Abstract:
The consequences of any failure of a blow out preventer assembly to operate correctly in an emergency can be far reaching. Thus, there is provided an apparatus for registering parameters in the bore of a member which is, in use, connected to a pressurised housing, the apparatus comprising: an electro-control package for attachment, in use, to the member; a test assembly placed, in use, in the member; the electro-control package and the test assembly having means for sending signals to and receiving signals from one another.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims a right of priority based upon European Patent Application No. 01305431.7, as filed in the European Patent Office on Jun. 22, 2001. 
   STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
   Not Applicable. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to a testing apparatus to test a Blow Out Preventer (BOP) stack or assembly and to a method of testing using such an apparatus. 
   2. Description of the Related Art 
   A BOP assembly is a multi closure safety device which is connected to the top of a drilled and often partially cased hole. The accessible top end of the casing is terminated using a easing spool or wellhead housing upon which the BOP assembly is connected and sealed. 
   The wellhead and BOP stack (the section in which rams are provided) must be able to contain fluids at a pressure rating in excess of any formation pressures that are anticipated when drilling or when having to pump into the well to suppress or circulate an uncontrolled pressurized influx of formation fluid. This influx of formation fluid is known as a ‘kick’ and restabilizing control of the well by pumping to suppress the influx or to circulate the influx out under pressure is known as ‘killing the well. An uncontrolled escape of fluid, whether liquid or gas, to the environment is termed a ‘blow out’. A blow out can result in a major leak to the environment which can ignite or explode, jeopardizing personnel and equipment in the vicinity, and pollution. 
   Although normal drilling practices provide a liquid hydrostatic pressure barrier to a kick, a final second mechanical safety barrier is provided by the BOP assembly. The BOP assembly must close and seal on tubular equipment hung or operated through the BOP assembly and ultimately must be capable of shearing and sealing off the well. Wells are typically drilled using a tapered drill string having successively larger diameter tubulars at the lower end. When running a completion or carrying out a workover various diameter of tubulars, coiled tubing, cable and wireline and an assortment of tools are run. 
   The consequences of any failure of the BOP assembly multi closure barriers and valves, shear and seal devices to correctly operate in an emergency can be far reaching. It is essential to initially contain the kick to prevent a blow out and then be capable of killing the well, and re-establishing control. 
   To verify the functions and performance of a BOP assembly, stringent tests have to be performed on a regular bases, either daily, weekly or at certain stages of the drilling operation to ensure the BOP is in full working order. When drilling or carrying out well intervention on a subsea well where the wellhead is at the seabed, the subsea BOP attached to the subsea wellhead is connected to a buoyant floating drilling vessel by a riser. A floating drilling vessel should maintain its station vertically above the well to enable well operations to be performed. 
   Failure to do so caused by weather conditions, current forces, equipment malfunctions, drift off or drive off, fire or explosion, collision or other marine incidents means it is necessary if possible to make the well safe, isolate the well at the seabed and disconnect the riser system. In a severe emergency, shearing any tubulars or equipment in the BOP bore, sealing the well to full working pressure and disconnecting the riser system is required to be achieved in under 30 seconds. 
   A conventional BOP assembly, surface or subsea, is attached to a wellhead and is provided with a number of ram BOPs to either seal around different set tubular diameters or to shear and seal the bore. These ram BOPs should be rated to perform at pressures in excess of any anticipated well pressures or kick control injection pressures being approximately 10 to 15 kpsi (69–103 MPa). A minimum of one annular BOP is provided above the ram BOPs to cater for any tubular diameter or for stripping in or out under pressure. An annular BOP is a hydraulically energized elastomeric toroidal unit that closes and seals on varying diameters of tubular member whether stationary or moving into or out of the well. Due to the nature of this pressure barrier element, a lower maximum rated working pressure of about 5 kpsi (34 MPa) is normally available. 
   Above the annulars, there are no further well pressure barrier elements with the riser only providing a hydrostatic head, liquid containment and guidance of equipment on a normal pressure controlled drilling operation. For a subsea riser system, the hydrostatic head of the different drilling liquids over the ambient sea water pressure means the low pressure zone above the subsea BOP assembly must still withstand, depending upon the depth of water, 5 kpsi (34 Mpa). 
   The conventional BOP assembly in effect provides a three zone pressure containment safety system. The three zones typically consists of the first high pressure lowermost section encompassing the rams, the medium pressure second zone, the annular or annulars and the low pressure third zone being the bore above to atmosphere and on a subsea system the riser bore to the surface vessel. 
   It is therefore important to be aware that BOP assemblies need to be tested rigorously in order to verify their full working order and that any potential problems can be identified and rectified before any emergency arises in order to maintain the integrity of a BOP assembly once it is in place. in deep water, BOP assemblies could remain subsea for several months. It is necessary for it to be fully tested at regular intervals and, throughout the subsea industry, this is typically at least once every week. 
   It is important therefore that the tests on the BOP assembly are carried out carefully and methodically to detect any potential problems but in a reasonable time to minimize risk exposure as testing prevents further downhole well operations especially if the well is open being partially drilled or when involved in a completion or work over. In the case of subsea wellheads which can be at a water depth of as much as 10,000 feet (3050 m), it typically takes approximately three to four hours plus to run the test apparatus into place and three to four hours plus to pull back to the surface after testing has been completed. A typical test sequence takes approximately 6 hours plus to complete if there are no queries or questionable readings. Thus, it is not unusual for a well to be out of operation for approximately 12 hours per week. This is clearly very significant in terms of risk exposure and lost revenue for the well owners and anything which can reduce the well downtime is therefore of great benefit. 
   Diagnosing any queries or questionable readings can take time even on an integral system, the variety being due to fluid compression, thermal changes of the fluids or to the equipment containing the fluids, riser/vessel movement and the large volumes in the choke and kill lines to the surface in comparison to the relatively small volumes of the BOP cavities and that of a small leak. 
   A faulty diagnosis or incorrect interpretation due to vague information could lead to the well being temporarily suspended and the BOP assembly being pulled. In deepwater it could take 6 days plus before well operations are resumed. 
   It is normal procedures when testing the BOP assembly to use a drill pipe or a test mandrel connected above a wellhead tool that will seal within the wellhead. It is also known to try to combine some of the BOP assembly tests with wellhead and surface manifold testing. When testing the BOP assembly it is necessary to ensure that all of the valves, seals, rams and annulars are tested to their maximum expected usage pressure. Each pressure test should be started by a minimum 5 minute low pressure test (e.g. at 300 psi) and then raised in increments to the final high test pressure. Typically, a wellhead/BOP test pressure that is stable and recorded for a minimum of 5 minutes is considered satisfactory. BOP rams are only designed to seal off pressure from below which means all tests have to be carried out either against the wellhead test tool or the well bore. The usual practice is to supply the test pressure to the BOP cavity under test alternating between the choke and kill lines to allow all functions on each side of the BOP stack to be tested from the bore outwards. 
   When testing the BOP assembly cavities around the test tubular, the BOP test pressures at certain stages of the well could exceed the pressure rating of the well casing so far installed. If a leak occurred from the BOP bore test past the wellhead test tool, the well could be pressured up and be hydraulically fractured, thus making the well unusable. To prevent this occurring the well fluid is allowed to vent up the bore of the wellhead test tool into the bore of the drill pipe where any leak can be monitored on the surface. One particular and critical test is the integrity of the shear blind ram BOP cavity. The shear blind rams are those which can cut the drill string or a pipe or tubing and then seal the BOP bore when there is a need to carry out an emergency disconnect of the riser system from the BOP stack. This, in effect, is the last and only resort for shutting down the well as when the pipe rams are closed on a tubular, the bore of the tubular is still open. Typically, the testing of the shear blind rams requires disconnecting the drill pipe or part of the test mandrel below the shear blind rams and pulling the upper part clear such that the shear blind rams can close. 
   However, after the mechanical release from the lower part of the test mandrel attached to a wellhead test tool, the bore through the remaining test equipment into the wellhead must be isolated to test up under the shear blind rams. This can be achieved by using either a one way flow mechanism which has the possibility to weep or leak, pressuring up the well casing or alternatively by tripping out of the hole and running a solid wellhead test tool. Either way, after the mechanical release or if a solid wellhead test tool is run, the integrity of the wellhead test tool to seal off in the wellhead cannot be verified before tested. 
   Even though the shear blind ram BOP cavity is a critical zone to test, the consequences of jeopardizing the integrity of the well casing is deemed too high a risk. Therefore, it is normal practice to test the shear blind ram BOP cavity only to the operationally safe allowable low casing working pressure using either no wellhead test tool or a test tool knowing that, if it leaked, no well damage can occur. 
   Furthermore, the test liquid pumped and measured on the vessel is supplied at the test pressure typically through either the choke or kill lines down to the appropriate test path into the subsea BOP bore. In addition, this conventional test procedure using the choke and kill lines involves a high volume relative to the small tested cavity volume above the wellhead test tool and in relation to any leaks, meaning that it is difficult to detect leaks. 
   To reduce premature damage to equipment and function elements, the operation and resetting of the BOP barriers means the valves, rams and annulars should only be opened or closed in a depressurized bore. 
   Therefore, the choke and kill lines must be vented down between each cavity test, i.e. they are depressurized and repressurized with tests only commencing after the pressure has balanced and stabilized. This is a time consuming process which greatly lengthens the testing time. The compressibility of the drilling liquids, usually drilling mud, and possible expansion or elongation of the lines to the BOP and variations in temperature all contribute to the difficulty of monitoring very small changes in the volume. A wise practice is to circulate the system with seawater which can reduce these effects but not eliminate them entirely. 
   Once a stable test pressure is achieved, the current BOP testing technique is to surface monitor the test pressure and establish a decay profile. However, when testing, there is a degree of interpretation required as to whether the decays are caused by the above mentioned side effects or a leak. This interpretation has to be carried out by personnel at the surface of the well and is based on experience and judgement rather than facts. 
   When drilling a well, the prime barrier to prevent an influx of formation fluid is provided by the hydrostatic head of the drilling mud column. It is essential that the consistency and properties of the drilling mud are as specified for certain sections of open hole. This is achieved by circulating a constantly surface trimmed liquid at a designated rate in relation to the liquid properties. In addition, any traces of an influx can be detected by the surface monitoring systems on the return line. 
   A stationary column of well liquid could unknowingly allow migration of formation fluid into the well bore and the properties of the well liquid could change due to deterioration, thus creating an unstable situation which could result in a kick. Therefore, allowing an open hole to stand stationary for any period of time is an unwise practice. Also, if a kick occurs, the optimum solution is to circulate the kick out under pressure which involves having a tubular member in the hole below the influx and preferably near the bottom of the hole. 
   Therefore, when having to test a BOP on a well with a balanced open hole, it is a wise practice to use part of the drilling string hung-off below the wellhead test tool. This means that after completing the BOP testing, the well fluids can be circulated and conditioned prior to opening the BOP and pulling the string up to remove the test tools. If a kick has occurred or occurs while pulling out of the riser, the BOP rams can be closed on the drill string and the well circulated. This cannot be achieved if there is a one-way upward flow mechanism in the wellhead test tool or a solid wellhead test plug has been used which would prevent circulation, endangering the operation. 
   U.S. Pat. No. 4,554,976 discloses a means of testing the shear blind rams of a BOP by splitting the tool into upper and lower portions. In order to test the rams, the upper portion of the tool is removed, the rams tested, and the tool reconnected before withdrawing the tool from the BOP. 
   U.S. Pat. No. 6,032,736 (Nutec) discloses a test mandrel for use in subsea testing of BOPs which allows the BOP test fluid to be pumped down the drill pipe to a telescopic arrangement. However, this has inherent problems due to possible leakage between the seals of the telescopic portions which makes it very difficult to distinguish a failed BOP. Accounting for the different heights of the wellhead test plug at different stages of the well is accounted for by using spacer pipes between the wellhead test plug and the telescopic test tool. Circulation of the well after testing is not possible unless wireline is run down the drill pipe to remove the blanking dart. 
   Also monitoring for leaks from around the wellhead test tool is via the test assembly into the drilling riser which has an immense volume in deep water. A means of testing the shear blind rams is not discussed. 
   SUT Paper (Society of Underwater Technology, UK)—“Acoustic BOP Test Tool” provides additional screwed sections of pipe which can be added to the drill pipe or test mandrel such that the tubular section can be set at the right height in the BOP stack for the different drilling phases. 
   This would also cater for the use of different wellhead test tools and to land in the wellhead at the different landing shoulders provided by the different casing hangers/seal assemblies as the well is drilled. The height of the tubular test assembly can be changed to meet the BOP space out. An acoustic pressure emitter can be included in the lower part of the test mandrel which transmits the pressure readings up the drill pipe to the surface. A mechanical communication path is required between the emitter and the surface. Again, circulation of the well and testing of the shear blind rams has not been discussed. 
   This description has mainly addressed the testing of BOP assemblies as multi-closure safety devices as a barrier in the drilling mode. Similar criteria applies when the BOP assembly is used when installing a completion in combination with a completion riser which means the BOP assembly is a critical high pressure isolation mechanism. 
   SUMMARY OF THE PREFERRED EMBODIMENTS 
   This invention is a system and technique which can accurately quantify tests and improve testing practices, jointly raising the level of safety and the commercial aspect of the well operation. 
   According to the present invention there is provided an apparatus for registering parameters in the bore of a member which is, in use, connected to a pressurized housing, the apparatus comprising: 
   an electro-control package for attachment, in use, to the member;
         the test assembly placed, in use, in the member;   the electro-control package and the test assembly having means for sending signals to and receiving signals from one another.       

   Preferably, the test assembly is one of the following: blow out preventer test assembly, wellhead tubing hanger running tool, spool tree or horizontal tree tubing hanger running and test tool, casing and seal assembly running tool, subsea test tree, wireline or coil tubing tool, hanger or plugs. 
   According to a second aspect of the present invention, an apparatus for testing closure elements in a blow out preventer (BOP) forming a BOP assembly which is, in use, connected to a wellhead, the apparatus comprising a shearable test tool assembly for use in combination with the BOP assembly and the wellhead; 
   an electro-control package for attachment, in use, to the BOP;
         the test tool assembly and the control package having means for sending signals and receiving signals from one another.       

   Preferably, the electro-control package is replaceable. 
   Preferably, the means for transmitting and receiving signals includes a plurality of emitters and transceivers. 
   Preferably, the emitters and/or transceivers use one of optical, electrical, electromagnetic, radio, hydraulic pulses or acoustic means as input and output for communication. 
   The test tool assembly may have sensing means for monitoring parameters inside and outside the tool bore, and for both above and below the tool. These parameters may include at least one of the following: pressure, temperature, velocity, density, and phase detection. The phase detection is preferably one of the following: drilling mud, cement, gas, oil, water and completion fluid. 
   Preferably, the control package has independent sensing means for monitoring the parameters in a BOP bore above the wellhead. Furthermore, the control package may have means for sending signals to and receiving signals from a control station. 
   The BOP assembly preferably includes at least one annular and at least one set of rams for sealing the bore of the member to create a test chamber. 
   In general, and especially when using subsea applications, the test tool is preferably connected to the surface only by means of a mandrel which may be split into upper and lower sections that are run on drill pipe or tubulars from the surface. 
   One difference between the present invention and conventional BOP testing means is that the apparatus of the present invention preferably lands in a specific location in the wellhead. Thus, instead of landing on components in the wellhead which vary with height as the well is drilled, a datum height is always used, ensuring that the assembly of the present invention is at a constant attitude within the BOP. Preferably, the assembly is landed on the wellhead internal lock and seal profiles for the wellhead running tool. If the wellhead components, which vary with height need to be tested, specific nose adapters may be fitted to the test tool. 
   If no specific landing shoulder or stop is available in the wellhead body, then the specific nose adapters or nose spacers landed on the respective wellhead component can ensure the apparatus is landed at a specific elevation. 
   By using a datum level which may be a slight reduction in the internal diameter of the wellhead housing, and therefore a known landing site, a datum anti torque resistance is registered when the test tool is located in the wellhead. Preferably, left hand rotation is used to lock the test tool into the wellhead and preferably high torque right hand rotation is available to release the test tool, without the risk of unscrewing the drill pipe. In this arrangement, left hand rotation preferably drives a cam in the test tool to energized locking dogs which lift the tool off the datum ledge and into the specific internal load bearing profile. This ensures that there is no deformation of the indicator profile on the datum ledge when the test tool is subjected to high pressure loads. In this way, the tool is sealed to the wellhead and the conventional annulus flow through path through the body of the tool is also sealed. 
   Typically, there is a hanging drill string below the test tool assembly and, in order to prevent this drill string having to be rotated and, thus, causing resistance, a pressure sealing swivel may be incorporated into the lower end of the test tool. 
   A test tool intelligent monitoring unit may be incorporated within the test tool, the monitoring unit can check data within the bore of the tool, and external to the bore, and both above and below the tool. In this way, pressure and temperature can easily be registered. Alternatively density phase sensors, flow meters, the rotation, tension and torque in the mandrel can also be monitored. 
   The electrical control package is preferably mounted on the BOP below the lower ram on a spare choke/kill outlet. The control package preferably includes actuated fluid control valves and chokes which provide double barrier fail closed isolation, fluid flow meters and, when a high pressure control line cannot be provided, a fluid intensifier. 
   Via the intelligent monitoring unit and the control package, surface personnel can readily monitor read/hear functions occurring at the wellhead and verify that the device is operating correctly. 
   The test tool may also comprise a one way upward flow valve located in the bore, the one way upward flow valve allowing fluid to escape from below the test tool. This flow path ensures that the well casing cannot be pressured up if there is a leak from the BOP bore past the test tool. The one way upward flow valve preferably comprises parallel seals which prevent the flow from cutting the seals or the sealing area. It is essential that this one way upward flow valve is reliable as, when the mandrels are separated in order to test the shear/blind rams, full test pressure will be exerted down the bore to the top of the one way upward flow valve. This full test pressure must not be allowed to enter the bore as this will pressure up the well and may damage the well casings. 
   As stated above, the test mandrel is split into upper and lower portions, joined by a mandrel coupling. Preferably, a hydraulic operated anti left hand rotation mechanism is incorporated into this coupling such that, when pressure is applied down the drill pipe against the one way upward flow valve, the anti left hand rotation mechanism is released, preferably by energizing a spring. 
   A bladder arrangement may be provided to prevent drilling mud clogging the mechanism. The bladder arrangement separates the hydraulic fluid from any drilling mud or sea water. Preferably, the mechanism is low torque, such that the tool can be unlocked without any vertical separation of the upper and lower mandrels. A conventional screw thread would lock up under either the weight or tension caused when operating from a heaving vessel. 
   During operation, the coupling system will lock out, thus preventing further rotation. This can be registered on the surface and the low pressure in the drill pipe can be vented down. Then, the drill pipe/upper mandrel can be pulled up, separating the coupler without dislodging the test tool which is locked and sealed in the wellhead. This allows the shear blind ram cavity to be fully tested to the maximum anticipated well pressure against the test tool, which has its bore isolated by the one way upward flow valve. 
   Pressure read outs can be taken from the BOP bore and from below the test tool to confirm any well casing is not being pressured up. When testing the shear blind rams, it is preferable that the upper mandrel is pulled up against, and sealed by, an upper annular prior to closing the shear blind rams. 
   Even if a pressure drop is noted, this does not specifically identify the location of the leak. The present invention permits separate and simultaneous monitoring of fluid flow on the choke and kill lines, the riser, booster line and through the drill pipe/upper mandrel, in particular to monitor any escape of fluid from the test chamber. After a successful test of the shear blind rams, the upper mandrel is preferably lowered and stabbed together, engaging and intermeshing anti rotation features on the couplings and these may be key slots on both couplings. With downward weight binding the test tool, right hand rotation will drive the mandrel coupling cam mechanism to lock the upper coupling to the lower coupling. The anti left rotation locks are in effective to right hand rotation. Again, when fully locked, a build up of torque will be seen at the surface and upward pull against the locked test tool verifies full load carrying make up is achieved. At this point, any sea water in the kill line, BOP, choke line and booster line should be replaced by drilling mud. 
   In the arrangement where the bore protector or wear bushing is to be left in place, it is preferred that the pressuring up of the drill pipe releases the wear bushing. By picking up the total drill string hanging weight, right hand rotation will open up the annulus flow through path, unseal and unlock the test tool. With pressure held on the drill pipe, the test tool can be pulled clear of the wear bushing. 
   The apparatus preferably includes a drop dart which can be released down the drill pipe to land and seal in the circulation sleeve of the test tool, in order that the well can be circulated prior to pulling the tool out of the hole. A hydraulic lock is formed between the dart and the circulation sleeve and the one way upward flow valve and therefore no circulation would occur. To overcome this, the circulation sleeve has a dual flow design which is activated by the dart depressing a spring loaded plunger in the circulation sleeve, thus venting fluid below the dart into a circulation port exiting below the tool. Pressure can now be applied down the drill pipe to allow the dart/sleeve to move down, thus opening a circulation path from the bore above the test tool to the bore below. The circulation port bypass the one way upward flow valve and neutralize the wear bushing hydraulically operated latch dogs. The BOP control package can verify the bore pressures and circulation pressures. In this way, the well can be circulated and, as the test tool is pulled out, fluid will equalize down the drill pipe, thus allowing a dry string to be pulled. 
   In the situation when premature well circulation has to be carried out, wire line or coil tubing can be run to retrieve the dart. As the dart is pulled, sealed friction or spring friction contacts will pull the circulation sleeve up into the closed position, thus returning the test tool to the test mode. 
   A further application of the apparatus of the present invention is as an emergency planned hang off tool. 
   Additionally, if a bad weather forecast is received when drilling the well, and a decision is made to suspend operations, the drill string can be pulled up to the last casing shoe, plus the water depth. The test assembly with a one way downward flow mechanism is inserted and locked in the bore between the test plug and the mandrel before being connected to the drill pipe and run down to the wellhead where the test tool assembly can then be locked and sealed to the wellhead. The surface installed one way downward flow mechanism unit will, on a surface installation, depress the plunger and move the circulation sleeve into the open position. This will allow a downward circulation through the bore but will isolate any pressure in the bore below the test assembly. The test tool will provide the bore upward barrier and an annulus barrier, which closes the well flow through path, prior to disconnecting the mandrel coupling and closing the shear blind rams. This arrangement thus provides independent mechanical double barrier isolation of the well, first in the wellhead and then by the BOP. 
   When returning after a disconnection of the BOP and riser, the internal pressure conditions of the BOP can be monitored prior to opening any barriers, due to the electro-control package. 
   The electro-control package may inject fluid into, or vent fluid from, the BOP bore at a known pressure and volume, preferably at the required test pressure. This allows simultaneous testing of the ram or annular barrier, the choke side and the kill side of the BOP bore. 
   The apparatus of the present invention can be used to carry out a full test procedure on the BOP and the wellhead and it permits the number of steps to be reduced thus ensuring the well down time is reduced and the cost effectiveness of any installation is improved. 
   Furthermore, the BOP allows the blind shear rams to be tested which, as referred to above, although vital, is often or even usually not carried out to the full working pressure. The testing procedure is carried out once the test assembly has landed at its datum height at the top of the wellhead housing. The test procedure should follow the operator&#39;s program. 
   Thus, the present invention comprises a combination of features and advantages which enable it to overcome various problems of prior devices. The various characteristics described above, as sell as other features, will be readily apparent to those skilled in the art upon reading the following detailed description of the preferred embodiments of the invention, and by referring to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     One example of the present invention will now be described with reference to the accompanying drawings, in which: 
       FIG. 1  is a schematic longitudinal cross sectional view through a conventional subsea BOP and test assembly; 
       FIG. 2  is a summary of the testing requirements of a conventional subsea BOP assembly; 
       FIG. 3  is a schematic longitudinal cross section through a wellhead test tool assembly for use in the present invention; 
       FIG. 4  is a schematic longitudinal cross section showing the assembly of  FIG. 3  in a BOP assembly during testing; 
       FIG. 5  is a longitudinal cross sectional view through a wellhead test plug; 
       FIG. 6  shows the casing hanger/wellhead function of the wellhead test plug; 
       FIG. 7  shows the wear bushing function of the wellhead test plug; 
       FIG. 8  shows a longitudinal cross sectional view through the mandrel coupling; 
       FIG. 8   a  shows a cross-sectional view of the release mechanism; 
       FIG. 9  is a longitudinal cross sectional view showing the drop dart circulation unit prior to opening; 
       FIG. 10  is a longitudinal cross sectional view showing the drop dart circulation unit with the plunger in the open position; 
       FIG. 11  shows the drop dart circulation unit with full circulation; 
       FIG. 12  shows the present invention being used to test the shear blind rams; 
       FIG. 13  is a schematic arrangement of the control package of the present invention; 
       FIG. 14  is a summary of a possible testing scenario using the apparatus of the present invention; and 
       FIG. 15  is a longitudinal cross sectional view showing the test assembly as an emergency planned hang-off tool. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   One of a number of conventional subsea BOP well assemblies  10  is shown schematically in  FIG. 1 . A wellhead  11  is formed at the upper end of a bore into the sea bed  12  and is provided with a wellhead housing  13 . The BOP assembly  10  is, in this example, comprised of a BOP Lower Riser Package (LRP)  15  and a BOP stack  16 . The LRP and the BOP stack are connected in such a way that there is a continuous bore  17  from the lower end of the lower part through to the upper end of the upper part of the BOP assembly. The lower end of the BOP stack is connected to the upper end of the wellhead housing  13  and is sealed in placed. The upper end  18  of the LRP is connected to the riser pipe  19  and connects the BOP assembly  10  to a surface structure (not shown). 
   Within the bore  17  and riser pipe  19 , a drill pipe or a tubular member  21  is provided and this is connected, at its lower end, to a test tool  22 . The test tool is landed on the internal wellhead components and seals to the wellhead housing. At the lower end of the test tool  22 , a further tubular  23  is provided and extends into the bore beneath the sea bed  12 . Wear bushing  24  and various well casings  25  have previously been set in the wellhead housing  13 . 
   The BOP stack is provided with a number of valve means for closing both the bore  17  and/or the tubular  21  and these include lower pipe rams  30 , middle pipe rams  31 , upper pipe rams  32  and shear blind rams  33 . These four sets of rams comprise the high pressure zone in the BOP stack and they can withstand the greatest pressure. The lower, middle and upper pipe rams are designed such that they close around the drill pipe or tubular member  21 . Of course, when the lower, middle and upper pipe rams are closed, whilst the bore  17  is sealed, the bore of the tubular  21  itself is still open. Thus, the shear blind rams are designed such that, when operated, they can cut through any tubular or drill pipe which may be in the bore  17  and provide a single barrier between the upwardly pressurized drilling fluid and the surface. 
   In the medium pressure zone, above the shear blind rams  33 , lower annular  34  and upper annular  35  are provided and these annulars also seal around the drill pipe or tubular member  21  when they are closed. 
   The low pressure zone is located above the upper annular  35  and includes the flex joint  20  connected to the riser  19 . The pressure containing means in this zone is merely the hydrostatic pressure of the fluid which is retained in the bore open to the surface. 
   Extending from the sea surface to the BOP assembly are choke  40 , kill  41  and booster  42  lines for the supply of fluid to or from the BOP stack. The booster line  42  is in fluid communication with the bore  17  via a booster line valve  43  and enters the bore  17  above the flex joint  20 . The choke line  40  is in fluid communication with the bore  17  in three locations, each location having an individual branch which is controlled by a pair of valves. The uppermost valves are inner  45  and outer  46  gas vents and the branch on which they are located extends into the bore  17  below the upper annular  35 . The choke line  40  extends, past the inner and outer gas vents, through a choke test valve  47 , and enters the bore  17  via upper, inner  48  and outer  49  choke valves above the middle pipe rams  31  and via lower, inner  50  and outer  51  choke valves below the lower pipe rams  30 . 
   On the opposite side of the BOP stack, the kill line  41  is equipped with a kill test valve  52  before the kill line  41  enters the bore  17  at two locations, again each of which is via a pair of valves; upper, inner  54  and outer  55  kill valves and lower, inner  56  and outer  57  kill valves respectively. The upper branch is between the upper pipe rams  32  and the shear blind rams  33  and the lower branch is between the lower  30  and middle pipe  31  rams. 
   In  FIG. 2 , a summary of the full test requirements of a conventional subsea BOP can be seen and it is clear that at least 13 steps are required to test the conventional arrangement. This can be compared with the suggested test schedule associated with the present invention shown in  FIG. 14 . 
   In  FIG. 3 , a wellhead test tool assembly  60  is shown and is comprised of an upper mandrel  61  and a lower mandrel  62 . The upper and lower mandrels are connected by means of a mandrel coupling  63 . The upper mandrel  61  is connected, at its upper end, to drill pipe  21  and the lower mandrel  62  is connected, at its lower end, to a wellhead test plug  70 . 
   The mandrel coupling  63  has, on its outer diameter, an annular return swedge  64  and has a number of cams (see  FIG. 8 ) which, when operated by right hand rotation of the upper mandrel, engage with dogs  65  to lock the upper and lower mandrel together. Seals  66  are provided to ensure a fluid tight connection. The mandrel coupling  63  is also provided with hydraulic means  67  for overriding the anti left hand rotation of the coupling. The lower section of the upper mandrel has a narrowed portion  68  which is, in use, at the same level as the shear blind rams  33  to facilitate emergency shearing of the upper mandrel if necessary during an emergency. 
   The test plug  70  has a number of sensors for monitoring the pressure within various parts of the test plug and these include a BOP bore pressure sensor  71 , a lower pipe annulus pressure sensor or wellhead/pipe chamber sensor  69 , a drill pipe pressure sensor  72  and a lower pipe bore pressure sensor  73  which measures the pressure in bypass passage  82  and below the test plug  70 . Seals  74  ensure a fluid tight seal between the wellhead test plug and the wellhead. The test plug  70  is provided with cams, (not shown) which, when operated, lock a number of dogs  75  such that the test plug is securely connected to the wellhead shown in  FIG. 4 . 
   When open, a passageway  76  is provided as a bypass for the wellhead seal. A second passageway  77 , also valved, is provided as a further bypass of the test tool. A signal receiver/transmitter  78  and associated electrical source  79 , which may be a battery, relay the measured pressure from sensors  69 ,  71 ,  72  and  73  to the control package and/or to a surface control station. The function and operation of circulation sleeve  80  and one way upward flow valve  81  is discussed with regard to FIGS.  9 , 10  and  11 . 
     FIG. 4  shows the arrangement of the BOP assembly  10  and the wellhead test tool assembly when in place and carrying out a test on the lower pipe ram  30 . Also shown in  FIG. 4 , and provided through a port below the lower pipe rams is an electro control package  140 , the details of which will be described more fully with reference to  FIG. 13 . When the lower pipe rams  30  are in the closed position and the lower inner choke valve  50 , the flow port valve  77  and the wellhead seal bypass port  76  are in the closed position, a chamber  88  is formed and the pressure within this chamber can be monitored by means of BOP bore pressure sensor  71  and by a additional pressure sensors in the control package  140 . The pressure and flow within the choke line  40  is also monitored to check the integrity of the lower inner choke valve  50 . 
   A more detailed cross section of the wellhead test plug is shown by  FIG. 5 . In particular, the pressure sensors  69 ,  71 ,  72  and  73  and the data-signal receiver/transmitter  78  and associated electrical source  79  are located at the upper end of the test plug. The data signal receiver/transmitter is used to send and receive signals to and from the control package  140  and/or a control station on the sea surface. The circulation sleeve  80  is shown in its upper, flow preventing position. When the sleeve is actuated to its lower position, it permits bypass flow past the high pressure check valve  81 . The test plug  70  is provided with bore pressure hydraulic retract wear bushing latch dogs  89  which, when the drill pipe is pressured up, release the wear bushing. The one way upward flow valve  81  is spring energized closed. A loaded plunger  99  is activated by a dropped dart  90  which depresses the plunger in the circulation sleeve  80  which then allows fluid to be vented from below the dart into a circulation port which exits below the tool and prevents a hydraulic lock. This then ensures that pressure can be applied down the drill pipe to allow the circulation sleeve  80  and the dart  90  to move down and open a circulation path from the bore above the test plug  70  to the bore below. At the lower end of the test plug  70 , a pressure sealing swivel  91  is incorporated to prevent any hanging drill string having to be rotated with the test tool. Preferably, a left hand thread  92  ensures that it is left hand rotation which locks the test tool into the wellhead by driving a cam  93  which energizes locking dogs  75  which move the test tool off the datum ledge  100  and into engagement with the specific internal load bearing profile  97  of the wellhead. A number of seals  74  are provided to ensure the correct fluid tight seals are provided between the tool and the wellhead. 
     FIG. 6  shows the test plug  70  in situ in a wellhead housing  13  and having a hanger test plug  95  attached at its lower end and acting as a nose adaptor on the swivel joint  91  providing engagement with a casing hanger  25 . Various adaptors can be used, dependent upon the object which is to be run below the test tool.  FIG. 6  also indicates how the dogs  75  engage with the wellhead housing  13  in the load bearing profile  97  rather than at the datum level  100 . To test the casing hanger seal assembly or the lower pipe annulus, the bypass plug  83  must be removed, preferably at surface level, to provide a test fluid communication path through the port  76  to the wellhead chamber. 
     FIG. 7  indicates how the test tool can be used to run or pull a wear bushing  24  as part of the test assembly. To carry out this function, no additional nose attachment is required on the test tool  70 . 
     FIG. 8  shows, in detail, the construction of the mandrel coupling  63  which joins the upper mandrel  61  and the lower mandrel  62 . The shear blind rams  33  are located adjacent to and above the mandrel coupling  63 . The coupling is provided with a hydraulically operated anti left hand rotation mechanism which, as can be seen in  FIG. 8A  which permits right hand rotation but prevents left hand rotation of the upper mandrel  61  relative to the lower mandrel  62 . When pressure is applied down the drill pipe into the upper mandrel  61  the anti left hand rotation mechanism  120  is released as the pressure in oil chamber  121  increases. The oil chamber can be serviced on the surface by filing and venting through respective ports  122  and  123 . A left hand thread  124  drives a cam  125  which activates a lock ring  126  to engage the upper mandrel  61  to the lower mandrel  62 . The release of this left hand thread is only permitted by actuation of the anti left hand rotation mechanism  120 . 
   In  FIG. 9 , a more detailed view of the drop dart circulation unit in the test tool  70  is shown. The dart  90  is allowed to drop down the drill pipe and will land and seal in the circulation sleeve  80  thus activating a spring loaded plunger  99  which then vents fluid through passageway  111  from below the dart/sleeve into the circulation port  127  below the tool. The depression of the plunger can be seen in  FIG. 10  which also shows how the vent ports  127  open to the plunger  99 .  FIG. 11  shows how the application of further pressure forces the circulation sleeve  80  to be moved such that the circulation ports  112  are aligned, thereby allowing fluid to bypass the one way upward flow valve  81  and to neutralize the wear bushing hydraulically operated latch dogs. Thus, the well can now be circulated prior to the test tool being tripped out and, as fluid will equalize down the drill pipe, a dry string can be pulled. 
     FIG. 12  shows the operation of the BOP assembly  10  and the test tool assembly when testing the shear blind rams  33 . It will be noted how the mandrel coupling  63  has been released such that the upper mandrel  61  is drawn up thus leaving only the lower mandrel  62  beneath the shear blind rams which have been closed. By closing at least one of the upper and lower choke valves  48 ,  49 ,  50 ,  51  and at least one of the upper and lower kill valves  54 ,  55 ,  56 ,  57  and the valve into the control package  140 , a chamber  130  is formed and can be pressured up to the maximum anticipated well pressure. In this way, the integrity of the shear blind rams  33  can be verified in a simple and quick manner. 
     FIG. 13  shows, in detail, a fully encompassing control package  140 . A minimum unit could consist of a signal receiver and transmitter unit combined with an electric or hydraulic operated fail closed prime master valve and secondary master valve with a high pressure line for pressuring up and venting down. 
   The preferred embodiment consists of a data signal receiver and transmitter  141  to communicate with the bore  17  of the BOP. A common two way fluid flow path  142  into the control package from the BOP has the appropriate fluid sensors  143  before the electrical or hydraulically operated fail closed prime master valve  144  and secondary master valve  145 . 
   A hydraulic supply  146  which provides the test fluid initially passes into either a controllable pressure regulator or a pressure intensifier  147  which will provide test fluid at the required pressure. To ensure a reasonable flow when required, a hydraulic accumulator  148  is also present. A controlled failed closed isolation valve  149 , an adjustable choke  150  and a volume flow meter  151  allow pressurized flow through a one way flow mechanism  152  into the common two way flow path  142 . 
   The vent or the return path  153  from the common two way flow passes through controlled fail closed choke  154  and isolation valves  155  which regulate the release of fluid into a vent return line  156 . This vent line can be connected to the riser bore  19 . 
   An electrical or electric hydraulic means of operating the functions in the control package is provided through a control processor  157 . The control processor also communicates with the various sensors  143  and  158 , the signal receiver and transmitter  141  and to the surface  159 . As an alternative to a mechanical link, an acoustic communication system  160  may be provided. It is possible to change the control package when the BOP bore is isolated via connection  161 . 
   This control package provides a controlled fluid flow with feedback for accurately pressuring up and venting down as required for testing the BOP and wellhead systems, while at the same time, it will fail close if a loss of control is experienced. 
   Based on the BOP configuration shown in  FIG. 12 , an example of the procedure for fully testing the BOP shown is as follows and is summarized in the table of  FIG. 14 : 
   (i) The initial simultaneous tests are carried out to check the integrity of: the choke line  40 , the choke test valve  47  (choke line side—CLS) and the outer gas vent valve  46  (CLS); the kill line  41  and the kill test valve  52  (kill line side—KLS); and the booster line  42  and the booster line valve  43  (booster line side (BLS). The pressure is monitored in each of the choke, kill and booster lines. 
   (ii) The second simultaneous tests are concerned with the integrity of the upper  49  and lower  51  outer choke valves (CLS), the inner gas vent valve  45  (CLS) and the LRP (Lower Rise Package)-BOP choke line connection, and with the upper  55  and lower  57  outer kill valves (KLS) and the LRP/BOP kill line connection. 
   (iii) The next step simultaneously tests the upper  48  and lower  50  inner choke valves (CLS) and the upper  54  and lower  56  inner kill valves (KLS). These tests will check the choke, kilt and booster lines and the associated valving from the line side. 
   Tests using the assembly can be as follows with certain valves not under test being set to enable any leaks to be monitored independently up either the riser or the choke or kill lines: 
   (iv) The seal between the test tool and the well head is tested together with the lower pipe rams  30 , the lower inner choke valve  50  (well side WS), the well head connector and the control package prime master  144 . The inner gas vent  45 , the upper  54  and lower  56  inner kill valves and the upper inner choke valve  48  are all in a closed position. 
   (v) This step checks the lower outer choke valve  51  (WS), the middle pipe rams  31 , the lower inner kilt valve  56  (WS) and the control package secondary master valve  145 . The inner gas vent  45 , the upper inner choke valve  48  and the lower inner kill valve  56  are in closed position. 
   (vi) The next test examines the integrity of the lower outer kill valve  57  (WS), the upper pipe ram  32  and the upper inner choke valve  48  (WS). The inner gas vent  45 , the lower outer choke valve  51  and the upper inner kill valve  54  are all closed. 
   To test the annular cavities, which can be classed as the medium pressure zone, is as follows: 
   (vii) The lower annular  34  is tested together with the upper inner kill valve  54  (WS) but this can only be tested to the pressure of the lower annular. The inner gas vent  45 , the upper  49  and lower  51  outer choke valve and the lower outer kill valve  57  are all in the closed position. 
   (viii) This step tests the integrity of the upper annular  35 , the inner gas vent valve  45 , (WS) and the LRPBOP stack connection and the upper outer kill valve  55  (WS), but only to the annular test pressure. The upper  49  and lower  51  outer choke valves and the lower outer kill valve  57  are all in the closed position. 
   (ix) This tests only the outer gas vent  46  (WS). The upper  49  and lower  51  outer choke valves, the upper  55  and lower  57  outer kill valves are all in the closed position. 
   To test the shear blind ram cavity, which is classed as the high pressure zone, is as follows: 
   (x) The test mandrel  60  is now separated at the coupling  63  between the upper  61  and lower  62  sections so that the shear blind rams  33  can be tested, together with the upper inner kill valve  54  (WS). The outer gas vent  46 , the upper  49  and lower  51  outer choke valves and the lower outer kill valve  57  are all in the closed position. 
   (xi) The final test checks the upper outer kill valve  55  (WS). The outer gas vent  46 , the upper  49  and lower  51  outer choke valve and the lower outer kill valve  57  are all in the closed position. 
   This now ensures that the barrier elements in either the high pressure or medium pressure zones have been tested at their correct working pressure and from both directions where applicable (i.e. rams and annulars are only tested from the well side). 
     FIG. 15  shows how the test assembly can be adapted to be used as a planned emergency BOP hang-off tool that, on installation, provides a prime bore and annulus barrier in the wellhead. Thus, in this arrangement, the BOP provides a second barrier to the environment in a planned emergency disconnect. 
   Whilst on the surface, a one way downward differential pressure flow unit  170  is installed, sealed and locked into the test plug  70 . On installation, the plunger  99  is depressed and this moves the circulation sleeve  80  into the full circulation mode. This can be achieved by using a long thread section  171  that allows the unit  170  to be screwed in using a connection  172  and a hand tool  177 . The one way upward flow mechanism  81  in the lower part of the test plug  70  is now bypassed. This permits circulation down the drill pipe and up the annulus, yet any back pressure up the drill pipe will be contained by the one way downward flow mechanism  170 . 
   The one way downward differential pressure unit  170  provides sufficient pressure differential to allow the release of the hydraulically activated anti-rotation coupling  63 . 
   In a planned emergency disconnector of the BOP lower riser package  15 , the adapted test assembly can be locked and sealed in the wellhead which closes off the bore and the annulus from upward pressure. All the sensors in the test assembly can monitor the parameters in the bore and the annulus, above and below the test plug. The pipe rams can be closed. After disconnecting the mandrel coupling  63  and closing the shear blind rams  33 , the shear blind rams form the second barrier to the environment. The LRP  15  can now be released. 
   On return of the drilling vessel and reconnection of the LRP  15 , the parameters in the wellhead and the BOP can be obtained prior to operating any function on the BOP stack, reconnecting the mandrel coupling  63 , rotating to open valve  77 , circulating the well and pulling back the pipe in the hole. 
   In a hang off situation, there may be no requirement to pull the wear bushing. To prevent this occurring in operation or testing, the wear bushing locking dogs  89  can be made ineffective by locking them in prior to running the test assembly. 
   While preferred embodiments of this invention have been shown and described, modifications thereof can be made by one skilled in the art without departing from the spirit or teaching of this invention. The embodiments described herein are exemplary only and are not limiting. Many variations and modifications of the system and apparatus are possible and are within the scope of the invention. Accordingly, the scope of protection is not limited to the embodiments described herein, but is only limited by the claims which follow, the scope of which shall include all equivalents of the subject matter of the claims.