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. 

Advanced Lift Systems : Pod Systems

Advanced Lift Systems : Pod Systems

Applications :

• Diverts fluids from below an isolation packer into the ESP, while  isolating  casing  from production fluids (eg for wells with worn casing or corrosive fluids) 
• Suspend long tailpipes, or heavy assemblies below an ESP 
• Dump flood applications, where fluid is produced from one zone and injected into another 
• Can be used to deploy a second ESP for back up purposes 
• Can be used to deploy a second ESP to ‘boost available downhole’ horsepower  and provide increased lift capability 
• Can be used in conjunction with a bypass system to produce multiple zone wells with multiple ESPs

Features :

• Fully encapsulates the ESP in a pressure tight shroud (Pod) 
• Available to suit a range of casing sizes, and ESP series 
• Available in a choice of metallurgies to suit well environment 
• Available to suit Single or Dual Pod configurations 

Description and Operation :

A Pod system is used to encapsulate an electrical submersible pump (ESP) within a sealed shroud. Fluids are diverted  into the annulus created by the Pod casing. The pump produces the fluids through the production tubing. 

The Pod system comprises of a Pod Hanger Assembly, Pod Sleeve assembly, Casing Joints, and a Bottom Crossover Assembly. Depending on the application Pod Clamps and a Nipple Sub assembly may also be included. Dedicated handling equipment is provided to aid assembly of the Pod system at the well site.   

The Pod system sub assemblies and accessories are described in more detail on individual datasheets. 

The Pod system can be used, or combined with other equipment to achieve a number of operational benefits. More information on these can be found overleaf.  

Pod System Exploded Diagram :

Casing Isolation Application :

The Pod system can be used in applications with corroded or worn casing, or where corrosive production fluids are anticipated. The ESP is encapsulated in the Pod. Tailpipe below the Pod includes a seal assembly which locates into a seal bore packer.  In this configuration the production fluid remains isolated from the casing. 

During operation the fluids from the reservoir are directed from below the packer, through the tailpipe and into the Pod. The fluid  is then lifted to surface by the ESP, through the production tubing. 

This configuration can also be used to suspend long tailpipe or other heavy completion assemblies below the ESP. As the ESP is suspended within the Pod assembly, all the tailpipe tensile load is transferred to the production tubing string by the Pod assembly.  

Refer to the table at the end of this post for applicable Pod Sizes.  

DuaLife Back-Up ESP :

The Pod system can be used as a means to deploy a second, or back up ESP within the well bore. The back up ESP can be suspended below the Pod assembly. Auto Flow Subs are included above each ESP to allow the non-operating ESP to be bypassed.   

When the lower ESP is operating, the fluid is produced by the ESP into the Pod. The fluid passes the upper ESP and enters the tubing string above the ESP through the open Auto Flow Sub. 

When the upper ESP is operating the fluid enters the tailpipe tubing string above the  lower ESP through the lower Auto Flow Sub. The fluid then flows into the Pod and is produced by the upper ESP. 

The Auto Flow Sub operation is detailed below. 

Pod clamps are fitted to the outside of the upper Pod to secure the lower ESP cable as it passes the outside of the assembly.  

DuaLife Back-Up ESP with Casing Isolation :

Where well control or casing corrosion is a concern, the lower ESP can  also be deployed within a Pod.  In this configuration the production fluids remain isolated from the casing.

UltraHi Boost System :

The Pod system can be used to enable ESPs to be operated in series for applications  with high lift (head) requirements. In this configuration the lower ESP discharges into the upper Pod, where it is ‘boosted’ by the upper ESP, and produced to surface through the production tubing.  

In high lift wells motor or shaft horse power ratings may become a limitation. In this configuration the total horse power requirement is shared between multiple ESPs. This  can enable high horse power systems to be deployed within casing constraints. 

The system can be designed so that each ESP can produce to the surface independently.   This provides additional built-in redundancy in the event that a pump should prematurely fail.

Multiple Zone System :

The Pod system can be combined with other Artificial Lift completion equipment to produce from multiple zones.

The lower ESP is housed  in a Pod. Below the Pod, a tailpipe string and seal assembly locates in a seal bore packer which separates the perforated zones. The fluid from the lower zone flows into the Pod and is produced by the lower ESP.

The upper ESP includes a bypass system.  The bypass tubing alongside the upper ESP allows the flow from the lower ESP to pass the upper ESP, where it reaches the Y-Tool.  

The fluid from the upper zone is produced by the upper ESP. The fluids from both zones are co-mingled at the Y-Tool and produced to surface through the production tubing.

Alternatively a concentric tubing string can be configured to enable the fluids to be produced separately (non-commingled) to surface through the two tubing strings.

Zones can be produced either independently, or simultaneously, while running upper, lower,

or both ESPs.

Auto Flow Sub Operation :

In  some ESP wells there will be  periods  where fluid has to flow through a non-operating ESP, for example in wells capable of natural flow, or wells equipped with a back up ESP. When fluid flows through a non-operational pump, the pump stages create a flow restriction, and unnecessary pump wear occurs.

The Auto Flow Sub allows fluids to flow past a non operational ESP and enter the tubing string unrestricted by the pump. When the ESP is not operating the Auto Flow Sub automatically by-passes the ESP by creating an open port between the annulus and the production tubing above the ESP.  When the ESP is started, the port is automatically closed, allowing the ESP to produce normally to surface.

The Auto Flow Sub can be used in any ESP application where the well can naturally flow, or where gas lift is included as a secondary artificial lift method.

The Auto Flow Sub can also be used in both Single and Dual Pod completions, to bypass the non operational ESP(s).  Refer to the diagram below for illustration of Auto Flow Sub operation in the dual Pod system:

Pod Casing and ESP Sizes :

The correct Pod casing size for a given application is based upon a number of variables :

• Casing size and weight. 
• ESP series. 
• External cables / control lines (dimensions). 
• Pod system configuration (e.g. single or dual ESP). 
• ESP motor cooling requirements. 
• Type of Pod system casing (coupled or flush joint). 

The table below shows typical Pod casing sizes, although each application should be sized individually:

Alternative Deployed ESP systems

Introduction to Alternative Deployed ESP systems

Todays focus on Marginal fields, requiring Artificial lift to enable or boost recovery. 

The most efficient and economical way to produce these small fields is to use submersible pumping systems The major costs are not the initial installation (CAPEX) but the OPEX involved in servicing the ESP.


PROBLEM: How to quickly and economically change out the submersible pumps offshore.

What is alternative deployed?

Alternative deployed ESP systems are installed on other than conventional tubulars.


Why?

1-High Cost of Conventional Deployment :

• Mobilization cost
• Operational cost

2-Timing of conventional deployment :

• Mobilization time & resultant deferred Oil

3-Need for live well deployment :

• eliminate reservoir damage

Alternative ESP Completion Options : 

• Dual LIFE* ESP Deployed on jointed tubing, external power cable :

          Fluid produced through jointed tubing (back up pump to minimize deferred oil)

• Standard ESP deployed on coiled tubing, external power cable :

           Fluid produced through the coiled tubing (eliminate rig requirement)

• Inverted ESP run on a load carrying wireline, stabbed into a packer/profile :

           Fluid produced up the casing annulus or production casing

• Inverted ESP run on coiled tubing, external power cable, stabbed into packer or landed in a profile :

          Fluid produced through the annulus

• Inverted ESP run on coiled tubing, internal power cable, stabbed into packer or landed in a profile  - REDACoil :

          Fluid produced through the casing/liner annulus