Stress distribution tuning in composite plugs and method

Abstract

A composite plug for sealing a well, the composite plug including a mandrel having an internal bore that extends along a longitudinal axis (X) of the mandrel; and plural elements located on the mandrel. At least one element of the plural elements is attached to the mandrel with a tunable thread, and the mandrel and the tunable thread are made of composite materials.

What is claimed is: 
     
         1 . A composite plug for sealing a well, the composite plug comprising:
 a mandrel having an internal bore that extends along a longitudinal axis (X) of the mandrel; and   plural elements located on the mandrel,   wherein at least one element of the plural elements is attached to the mandrel with a tunable thread,   wherein the mandrel and the tunable thread are made of composite materials.   
     
     
         2 . The composite plug of  claim 1 , wherein the at least one element is one of a mule shoe, an upper slip ring, an upper wedge, a sealing element, a lower wedge, and a lower slip ring. 
     
     
         3 . The composite plug of  claim 1 , wherein the tunable thread is a buttress thread. 
     
     
         4 . The composite plug of  claim 1 , wherein the at least one element is attached to the mandrel only with the tunable thread. 
     
     
         5 . The composite plug of  claim 1 , wherein at least another element of the plural elements is attached to the mandrel with another tunable thread. 
     
     
         6 . The composite plug of  claim 5 , wherein the at least one element is a mule shoe and the at least another element of the plural elements is one of an upper slip ring, an upper wedge, a sealing element, a lower wedge, and a lower slip ring. 
     
     
         7 . The composite plug of  claim 5 , wherein the tunable thread is different from the another tunable thread. 
     
     
         8 . The composite plug of  claim 5 , wherein the tunable thread is manufactured with a direct mold method and the another tunable thread is manufactured with a filament wound method. 
     
     
         9 . The composite plug of  claim 1 , wherein the tunable thread is manufactured with a direct mold method. 
     
     
         10 . The composite plug of  claim 1 , wherein the tunable thread is a buttress thread and a tooth of the tunable buttress thread has a steep face and a slanted face, and an angle of the steep face with the longitudinal axis of the mandrel is selected to be larger than 90. 
     
     
         11 . A method for using a composite plug in a well for sealing the well, the method comprising:
 lowering the composite plug into the well, wherein the composite plug includes a mule shoe attached to a mandrel with only a tunable thread;   sending a signal to a setting tool to deploy the composite plug; and   pulling out of the well the setting tool by applying a tensile load to the setting tool so that a connection between the setting tool and the plug is broken while the tunable thread holds the mule shoe attached to the mandrel.   
     
     
         12 . The method of  claim 11 , wherein the mandrel has an internal bore that extends along a longitudinal axis (X) of the mandrel and plural elements are located on the mandrel, and
 wherein the mandrel and the tunable thread are made of composite materials.   
     
     
         13 . The method of  claim 11 , wherein the tunable thread is manufactured with a direct mold method. 
     
     
         14 . The method of  claim 11 , further comprising:
 applying the tensile load to the setting tool to be smaller than a maximum force at which teeth of the tunable thread are sheared.   
     
     
         15 . The method of  claim 11 , wherein the tunable thread is a buttress thread. 
     
     
         16 . A method for manufacturing a composite plug for sealing a well, the method comprising:
 providing a loading direction of a mule shoe of the composite plug, wherein the mule shoe is attached with only a tunable thread to a mandrel of the plug;   providing a maximum value of a force that the mule shoe needs to withstand while in the well;   providing a value for an angle between (1) a steep face of a tooth of the tunable buttress thread and (2) a longitudinal axis of the mandrel;   selecting a method for making the mule shoe from a composite material; and   making the mule shoe to have the tunable thread with the given angle.   
     
     
         17 . The method of  claim 16 , wherein the method for making the mule shoe is a direct mold method. 
     
     
         18 . The method of  claim 16 , further comprising:
 making the mandrel to have a mating tunable thread that mates with the tunable thread of the mule shoe.   
     
     
         19 . The method of  claim 16 , further comprising:
 attaching another element of the plug to the mandrel with another thread.   
     
     
         20 . The method of  claim 19 , wherein the another element is one of an upper slip ring, an upper wedge, a sealing element, a lower wedge, and a lower slip ring. 
     
     
         21 . The method of  claim 19 , wherein the another thread is another tunable thread. 
     
     
         22 . The method of  claim 21 , wherein the another tunable thread is different from the tunable thread. 
     
     
         23 . The method of  claim 19 , wherein the another thread is a round or v-shaped thread. 
     
     
         24 . The method of  claim 19 , wherein the tunable thread is manufactured with a direct mold method and the another thread is manufactured with a filament wound method. 
     
     
         25 . The method of  claim 16 , wherein the tunable thread is a buttress thread.