Tubing Plug Apparatus for Performing Down-Hole Pressure Tests

In flowing wells, the production is delivered from the formation to the surface through a tubing string. Tubing strings are normally fluid isolated from the well itself. This is to avoid communication of one geological formation to another. The integrity of the tubing string is quite important. After a period of time, small leaks may develop in the tubing string. One or more leaks will hamper production of the well and may create severe problems. The present invention is a pressure test apparatus which enables selected portions of the tubing string to be closed off and a pressure test run on the tubing thereabove.

Pressure testing of tubing strings is a preventive maintenance step which protects against catastrophic growth of leaks in a tubing string. For example, several tubing strings may be placed in a single well to communicate with different pay zones. The present invention enables testing of a tubing string at different horizons. Suppose, for example, that a tubing string is 10,000 feet long and communicates with a bottom hole zone of high pressure. It passes through two low pressure zones. Assume the well includes separate tubing strings to the low pressure zones which are isolated by suitable packer elements. Pressure from the 10,000 foot string leaked into the well may substantially cut production. However, a leak in the near vicinity of the low pressure zones will not only cut production from the high pressure zone, but the pressure may in fact overcome the low pressure zone fluid drive and reduce production from that zone almost to zero. The present invention is able to be run in a tubing string to pressure test the string. It is lowered in a string to a specified elevation. At the lowermost elevation, the device is landed at a collar and the pressure is tested. Leaks in the tubing string are indicated by failure of the string to maintain an adequate pressure level. If leaks are found, the tool is then moved up to different elevations in the string and additional tests are run. If the pressure is not held for a period of time, a leak above the tool is again indicated. The joint of tubing which leaks can thus be located by successive tests. The apparatus of the present invention can be used to take multiple readings so that pressure retention of the tubing string is observed. The rate of drop of pressure during a retention test and the depth of the tool in the string can be used to locate and estimate the size of a leak, thereby enabling repairs to the tubing string.

The present invention is a pressure test apparatus for use in testing a tubing string for pressure retention at various elevations. The apparatus includes a fishing neck which enables it to be connected to a set of sinker bars to enable it to be run down-hole. The fishing neck is attached to an upper mandrel which terminates at a value element. The valve element is captured internally of an upper outer mandrel which has an internal valve seat. The mandrel is hollow through its length to enable the valve element to slide within certain limits. Lateral openings through the upper outer mandrel communicate fluid from the exterior to the valve seat which, when open, communicates through a pipe and along the length of the tool on the interior. The pipe supports an expandable resilient element. It is preferably formed of an elongate resilient sleeve. The pipe is slidable with respect to an outer lower mandrel. The outer lower mandrel has a tapered upper edge which forces its way under the resilient element and expands it radially outwardly to plug the tubing string. Expansion of the resilient element is dependent on compression of the tool. The lower end of the tool is held in a collar by means of a bifurcated collar finder which locks into a collar on relatively downward movement. This stabilizes the lower end of the tool, enabling weight on the upper end of the tool to compress it, thereby expanding the resilient element and additionally closing the check valve in the apparatus to prevent further fluid flow. This completely plugs the tubing string and enables a pressure test to be run in the tubing above the present invention. It is moved upwardly by a simple pull which opens the check valve means to relieve pressure built up above the tool. An upward pull also releases the collar lock.

FIGS. 1A and 1B together show the present invention in an elongate sectional view along a diameter and disclose details of construction.

The oil tool 10 includes an upper mandrel 11 which incorporates a standard API fishing neck 12 at the upper end. The mandrel 11 has an elongate smaller diameter portion 13 which terminates at an enlarged shoulder 14. The shoulder 14 limits upward travel of the mandrel 11. An upper outer mandrel 15 encircles and receives the mandrel 11. The mandrel 15 has an axial passage which terminates at a chamber 16. The chamber 16 is concentric with and slightly larger than the axial passage 17. The axial passages 16 and 17 connect at a transverse shoulder 18 which abuts the enlargement 14 on the mandrel 11, thereby limiting its range of upward movement.

The mandrel 15 has lateral passages 19 which open to the chamber 16. The chamber 16 is in fluid communication with the fluids in the tubing string above the tool.

The mandrel 11 incorporates a tapered conic point 20 at its lower end. A seal member 21 is placed on the taper 20 and cooperates to form a check valve. The mandrel 15 is threadedly connected at 22 to a sub 23. The sub 23 is axially drilled at its upper end to provide an extension to the chamber 16. The axial passage is tapered at 24 to define a valve seat for the valve element on the lower end of the mandrel 11. The valve seat 24 is contoured in size to close the axial passage through the tool when the valve element 20 is forced downwardly against the valve seat. The sub 23 is also threaded to a pipe 25. The interconnection is at a set of threads 26. The pipe 25 continues the axial passage through the tool, which begins with the lateral passages 19.

The pipe supports a resilient element 28 on its exterior. The resilient element is in the form of an elongate sleeve. The resilient sleeve 28 is fairly thick. It has a lower shoulder 29 and an upper shoulder portion 30. The upper shoulder 30 is abutted against a sleeve lock member 31. The sleeve lock member 31 is captured on the exterior of the pipe 25 so that it may not slide. The lock member 31 has an undercut shoulder to define a step which supports and holds the sleeve 28. The upper end of the sleeve 28 is intended to remain stationary and does not slide.

In FIG. 1B, the pipe 25 terminates in an enlargement 35 which has a central bottom opening 36 and lateral ports 37. The enlargement 35 is captured in a lower outer mandrel 38. The lower outer mandrel 38 defines an internal chamber 39. The chamber 39 permits lengthwise movement of the enlargement 35 within limits. The upper limit is defined by a shoulder 40. When the tool is elongated by pulling the pipe 25 upwardly, the enlargement 35 is limited in travel at the shoulder 40. In that position, the lateral passage 37 is aligned with an external opening 41 which provides pressure relief through the tool. This is helpful in pulling the tool upwardly in a tubing string filled with liquid. It is immaterial whether the flow in the tubing string is through the axial passage or on the exterior.

The chamber 39 is defined at its lower end by an abutting shoulder 43. The shoulder 43 is the upper end of a lower sub 44. The sub 44 is joined to the outer lower mandrel 38 at a threaded connection 45. The sub 44 incorporates an axial passage 46 along its length.

The sub 44 is theaded to an elongate hollow member 48 which comprises a portion of the collar lock mechanism. The collar lock mechanism is a bought item which can be obtained from any sources. The collar lock mechanism includes the hollow member 48 which is hollow through its length to complete the fluid communication path through the tool 10 of the present invention. It includes a shoulder 49 which limits travel of an encircling collar 50. The collar 50 is slidably received on the exterior with its upper travel limited by the shoulder 49. Its lower travel is limited by a similar shoulder 51. The collar 50 supports a pair of facing fingers 52. They are elongate and are adapted to flex inwardly and outwardly. Two fingers are adequate, but three or four can be incorporated if desired. The fingers are profiled at the lower end. An outwardly protruding contour 53 is adapted to fit between the ends of joints of tubing adjacent to a collar. The contour 53 latches into the space adjacent to a collar. It is spring loaded outwardly to be forced into the space. The profile 53 terminates at a lower transverse shoulder 54. It is not possible for the shoulder 54 to ride over the top end of a tubing joint adjacent to a collar. By contrast, a tapered shoulder 55 on the upper end of the profile is able to ride over the tubing shoulder at a collar. The fingers include at their lower ends openings 56. They enable the fingers to be tied or pulled together. When running the tool down-hole before operation, the fingers are preferably pulled together or tied. When they are tied together, they are pulled inwardly and are not able to deflect outwardly and thereby lock into a collar. When they are free to flex, however, flexure is controlled and limited by the position of the fingers relative to the tubing member 48.

The collar 50 is free to slide lengthwise on the tubing member 48. In the up position of FIG. 1B, inward flexure is forbidden. This results from the shape or contour of the hollow member 48. It limits radially inward flexure of the fingers. However, the apparatus is able to find a collar in the tubing string when the fingers are extended below the position of FIG. 1B. The fingers 52 are moved laterally downwardly and away from the tubing 48. The exterior of the tubing is profiled to prevent inward deflection. In the extended finger position, they are free to deflect. As the tool is pulled upwardly in the tubing string, they deflect noticeably on passing each collar. This deflection in the pulling equipment can be felt by a surface operator. When the tool is pulled upwardly past an elevation of interest, it is then lowered downwardly because it normally is weighted. A downward push on the tool forces the collar 50 upwardly on the tubing member 48. When this occurs, the fingers 52 are then moved adjacent to the lower end of the tubing member 48. This limits their inward deflection and causes the apparatus to lock into the next collar. The fingers 52 deflect outwardly and the profiled protrusions 53 engage the collar between adjacent joints and the lower end of the tool is locked relative to that location. The tool is then set for a pressure test. Weight above the tool is applied to the tool, thereby forcing the upper mandrel 11 downwardly. This closes the fluid path through the tool by engaging the valve member 20 in the valve seat 24. The weight compresses the tool by forcing the pipe 25 downwardly. This causes the resilient sleeve 28 to expand. It expands by forcing the tapered upper end of the outer lower mandrel 38 beneath the sleeve. This expands the resilient element and closes the exterior of the tool, creating a complete pressure seal across the tubing string and thereby closing the tubing for pressure test.

After testing, the tool is released by an upward pull. The upward pull first disengages the valve permitting fluid communication. It pulls the pipe 25 upwardly and carries the resilient sleeve upwardly and away from the tapered surface which forces it outwardly. This restores the resilient sleeve 28 to the illustrated dimensions and opens the exterior of the tool to fluid communication in the tubing string. Additional upward pull on the tool pulls the tubing 48 up from the fingers 52. When the shoulder 51 moves upwardly relative to the collar 50 and abuts it, then the fingers are pulled free. The fingers are freed to deflect inwardly and thereby disengage that particular collar. The tool is then pulled upwardly in the tubing string to another location for subsequent testing or removal from the well.

The foregoing is directed to the preferred embodiment of the present invention. The scope is determined by the claims which follow.