Patent Application
20210095527
The present disclosure relates to an assembly and method for pressure control across a sealing system.
Underground drilling, such as gas, oil, or geothermal drilling, generally involves drilling a bore through a formation deep in the earth. Such bores are formed by connecting a drill bit to long sections of pipe, referred to as a “drill pipe,” to form an assembly commonly referred to as a “drill string.” Rotation of the drill bit advances the drill string into the earth, thereby forming the bore. Directional drilling refers to drilling systems configured to allow the drilling operator to direct the drill bit in a particular direction to reach a desired target hydrocarbon that is located some distance vertically below the surface location of the drill rig and is also offset some distance horizontally from the surface location of the drill rig. Steerable systems use bent tools located downhole for directional drilling and are designed to direct the drill bit in the direction of the bend. Rotary steerable systems use moveable blades, or arms, that can be directed against the borehole wall as the drill string rotates to cause directional change of the drill bit. Finally, rotary steerable motor systems also use moveable blades that can be directed against the borehole wall to guide the drill bit. Directional drilling systems have been used to allow drilling operators to access hydrocarbons that were previously un-accessible using conventional drilling techniques.
In order to lubricate the drill bit and flush cuttings from its path, a fluid, referred to as “drilling mud,” is directed through an internal passage in the drill string and out through the drill bit. The drilling mud then flows to the surface through the annular passage formed between the drill string and the surface of the bore. Since the drilling mud must be highly pressurized, the drill string is subjected to a large pressure gradient in the radial direction, as well as high axial and torque loading due to the forces associated with rotating and advancing the drill bit and carrying the weight of the drill string.
Sealing is used to keep lubricated fluids in, while preventing the addition of contaminants, such as mud and water. Sealing around rotating shafts is performed in numerous ways. Sealing moving shafts is difficult in high pressure, dynamic operations, such as at high differential pressures and relatively high shaft rotational speeds typical in drilling operations. In general, the contact stress between the seal and shaft increases with increasing differential pressure. As the pressure differential across the seal increases, the differential pressure acts on the unsupported area of the sealing element to create a high force, especially a high radial force, on the stationary sealing element acting against the rotating shaft. At some point, the seal can deform, extrude, or heat up to the point of leakage or failure.
There is a need to provide better pressure control for a sealing system that limits the pressure differential across a sealing element. An embodiment of the present disclosure is a sealing assembly. The sealing assembly includes a housing having an outer surface, an inner surface, a main cavity defined by the inner surface, a first end and a second end spaced from the first end along a central longitudinal axis. The sealing assembly further includes a sealing unit mounted to the inner surface. The sealing unit includes an internal passage configured to receive a rotatable shaft, a first sealing element, and a second sealing element positioned uphole with respect to the first sealing element along the central longitudinal axis. The sealing assembly further includes a first valve carried by the housing and hydraulically coupled to the first sealing element and the main cavity. The first valve is configured to open at a first pressure level. The sealing assembly further includes a second valve carried by the housing and hydraulically coupled to the second sealing element and the main cavity. The second valve is configured to open at a second pressure level that is higher than the first pressure level. The sealing assembly is configured such that when the pressure exceeds the first pressure level and the second pressure level, the first relief valve and the second relief valve open sequentially so as to distribute pressure across the first sealing element and the second sealing element sequentially.
Another embodiment of the present disclosure is a sealing assembly configured for a pressurized sealing environment. The sealing assembly includes a housing having an outer surface, an inner surface, a main cavity defined by the inner surface, a first end and a second end spaced from the first end along a central longitudinal axis. The sealing assembly further includes a sealing unit mounted to the inner surface. The sealing unit includes an internal passage configured to receive a rotatable shaft, and at least two sealing elements positioned along the central longitudinal axis and in contact with the rotatable shaft. The sealing assembly further includes at least two valves carried by the housing and hydraulically coupled to the at least two sealing elements and the main cavity. The at least two valves are configured to transition from a closed configuration into an open configuration when the pressure exceeds different respective pressure levels. The sealing assembly is configured such that as the pressure exceeds the two different respective pressure levels and the at least two relief valves transition from a closed configuration into an open configuration, the pressure is distributed across the at least two sealing elements sequentially.
A further embodiment of the present disclosure is a method that includes causing drilling fluid to flow through an internal passage of a drill string carrying a tool assembly having a sealing unit comprising a first sealing element and a second sealing element each in contact with the shaft. The method further includes causing a shaft to rotate within the tool assembly, wherein the first and second sealing elements are in contact with the shaft. The method further includes opening a first valve of the tool assembly corresponding to the first sealing element when a pressure exceeds a first pressure level so as to distribute pressure across the first sealing element. The method further includes opening a second valve corresponding to the second sealing element when the pressure exceeds a second pressure level that is higher than the first pressure level, such that, the pressure is distributed is across the first sealing element and the second sealing element.
Another embodiment of the present disclosure is a sealing assembly. The sealing assembly includes a housing having an outer surface, an inner surface, a main cavity defined by the inner surface, a first end and a second end spaced from the first end along a central longitudinal axis. The sealing assembly further includes a sealing unit mounted to the inner surface. The sealing unit includes an internal passage configured to receive a rotatable shaft, a first sealing element, a second sealing element positioned uphole with respect to the first sealing element along the central longitudinal axis, a third sealing element positioned uphole with respect to the first sealing element and the second sealing element along the central longitudinal axis, and a fourth sealing element positioned uphole with respect to the first sealing element, the second sealing element, and the third sealing element along the longitudinal axis. The sealing assembly further includes a first valve carried by the housing and hydraulically coupled to the first sealing element and the main cavity. The first valve is configured to open at a first pressure level. The sealing assembly further includes a second valve carried by the housing and hydraulically coupled to the second sealing element and the main cavity. The second valve is configured to open at a second pressure level that is higher than the first pressure level. The sealing assembly further includes a third valve carried by the housing and hydraulically coupled to the third sealing element and the main cavity. The third valve is configured to open at a third pressure level that is higher than the first pressure level and the second pressure level. The sealing assembly further includes a fourth valve carried by the housing and hydraulically coupled to the fourth sealing element and the main cavity. The fourth valve is configured to open at a fourth pressure level that is higher than the first pressure level, the second pressure level, and the third pressure level. The sealing assembly further includes a compensation piston disposed in the main cavity. The compensation piston is movable relative to the sealing unit in response to an increase in pressure, wherein when the pressure exceeds the first pressure level, the second pressure level, the third pressure level, and the fourth pressure level, the first valve, the second valve, the third valve, and the fourth valve open sequentially so as to distribute pressure across the first sealing element, the second sealing element, the third sealing element, and the fourth sealing element sequentially.
The foregoing summary, as well as the following detailed description, will be better understood when read in conjunction with the appended drawings. The drawings show illustrative embodiments of the disclosure. It should be understood, however, that the application is not limited to the precise arrangements and instrumentalities shown.
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The sealing unit 110 is also configured to slidingly receive the rotating shaft S. As shown, the sealing unit 110 may be mounted to the inner surface 106B, yet is located downhole with respect to the valve assembly 112. The sealing unit 110 may include one or more separate sealing elements 116 supported by one or more carriers 117A-117D. In the illustrated embodiment, the sealing unit 110 includes four sealing elements 116A, 116B, 116C, and 116D and four respective carriers 117A, 117B, 117C, and 117D, respectively. In the present disclosure, the reference number 116 and 116A though 116D are used interchangeably to refer to similar configured sealing elements. As shown, the sealing unit 110 includes a first sealing element 116A and a second sealing element 116B located uphole relative to the first sealing element 116A. The sealing unit 110 further includes a third sealing element 116C located uphole relative to the first sealing element 116A and the second sealing element 116B. The sealing unit 110 also includes a fourth sealing element 116D located uphole relative to the first sealing element 116A, the second sealing element 116B, and the third sealing element 116C. The sealing elements 116A-116D are lined up next to each other. An internal passage (not numbered) extends through each sealing element and is configured to receive the rotatable shaft S. In the illustrated embodiment, the sealing unit 110 includes four sealing elements. However, the sealing unit 110 may include more than four sealing elements, or less than four sealing elements may be used. For example, each sealing unit may include a first sealing element 116A and a second sealing element 116B.
Each sealing element 116A-116D is defined by a seal that is in sealing contact with the rotatable shaft S. The sealing elements 116A-116D are configured to compress against the inner surface 106B of the pressure control tool assembly 100, forming a seal against the inner surface 106B. The seal divides a high pressure side located downhole relative to the sealing elements 116A-116D and a lower pressure side located uphole relative to the sealing elements 116A-116D. In this regard, the sealing elements 116A-116D function as differential pressure sealing elements. Each sealing element 116A-116D can define a ring shape that seats into respective annular grooves defined by the housing 102 (not depicted). In the illustrative embodiment, the sealing elements 116A-116D are annular rings that form a seal with the rotating shaft S. In one example, the sealing elements 116A-116D are T-seals. In another example, the sealing elements 116A-116D are O-rings. In yet another example, the sealing elements 116A-116D are quad seals. In another example, the sealing elements 116A-116D are packing material. In yet another example, the sealing elements 116A-116D may be comprised of metal and polished to form a seal with the rotating shaft S. Each of the sealing elements 116A-116D are held by a respective carrier 117A-117D.
The valve assembly 112 is configured to help distribute pressure across the different sealing elements. As shown, the valve assembly is located uphole relative to the main cavity 114 and the sealing unit 110. The valve assembly 112 may include at least two separate valves. In the illustrated embodiment, the valve assembly 112 includes four valves: a first valve 120A, a second valve 120B, a third valve 120C (not depicted), and a fourth valve 120D (not depicted). The number of valves generally correspond to the number of sealing elements. For clarity in illustration and description, only the first valve 120A and the second valve 120B are illustrated in the figures. Each of the valves 120A-120D are positioned such that the valves 120A-120D generally surround the central axis A of the tool assembly 100. The valves 120A-120D are configured to open as pressure increases inside the pressure control tool assembly 100. Each valve 120A-120D can be rated to transition from a closed configuration into an open configuration at a predetermined pressure level. In one example, the predetermined pressure level can be about 3000 psi. In such an example, with four valves as described, a total pressure of 12,000 psi can be distributed across four sealing elements. The sequential distribution of pressure along pressure increases reduces contact stresses and the likelihood of heel extrusion of sealing elements and wear.
The first valve 120A includes a first input passageway 122A1 that is hydraulically coupled to the main cavity 114. In particular, the first input passageway 122A1 extends from the first valve 120A to the main cavity 114 through the housing body 108. The first valve 120A further includes a first output passageway 122A2 that is hydraulically coupled to the first sealing element 116A of the sealing unit 110. Similarly, the second valve 120B includes a second input passageway 122B1 hydraulically coupled to the main cavity 114, and a second output passageway 122B2 hydraulically coupled to the second sealing element 116B of the sealing unit 110. The first output passageway 122A2 extends from the first valve 120A to a location between the first sealing element 116A and the second sealing element 116B. The second input passageway 122B1 extends from the second valve 120B to the main cavity 114. The second output passageway 122B2 extends from the second valve 120B to a location between the second sealing element 116B and the third sealing element 116C. As can be seen in the drawings, each input and output passageway described above does not define a linear path through the housing body 108. More specifically, each passageway has one or more deviations to direct fluid from the valve to its outlet point. As used herein, a deviation may be a curve or bend in the passageway.
In the illustrative embodiment, the third valve 120C and the fourth valve 120D each include an input passageway (not depicted) coupled to the main cavity 114, and an output passageway (not depicted) coupled to the third sealing element 116C and the fourth sealing element 116D of the sealing unit 110, respectively. The third input passageway extends from the third valve 120C to the main cavity 114. The third output passageway extends from the third valve 120C to a location between the third sealing element 116C and the fourth sealing element 116D. The fourth input passageway extends from the fourth valve 120D to the main cavity 114. The fourth output passageway extends from the fourth valve 120D to a location between the fourth sealing element 116D and the end of the sealing unit 110. As described above, each input and output passageway for the third and fourth valves do not define a linear path through the housing body. More specifically, each passageway has one or more deviations to direct fluid from the valve to its outlet point. As used herein, a deviation may be a curve or bend in the passageway.
The valves 120A-120D are configured to transition from a closed configuration into an open configuration when the pressure exceeds a predetermined pressure level. The open configuration is when the pressure in the input passageway exceeds the predetermined pressure level, causing the plug 126 to compress the spring and separate from the valve wall to allow fluid to enter the output passageway. In this manner, fluid can be directed toward the sealing element and pressure is therefore distributed across that sealing element. As pressure increases, the second valve 120B transitions into the open configuration when pressure exceeds a predetermined level. This continues until each valve transitions from the closed configuration into the open configuration. In one example, the predetermined pressure level for each valve can be about 3000 psi. In such an example, with four valves as described, a total pressure or 12,000 is psi can be distributed across four sealing elements. The sequential distribution of pressure along with increase in pressure reduces contact stresses and the likelihood of heel extrusion of the sealing elements.
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The practical result is that relatively equal pressure differentials across each of the sealing elements 116A-116D is obtained. For example, in an alternative embodiment where the pressure control tool assembly has five sealing elements, if a 15,000 psi pressure was applied to the pressure control tool assembly, then the mechanism described would provide a differential pressure of 3,000 psi across each of the five sealing elements. In the illustrated embodiment, the pressure levels which cause the valves to open vary depending on the application. For example, in an alternative embodiment where the pressure control tool assembly has 15 sealing elements, if a 15,000 psi pressure was applied, then the pressure level that each seal would withstand would be 1,000 psi. If pressure begins to decrease, the valves will close, and a higher level of pressure will be trapped within each sealing element. This pressure will remain in each sealing element but will likely decay with time as each sealing element repositions itself.
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Accordingly, the tool assembly configuration limits the pressure differential that occurs across any one sealing element by relieving some of the working pressure to a location between the respective sealing element and the adjacent downhole sealing element. As described above, each valve can be rated to open at the predetermined pressure level, e.g. 3000 psi. With four valves as described, a total pressure of 12,000 psi can be distributed across the four sealing elements, at a differential pressure of 3,000 psi per sealing element. The sequential distribution of pressure as the pressure increases reduces contact stresses and the likelihood of heel extrusion.
The present disclosure is described herein using a limited number of embodiments, these specific embodiments are not intended to limit the scope of the disclosure as otherwise described and claimed herein. Modification and variations from the described embodiments exist. For example, the terms “uphole” and “downhole” are only meant to describe the ends of the tool assembly. The tool assembly may be completely inverted. In addition, in alternative embodiments, the valves may be electrically or pneumatically controlled. Further, while embodiments of the present disclosure are shown and described with reference to oil and gas drilling systems, the sealing system and assembly as described herein may be used anywhere a high pressure seal is required, including environments involving a rotating shaft or a feature that compromises a standard static seals capability.
More specifically, the following examples are given as a specific illustration of embodiments of the claimed disclosure. It should be understood that the invention is not limited to the specific details set forth in the examples.
