Wells – Processes – With indicating – testing – measuring or locating
Reexamination Certificate
2000-11-27
2002-05-21
Suchfield, George (Department: 3672)
Wells
Processes
With indicating, testing, measuring or locating
C073S152540, C166S337000
Reexamination Certificate
active
06390194
ABSTRACT:
BACKGROUND—FIELD OF THE INVENTION
The subject invention relates generally to a method and apparatus for testing the pressure integrity of blowout preventer systems which are used to control the flow of high pressure fluids from a well. More particularly, the subject relates to a blowout preventer test tool that enables a tool operator to test the pressure integrity of various size blowout preventers without removing the test tool from a well between tests. More particularly still, the subject invention relates to a blowout preventer test tool that enables a tool operator to test the pressure integrity of variable bore rams against different size pipe without removing the test tool from a well between tests. More particularly still, the subject invention relates to a blowout preventer test tool which allows a well to be safely and efficiently shut in should a “kick” be experienced during testing operations.
BACKGROUND—DESCRIPTION OF RELATED FIELD
During the drilling of oil and gas wells, the hazard of a sudden and violent expulsion of fluids, often referred to as a “blowout,” is always present where wells are drilled into porous and permeable rocks containing pressurized gas, oil, and water. Blowouts are extremely dangerous to human life, and can cause extensive damage to property. Furthermore, blowouts waste time, money, and formation pressure needed to commercially raise oil and gas from an underground reservoir to the surface.
During the drilling process, the primary mechanism for preventing a well from “blowing out” is the hydrostatic pressure imparted on the exposed formation(s) in the well by a column of fluid, typically drilling mud, contained within the well bore. Ideally, this hydrostatic pressure should be roughly equivalent to the pore pressure of said formation(s), resulting in a balanced system. In the event that such hydrostatic pressure is insufficient, the high pressure gas and liquids contained within said formation(s) can invade the well bore and displace drilling fluid from the well. This phenomenon is commonly known as a “kick.” If prompt corrective action is not taken at the first indication of a kick, control of the well can be lost and a blowout can occur.
Blowout prevention systems have been developed to protect against the uncontrolled flow of fluids from a well. Blowout prevention systems provide a means of shutting in a well at or near the surface of the well in order to gain control of a kick before it becomes a blowout. A typical blowout preventer system or “stack” typically consists of a number of individual blowout preventers, each designed to seal the well bore and withstand pressure from the formation.
Drilling operations conducted from moveable drilling rigs such as drill ships, semi-submersible rigs and certain jack-up rigs differ from operations conducted from platform-supported drilling rigs in many respects. Among these differences is the location of the blowout preventer and wellhead assemblies. When drilling from drill ships, semi-submersible rigs and certain jack-up rigs, the blowout preventer and wellhead assemblies are not located on the drilling rig, but rather on the sea floor; as a result, specialized equipment known as “subsea” blowout preventers and wellheads are utilized. A large diameter, flexible pipe known as a riser is used to connect the subsea assemblies to the offshore rig. During drilling operations, drill pipe and other downhole equipment is lowered from the rig through the riser, as well as through the subsea blowout preventer assembly and wellhead, and into the hole which is being drilled.
Although there are numerous different types of blowout preventers, one very common variety is the ram-type blowout preventer. Ram preventers utilize sets of large, opposing piston-like elements (rams) which can be selectively closed to seal off a well bore. Pipe rams can be used to seal a well when drill pipe is in use by closing around the pipe and sealing off the annulus formed between the outer surface of the drill pipe and the inner surface of the well. Blind rams can be used to completely seal off a well bore when no pipe is in use. In very extreme cases, shear rams can also be used to completely cut through drill pipe in the well and seal off the well.
Because pipe rams form a seal around the outer surface of drill pipe, the rams must generally be designed to close around a particular size of drill pipe. For example, pipe rams which are designed to be used with 5-inch outer diameter drill pipe are specifically designed to accommodate only that size pipe; such rams will generally not form a seal around pipe having a larger or smaller outer diameter. Additionally, specialized rams known as variable bore rams exist which can be used to form a seal around different size drill pipe within a given range of pipe diameters.
Although certain wells can be drilled using a single size drill pipe, it is very common to use a tapered drill string in the drilling process. The term “tapered drill string” refers to a drill string which consists of larger diameter drill pipe in one portion of a well, and smaller diameter drill pipe in another portion of said well. By way of example, a typical tapered drill string might involve the simultaneous use of both 5-inch outside diameter drill pipe, as well as 3½-inch outside diameter drill pipe in the same well. As such, a blowout preventer system utilized in connection with such a tapered drill string must be capable of sealing off the annular space around both the larger and the smaller drill pipe size.
Because blowout preventer systems are generally considered emergency equipment, active blowout preventer systems must be frequently checked and pressure-tested to ensure that they remain in good working condition. In many instances, governmental regulations require frequent testing of blowout preventer equipment. In order to accomplish such testing on subsea blowout preventer assemblies, a tubular test tool is typically coupled to a drill pipe string or other work string and lowered from the drilling rig to the blowout preventer assembly which is located on the sea floor. First, a test plug at the base of the test tool is seated within a well head assembly which is located immediately below the blowout preventer assembly. Thereafter, a selected blowout preventer is individually closed to form a seal around the outer surface of the tubular test tool, thereby creating an enclosed zone between the test plug and the closed blowout preventer. High pressure fluid is thereafter introduced into the enclosed zone created between the test plug and the blowout preventer in order to test the pressure integrity of said blowout preventer. This process is then repeated to test the other blowout preventers of the blowout preventer assembly. After all blowout preventers of a particular size have been tested, the entire test tool must generally be pulled out of the well, and a different size test tool must be run into the well before another size blowout preventer can be tested in the same manner.
It is important to note that in a subsea application, blowout preventers can be located several thousand feet below a drilling rig. For this reason, tripping a test tool in and out of a well via drill pipe often requires a significant amount of time to accomplish. Because drilling rigs are typically contracted on the basis of a “daily rate”, the more time required to perform operations, including blowout preventer testing operations, the more expensive a particular drilling project becomes. As such, there is a need to conduct blowout preventer tests in an efficient manner, and to minimize the number of pipe trips required to conduct such test blowout preventers.
Several inventions have been directed toward providing a test tool for blowout preventer assemblies. U.S. Pat. No. 4,090,395 to Dixon et al. discloses an apparatus which can be used for testing both blowout preventers and wellhead casing hanger seals. The apparatus disclosed in Dixon includes a tubular member which is equipped with a means for sealing off a casi
Young James Lee
Young Joe Alfred
Anthony Ted M.
Suchfield George
LandOfFree
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