Removing The BOP:

The initial test of a bop is when it is install or on a test stump before installation, however even when tested on a test stump the bop must be retested to insure the new connecting flange is holding. Off-hole maintenance is the key to reliable well control, but it is possible a time will come when the BOP stack will have to undergo major repairs while in use over an open hole and live well. I have read in many papers, the BOP is the primary well control equipment, this is wrong; it is not the primary control equipment. (It is the secondary equipment.) The drilling or workover fluid in the wellbore is the primary well control, over the years I have been involved in many debates as what you can do or can't do with or without a BOP. To clear up any misunderstanding as to what is meant by well control and the well control barriers let me make it quite clear. Current regulations in certain drilling markets require three containment barriers for temporary abandonment of a well. Most country state there has to be two safety barriers per well. If one barrier is to be removed a second barrier must be in place before the faulty barrier is removed. By removing the BOPs or should it malfunction you have in-fact only one barrier. I could very easily tell of a case where the BOP was picked up to free up a wear bushing, and the hours spent trying to stab back and hammer up the bolts with fluid flying all over the place. For a BOP to be removed from a well the well must be in a secure condition. Drilling fluid alone is not secure. Some form of plug must be set. Any repairs above the shear rams can be done over the hole by using the shears as your second barrier. As an added safety precaution and providing there is a drilling spool between the shear rams and the bottom rams a kill string can be run in the hole to the casing shoe and hung off on the bottom rams. The kill line must always to be installed below the shear rams, it is then possible to move a circulating / choke line down to the well head. By doing this you can monitor the well and keep the hole full should it be losing fluid. Not to long a go I had a letter from a consultant asking me "Why use a drilling spool between the blind/shear and the bottom rams" Well Jess if you still read the site here is one good reason and It dose not take to much imagination to see a second good reason.? Drilling Spool However let me just say it is not good drilling practice to kill a well using the bottom rams. However I have always considered the saying "If it can happen, it will happen" and as an ex Boy Scout there is nothing wrong with being prepared. Although hanging off a drill string is common practise on sub sea wells hanging pipe off on a jack up or land rig may not be so common now day, but was a regular practice in bad whether area in the passed and I can assure you it will not damage the BOPs. There is some where in the manufactures manual that will tell you just what can be hung off. +/- 250000 lbs If the repair work is below the shear ram the hole will have to be plugged. In most case's the quickest way would be to run a retrievable bridge plug then change out the BOP. Retrievable Bridge Plugs such as the T725 TS-U high pressure packer style retrievable bridge plug can be run using the T577 TS-U retrieving tool. Its large internal bypass system allows for multiple setting and releasing under extreme pressures. The plug setting operation requires the setting string to be picked up, turn one quarter to the right at the plug and slacked off. The running and retrieving tool has a spring load design that minimizes the possibility of the bridge plug coming free during running and retrieving. The strong compression spring keeps the bridge plug J-pins securely locked in the retrieving tool jay until sufficient weight collapses the spring allowing the retrieving tool to be removed. To release from the set down, apply right hand torque and pick up. The bypass system will allow pressure to equalize before the upper slips are pulled on and released from the casing wall. This and other retrievable bridge plugs are extremely easy to run by the drilling crew and have the added advantage that they can be set shallow or deep. Sets or releases are one quarter turn to right, with the retrieving tool being guider over the plug like an overshot, they equalizes before the upper slips are released. A tip when running such a plug, It is advisable to cover the top of the plug before any work commences this can be done by dropping sand down the wellbore allowing it to settle over the retrieving stem. 3 or 4 foot of sand will catch any junk drop down the hole and stop it from going down the side and later picked or washed up. I tend to favour the storm valve. Again you can run some of the drillstring into the hole and hang it off using the storm valve with the inside BOP installed below. For this to be effective you must have a minimum weight below the storm valve. By using a simple rule of the thumb you can work this out. Take the area of the inside diameter of the casing and multiply it by 1000. Although some people like to run a kill string made up of tubing, the idea of hanging of on the wellhead using a tubing hanger is asking for problems. The lock down bolts are not designed for this and I have my doubt as to if they can take the maximum rate that the bop would take. I say this from the experience of seeing the bolts shear while an annular test was being preformed on a tubing string after the well had been completed and before the bops were removed (the pressure being applied at the time of the test was 3000 psi)