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Jar deviceRelated Patent Categories: Wells, With Jar Means For Releasing Stuck PartJar device description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070074867, Jar device. Brief Patent Description - Full Patent Description - Patent Application Claims
FIELD OF THE INVENTION [0001] The invention pertains to jars used in downhole environments to provide an impact force, such as tools used to loosen stuck tool strings or for fishing. BACKGROUND OF THE INVENTION [0002] Jars, such as hydraulic jars, are used in downhole environments to provide impact force. Such tools are useful when a fishing or drilling string is stuck within a well bore and it is necessary to apply an impact force at the stuck location of the string to attempt to loosen it. Similarly, jars can be used in conjunction with fishing tools to provide the fishing tool with sufficient force for operation, for example, by providing an upward jarring force after the fishing tool has engaged a stuck tool. [0003] Jars may be constructed to provide an impact force in either the "up," or "upward" (toward the surface) or "down," or "downward" (away from the surface) directions. Those of skill in the art will recognize that "up" and "down" are so defined because use of horizontal drilling techniques may result in situations in which "up" and "down" are not vertical. Similarly, as used herein, the "lower" portion of a tool or a part thereof is in the "downward" direction in respect to the "upper" portion. For maximum flexibility, ajar can be constructed to provide bidirectional impact, that is, it can fire (provide impact blows) in either the "up" or "down" directions at the choice of the operator on the surface. [0004] However, in some applications, particularly those using coiled tubing, the length of the tools used is of great importance. With coiled tubing, it is greatly desirable to have shorter tools, because multiple tools must often be assembled in combination at the surface, and the coiled tubing operation does not allow for successive assembly of tools as the string is run into a pressured hole. Accordingly, it is sometimes desirable to use ajar which fires in only one direction, because the needed apparatus is shorter than one designed for bi-directional use. [0005] Jars used in these applications operate by setting, or cocking, the jar, then applying an upward or downward force on the jar. These jars comprise a mandrel, which moves relative to the tool body and which bears the primary impact of the jar. Both the mandrel and the tool body generally have anvil surfaces which form the contact surfaces where the mandrel and the tool body meet. When the tool is released from the set position, the mandrel and the tool body move relative to each other at high speed, and the respective anvil surfaces strike with great force, thus producing the impact force of the jar. The relative direction of travel of the mandrel to the tool body is determined by whether the jar is fired up or down. [0006] Although the operation of such tools provides large impact forces where needed, the result is also a large amount of stress on the jar and its various parts. Accordingly, repeated operations of these tools can result in rapid wear and the need to replace or repair the jar. Because reliability of operation is important, it is desirable that ajar be designed and constructed to accommodate repeated high stress. However, the tools are size-constrained by the standard sizes used for downhole operations and the need for limiting the length of the tool, especially in conjunction with coiled tubing operations. In current jars, these factors have limited the ability of the tool to withstand repeated operations without the need for repair or replacement. [0007] Accordingly, it is a goal of the invention to provide a jar that is substantially shorter than current jars. [0008] It is another goal of the invention to provide ajar with improved capability to withstand repeated operation cycles. [0009] It is a further goal of the invention to provide a jar capable of improved impact force. SUMMARY OF THE INVENTION [0010] In the preferred embodiment, the invention comprises a hydraulic jar with a mandrel, a spline body, and a hydraulic timing device. The jar comprises an annular tool body, which is mechanically engaged with the spline body at the lower end of the jar. In the preferred embodiment, the spline body is threaded into the tool body. At its lower end, the spline body has a first anvil face which provides an impact surface for operation of the jar when the tool is fired downward. At its upper end, the spline body has a second anvil face which provides an impact surface for operation of the jar when the tool is fired upward. [0011] The mandrel comprises an annular body which is essentially cylindrical, and which extends through the spline body into the tool body. The lower end section of the mandrel forms a first stop, the upper end of which comprises an anvil face for engaging the first anvil face of the spline body. The upper end section of the mandrel forms a second stop, the lower end of which comprises an anvil face for engaging the second anvil face of the spline body. Thus, the mandrel body can slide up and down through the spline body, its travel limited only by the engagement of the first and second stops with the spline body. [0012] In the preferred embodiment, the first stop of the mandrel is a formed portion of the mandrel body, which maximizes the strength of the mandrel. Such maximum strength is desirable due to the force of the impact when the first stop strikes the spline body when the jar is fired. However, the first stop may be made replaceable by making it detachable from the remainder of the mandrel body, as by providing a threaded engagement. In such a case, it is desirable that the threads be radially as far as possible from the longitudinal axis of the jar to avoid undermining the strength of the jar. [0013] The mandrel body comprises a plurality of longitudinal spline slots, which are preferably milled into the outer surface of the mandrel body. Similarly, the spline body comprises a plurality of longitudinal splines which are fittable into the spline slots in the mandrel body. In the preferred embodiment, the spline body comprises a plurality of longitudinal spline slots milled into the inner surface of the spline body which do not extend to either end of the spline body, and splines are set into the spline slots in the spline body. Additionally, in the preferred embodiment, the spline body comprises a plurality of sections, preferably two longitudinal halves, into which the splines could be set and which can then be fitted around the mandrel body with the splines in slideable engagement with the spline slots of the mandrel body. Alternatively, the splines may be manufactured as part of the inner surface of the spline body. [0014] The spline body and the mandrel are preferably of high strength ferrous or stainless steel. A variety of appropriate materials may be used. Those of skill in the art will recognize that some applications, such as drilling applications, will impose higher torques on the device and will thus require stronger splines than will other applications. [0015] In the preferred embodiment, the spline body can be assembled around the mandrel prior to being threaded into the tool body, allowing for a stronger, one-piece mandrel, as well as for ease of assembly and, if necessary, replacement of tool parts while simultaneously avoiding having any internal threaded structures in the impact path. Accordingly, this embodiment provides significant strength advantages and simultaneously provides for ease of maintenance. [0016] As those of skill in the art will recognize, it is possible to make variations of the structure of this device without departing from the spirit of the invention. For example, the spline body could potentially be a cast piece, with the splines extending from the inner surface without the need for milled spline slots or separately formed splines. [0017] The spline body additionally preferably comprises a vent extending from the first anvil face of the spline body, through the spline body, providing fluid communication with the outside of the tool body and the annular space inside of the tool body. In the preferred embodiment, the second stop of the mandrel is formed to allow fluid communication between the volumes above and below it within the tool body, that is, it does not form a seal with the tool body. Also in the preferred embodiment, an annular mandrel extension is threaded into and in sealing engagement with the second stop of the mandrel, and a floater provides a seal in the annular space above the second stop of the mandrel. The floater serves to equalize hydraulic pressure above and below it, so that the hydraulic fluid within the hydraulic timer (discussed below) is not contaminated by fluid from outside the tool, but the pressures between the two fluids are automatically equalized. [0018] In the preferred embodiment, the mandrel extension further extends into an annular piston body, which is in mechanical engagement with the tool body and serves as an extension thereof. The piston body preferably provides the housing for a hydraulic timing device, although other timing devices, such as mechanical devices known to those of skill in the art, could be used. [0019] Prior art hydraulic timing devices sometimes utilize sliding metal-to-metal seals which maintain a sealing engagement with the face of an internal annular body, such as the piston body of the present invention, and a selective sealing engagement with the inside circumference of an external annular body, such as the floater body or pressure body of the present invention. These devices are prepared for firing by first positioning the seal in a sealing engagement with the external annular body by choosing a "vertical" position in which the inside circumference of the external annular body is small enough to engage the seal. The triggering device comprises a fluid channel, which allows a small amount of hydraulic fluid to "leak" around the seal at a known rate, thus allowing the seal to move at a regulated rate relative to the external annular body when tensile or compressive force is applied by the operator at the surface. The fluid channel may be an integral part of the seal, such as a small channel in the seal material, or may otherwise be formed to provide a fluid pathway around the seal. The external annular body is formed with a transition region in which its internal circumference increases beyond the maximum circumference of the seal, so that when the seal reaches this point, the hydraulic seal will be rapidly released and the jar will "fire" in a sudden release of applied force. [0020] In the preferred embodiment of the present invention, a sliding metal-to-metal seal is in sealing engagement with the face of the floater body or the pressure body, and in selective sealing engagement with the outer circumference of the mandrel extension. In the preferred embodiment, the selective sealing engagement is accomplished by shaping the mandrel extension so that its outer circumference varies, to provide a region of sufficient circumference to engage the sliding metal-to-metal seal, and a region of insufficient circumference to engage the seal. The device is set for firing by positioning it so that the seal is engaged with the outer circumference of the mandrel extension, then applying tensile or compressive force to the assembly. A fluid channel is provided to allow a controlled "leak" of hydraulic fluid around the seal, allowing the seal to slide in a controlled fashion to the point at which the outer circumference of the mandrel extension slopes inward and the seal is released. Those of skill in the art will recognize that the timing of the device can be altered, for example by changing the size of the fluid channel or the length of the section of the mandrel extension which provides sealing engagement with the sliding seal. [0021] Providing a sliding seal which springs inward greatly enhances the strength of the device, because the floater body and the pressure body are of uniform thickness. In the prior art, the thickness of the floater body or pressure body had to decrease at the point at which the seal would release, and remain at this decreased thickness for the length of travel of the mandrel, so that the seal would not catastrophically re-engage with the inner circumference of the floater body or pressure body. Maintaining a uniform thickness of the floater body or pressure body prevents a "weak spot" in the wall of the floater body or pressure body due to the inverse relationship of the hoop stress to the wall thickness. Continue reading about Jar device... Full patent description for Jar device Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Jar device patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. 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