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Dynamic Underbalance for Scale Removal

IP.com Disclosure Number: IPCOM000200110D
Publication Date: 2010-Sep-28
Document File: 3 page(s) / 115K

Publishing Venue

The IP.com Prior Art Database

Abstract

Many oil companies faced decline in production due to scale build up in perforation tunnels. They have tried re-perforation and/or mechanical scale removal techniques with limited success. An alternative method, Dynamic Underbalance (DUB) for Scale Removal, creates a rapid pressure drop across the front of the scaled perforations to enhance cleaning up and improve production. This paper discusses the process in which this can be achieved.

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Dynamic Underbalance for Scale Removal

Abstract:

Many oil companies faced decline in production due to scale build up in perforation tunnels. They have tried re-perforation and/or mechanical scale removal techniques with limited success.  An alternative method, Dynamic Underbalance (DUB) for Scale Removal, creates a rapid pressure drop across the front of the scaled perforations to enhance cleaning up and improve production.  This paper discusses the process in which this can be achieved.

Description:

The process is designed to effectively remove barium sulfate scale within the producing perforation tunnels by inducing a considerable DUB condition via vents subs and atmospheric pressure chambers.

Static underbalance is when wellbore pressure is initially below the reservoir pressure.  It is widely known that this condition promotes perforation clean up during the perforating event. DUB extends the idea of static underbalance perforating by rapidly creating a large but brief localized underbalance condition close to the perforations. This is achieved by adding vent sub(s) and surge chamber(s) to a conventional perforating assembly. When the prima cord running through the perforating assembly is detonated, the vent sub is opened allowing well fluids to rapidly enter the surge chamber. The rapid filling of the surge chamber creates a pressure drop across the sand face.

Modeling software is use to select number of vent(s) and chamber(s) required to establish the intended localized DUB for scale removal.  Size of equip is usually limited by the completion restrictions that the assembly must be ran through. The model predicts pressure transients from gun detonation out to several seconds if required. It demonstrates that for a few hundred milliseconds after the gun detonation, the wellbore pressure is dropped significantly below reservoir pressure and this effect is called DUB. The objective is to allow the large differential pressure to flush back perforating debris and crushed rock to clean the newly formed perforating tunnel, and scale from existing perforations.

In this case the costumer elected not to shoot new perforations. Existing perforations are to be treated with an assembly consisting of vents subs and surge chamber to create a localized DUB.  The vents open allowing well fluids to rapidly enter through the vents then into the surge chamber which creates a period of reduced pressure across the sand face to surge the scale out of the existing perforations and into the wellbore and surge chambers.

 


Tool String Schematic:

 

   

Vent sub facing down - Loc [1]

Empty gun or chamber

 Vent sub facing up - Loc [2]

Note: Configuration is not limited to what is show in diagram, various combin...