Method and Apparatus for Inserting a Tubular String into a Well

Abstract

A valve to act as a barrier to fluid movement in a tubular is provided. A flapper in the valve may be opened by application of a selected pressure differential across the flapper. The flapper opens to allow a cylinder to shift and cover the open flapper. A method of placing a tubular string within a well using the valve as an isolation valve to form gas filled chambers for floating the tubular string into the well is also disclosed.

I claim: 
     
         1 . An isolation valve sub for placement in a string of tubulars, comprising:
 a lock housing adapted for joining to a first tubular;   an upper spring housing joined to the lock housing and a first spring enclosed in the upper spring housing;   a lower spring housing joined to the upper spring housing and a second spring enclosed in the second spring housing and a spring stop for the enclosed spring;   an upper flow tube concentric within the upper spring housing and adapted to move axially in response to force from the first spring;   a lower flow tube concentric within the lower spring housing and adapted to move axially in response to force from the second spring;   a destructible element adapted to receive axial force from the lower flow tube;   a pivotably mounted flapper, disposed to apply force to the lower flow tube; and   a lower lock housing joined to the second spring housing and adapted to be joined to a second tubular.   
     
     
         2 . The isolation valve of  claim 1  further comprising a housing adapter disposed between the upper spring housing and the lower spring housing. 
     
     
         3 . The isolation valve of  claim 1  further comprising a bearing disposed between the first spring and the upper spring housing. 
     
     
         4 . The isolation valve sub of  claim 1  further comprising a snap ring disposed on the upper flow tube and being adapted to slidably move axially within the upper spring housing and expand radially to lock at a position in the upper spring housing; 
     
     
         5 . The isolation valve of  claim 1  wherein the destructible element is positioned on the lower flow tube and restrains downward movement of the lower flow tube until a given force acting on the element is exceeded. 
     
     
         6 . The isolation valve of  claim 1  wherein the lock housing, upper spring housing, lower spring housing and lower lock housing all have an outside diameter no greater than the outside diameter of the string of tubulars. 
     
     
         7 . The isolation valve of  claim 1  wherein the valve includes a central flow path of a substantially constant diameter with no flow restrictions. 
     
     
         8 . A method for placing a tubular string in a well comprising:
 locating a plurality of isolation valves along the tubular string thereby forming isolated chambers within the tubular string filed with a gas; and   placing the tubular string within a well with the isolation valves in a closed position.   
     
     
         9 . A method as claimed in  claim 8  wherein the gas is air or nitrogen.