System and method for low-pressure well completion

Abstract

A low-pressure wellhead system with tubular heads and mandrels secured independently using threaded unions. A casing mandrel is secured to a wellhead by a first threaded union. Likewise, a tubing head spool is secured to the casing mandrel using a threaded union. A tubing hanger is also secured to the tubing head spool using a threaded union. An adapter flange may also be secured to the tubing hanger by a threaded union. Because this low-pressure wellhead is faster and easier to assemble and provides full bore access, there is less rig downtime, thus rendering the well completion process faster and more economical.

1 . A wellhead system for stimulating and extracting subterranean hydrocarbons from a low-pressure well, the system comprising: 
 plurality of tubular heads independently secured by threaded unions, each tubular head supporting a mandrel for suspending a tubular string in the well, each mandrel being secured to the tubular head by a threaded union.    
   
   
       2 . The wellhead system as claimed in  claim 1  comprising two independent tubular heads separated by a mandrel.  
   
   
       3 . The wellhead system as claimed in  claim 1  wherein each threaded union comprises a nut.  
   
   
       4 . The wellhead system as claimed in  claim 3  wherein the nut is one of a wring nut, a spanner nut and a hammer union.  
   
   
       5 . The wellhead system as claimed in  claim 1  wherein the tubular strings suspended by the mandrels are concentrically disposed within a surface casing suspended by a wellhead, the wellhead being supported by a conductor assembly dug into the earth.  
   
   
       6 . The wellhead system as claimed in  claim 1  comprising: 
 a casing mandrel threadedly secured to a wellhead, the wellhead securing and suspending a surface casing;    a tubing head spool threadedly secured to the casing mandrel, the casing mandrel securing and suspending a production casing; and    a tubing hanger threadedly secured to the tubing head spool, the tubing hanger securing and suspending a production tubing.    
   
   
       7 . The wellhead system as claimed in  claim 6  further comprising an adapter flange threadedly secured to the tubing hanger, the adapter flange having an upper flange for connecting to a flow-control device.  
   
   
       8 . The low-pressure wellhead system comprising: 
 an independent screwed wellhead having independently secured tubular heads for supporting respective tubular strings in a well bore; and    a plurality of threadedly secured mandrels supported by the tubular heads, the mandrels securing and suspending the tubular strings in the well bore.    
   
   
       9 . The wellhead system as claimed in  claim 8  comprising a first tubular head and a second tubular head, a first mandrel located between the first and second tubular heads and a second mandrel supported above the second tubular head.  
   
   
       10 . The wellhead system as claimed in  claim 9  wherein: 
 the first tubular head is a wellhead that secures and suspends a surface casing in the well bore;    the first mandrel is a casing mandrel that secures and suspends a production casing in the well bore;    the second tubular head is a tubing head spool supporting the second mandrel at an upper end of the tubing head spool; and    the second mandrel is a tubing hanger that secures and suspends a production tubing in the well bore.    
   
   
       11 . The wellhead system as claimed in  claim 8  wherein the tubular heads and mandrels are secured by threaded unions.  
   
   
       12 . The wellhead system as claimed in  claim 11  wherein the threaded unions are one of a wring nut, a spanner nut and a hammer union.  
   
   
       13 . A method of completing a low-pressure well comprising steps of: 
 securing a first mandrel to a first tubular head using a first threaded union, the first tubular head supporting a first tubular string in the well, and the first mandrel supporting a second tubular string in the well;    securing a second tubular head to the first mandrel using a second threaded union; and    securing a second mandrel to the second tubular head using a third threaded union, the second mandrel supporting a third tubular string in the well.    
   
   
       14 . The method as claimed in  claim 13  further comprising a step of securing an adapter flange to the second mandrel using a fourth threaded union.  
   
   
       15 . The method of completing a low-pressure well after a conductor assembly has been installed in the ground above a subterranean hydrocarbon formation, the method comprising steps of: 
 landing a wellhead onto the conductor assembly, the wellhead securing and suspending a surface casing in the well;    securing a casing mandrel to the wellhead using a first threaded union, the casing mandrel securing and suspending a production casing in the well;    securing a tubing head spool to the casing mandrel using a second threaded union; and    securing a tubing hanger to the tubing head spool using a third threaded union, the tubing hanger securing and suspending a production tubing in the well.    
   
   
       16 . The method as claimed in  claim 15  further comprising the step of securing an adapter flange to the tubing hanger using a fourth threaded union.  
   
   
       17 . The method as claimed in  claim 15  further comprising steps of: 
 after the step of securing the casing mandrel to the wellhead, securing a frac stack to the casing mandrel using a fourth threaded union, the frac stack having conduits for conveying proppants and pressurized fluids into the production casing for fracturing the subterranean hydrocarbon formation; and    prior to the step of securing the tubing head spool to the casing mandrel, removing the frac stack from the casing mandrel.    
   
   
       18 . The method as claimed in  claim 17  wherein the step of securing the frac stack using the fourth threaded union further comprises the steps of: 
 securing a frac stack adapter flange to the underside of the frac stack; and    securing an adapter pin to the casing mandrel, the adapter pin having pin threads for engaging box threads of the frac stack adapter flange.    
   
   
       19 . A method of installing and completing a low-pressure wellhead system for the extraction of hydrocarbons from a subterranean hydrocarbon formation, the method comprising the steps of: 
 digging away earth above the subterranean hydrocarbon formation to accommodate a conductor;    installing a conductor window on the conductor;    running surface casing until a wellhead is seated above the conductor;    cementing the surface casing in place;    removing the conductor window to expose the wellhead;    mounting a blowout preventer and drilling flange to the wellhead using a first threaded union;    inserting a test plug into the wellhead system to test a pressure-integrity of the wellhead system;    removing the test plug after the testing of the pressure-integrity of the wellhead is complete;    installing a wear bushing in the drilling flange;    drilling a bore to accommodate a production casing;    running in the production casing until a casing mandrel connected to a top end of the production casing is seated in a casing bowl of the wellhead;    cementing in the production casing;    removing the blowout preventer and drilling flange;    securing the casing mandrel to the wellhead using a second threaded union;    securing a tubing head spool to the casing mandrel using a third threaded union;    running in a production tubing until a tubing hanger is seated in the tubing head spool; and    securing the tubing hanger to the tubing head spool using a fourth threaded union.    
   
   
       20 . The method as claimed in  claim 19  further comprising a step of securing an adapter flange to the tubing hanger using a fifth threaded union.  
   
   
       21 . The method as claimed in  claim 20  further comprising a steps of: 
 after the step of securing the casing mandrel to the wellhead, securing a frac stack to the casing mandrel using a fifth threaded union, the frac stack having conduits for conveying proppants and pressurized fluids into the production casing for fracturing the subterranean hydrocarbon formation; and    prior to the step of securing the tubing head spool to the casing mandrel, removing the frac stack from the casing mandrel.