Abstract:
A downhole tool ( 100 ) for selectively providing fluid communication between the interior and the exterior of the tool ( 100 ). The tool ( 100 ) comprises a housing ( 102 ), a safety mandrel ( 130 ) slidably received within the housing ( 102 ) and an operating mandrel ( 114 ) slidably received within the housing ( 102 ). The safety mandrel ( 130 ) operates between a first position and a second position relative to the housing ( 102 ) in response to pressure being applied to the exterior of the housing ( 102 ). The operating mandrel ( 114 ) operates from a noncirculating position to a circulating position in response to pressure being applied to the interior of the housing ( 102 ) once the safety mandrel ( 130 ) has operated to its second position.

Description:
TECHNICAL FIELD OF THE INVENTION 
     This invention relates, in general, to an apparatus and method used during formation testing and, in particular to, an internal pressure operated circulating valve that is placed in the operating position only if sufficient annular hydrostatic pressure unlocks a safety mandrel. 
     BACKGROUND OF THE INVENTION 
     Without limiting the scope of the present invention, its background is described in connection with performing tests to determine the production capabilities of a formation traversed by a wellbore, as an example. 
     During the course of drilling an oil or gas well, the wellbore is typically filled with a fluid known as drilling fluid or drilling mud. One of the purposes of this drilling fluid is to contain formation fluids within the formation intersected by the wellbore. To contain these formation fluids, the drilling mud is weighted with various additives so that the hydrostatic pressure of the drilling mud at the formation depth is sufficient to maintain the formation fluid within the formation without allowing it to escape into the wellbore. 
     When it is desired to test the production capabilities of the formation, a test string is lowered into the wellbore to the formation depth and the formation fluid is allowed to flow into the test string in a controlled testing program. Lower pressure is maintained in the interior of the test string as it is lowered into the wellbore. This is usually done by keeping a valve in the closed position near the lower end of the test string. When the testing depth is reached, a packer is set to seal the wellbore thus closing in the formation from the hydrostatic pressure of the drilling fluid in the well annulus. The valve at the lower end of the test string is then opened and the formation fluid, free from the restraining pressure of the drilling fluid, can flow into the interior of the test string. 
     The testing program typically includes periods of formation flow and periods when the formation is closed in. Pressure recordings are taken throughout the program for later analysis to determine the production capability of the formation. If desired, a sample of the formation fluid may be caught in a suitable sample chamber. 
     At the end of the testing program, a circulation valve in the test string is typically opened so that formation fluid in the test string may be circulated out. Since the hydrostatic pressure of the drilling fluid near the formation is generally much higher than the formation fluids in the test string, it is usually only necessary that the annulus be placed in fluid communication with the interior of the test string to start to reverse out the formation fluids from the test string. Following this circulation step, the packer may be released so that the test string may be withdrawn from the wellbore. 
     Typically, the circulating valves used in a test string may include a sliding sleeve that is opened in response to pressure in the annulus. It has been found, however, that when it is desirable to have more than one circulating valves in a test string to be operated at different times, each tool must be set to operate at a different pressure. Since 500 psi typically separates the pressures at which respective circulating valves will operate, extremely high pressures would be required to operate the later circulating valves in such a configuration, which may damage the well casing. 
     To overcome this problem, attempts have been made to utilize internal pressure operated circulating valves that operated in response to pressure in the test string. It has been found, however, that internal pressure operated circulation valves may be inadvertently opened as the result of an increase in the pressure within the test string. For example, when the test string is made up and lowered into the wellbore, it is desirable to periodically pressure test the test string to assure that the pipe joints have been adequately made up. Such testing requires closing of a valve in the lower part of the test string and applying pump pressure to the interior or the test string at the surface of the well. If the test string includes an interior pressure operated circulation valve, it may be inadvertently opened during such a test string pressure test. 
     It has also been found that internal pressure operated circulation valves may be inadvertently opened as the result of an unexpected increase in pressure from a formation that is not properly under control. If an internal pressure operated circulation valve is not operated during a testing program and is pulled out of the hole in the unoperated position, such a pressure upset from the formation could open an internal pressure operated circulation valve and allow formation fluids to be release at the surface. 
     Therefore, a need has arisen for an internal pressure operated circulation valve that will not inadvertently opened as the result of an increase in the pressure within the test string during a pressure test of the test string. A need has also arisen for such an internal pressure operated circulation valve that will not inadvertently open as a result of an unexpected pressure surge from the formation particularly when the internal pressure operated circulating valve is at or near the surface. 
     SUMMARY OF THE INVENTION 
     The present invention disclosed herein comprises an internal pressure operated circulation valve that will not inadvertently open as the result of an increase in the pressure within the test string during a surface pressure test of the test string. Likewise, the integral pressure operated circulation valve of the present inception will not inadvertently opened as a result of an uninspected pressure surge from the formation. 
     The internal pressure operated circulation valve of the present invention comprises a housing, a safety mandrel and an operating mandrel. The safety mandrel is slidably received within the housing. The safety mandrel operates from a first position to a send position relative to the housing in response to pressure being applied to the exterior of the housing. The operating mandrel is also slidably received within the housing. The operating mandrel operates from a noncirculating position to the circulation position in response to pressure being applied to the interior of the housing. The operating mandrel, however, will only operate to the circulating position when the safety mandrel has operated to the second position. When the operating mandrel is in the circulating position, fluid flow through a circulating port formed through a wall of the housing is permitted. 
     A portion of the safety mandrel is slidably received within the operating mandrel to selectively prevent the operation of the operating mandrel. In one embodiment, the safety mandrel physically preventing the movement of the operating mandrel in the second direction. In another embodiment, the safety mandrel prevents the operation of the operating mandrel by preventing the pressure applied to the interior of the housing from acting on the operating mandrel. 
     The internal pressure operated circulation valve of the present invention may include a biasing device, such as a coil spring, to urge the safety mandrel to its first position such that a predetermined pressure applied to the exterior of the housing is required to operate the safety mandrel to its second position. The internal pressure operated circulation valve of the present invention may also include a frangible restraining device, such as one or more sheer pins, to selectively prevent the movement of the operating mandrel such that a predetermined pressure applied to the interior of the housing is required to operate the operating mandrel to the circulating position. 
     In the method of the present invention, an operating mandrel disposed within a housing is operated by, disposing a safety mandrel in the housing for initially preventing the operation of the operating mandrel, applying pressure to the exterior of the housing to operate the safety mandrel between a first position and a second position relative to the housing and applying pressure to the interior of the housing to operate the operating mandrel from a nocirculating position to a circulating position, thereby permitting fluid flow through a circulating port formed through a wall in the housing. 
     In the method, the safety mandrel initially prevents the operation of the operating mandrel by disposing a portion of the safety mandrel within the operating mandrel. In one embodiment, this is achieved by physically preventing the movement of the operating mandrel in the second direction. In another embodiment, this is achieved by preventing the pressure applied to the interior of the housing from acting on the operating mandrel. 
     The method of the present inventon may require that a predetermined pressure be applied to the exterior of the housing to operate the safety mandrel to the second position by biasing the safety mandrel to the first position with a biasing device. Likewise, the method of the present invention may require that a predetermined pressure be applied to the interior of the housing to operate the safety mandrel to circulating position by frangibly restraining the operating mandrel. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the features and advantages of the present invention, references now made to the detailed description of the invention along with the accompanying figures in which corresponding numerals in the different figures refer to corresponding parts and in which: 
     FIG. 1 is a schematic illustration of an offshore oil or gas drilling platform operating a test string including an internal pressure operate circulating valve of the present invention; 
     FIGS. 2A-2C are quarter sectional views of an internal pressure operated circulating valve of the present invention in its various operating positions; and 
     FIGS. 3A-3C are quarter sectional views of an internal pressure operated circulating valve of the present invention in its various operating positions. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     While the making and using of various embodiments of the present invention is discussed in detail below, it should be appreciated that the present invention provides many applicable inventive concepts which can be embodied in a wide variety of specific contexts. The specific embodiment discussed herein are merely illustrative of the specific ways to make and use the invention, and do not limit the scope of the invention. 
     Referring to FIG. 1, an offshore drilling and testing operation is schematically illustrated and generally designated  10 . A semi-submersible platform  12  is centered over a submerged oil or gas formation  14  located below the sea floor  16 . A well comprising a wellbore  18  is lined with a casing string  20  extending from the platform  12  to formation  14 . Casing string  20  includes a plurality of perforations  22  at its lower end which provide communication between formation  14  and the interior of the wellbore  18 . 
     A wellhead installation  24  which includes blowout preventors  26  is located on sea floor  16 . A conductor  28  extends from wellhead installation  24  to platform  12 . Platform  12  includes a work deck  30  that supports a derrick  32 . Derrick  32  supports a hoisting apparatus  34  for raising and lowering pipe strings such as formation testing string  36 . A supply conduit  38  is provided that extends from a hydraulic pump  40  on deck  30  of platform  12  and extends to the wellhead installation  24  at a point below blowout preventors  26  to allow the pressurizing of the well annulus  42  surrounding test string  36 . 
     During testing, a seal assembly  44  is used to isolate formation  14  from fluids in well annulus  42 . A perforated tail piece  46  is provided at the lower end of test string  36  to allow fluid communication between formation  14  and the interior of test string  36 . The lower portion of test string  36  also includes intermediate conduit portion  48  and torque transmitting pressure and volume balanced slip joint  50 . An intermediate conduit portion  52  is provided for imparting setting weight to seal assembly  44 . Near the lower end of test string  36  is located a tester valve  54  which may typically be an annulus pressure operated tester valve. A pressure recording device  56  is located below tester valve  54 . Immediately above tester valve  54  is an internal pressure operated circulating valve  58  of the present invention. 
     Even though FIG. 1 depicts an offshore environment, it should be understood by one skilled in the art that the downhole component described herein is equally well-suited for operation in an onshore environment. 
     Referring now to FIGS. 2A-2C therein is depicted quarter sectional views of one embodiment of an internal pressure operated circulating valve of the present invention that is generally designated  100 . Valve  100  includes a cylindrical outer housing  102  having an upper housing adapter  104  which includes threads  106  for attaching valve  100  to the portion of test string  36  located above valve  100 . At the lower end of housing  102  is a lower housing adapter  108  which includes an external threaded portion  110  for connection of valve  100  to that portion of test string  36  located below valve  100 . 
     Slidably and sealably received within inner bore  112  of housing  102  is operating mandrel  114 . Operating mandrel  114  is initially frangibly retained in its noncirculating position by one or more shearable members such as a shear pin  116  which is disposed through a radial bore  118  of housing  102  and received within a radially extending bore  120  of operating mandrel  114 . The exact number and size of the shearable members will be determined based upon the desired operating pressure for operating mandrel  114 . 
     In the noncirculating position as depicted in FIG. 2A, operating mandrel  114  prevents the flow of fluids between the exterior of valve  100  and the interior of valve  100  through circulating port  122 . Operating mandrel  114  includes a plurality of spring fingers, one of which is finger  124 . Spring finger  124  is terminated by head  126 . In the noncirculating position, head  126  rests against the upper shoulder of annular ledge  128  of housing  102 . 
     Slidably and sealably received within inner bore  112  of housing  102  below operating mandrel  114  is safety mandrel  134 . Safety mandrel  130  includes an upper end  132  that is closely received within head  126  of operating mandrel  114  to physically prevent the movement of operating mandrel  114 . 
     A coil compression spring  134  has its upper end engaging the lower shoulder of annular ledge  128  and has its lower end engaging annular upper end surface  136  of safety mandrel  130 . Spring  134  biases safety mandrel  130  downwardly to maintain upper end  132  against head  126  and prevent movement of operating mandrel  114 . In this position of valve  100 , internal pressure testing of testing string  36  may periodically occur without moving operating mandrel  114  or loading shearable members  116 . 
     Spring  134  is initially retained in a substantially uncompressed state until external pressure applied to safety mandrel  130  through communication port  142  of housing  102  acts between seals  138  and  140 . When the external hydrostatic pressure reaches a sufficient level, safety mandrel  130  travels upwardly relative to housing  102  compressing spring  134 , as best seen in FIG. 2B. A rupture disk  143  may be placed within communication part  142  to selectively prevent the external hydrostatic pressure from communicating with safety mandrel  130  until the external hydrostatic pressure reaches a sufficient level to burst rupture disk  143 . Once safety mandrel  130  has traveled upwardly, safety mandrel  130  no longer physically restrains the movement of operating mandrel  114 . If the external hydrostatic pressure is reduced below the predetermined level, valve  100  is reset into the position depicted in FIG. 2A due to the bias force of spring  134 . The procedure may be repeated without moving operating mandrel  114 . 
     When valve  100  is in the position depicted in FIG. 2B, application of internal pressure then acts on operating mandrel  114  between seals  144  and  146  thus urging operating mandrel  114  downwardly. When sufficient pressure is applied, pin  116  shears thus permitting operating mandrel  114  to move downwardly. As operating mandrel  114  moves downwardly, the spring fingers, such as spring finger  124 , are no longer restrained by upper end  132  of safety mandrel  130  and spring inwardly around annular ledge  128  of housing  102 , as best seen in FIG.  2 C. 
     It should be apparent to those skilled in the art that the use of directional terms such as above, below, upper, lower, upward, downward, etc. are used in relation to the illustrative embodiments as they are depicted in the figures, the upward direction being towards the top of the corresponding figure and the downward direction being toward the bottom of the corresponding figure. It is to be understood that the downhole component described herein may be operated in vertical, horizontal, inverted or inclined orientation without deviating from the principles of the present invention. 
     In operation, valve  100  is initially assembled at the surface as shown in FIG.  2 A. Thereafter, valve  100  is incorporated into a test string such as that shown in FIG.  1  and lowered into the wellbore as shown in FIG.  1 . When in this configuration, tester valve  54  of FIG. 1 may be repeatedly opened and closed by application of annulus pressure in order to conduct pressure tests of test string  36  which may shift safety mandrel  130  but will not shift operating mandrel  114  of valve  100 . Thereafter, fluids may be pumped through test string  36  and into formation  14 , for example, for acid-treating formation  14 . After testing and treatment, but prior to raising test string  36  out of wellbore  18 , it is desirable to reverse circulate fluids from test string  36 . Such is accomplished by moving the operating mandrel downwardly so that circulation port  122  is in communication with the interior of housing  102 . Thereafter, fluid is pumped downwardly in the annulus through port  122  and upwardly through test string  36  thereby reverse circulating fluids from test string  36 . 
     Valve  100  is opened by shifting safety mandrel  130  then shifting operating mandrel  114  as follows. With valve  100  in the configuration of FIG.  2 A and suspended on test string  36  as shown in FIG. 1, the hydrostatic pressure of the annulus fluids upwardly bias safety mandrel  130  via communication port  142 . Seal  138  defines an outer diameter and seal  140  an inner diameter of safety mandrel  130 . When the hydrostatic force reaches the predetermined level necessary to overcome the bias force of spring  134 , safety mandrel  130  moves upwardly with upper end  132  of safety mandrel  130  no loner contacting head  126  of spring finger  124  of operating mandrel  114 . Alternatively, rupture disk  143  may be placed within communication port  142  which may be set to burst at a predetermined pressure. 
     After safety mandrel  130  has moved to its upper position as best seen in FIG. 2B, test string  36  is pressurized thus permitting pressurized fluid to act on operating mandrel  114 . Seal  144  defines an outer diameter and seal  146  defines the inner diameter of operating mandrel  114 . When the pressure reaches the predetermined level necessary to shear the shear pins  116 , operating mandrel  114  moves quickly downwardly. In the lower position of operating mandrel  114 , as best seen in FIG. 2C, seal  144  is below port  122  and thus fluid communication is permitted between the annulus and the interior of housing  102  thereby allowing reverse circulation. 
     Once operating mandrel  114  has opened circulating port  122 , it remains open. When the formation fluids are circulated out of test string  36  and fully replaced by the fluids from the annulus, test string  36  may be pulled from the wellbore. 
     Thus, it can be seen that prior to the operation of safety mandrel  130 , for example during a surface test string pressure test, there is no risk of inadvertently opening circulation port  122  since interior pressure will not operate operating mandrel  114 . Before pressure in test string  36  can be so communicated, safety mandrel  130  must be urged upwardly until upper end  132  no longer interferes with the movement of operating mandrel  114 . It should be noted that if interior pressure is not applied to operating mandrel  114  while safety mandrel  130  is in the uppermost position, spring  134  will return safety mandrel  130  to the position seen in FIG. 2A when the bias force of spring  134  becomes greater than the hydrostatic force acting upwardly on safety mandrel  130 . 
     Referring now to FIGS. 3A-3C therein is depicted quarter sectional views of another embodiment of an internal pressure operated circulating valve of the present invention that is generally designated  200 . Valve  200  includes a cylindrical outer housing  202  having an upper housing adapter  204  which includes threads  206  for attaching valve  200  to the portion of test string  36  located above valve  200 . At the lower end of housing  202  is a lower housing adapter  208  which includes an external threaded portion  210  for connection of valve  200  to that portion of test string  36  located below valve  200 . 
     Slidably and sealably received within inner bore  212  of housing  202  is operating mandrel  214 . Operating mandrel  214  is initially frangibly retained in its noncirculating position by one or more shearable members such as shear pin  216  which is disposed through a radial bore  218  of housing  202  and received within a radially extending bore  220  of operating mandrel  214 . In the noncirculating position as depicted in FIG. 3A, operating mandrel  214  prevents the flow of fluids between the exterior of valve  200  and the interior of valve  200  through circulating port  222 . Operating mandrel  214  includes a communication port  225 . 
     Slidably and sealably received within inner bore  212  of housing  202  above operating mandrel  214  is safety mandrel  230 . Safety mandrel  230  includes a lower end  232  that is closely received within operating mandrel  214  to prevent internal pressure from entering communication port  225  thereby preventing the movement of operating mandrel  214 . 
     A coil compression spring  234  has its upper end engaging the lower shoulder  237  of housing  202  and has its lower end engaging annular upper end surface  236  of safety mandrel  230 . Spring  234  biases safety mandrel  230  downwardly to maintain lower end  232  within operating mandrel  214  and prevent movement of operating mandrel  214 . In this position of valve  200 , internal pressure testing of testing string  36  may periodically occur without moving operating mandrel  214  or loading shearable member  216 . 
     Spring  234  is initially retained in a substantially uncompressed state until external hydrostatic pressure acting between seals  238  and  240  through communication port  242  of housing  202  reaches a predetermined level. When the external hydrostatic pressure reaches a sufficient level, safety mandrel  230  travels upwardly relative to housing  202  compressing spring  234 , as best seen in FIG. 3B. A rupture disk  243  may be placed within communication port  242  to selectively prevent the external hydrostatic pressure from communicating to safety mandrel  230  until the external hydrostatic pressure reaches a sufficient level to burst rupture disk  243 . Once safety mandrel  230  has traveled upwardly, seal  241  no loner prevents internal pressure from entering communication port  225 . If the external hydrostatic pressure is reduced below the predetermined level, however, valve  200  will reset into the position depicted in FIG. 3A due to the bias force of spring  234 . This procedure may be repeated without moving operating mandrel  214 . 
     When valve  200  is in the position depicted in FIG. 3B, application of internal pressure acts on operating mandrel  214  between seals  244  and  246  thus urging operating mandrel  214  downwardly. When sufficient pressure is applied, pins  216  shear thus permitting operating mandrel  214  to move downwardly, as best seen in FIG.  3 C. 
     In operation, valve  200  is initially assembled at the surface as shown in FIG.  3 A. Thereafter, valve  200  is incorporated into test string  36  as shown in FIG.  1  and lowered into wellbore  18 . After testing and treatment, but prior to raising test string  36  out of wellbore  18 , it is desirable to reverse circulate fluids from test string  36  which may shift safety mandrel  230  but will not shift operating mandrel  114  at valve  200 . Such is accomplished by moving operating mandrel  214  downwardly so that circulation port  222  is in communication with the interior of housing  202 . Thereafter, fluid is pumped downwardly in the annulus through port  222  and upwardly through test string  36  thereby circulating well fluids from test string  36 . 
     Valve  200  is opened by shifting safety mandrel  230  then shifting operating mandrel  214  as follows. With valve  200  in the configuration of FIG.  3 A and suspended on test string  36  as shown in FIG. 1, the hydrostatic pressure of the annulus fluids upwardly bias safety mandrel  230  via communication port  242 . Seal  238  defines an outer diameter and seal  240  an inner diameter of safety mandrel  230 . When the hydrostatic force reaches the predetermined level necessary to overcome the bias force of spring  234 , safety mandrel  230  moves upwardly with lower end  232  and seal  241  of safety mandrel  230  no longer contacting operating mandrel  214 . A rupture disk  243  may additionally be placed within communication port  242  that is set to burst at a predetermined pressure. 
     After safety mandrel  230  has moved to its upper position as best seen in FIG. 3B, test string  36  is pressurized thus permitting pressurized fluid to travel through communication port  225  and act on operating mandrel  214 . Seal  244  defines an outer diameter and seal  246  defines the inner diameter of operating mandrel  214 . When the pressure reaches the predetermined level necessary to shear the shear pins  216 , operating mandrel  214  moves quickly downwardly. 
     In the lower position of operating mandrel  214  as best seen in FIG. 3C, seal  244  is below port  222  and thus fluid communication is permitted between the annulus and the interior of housing  202  thereby allowing reverse circulation. 
     Thus, it can be seen that prior to operating of safety mandrel  230  there is no risk of inadvertently opening circulation port  222  since interior pressure will not operate operating mandrel  214 . Before pressure in test string  36  can be so communicated, safety mandrel  230  must be urged upwardly until seal  241  is above communication port  225  of operating mandrel  214 . 
     Once operating mandrel  214  has opened circulating port  222 , it remains open. When the formation fluids are circulated out of test string  36  and fully replaced by the fluids from the annulus, test string  36  may be pulled from wellbore  18 . 
     While this invention has been described with a reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications and combinations of the illustrative embodiments as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to the description. It is therefore, intended that the appended claims encompass any such modifications or embodiments.