Velocity String 

In simple terms, Velocity String is a type of small-diameter string normally applied in wellbore of gas wells to throttle and speed up fluid.

Many flowing oil and gas wells experience decreased production over time, and eventually can stop producing completely. 

Factors causing this problem include declining reservoir pressure and gas velocities and liquid loading preventing reservoir fluids from entering thewellbore. Thus now many fields have installed a small diameter coiled tubing string (velocity or siphon string) to restore a well that is“liquid loaded”back to flow production. Deployed by coiled tubing (CT) device, connected by specialized wellhead tool, and with advancedly-designed length, 1.0”~2.0”CT will be hung into the original production tubing in the well to form new production string. Considering different production status, generally two production methods will be applied- gas production via CT or gas production via annulus between CT and production tubing.

 

Wellhead Tools                                                                                 

 

1.    CT hanger system                                                                                                                                  

2.    Hanger spool                                                                                                                                           

3.    Gate valve                                                                                                                                               

4.    Flange                                                                                                                                                     

5.    Needle valve                                                                                                                                           

6.    Sealing device                                                                                                                                        

7.    AMMT slip connector

 

Down-hole Tools

 

1.    Landing nipples

2.    Pump out sub below down hole plug 

3.    Bottom slip connector

4.    CT Pump out plug 

5.    Down-hole plug for Landing nipple 

6.    Retrievable landing seat

PS:A small-diameter tubing string run inside the production tubing of a well as a remedial treatment to resolve liquid-loading problems. As the reservoir pressure in a gas well depletes, there may be insufficient velocity to transport all liquids from the wellbore. In time these liquids accumulate and impair production. Installing a velocity string reduces the flow area and increases the flow velocity to enable liquids to be carried from the wellbore. Velocity strings are commonly run using coiled tubing as a velocity string conduit. Safe live-well working and rapid mobilization enable coiled tubing velocity strings to provide a cost effective solution to liquid loading in gas wells.