Abstract:
A well pressure activated pack off head comprising a hollow body formed for coaxial connection to the wellhead which provides for unobstructed passage of a data transmitting wireline therethrough. Disposed coaxially within the hollow body is a pack off rubber with a passage formed along its longitudinal axis for passage of a data transmitting wireline. Located below the pack off rubber is a piston in pressure communication with the wellbore. High pressure inside of the wellbore squeezes the piston against the pack off rubber and compresses it tightly around the wireline. A pressure seal is formed between the pack off rubber and the wireline when the pack off rubber is sufficiently compressed by the piston.

Description:
RELATED APPLICATIONS 
     This application claims priority from abandoned U.S. Provisional Application No. 60/251,292, filed Dec. 5, 2000, the full disclosure of which is hereby incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates generally to the field of oil and gas well services. More specifically, the present invention relates to an apparatus that provides a pressure seal around a wireline during oil field service operations. 
     2. Description of Related Art 
     Numerous techniques, generally known as well logging, exist for collecting geological data from oil and/or gas wells, where the geological data is useful for locating potential hydrocarbon bearing reservoirs. Well logging is also used for estimating the capacity of the potential hydrocarbon bearing reservoirs. Many types of well logging practices exist. They include neutron logs, induction logs, and acoustic logs. In each of the aforementioned well logging techniques a well logging tool is deposited into the wellbore and travels through the well bore collecting geological data about the region surrounding the well bore. Generally the well logging tool produces a signal, either electrical, nuclear, or acoustical, which is directed into the area adjacent the well bore. The reflection or propagation of the emitted signal is then retrieved by the tool or by another piece of equipment suitably located. The retrieved signals are stored and analyzed in order to evaluate the potential for hydrocarbon production in the particular geological formation being analyzed, monitor reservoir performance, or to evaluate wellbore mechanical integrity. 
     Generally, the well logging tool is inserted into the well bore attached to a wireline. The tool is raised and lowered by the wireline, and data is transmitted through the wireline for introducing signals to the well logging tool from the surface. The wire line can also transmit data recovered from within the well bore to the surface for collection and analysis. 
     As a secondary safety measure, a pressure containment apparatus, or pack off head, is often installed on the well during wireline operations. Wireline (or slick-line) pack off heads (oil savers) have been used by the oil field service industry for many years. A pack off head is designed to make a pressure seal around a wireline to contain the well pressure during trips in and out of the well. If during wireline operations a well kick were experienced, an unsafe condition would occur if the well head was not contained but instead left open to atmosphere. A typical pack off head includes a hard rubber insert with a passage where the wire line passes through the annulus. To seal around the wireline, the hard rubber insert is axially compressed, which reduces the cross sectional area of the passage. Reducing the cross sectional area of the passage causes the inner radius of the passage to fit snugly around the outer radius of the wire line, thus preventing fluid flow through the passage. Although the passage snugly seals around the outer radius of the wire line, the wire line is still able to freely traverse through the passage. 
     Traditionally, pack off heads have been manual or hydraulic. A manual style pack off head is usually comprised of a threaded cap that compresses the rubber packing element as the cap is screwed down onto the head assembly. This operation is typically performed by hand. The hydraulic style pack off head has a hydraulic cylinder that is expanded via hydraulic pressure provided by a hand pump connected to the head by a hydraulic hose. The pack off head cylinder expands as pressure is supplied to it, expansion of the pack off head cylinder in turn compresses the pack off element. Both the manual and the hydraulic pack off heads compress a packing element to provide a seal around the wireline and both require personnel to perform this function. 
     Therefore, a method or an apparatus is desired that provides an automatic pressure sealing function around a wireline when the pack off head is located in an area that is not accessible to be either manually or hydraulically operated while a wireline is being lowered into and drawn from a hydrocarbon producing wellbore. 
     BRIEF SUMMARY OF THE INVENTION 
     One embodiment of the present invention discloses a well pressure activated pack off head to be used in conjunction with a wellhead situated on a hydrocarbon producing wellbore. The well pressure activated pack off head comprises a hollow body formed for coaxial connection to the wellhead, the hollow body must also provide for unobstructed passage of a data transmitting wireline therethrough. 
     Disposed within the hollow body is a pack off rubber with a passage formed along its longitudinal axis for passage of a data transmitting wireline therethrough The pack off rubber is coaxially situated within the hollow body. The pack off rubber can be formed from numerous materials, but the material must be pliable enough under the conditions of use to provide a pressure seal between it and the wireline passing through its axis. 
     Also located in the hollow body, above and proximate to the pack off rubber, is a pack off bushing. The pack off bushing is coaxial to the hollow body and has an axial passage formed along its axis to allow for passage of a data transmitting wireline through its axis. The pack off bushing should have a higher hardness than the pack off rubber, typical materials include brass or hard face steel. 
     The well pressure activated pack off head further includes a piston coaxially situated within the hollow body and also has an axial passage formed concentric along its axis that allows for passage of a data transmitting wireline through it. The bottom of the piston is its wellbore pressure side and its top is its ambient pressure side. The wellbore pressure side of the piston is in pressure communication with the wellbore. The ambient pressure side of the piston is in pressure communication with the ambient space surrounding the pressure pack off head. The piston is situated below the pack off rubber, which puts the pack off rubber between the piston and the pack off bushing. 
     When the pressure of the wellbore, and thus the wellbore pressure side, exceeds the ambient pressure, the pressure differential experienced by the piston urges it toward the pack off bushing and pack off rubber. Continued upward movement of the piston causes the piston to contact the pack off rubber and push the pack off rubber against the pack off bushing. This pushing action compresses the pack off rubber between the piston and the pack off bushing such that compression of the pack off rubber compresses the pack off rubber axial passage around the data transmitting wireline. Compression of the pack off rubber axial passage around the data transmitting wireline eventually provides a pressure seal between the pack off rubber axial passage and the data transmitting wireline passing therethrough. The well pressure activated pack off head can also include a rubber compressor disposed between the piston and the pack off rubber, the rubber compressor transmits the axial compressing force from the piston to the pack off rubber. 
     To prevent pressure spikes in the wellbore from causing transient high forces upon the pack off rubber, the pressure pack off head includes a pressure regulator that controls the pressure between the wellbore and the piston. One example of a pressure regulator is a restriction orifice that regulates the pressure differential across the piston which limits the maximum force that the piston can apply to the pack off rubber (or the rubber compressor). 
     Also included in the well pressure activated pack off head is a spring that urges the piston away from said pack off rubber when the spring force exceeds the force experienced by the piston resulting from the pressure differential across its two sides. The size, configuration, and material of the spring is based on the application of the well pressure activated pack off head. 
     An alternative embodiment of the well pressure activated pack off head also includes a hollow body, a piston, a pack off rubber, and a pack off bushing axially situated in the hollow body. Here the piston has a wellbore pressure side and an ambient side. Also included in this alternative is a hydraulic piston and a means for communicating pressure from the ambient pressure side of the piston to the hydraulic piston. 
     Within the pressure communication means is a pressure regulator that controls the pressure that is delivered to the hydraulic piston from the ambient pressure side of the piston. As in the first embodiment, the pressure control means limits pressure excursions experienced in the wellbore from exerting high compression forces onto the pack off rubber. 
     Like the first embodiment, the alternative embodiment operates on the principal that the wellbore pressure will exceed the ambient pressure around the pack off head. The pressure differential is then utilized to produce a force that compresses the hydraulic piston against the pack off rubber, this squeezes the pack off rubber around the data transmitting wireling to providesa pressure seal around the pack off rubber and the data transmitting wireline. Also included in the alternative embodiment of the well pressure activated pack off head is a spring axially provided in the hollow body situated to urge the hydraulic piston away from the pack off rubber when the force experienced by the pressure differential across the hydraulic piston is lower than the spring force. 
     A third embodiment of a well pressure activated pack off head also comprises a hollow body, a pack off rubber, a pack off bushing, and a piston axially located in the hollow body. Like the other embodiments, these components are all formed to allow free passage of a wireline along their axis. 
     The piston has a top side, a bottom side, and a shaft connecting the piston top side to a rubber compressor. The piston bottom side is in pressure communication with the wellbore, and the pack off rubber is situated between said pack off bushing and said rubber compressor. 
     Like the other embodiments, this embodiment works on the principal of a force resulting from a pressure differential across an object. Because the wellbore pressure will generally exceed the ambient pressure around the well pressure activated pack off head, those two pressures are disposed across opposite faces of an object to produce a force, here the object is the piston. The resulting force across the piston is used to compress the pack off rubber against the pack off bushing. A compressed pack off rubber will result in a pressure seal between it and a data transmitting wireline passing through the axial passage of the pack off rubber. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     FIG. 1 illustrates a cross section of the well pressure activated pack off head. 
     FIG. 2 shows a cross section of an alternative embodiment of the well pressure activated pack off head. 
     FIG. 3 depicts yet another alternate embodiment of the well pressure activated pack off head. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to the drawing herein, a Well Pressure Activated Pack Off Head  30  according to one embodiment of the invention is shown in FIG.  1 . The cross-sectional view of FIG. 1 illustrates that the Well Pressure Activated Pack Off Head  30  includes a pack off bushing  39 , a pack off rubber  33 , a pressure port  37 , a spring  32 , a rubber compressor  41 , a hollow body  20 , and a piston  34 . Each component of the Well Pressure Activated Pack Off Head  30  should contain an axial passage suitable for passage of a well logging wireline  15  through the Well Pressure Activated Pack Off Head  30 . To ensure that the pack off rubber  33  properly seals around a wireline  15 , it is important that the pack off rubber  33  material be sufficiently pliable to perform under the extreme cold or hot conditions for which it will be used, and yet be of adequate resiliency to sustain the pressure applied to it to preclude leakage between the pack off rubber  33  and the wireline  15 . 
     Use of the Well Pressure Activated Pack Off Head  30  is not limited to traditional grade or sea surface oil and/or gas wells but can also be used with subsea applications and other applications where the well head is in an inaccessible or difficult to monitor location. Utilization of the Well Pressure Activated Pack Off Head  30  in place of prior art pack off heads eliminates the need to constantly monitor and adjust the sealing force of the pack off rubber of these prior art pack off heads. Further, the Well Pressure Activated Pack Off Head  30 , when used during any wireline operation, such as well logging, well perforating, or mechanical services, is capable of providing safety measures in a well where the wellbore pressure exceeds the pressure of the surrounding formation. 
     One of the advantages of the present invention is that an automated pressure seal can be provided around the wireline  15  at the wellbore entrance. Because the pressure seal is automated, the risk of human error during operations is reduced. Also reduced are the resources of added personnel required to monitor and adjust a manually operated pack off head. During wireline operations, gas bubbles from hydrocarbons entrained in the wellbore, and adjacent formations, can begin to form beneath the wireline tool as the tool is traversed through the wellbore If enough gas bubbles form below the wireline tool, the buoyancy provided by the gas bubbles can exert an upward force onto the tool which in turn attempts to eject the tool from the wellbore. This is known as a “well kick”. Well kicks can be detected by the well operators at the surface by monitoring the fluids that are exiting the wellbore. 
     If well operators determine that a well kick is imminent, they can actuate the rams provided on a well blow out preventer (not shown). If the situation is determined to be severe enough, a shear ram will be actuated which will shear whatever is inserted through the wellbore, either the wireline  15  or a drill string. Shearing the wireline  15  will allow whatever is located in the wellbore beneath the shear ram to fall deep into the wellbore, which can terminate hydrocarbon production from the wellbore, this is an undesireable result. Other undesireable effects of using shear rams include leaving expensive well logging tools in a wellbore, some of which are radioactive, and wireline  15  becoming entangled with drill pipe. Implementation of the Well Pressure Activated Pack Off Head  30  can seal the well during some well kicks and therefore eliminate the need to immediately suspend well operations. 
     The Well Pressure Activated Pack Off Head is generally attached to a wellbore by threaded attachment of the coupling  36 . This provides pressure communication between the pack off head passage  38  and the wellbore, which in turn puts the piston wellbore side  34   a  in pressure communication with the well bore as well. The pressure port  37  provides pressure communication between the piston spring side  34   b  and the ambient conditions experienced by the Well Pressure Activated Pack Off Head  30 . In surface operations this will be atmospheric pressure, in subsea applications the ambient pressure will be the pressure at the sea floor. Accordingly, when the wellbore pressure exceeds ambient pressure, a pressure differential will exist across the piston  34 . This pressure differential produces a resultant force which pushes the piston  34  upwards against the rubber compressor  41 . When the rubber compressor  41  is pushed upward by the piston  34 , the rubber compressor  41  will compress the pack off rubber  33  against the pack off bushing  39 . This reduces the cross sectional area of the rubber inner passage  33   a  and squeezes the rubber inner passage  33   a  tightly around the wireline  15 , thus providing a seal to prevent leakage across the pack off rubber  33 . Leakage between the outer radius of the piston  34  and the inner passage of the pressure pack off head body  30   a  is prevented by a piston seal  35 . Although the pack off rubber  33  is sealingly engaged tightly around the wireline  15 , the wireline  15  must still able to freely transverse through the pack off head passage  38 . 
     Because of the wear experienced by the pack off bushing  39  and the rubber compressor  41 , it is preferred they be formed from a material that can withstand repeated traversals of wireline  15  through their axis without experienced undue wear. Suitable materials would include either brass or hard faced steel. However, the operating environment in which the well pressure activated pack off head is exposed to will also be a factor in deciding exactly which material to use for these components. 
     During wireline operations the rubber inner passage  33   a  will experience some wear. Although the wear will result in material loss of the inner annulus of the pack off rubber  33 , the pack off rubber  33  will continue to seal against the wireline  15  because of the constant compressive force applied to it by the rubber compressor  41 . When the piston wellbore side  34   a  is no longer exposed to the borehole pressure, or the borehole pressure is sufficiently decreased below the spring force of the spring  32 , the spring  32  will return the piston  34  to its original position against the pressure pack off head body  30   a.  The dimensions and characteristics of the spring  32  are determined based on the well parameters. When the spring  32  moves the piston  34  away from the rubber compressor  41 , the rubber compressor  41  will cease to apply force to the pack off rubber  33 , and therefore no longer compress it. 
     The cross sectional area of the pressure port  37  can be adjusted to regulate the fluid flow from the ambient pressure side of the piston  34  to the ambient space surrounding the Well Activated Pressure Pack Off Head  30 . The cross sectional area of the pressure port  37  can be enlarged by drilling a larger aperture, or can be reduced by adding a restriction orifice  37   a  or a ferrel. Regulating the fluid flow exiting the pressure port  37 , and more specifically limiting this flow, will dampen the upward movement and impulse force that the piston  34  applies to the pack off rubber  33 . It is desired to not allow pressure spikes onto the pack off rubber  33  as this can cause episodes of increased squeezing force onto the wireline  15 , which can damage it. 
     In FIG. 2, one alternative embodiment of the Well Pressure Activated Pack Off Head  80  is depicted. This embodiment also implements a pack off head upper body  81 , a pack off head lower body  82 , a piston  85 , a pack off rubber  33 , a pack off bushing  39 , and a bushing spring  40 . In this embodiment of the Well Pressure Activated Pack Off Head  80 , the piston  85  includes a piston bottom  85   a  and piston shaft  85   b.  Attached to the top of the piston shaft  85   b  is an alternative embodiment of the rubber compressor  89 , and provided on the piston shaft  85   b  is a piston spring  86 . The piston shaft  85   b  is formed to fit within an aperture  81   a  formed concentrically on the bottom of the pack off head upper body  81 . 
     Because the piston bottom  85   a  is in pressure communication with the wellbore the piston  85  will be forced upward when the wellbore pressure is greater than the pressure at the piston top side  85   c.  Continued upward movement of the piston  85  causes the rubber compressor  89  to impinge the pack off rubber  33  against the pack off bushing  39  and squeeze the inner radius of the pack off rubber  33  against the wireline  15 . Here, the bushing spring  40  will be compressed when the pack off rubber  33  is squeezed against the pack off bushing  39 , and will expand to its original configuration when the spring force of the bushing spring  40  surpasses the force applied by the piston  85  due to wellbore pressure. Similarly, when upward force supplied to the piston  85  by the wellbore pressure is less than the spring force of the piston spring  86 , the piston spring  86  will expand and push the piston  85  away from the pack off rubber  33 . 
     To prevent pressure communication across the piston  85 , a piston head seal  87  is provided to provide a sealing function between the piston  85  and the inner surface of the pack off head lower body  82 . The piston shaft seal  88 , situated between the piston shaft  85   b  and the pack off head upper body  81 , provides a pressure seal between the piston top side  85   c  and the aperture  81   a.    
     FIG. 3 depicts yet another embodiment of the Well Pressure Activated Pack Off Head  70 . The Well Pressure Activated Pack Off Head  70  includes a piston  75 , a hydraulic piston  78 , a rubber compressor  79 , a spring  32 , an annulus  73 , tubing  74 , a pressure regulator  71 , a pack off head upper body  76 , a pack off head lower body  77 , a pack off bushing  39 , a pack off rubber  33 , and a reservoir  72 . In this embodiment, the bottom of the piston  75  is exposed to the wellbore pressure, so that when the pressure of the wellbore is different than the pressure of the reservoir  72 , the piston  75  will experience a pressure gradient across its body. Further, when the pressure gradient results in an upward force that overcomes the static friction of the piston  75 , the piston  75  will move upward. 
     The reservoir  72  is filled either with a fluid, including a gas (such as air or nitrogen), hydraulic fluid, or grease. When the piston  75  (which is situated in the pack off head lower body  77 ) is moved upward the volume of the reservoir  72  is decreased, which forces some of the contents of the reservoir  72  into the tubing  74 . The fluid contents of the reservoir  72  that enters the tubing  74  is directed into the annulus  73 , which in turn increases the pressure of the annulus  73 . Situated on the tubing  74 , the pressure regulator  71  controls the pressure of the fluid flow into the annulus  73 . 
     When the pressure in the annulus  73  (as supplied via the tubing  74 ) exceeds the spring force of the spring  32 , the hydraulic piston  78  moves downward and pushes the rubber compressor  79  against the pack off rubber  33 . Continued movement of the rubber compressor  79  against the pack off rubber  33  ultimately squeezes the pack off rubber  33  against the pack off bushing  39 , this reduces the inner radius of the pack off rubber  33  and results in a seal against the wireline  15 . The pack off rubber  33  will continue to provide a seal along the wireline  15  until the force applied to the hydraulic piston  78  by the annulus pressure is less than the spring force of the spring  32 . 
     The pressure regulator  71  works the same as a pressure control valve. The purpose of the pressure regulator  71  is to provide a constant supply of pressure to the hydraulic piston  78 , this eliminates high pressure excursions experienced by the well bore from acting on the hydraulic piston  78 . If the hydraulic piston  78  is exposed to sudden episodes of high pressure, it will then translate Act the pressure to a sudden high force onto the rubber compressor  79  and ultimately the pack off rubber  33 . Sudden high forces applied to the pack off rubber  33  by the rubber compressor  79  will in turn cause the pack off rubber  33  to squeeze the wireline  15  such that the wireline  15  can be damaged. 
     The present invention described herein, therefore, is well adapted to carry out the objects and attain the ends and advantages mentioned, as well as others inherent therein. While a presently preferred embodiment of the invention has been given for purposes of disclosure, numerous changes in the details of procedures for accomplishing the desired results. For example the invention can be used as an additional safety measure for any wireline procedure, such as perforations and plug setting, These and other similar modifications will readily suggest themselves to those skilled in the art, and are intended to be encompassed within the spirit of the present invention disclosed herein and the scope of the appended claims.