Wells – Processes – Placing or shifting well part
Reexamination Certificate
2002-03-01
2004-10-05
Bagnell, David (Department: 3672)
Wells
Processes
Placing or shifting well part
C166S075150, C166S177300, C166S188000, C166S373000
Reexamination Certificate
active
06799638
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to cementing pipe within a wellbore. More particularly, the present invention relates to selectively releasing wiper plugs contained within enclosed launching assemblies for cementing casing, subsea casing strings and casing liners in wells.
BACKGROUND OF THE INVENTION
Pipe used to case wellbores is cemented into the wellbore to anchor the well pipe and isolate differently pressured zones penetrated by the wellbore. Pipe used for this purpose is generally referred to as “casing.” The cementing step is initiated by pumping a cement slurry down into the casing from the well surface. The cement slurry flows out from the bottom of the casing and returns upwardly toward the surface in the annulus formed between the casing and the surrounding wellbore.
In the cementing process, the fluid normally used in the drilling of the wellbore, referred to herein generally as “drilling fluid,” is displaced from the casing ahead of the cement slurry pumped into the casing. When a sufficient volume of the cement slurry has been pumped into the well pipe, drilling fluid is used to displace the cement from the well pipe to prevent the pipe from being obstructed by the cured cement.
The drilling fluid and cement slurry are separated during the displacements with appropriate liquid spacers, or more preferably, with sliding wiper plugs that seal along the inside of the well pipe, wiping the inside of the pipe and isolating the cement slurry from the drilling fluid. When using wiper plugs to separate the drilling fluid and cement, the cement slurry is pumped behind a first wiper plug to push the plug through the casing, forcing the drilling fluid in the casing to flow ahead of the plug. The drilling fluid displaced from the bottom of the casing flows upwardly through the annulus and returns toward the well surface.
When a sufficient volume of cement has been pumped behind the first wiper plug, a second wiper plug is positioned in the casing and drilling fluid is pumped into the casing behind the second plug to push the cement slurry through the casing. A flow passage in the first plug opens when it reaches the casing bottom to permit the cement slurry to flow through and past the plug, out the casing bottom. Once the first wiper seal has been opened and its seal terminated, the continued advance of the second plug through the casing displaces the cement slurry past the first plug, around the end of the casing, and up into the annulus. The second plug stops and maintains its sealing engagement with the casing once it arrives at the bottom of the casing.
When the casing string extends back to the drilling rig, the first and second plugs and cement are manually inserted into the casing at the drilling rig floor. Remotely set plugs are used when the well casing that is to be cemented does not extend back to the drilling rig floor. For example, a “liner,” which is a string of casing that hangs from the bottom of a previously installed larger diameter section of casing, does not extend back to the drilling rig floor. Subsea completions in offshore wells also involve strings of casing that do not extend back to the drilling rig.
Installing and cementing strings of casing that do not extend to the drilling rig is typically done by installing the casing string with a smaller diameter running string. If wiper plugs are employed in this process, they are carried on a running tool at the lower end of a small diameter string of drill pipe that extends from the drilling rig and connects to the top of the larger diameter casing string that is to be cemented. The drilling fluid and the cement slurry required to perform the cementing operation are initially pumped from the surface through the small diameter drill pipe, through circulating openings in the wiper plugs and into the casing. The plugs are “remotely set” from the rig floor using setting devices that are inserted into the string at the rig floor and pumped down to the plugs carried on the running tool. The cement slurry exiting the bottom of the casing string returns in the annulus to the point at which the casing string is hung off from the higher casing string or sub sea wellhead.
In a typical operation of remotely set wiper plugs carried at the end of a running tool on a drill string, a brass ball, or a weighted plastic ball or dart or other setting device is inserted into the drill string at the surface ahead of the cement slurry. The ball passes through the opening in the upper wiper plug and lands in and closes a smaller circulation opening in the lower plug. The resulting pressure increase releases the lower plug for movement through the casing. When sufficient cement has been pumped into the drill string and casing from the surface, a latch-down plug or seal dart is inserted into the drill string and pumped down to the upper wiper plug still secured to the running tool. Arrival of the latch-down plug at the upper plug closes the circulation opening and releases the upper plug for movement through the casing string. The upper plug is then pumped to the bottom of the casing to completely displace the cement slurry from the casing.
Remotely set wiper plugs are also employed in rig floor cementing assemblies that employ multipurpose tools that function as combination fillup tools and cementing tools. These combination tools, as described in U.S. Pat. No. 5,918,673, may include remotely releasable plugs in the surface operated assembly to eliminate the need for a separate plug container or other similar device at the rig floor for deploying the cementing plugs.
A common requirement of remotely set wiper plugs, including those used in the combination tool assembly, is the need for the plugs to accommodate circulation of fluids before they are released to travel through the casing string. The size of circulation openings is a major consideration in the design of the wiper plugs and their launching mechanisms.
In use, the materials and components of the wiper plug must withstand the pumping pressure differentials and the erosion experienced during different phases of the cementing procedure. Any sealing surface exposed to the flow of the cement slurry and drilling fluids is subject to erosion damage and possible failure, particularly when the seals are formed of plastic or other non-durable materials. Accordingly, substantial volumes of durable material are required in the construction of conventional wiper plug assemblies to meet the strength and erosion resistance requirements imposed on the assemblies before their release.
The increased strength and durability of the plugs are typically achieved at the expense of the size of the circulation openings through the plugs. Because of their relatively small circulation openings, remotely set wiper plugs carried in a combination tool or connected with the drill pipe can create a restricted flow passage for pumped fluids. These flow restrictions can increase the possibility of packing off and other problems and can limit pumping rates for the drilling fluids as well as the cement slurry.
The wiper plugs used in cementing must also be constructed of materials that may be easily drilled up or milled away at the end of the cementing operation. Because of this requirement, the use of high-strength metal is undesirable in the construction of the wiper plugs. The necessary strength and durability requirements are met in conventional wiper plugs by using larger volumes of soft metals and other easily removable materials. The required large volumes of material can require small passage openings that can contribute to the restriction of flow of fluids through the wiper plugs.
The requirement for relatively large volumes of soft structural metal or durable plastics within conventional, remotely actuated wiper plugs also renders the use of certain designs impractical within smaller internal diameter well casings. For example, in well casings having an internal diameter of 7″ or less, the volume of materials required to provide the support and release functions of a
Bagnell David
Gay Jennifer
Halliburton Energy Service,s Inc.
Roddy Craig W.
Torres Carlos A.
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