RIIL.ES FOR ABANDONMENT OF WELLS 1. In most cases sufficient casing should be left in a well to serve as a conductor from the ground surface to the point of shut-off. This requirement is based on the fact that it is fre quently impossible to prove immediately and directly the effec tiveness of plugging. It may be necessary to note the behavior of neighboring wells for a considerable period of time before it is shown that plugging has been effective. In some cases the con dition of surrounding wells may demonstrate that plugging was not effective, and that further work is necessary at the abandoned well. The well could not be economically re-entered if all the casing had been removed. Furthermore, in soft formations it oes not pay to attempt to pull casing below the shoe of the ext larger casing, as ordinarily only one or two joints of casing i contact with the walls of the hole can be recovered.
2. It is generally required that cement plugs be placed between zones of oil or gas producing formations, in order to irevent the possible passage of water from one to another. In (lost wells it will be necessary to remove or shoot the casing >etween the depths at which plugging should be done, so that !ement may reach the walls of the well. Wells which have sidetracked casing require a larger shot than those which have lot. The casing in a well, between the shoe of the water string Ind a point at least 15 ft. below, should be pulled out or broken up by shooting, and the well should be plugged with cement for at least 20 ft. up into the water string.
3. In case of effective water shut-off, wells which do not have suitable formations in which to plug below the shoe of the water string, should be plugged (inside of such string) for at least 20 ft. directly above the shoe.
4. Each cement plug put into a well must be allowed to set at least 24 hours (and a longer time is advisable) after which time it must be determined that the cement has properly set before further plugging is done.
5. When a well is producing "bottom" water, the level at which fluid (water and oil) stands in the well should be accurately determined both before and after plugging. If possible the well must be plugged in a formation which will separate the water bearing formation from the overlying oil or gas bearing forma tions. The well must be tested by bailing to determine the effectiveness of the plugging. After such test has been made plugging should continue as indicated in rules 2 and 3.
6. When a well is making "top" water around the shoe of the water string, it will be necessary, in addition to the plugging between formations as required in rules 2 and 3, to place a cement plug in a suitable formation directly below the water string. If a suitable formation for the plug is not present, the
water string should be shot or removed above the shoe at a point opposite an impervious formation, and a cement plug should be placed tightly against the formation where the casing was shot or removed.
7. When a well is making "top" water through the water string it should be plugged as provided in rules 2 and 3.
8. When a well penetrates "intermediate" water below the water string, it should be plugged in a formation which separates the water bearing formation from the overlying and underlying oil or gas bearing formations. The depth to the fluid level should be measured, and a test made as indicated in rule 5.
9. When a well penetrates "intermediate" water above the shoe of the water string, and mud-laden fluid or cement has been effectively used for the protection of oil or gas bearing formations back of the casing, the water string should not be disturbed unless it is proposed to put in cement plugs between oil and gas bearing formations. Where the original protection sought by mud or cement was ineffective, it will be necessary to shoot or rip the water string at places where plugs will be required to separate oil or gas bearing formations. To test the effectiveness of the origi nal protection, the water string should be perforated or ripped opposite the oil or gas bearing formations. If the test demon strates that proper protection was obtained, the casing should be plugged to points at least 10 ft. above and below the perforation or ripping, in order to seal the openings in the casing. A water string which protects oil or gas bearing formations behind the casing by means of cement and mud, may be cut off (not shot) about 20 ft. above the shoe of the next larger casing. A cement plug should then be placed at the top of the casing.
10. When the source of water can not be definitely determined it will be necessary to use all the methods provided for every possible source.
When plugs are placed in an old well it is essential that the casing be removed or shattered so that the plug will bond with the walls of the hole, otherwise open channels between the casing and the wall may remain. Thorough ripping of the casing may sometimes be sufficient, but if the casing can be actually removed from the portion of the well involved there is greater assurance of thorough plugging. The removal of the casing is best done by cutting it into five-foot lengths, and as each section is cut off it should be split several times, and as nearly as possible from end to end. As they are cut off these ripped sections can be pounded down, or crumpled, with the drilling tools.