Sunday, June 15, 2008

Basic Completion Concepts

5-1/2" chrome tubing ready to be ran
Crew prepping completion eqpt
Cycling the Tubing-Retrieved Surface Controlled SubSurface Safety Valve (TR-SCSSV)

The last time we covered basic drilling concepts, we were discussing the principles of perforation. After perforation, the wellbore would normally contain completion fluid which provides a hydrostatic column against formation pressure. Simply put, this keeps formation fluid from entering the wellbore until we are ‘ready’ to produce.
The last piece of tubular to be run is the completion string. A completion string consists of tubing (similar to casing, but normally are called tubing if the outer diameter or OD is < 5-1/2”) and completion ‘jewelry’. The common sizes I’ve ran are 2-7/8”, 3-1/2’ and 5-1/2”. Carbon steel or 13Chrome tubing is typically used in our environment. 13 Chrome tubing or sometimes called CRA (corrosion resistant alloy) is used for reservoir with high CO2 content.

Completion jewelry consists of downhole equipment such as safety valve (a barrier to stop flow of fluid up the wellbore), sliding sleeve door (SSD), packer (to isolate different zones of production), nipples (to enable installation of plugs or valves downhole with the use of slick line), downhole pressure gauge (to read downhole pressures obviously), etc. The choice of completion strategy depends on the operating company and its engineers, typically juggling between productivity of the well and cost, like everyone else.

Packers are used especially when we have more than one zone of interest. Packers isolate each zone from the other so that when you’re done producing from one, you could isolate the zone with a plug and perforate another zone. You could also produce from multiple zones simultaneously. Whatever tickles the reservoir engineers! Some companies have moved to monobore completion where the wells are packer-less and production casing-less. The tubing is cemented, the well is produced and junked with no potential for workovers (more about workovers next time).

Once the completion string is in the hole, a Christmas tree is installed. This is just a block with multiple valves that control the flow of the well bore into the surface facility. The Christmas tree is also the last line of defence against kicks and blowouts (unwanted or unplanned entry of formation fluid into the wellbore that could cause disasters at surface. I will upload some videos of kicks when I get back to the beach). FMC and Cameron are 2 of the major players supplying wellhead equipment and Christmas trees. Now that the Christmas tree is installed, we are ready to either test or produce the well.


OP Rizal said...

bro, good info! actually how the packers are going to isolate the zone that you've mentioned, is it the OD of the packers tight to the ID of the casing? does the packers permanently placed in the well bore like casing equipments?

opcharlie said...

there's a rubber element around the packer that gets inflated and creates a seal between the completion string and the inside of the casing - yes, you're right on the money. yes packers are permanent features but can be retrieved in workover operations using several methods, tubing cut, straight pull and other proven methods.