Oilfield Consultant in Surface and Subsea Wellheads Equipment,Christmas Trees,Flow Control Equipment,Seals(Elastomerics & Metal-to-Metal)                  Contact me NEW E-mail: country45ve@yahoo.com

dmc43-1.JPG (14257 bytes)



This special well's completions are used when reservoir conditions are special too, and two string of tubes has to be installed downhole, for reach two reservoirs of oil, at different depth situations, that in many cases may come in a mix of oil and gas, oil only,oil with different grades API , so the case is special, and two drills at different depth has to be made. Next is a good example in the drawing ahead, this is a dual assembly hook-up for 15,000 PSI working pressure, and H2S PSL-4/PR-2.

    dmc41.jpg (18236 bytes)              dmc42.jpg (16741 bytes)   dmc43.jpg (24816 bytes)


Sections A,B,C,D, which means the conductor and casing sections, are generally typical configurations as many other, the critical difference appears in the tubing head section that in many cases is SS for H2S service and so is the dual tubing hanger, which in this assembly is special, and is sometimes called parent hanger(see image of the right above), is a device that is very sensitive to any mistake, and special tools and extra safety has to be considered, for avoiding a potential damage, due to the metal-to-metal seals.

As you can notice a dual assembly is easy to identify at first sight, by only seeing the Christmas tree, and two handwheels are installed one in front of the valve and the other in the back. The lower handwheel means the deepest tube string that belongs to, and the upper means the short string, but in many cases this is not a general agreement, and the interpretation of this is the opposite. The two images ahead shows a dual tubing hanger in blue color with a dual seal assembly and the dual tubing bonnet in the top this system is simple and suitable for up to 10,000 PSI WP , notice the alignment slots that the tubing hanger has, this is for the orientation of the component and for easy installation.

  dmc39.JPG (22261 bytes)     dmc40.JPG (24242 bytes)

   This two pictures are for a dual completion 11-5,000 PSI WP top flg. and a dual tubing hanger system 3 x 3 -5,000 PSI WP w/ a 5-3/64" CL. image on the left is the drawing in 2D and the one of the right is a photo realistic representation.


  dmc44.jpg (27026 bytes) dmc46.JPG (33427 bytes)

   dmc45.jpg (19059 bytes)

Next drawing the dual Christmas tree top cap, this is a flow assembly 15,000 PSI observe the segmented flanges that each one has, as well as, independent pressure gauges, so the wire line companies are able to work-over each one alone without any trouble; the tool employed for this interventions is special, many supplies in Houston market manufacture the structure, as a rotary platform where an attachment segmented flange is connected to the tree top cap , where the service man by turning a lever slower down the plugging tool inside one string ,until it reaches the dual tubing hanger's H-BPV threads.




Some of the basic Center Lines for dual completions ahead, that means the exact separation between center lines of each tube string.



2-3/8" x 2-3/8"


2-7/8" x 2-7/8"


3-1/2" x 3-1/2"


Some of the possible tube strings mix combinations in each tubing head, and again with the center lines, as follow:

Tubing Head top

API Flange Size

Working Pressure




7-1/6" 3,000 - 15,000 2-3/8" x 2-3/8" 3-35/64"
9" 3,000 - 10,000 2-3/8" x 2-3/8" 3-35/64"
11" 3,000 - 10,000 2-3/8" x 2-3/8"

2-7/8" x 2-7/8"

3-1/2" x 3-1/2"




Note: This are some of the most used combinations.


Updated on:01/25/04Copyright @2003 Daniele Molaro Consulting

Note:This is only a brochure and is not intended to be used as a manufacturing's parts data information;our mission is announce our technical & engineering service and assist customers bringing them technical support, please contact us regarding this WEB site,or for assistance on site.