Bubble Shroud Completions

The bubble shroud can be used in five main applications: 

1. Dual completions 
2. Well testing 
3. Casing leak isolation 
4. Casing corrosion prevention 
5. Vertical / horizontal booster service 

The design goal was to isolate the intake side of the pump from the main annular region without using an ESP pump packer. The chosen method of isolating the pump in a sealed pressure vessel, with the produced fluid entering through an extended tail pipe that has proven to be very successful and has been applied in many novel completions.

The produced fluid can be taken from any point below the bubble shroud with the pump seeing normal operating conditions and the motor being cooled properly.

Internal conditions simulate, or are equivalent to, the pumping conditions that would normally apply in a production well. However, by using a bubble shroud the ESP can be totally isolated from the annular region by mounting a standard, single bore, mechanical set packer on the end of the tail pipe. 

The perforations are isolated from the annular region by the packer (2) mounted on the tail pipe (1).  

When the pump is started the produced fluid flows up through the tail pipe (1) and into the base (3) of the bubble shroud. The base is screwed onto a number of joints of casing (4), which along with the head (9) makes up the body of the bubble shroud. The head consists of a casing pup joint with and ‘O’ ring sealed insert similar to a tubing hanger.

The produced fluid then flows into the pump intake (6) where pressure is added to overcome the wells TDH requirements and is discharged into a pup joint (7) that made up to the head (9). The produced fluid is then pumped to surface in the production tubing (10). 

As the bubble shroud must be fully sealed to ensure that there is no produced fluid loss into the annulus, a packer penetrator (8) connected to the main cable (11) and is mounted in the head (9). The packer penetrator is rated for 5000 psi from either side and reliably completes the pressure integrity of the bubble shroud.

Standard sized bubble shrouds are available for 7” and 9 5/8” (or larger) casing.

Note:

The bubble shroud fully encloses the pump and the internal annular volume will be at the flowing reservoir pressure. Thus, there are a few considerations when applying this technology : 

1. The standard can has no means for gas venting, gas locking may occur in high GOR wells or wells produced with BHP < Bubble Point Pressure. To address this issue, a bubble shroud is being developed with a gas venting system. 
2. The bubble shroud must be installed sufficiently deep in the well that intake pressures are maintained and pump off does not occur. If the ESP is usually installed at 6000ft with no operating problems, then the bubble shroud would normally be installed at the same depth. 
3. If a standard mechanical set packer is used to seal the producing zone from the annulus it will be mounted on the end of the can or on a tail pipe. The wellhead lower pigtail is made up and the complete string is turned to set the packer, from past experience this should not damage the cable. 
4. Order backup ‘O’ rings and lock plate screws for the head in case of loss or damage.