temperature difference between room temperature and the maximum operating temperature of the instrument.

[0086] The expansion coefficient of the balancing fluid can be obtained through experiments or from the technical parameters of the manufacturer.

[0087] The expansion volume △V of the equilibrium fluid is calculated according to formula (1). Assuming that the change in the volume of the internal space caused by the piston sliding from the innermost end to the outermost end is △Vc, it is required that △Vc>△V. In fact, we also need to leave enough margin, which requires: △Vc≥1.5~2△V.

[0088] After determining the compensation volume △Vc of the piston, according to the size and structure of the balance chamber, once the diameter d of the piston is determined, the piston stroke L can be easily calculated:

[0089] L>(4△Vc) / (πd^2)--------------------------(2)

[0090] The piston stroke is designed according to the calculation results, so that when the balancing device is used within the designed pressure and temperature range, the pressure inside and outside the balancing chamber can be balanced, and the balancing chamber shell can be protected from being crushed.

[0091] (2) Setting the pressure difference threshold of the balancing valve and the relief valve

[0092] The pressure of the first pressure difference threshold set by the overflow valve is P1, the pressure of the second pressure difference threshold set by the balance valve is P2, and the maximum pressure from inside to outside and from outside to inside that the weakest part of the first cavity of the balance chamber can withstand are P 1max , P 2max , the pressure difference threshold of the balancing valve and the overflow valve must be set according to the mechanical strength of the balancing chamber and other parts constituting the closed first cavity. The pressure must meet the following requirements:

[0093] P1 <P 1max ------------(3)

[0094] P2 <P 2max ------------(4)

[0095] This ensures that the maximum internal and external pressure difference formed by the balance tank during normal operation cannot exceed the pressure bearing capacity P of the weakest part. 1max and P 2max Otherwise, the balancing device will be damaged before the balancing valve and relief valve are opened.

[0096] (3) Design of the second elastic member

[0097] When designing the present invention, there are certain requirements for the selection of the elastic coefficient K of the second elastic member. Assuming that the pressure of the first pressure difference threshold of the overflow valve is P1, when the pressure of the balancing fluid in the first cavity is greater than P1, the balancing fluid overflows, and the elastic coefficient of the second elastic member is K, the cross-sectional area of ​​the piston is S, and the designed free stroke is L, then:

[0098] The elastic force generated by the second elastic member at the maximum stroke is:

[0099] F=K×L---------------(5)

[0100] Then it must be maintained: P1>F / S---------------(6)

[0101] This ensures that the overflow valve will not be opened before the piston moves to the maximum stroke, preventing the overflow valve from disrupting the normal operation of the balancing device.

[0102] Although the present invention has been described with reference to preferred embodiments, various modifications may be made thereto and parts thereof may be replaced by equivalents without departing from the scope of the present invention. In particular, the various technical features mentioned in the various embodiments may be combined in any manner as long as there are no structural conflicts. The present invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A pressure balancing device, characterized in that: The balancing device comprises a balancing chamber, a piston and a balancing fluid located in the balancing chamber, and an overflow valve arranged on the wall of the balancing chamber; wherein, The piston divides the balancing chamber into a first cavity and a second cavity, the first cavity is injected with the balancing fluid, and a connecting hole is opened on the wall of the balancing chamber at the second cavity, and the connecting hole connects the second cavity with the outside of the balancing chamber; The overflow valve is located in the first cavity, and has a one-way conducting structure from the first cavity to the outside of the balancing chamber. The overflow valve can be opened under the action of the pressure difference between the first cavity and the outside of the balancing chamber.

2. The pressure balancing device according to claim 1, characterized in that: The balancing device further comprises a balancing valve which is arranged on the wall of the balancing bin and located in the first cavity. The balancing valve has the same structure as the overflow valve but has an opposite conduction direction.

3. The pressure balancing device according to claim 1, characterized in that: The overflow valve comprises a valve body, a sealing member and a first elastic member; Among them, the valve body is provided with an axially penetrating inner cavity, the inner diameter of a portion at one end of the inner cavity gradually changes along the axial direction and forms a sealing surface, and the sealing member is arranged at the sealing surface; the sealing member cooperates with the first elastic member arranged in the inner cavity, and the first elastic member can make the sealing member fit tightly with the sealing surface.

4. The pressure balancing device according to claim 3, characterized in that: The sealing surface is located at the inlet end of the inner cavity, the inner diameter of the inner cavity at the sealing surface gradually decreases from inside to outside along the axial direction of the inner cavity, and the sealing member is located in the inner cavity and connected or abutted with one end of the first elastic member; or The sealing surface is located at the outlet end of the inner cavity, and the inner diameter of the inner cavity at the sealing surface gradually increases from the inside to the outside along the axial direction of the inner cavity. The sealing component is located outside the inner cavity, and the inner cavity has a connecting rod with one end extending out of the outlet end and connected to the sealing component, and the connecting rod cooperates with the first elastic component.

5. The pressure balancing device according to claim 3, characterized in that: The relief valve further comprises a pressure regulating member disposed in the inner cavity, wherein the pressure regulating member is located at the other end of the first elastic member relative to the end where the sealing member is located; The pressure regulating member can move in the inner cavity along the deformation direction of the first elastic member to adjust the pre-deformation amount of the first elastic member, so as to adjust the magnitude of the acting force between the tightly fitting sealing member and the sealing surface.

6. The pressure balancing device according to claim 5, characterized in that: The outer diameter of the pressure regulating member matches the inner diameter of the inner cavity, and the outer peripheral surface of the pressure regulating member matches the inner wall thread of the inner cavity, and the center of the pressure regulating member has a central hole connected to the inner cavity; or, The outer diameter of the pressure regulating member is smaller than the inner diameter of the inner cavity, and the pressure regulating member is sleeved on a connecting rod in the inner cavity and is threadedly matched with the connecting rod.

7. The pressure balancing device according to claim 1, characterized in that: The balancing device further comprises a second elastic member, two ends of which are respectively connected to the balancing chamber and the piston, and the second elastic member can enable the piston to move in the direction from the second cavity to the first cavity.

8. The pressure balancing device according to claim 7, characterized in that: The second elastic member is disposed in the first cavity, and the second elastic member is a tension spring; or, The second elastic member is disposed in the second cavity, and the second elastic member is a spring.

9. The pressure balancing device according to claim 1, characterized in that: The balancing fluid is silicone oil or hydraulic oil.

10. The pressure balancing device according to any one of claims 1 to 9, characterized in that: The volume change ΔVc corresponding to the movement stroke of the piston in the balancing chamber and the volume change ΔV when the balancing fluid expands satisfy: △Vc≥1.5~2△V Among them, △V satisfies the relationship: △V=α×V×△T In the formula, α is the expansion coefficient of the balancing fluid, V is the volume of the balancing fluid at room temperature, and ΔT is the temperature difference between the room temperature and the maximum working temperature of the balancing fluid.

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