Abstract

New completion techniques using expandable casing with swelling elastomers to seal the annulus, or just swelling elastomers used as packers are becoming available. Diagnostic services are required for these new completions such as evaluation of the annular seal, analogous to cement evaluation. Both conventional and new generation Wireline ultrasonic measurements have been used to characterize and possibly evaluate zonal isolation using swellable elastomers. So far, the following 360 degs circumferential measurements were studied: Ultrasonic radii, acoustic impedance (AI), as well as attenuation and third interface Echo (TIE) reflections from flexural wave data. Radii measurements show a "springback" effect, indicating that expansion against the formation has been achieved. Flexural attenuation has a much better dynamic range over the elastomer sections compared to the acoustic impedance measurements. Both measurements do not consistently distinguish rubber-backed casing with ordinary casing in our examples.

The TIE from the latest generation imaging tool tracking the external rubber interface, may provide the measurement the industry needs. First results look promising and further experiments to characterize the tool response are ongoing. The casing geometry of expanded liners was also studied.

Introduction

The introduction of expandable metal technology and new "smart" materials like swelling elastomers will provide more options for well construction and completion:

  • New techniques in zonal isolation are now possible for over - underpressured, fractured zones and zones with fluid losses [1], [2],

  • Allowing monobore well design [3],

  • Production of selected zones will be made easier, like selective perforation, completion, and stimulation [4],

  • Multilateral junction sealing will be made easier.

The effectiveness of zonal isolation and long-term well integrity for this new technology needs to be evaluated and proven.

" Smart Material" - Swelling Elastomers

Swelling elastomers are now offered by several service companies and have been used by operators for a variety of applications: As a means to establish zonal isolation in liner completions where conventionally a cement column would be used [5], as a production separation packer (swelling packers are used to replace conventional hydraulically or mechanically set packers) [6], and as an integral part of an expandable open hole clad [1].

By incorporating filler materials into an elastomeric matrix the material reacts or swells with time if in contact with water, depending on the elastomer and the requirements [7]. A water swellable elastomer swells through the absorption of (saline) water (osmosis process). An oil swellable elastomer swells primarily through the absorption of hydrocarbons (diffusion process). The typical swelling ratio is about 1.75 to 2.5 and swelling pressures are up to 150 bar. Swelling time is from 5–100 days depending on produced water salinity, temperature and oil viscosity and composition. The longevity of swelling elastomers still has to be quantified.

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