Abstract:
Method and apparatus are disclosed for confirming the integrity of a seal system extending between a conduit disposed within a subterranean well and a surface or top Christmas tree assembly such that the confirmation steps do not adversely thereafter effect the sealing integrity of the system when exposed to high pressure and/or temperature environments.

Description:
BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     The invention relates to an apparatus and method for confirming the integrity of a seal system positioned within a subterranean well Christmas tree and one or more conduits, such as production tubing and/or casing, held therein. 
     (2) Background of the Invention 
     Casing and production tubing are disposed within a subterranean well subsequent to the drilling, workover or completion thereof. A length of casing having the largest diameter is first introduced at the top of the well through which a smaller diameter length of casing also is introduced for extension below the lowermost end of the largest diameter casing and secured to the lowermost end of the largest diameter casing by means of a liner hanger. Thereafter, the series of casing conduit sections may be telescopically concentrically disposed within the well, depending upon the depth of the well and the location of the production zone or zones. Typically, the smallest diameter casing section will carry interior thereof a length of production tubing. The uppermost conduits are secured together at the top surface of the well through a “Christmas tree” which is a valving system holding the casing and production conduits in sealed relationship and having valving mechanisms for controlling fluid flow therethrough. 
     Conventional methods of testing wellhead and Christmas tree cavities defined between the housing of the Christmas tree and the outer diameter of one of the conduit members employ the use of oils or water fluids. Temperatures encountered during flowing conditions of high pressure, high temperature wells have the potential to heat these fluids to a point where the fluid expansion can potentially collapse the metal seal sleeves and elastomeric seals. Additionally, the use of water can ultimately cause corrosion to metal parts, and the use of oil can ultimately degrade elastomers. 
     The present invention is directed to the problems as above addressed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1A is a partial exterior, partial vertical cross-sectional view of a Christmas tree assembly of a subterranean well showing the cavity between the sealing members and an injector in place extending to a line and compressor/pump assembly for introduction of an inert gas and a hydrocarbon marker therein. 
     FIG. 1B is a view similar to that of FIG. 1A showing the seal means of the Christmas tree extending between enlarged concentrically disposed casing conduit members within the Christmas tree and the interior of the housing of the Christmas tree. 
    
    
     SUMMARY OF THE INVENTION 
     A method is provided for confirming the sealing integrity of a seal system having members positioned in a cavity between a subterranean well conduit, such as casing, or production tubing, and an interior sealing surface of a Christmas tree valve assembly. The method includes the steps of first introducing through a sealable opening of an injection path in communication with the cavity and into the cavity between the seal members a first inert gas combined with a gaseous hydrocarbon marker such as helium, freon or propane for detecting the presence of the inert gas exterior of the Christmas tree assembly. The pressure within the cavity is increased to a first pre-determinable amount. The absence of the marker in the atmosphere immediate the exterior of the Christmas tree is then verified. If the verification step confirms the absence of the gaseous hydrocarbon marker immediate the cavity, the pressure within the cavity is decreased to a second pre-determinable amount, which is lower than the first pre-determinable amount and the injection path then is sealed. 
     The invention also provides an apparatus for confirming the integrity of the seal system within the Christmas tree, means such as an injector extending from a line in communication with a compressor and a pump is introduced into the cavity and between the seal members to inject through the injection path into the cavity a first inert gas combined with the hydrocarbon marker. Means including a compressor and/or pump are used to apply pressure within the cavity to the inert gas and hydrocarbon marker to a pre-determinable amount and, once the absence of the marker in the atmosphere immediate the exterior of the Christmas tree is verified, are used to decrease the pressure within the cavity to a second pre-determinable amount which is lower than the first pre-determinable amount. 
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Now, with first reference to FIG. 1A, there is shown a Christmas tree assembly  100  consisting generally of a block valve assembly  101  having an outer housing  102  through which is disposed a seal block securing the uppermost end of a production tubing conduit  104  threadedly secured to the block  103  at threads  105  and secured by means of a seal sleeve  106  to the housing  102 . A conventional valve wheel  107  is disposed through the block valve assembly  101  for manipulating valves between open and closed positions. The Christmas tree assembly  100  has at its uppermost end a conventional pressure gauge and needle valve  109  disposed lowerly and in communication therewith and, in turn, secured to a tree cap adapter  110  which is secured at the uppermost end of the housing  102  of the block valve assembly  101 . 
     The seal block  103  has a series of first seal members  111 A and  111 B radially disposed around the exterior of the uppermost end of the seal block  103  for sealing securement of the block  103  to a smooth interior wall surface  112  of the block  103 . Likewise, a lower second seal assembly  113  is circumferentially disposed around the exterior of a lower portion of the seal block  103  for sealing engagement around an enlarged interior surface portion  112 A of the housing  102 . The seal members  111 A,  111 B and  113  bridge a cavity  114  defined therebetween and within the housing  102 . Dotted line  115  in FIG. 1A represents an injection path extending between the uppermost end of the cavity  114  and an injector  115  which is, in turn, secured at one end thereof to a gas line  116  in communication with a compressor and pump assembly  117 , which may be portable, and driven by gas or electricity. A bleed valve  118  is in communication with the line  116  for bleeding off pressure subsequent to verification of the absence of the hydrocarbon marker around the Christmas tree. Subsequent to removal of the injector  115 , a threaded seal cap, such as cap  118 , may be threadedly sealingly secured to the housing  102  to assure sealing integrity within the cavity  114 . 
     Turning now to FIG. 1B, similar components are like-numbered. FIG. 1B illustrates a series of additional seal assemblies  119 A and  119 B defining a cavity  120  therebetween exteriorly surrounding the production tubing  104 . Additionally, the Christmas tree assembly  100  further includes lowerly of the cavity  120  a similarly disposed seal element  121 A and  121 B providing the seal means within the Christmas tree assembly  100  for engagement around the exterior of a casing conduit  122  concentrically disposed around the exterior of the production tubing  104 . 
     When the casing and production tubing components are tied off at the top of the well, the Christmas tree assembly  100  is in place there-around with the production tubing  104  being secured at its uppermost end by threads  105  to the seal block  103 . The seal sleeve  106  secures the seal block  103  to the interior of the housing  102  for hanging the production tubing therein. In order to assure that the seal members  111 A,  111 B and second seal assembly  113  have required sealing integrity relative to the interior surface  112 A in the housing  102 , the cap  118  is removed and the injector  115  is disposed relative to the injection path  115 A, and the injector  115  extends to the line  116  which, in turn, is disposed relative to a combination compressor and pump assembly  117 . The compressor and pump assembly  117  are used to introduce the combination of an inert gas with a gaseous hydrocarbon marker through the line  116 , the injector  115  and into the injector path  115 A to the cavity  114 . 
     Any known inert gas may be used in conjunction with the present invention. By “inert” is meant any gaseous compound which will not react with the marker gas in such fashion that the marker cannot be detected during testing and which is safe and non-hazardous when used around oil and gas well Christmas trees. Preferably, nitrogen is used. The gaseous marker must be compatible with the selected inert gas and must be capable of being detected by smell, or the use of a conventional gas detection device sensitive to pre-determinable amounts of the particular marker. Any hydrocarbon-based gaseous marker may be utilized, such as freon, hydrogen, helium, or any other chlorofluorocarbon constituent or halogen-containing gaseous component. 
     As the gas and marker are introduced under pressure within the line  116  to the cavity  114 , the pressure within the cavity is increased, considerably and, typically, up to about 20,000 psi. The absence of the marker in the atmosphere immediate the exterior of the Christmas tree is then verified by use of a hand-held verification device of known construction and availability to those skilled in the art or by detection of same through the human nose. If marker absence is verified, pressure within the line  116  and the cavity  114  is bled off through the bleed valve  118  so that pressure within the cavity  114  is approximately one atmosphere. The injector  115  is removed relative to the injector path  115 A and a threaded seal cap  118  is secured to close the outer end of the injector path. Of course, if the absence of the marker is not verified and, in fact, the marker component is detected, the housing  102  of the Christmas tree assembly  100  may be removed, or opened, to permit replacement of the respective seal assemblies, or other remedial action taken. Regardless of the presence or absence of the marker in the atmosphere around the exterior of the Christmas tree, use of the present invention will result in the original seal means, or replacement or repaired seal means not being exposed thereafter to resulting oil or water corrosion or the like encountered as the result of use of prior art techniques. 
     During the method as above-described, pressure will normally be held at the increased and preselected first level for a period of about one hour. Thereafter, the pressure is reduced and the test gas is vented down to atmospheric pressure and the cavity and injector line sealed. It will be appreciated that use of the present method leaves the cavities between the seal assembly members filled with an inert gas at atmospheric pressure, thus enabling the gas to expand during well flow conditions but still be within the acceptable pressure limits of the sealing mechanisms. 
     Although the invention has been described in terms of specified embodiments which are set forth in detail, it should be understood that this is by illustration only and that the invention is not necessarily limited thereto, since alternative embodiments and operating techniques will become apparent to those skilled in the art in view of the disclosure. Accordingly, modifications are contemplated which can be made without departing from the spirit of the described invention.