It is desirable that when tubing utilized as production equipment for oil and gas wells is initially installed in the well, or when being reinstalled following remedial work on the well, to ascertain the integrity of each section or joint of tubing. Tubing failures can be very costly due to the relatively high expense of the equipment and manpower required to pull out the defective tubing joint, and because of the lost production which may result during the time the well is off production. It is a commonly practiced procedure, when tubing is run into a well, to pressure test each joint of tubing in order to determine whether each joint has become fatigued, or has developed pinhole leaks or has in some other way been weakened so as to decrease its capability of satisfactorily conveying fluids under high pressure. It is known to apply internal fluid pressure to each joint of tubing in a tubing string to determine the integrity of each joint in a process commonly referred to as “hydrotesting” the tubing. This is process involves the use of pressurized water and a calibrated pressure meter to determine if the tubing is watertight at a pre-determined pressure. The applied pressure can range anywhere from 5,000 to 20,000 pounds per square inch.
The hydrotesting process typically employs a pair of axially spaced test cups made of an elastomeric material and mounted on the mandrel portion of a test tool inserted in the tubing joint to be tested by a wireline or winch. Slips on the test tool are set placing the test tool within the joint to be tested, so that the test tool will set within each joint to be tested, and allowing the wireline to be disconnected from the test tool without the test tool falling through the tubing. The test cups are backed against stops carried on the mandrel in opposed relation, and fluid is admitted through a tubular portion of the mandrel which is perforated to allow the fluid to fill the space between the test cups. As the fluid thus admitted to the space between the test cups is pressured up, the test cups flare out and undergo expansion so as to form a fluid-tight seal with the internal wall of the tubing under test. Continued increase in the pressure of the fluid between the test cups correspondingly increases the pressure on the walls of the tubing under test so that any propensity to fail under the high pressure thus developed is manifested by the failure of the tubing section, or ejection of the test fluid through pinhole leaks or fractures which may have previously developed in the tubing section. An example of an oilfield tubing hydrotesting apparatus is disclosed in U.S. Pat. No. 4,149,566 to Stowe.
The mandrel of the testing tool is sized to pass easily into the tubing to be tested. The mandrel carries slips, usually below the test cups, and a fixed upper back-up flange which functions as a stop or abutment against which the base end of the upper cup which limits axial movement of the upper cup during testing. In similar fashion, a lower back-up flange functions as a back-up member limiting axial movement of the lower cup. Between the upper cup and the lower cup the testing tool comprises means for the release of fluid inside the mandrel to exit to the outside, such as perforations. When the mandrel portion of the testing tool is inserted in the tubing to be tested and the test cups have been placed in position within the tubing joint, a hydraulic conduit is connected to the top of the testing tool and fluid is introduced into the test tool through the tubular portion of the mandrel, which fluid fills the interior of the tubing between the test cups so as to force the test cups apart and against the upper and lower back-up flanges. The pressure of the fluid introduced to the interior of the tubing is then increased, with the result that the opposing test cups seal against the interior wall of the tubing. The pressure of the test fluid is then further increased until a desired magnitude of pressure within the tubing is attained.
Once this test pressure is exceeded, if the tubing does not fail, or if a pinhole or previously developed fracture of some type is not revealed by fluid leakage or by loss of pressure, the tubing is considered to have successfully passed the pressure test, and the pressure of the internal fluid can be relieved. With the slips of the test tool assembly holding it within the tubing joint just tested, an additional joint of tubing can be made up to the tubing string and run into the well. A wireline overshot is then run into the tubing to retrieve the test tool and bring it into the newly installed joint of tubing and that joint tested as described above. This process is continued until the tubing is completely installed within the well.
If there is a failure in the test cups, the slips, or if there is an unexpected pressure buildup below the test tool resulting from inflow of reservoir fluids such as gas, water or oil, the test tool can be violently propelled through the top of the tubing which, in the known practice, is left open during the hydrotest operation. This potentially explosive expulsion of the test tools from the top of the tubing creates a potential hazard to personnel and property. Moreover, if the tool is expelled because of a fluid buildup below the test tool, once the tool is expelled through the tubing, there can be a release of well fluids into the environment.