CSG exploration and production: why use inert casing and centralisers?

web size IMG_20150412_132932There is a range of casing and centralizer materials used by contractors for the exploration and production of Coal Seam Gas (CSG). Depending on the objectives and targets of the well, inert materials can often provide an effective solution to common problems.

In CSG production wells, single casing string bores can be constructed from steel, stainless steel or fibreglass casing. However, bores constructed with fibreglass provide a corrosion resistant alternative to conventional construction practices.

Corrosive groundwater

In areas where corrosive groundwater is present, mild steel – which is widely used for casing – can be affected particularly when in contact with groundwater that has a high concentration of dissolved CO2. In such environments, casing life can be very short and use of inert casing material such as fibreglass is the primary method of ensuring long bore life.

What spacer should you use?

When using fibreglass casing, correct spacer materials and specifications must be selected. Any friction or movement of an ill-fitting spacer can damage the casing, causing extremely costly and harmful leakages during CSG operations. Standard metallic spacers involving stop collars are also problematic, as bolts along the collar can punch cracks or holes into the fibreglass.

Contractors have the responsibility by law to ensure that bores are constructed and maintained so that casing integrity and zonal isolation is achieved. Because of this, selecting the most suited completion equipment for the particular well specifications becomes imperative to the overall safety and success of the well.

An alternative to metallic centralizers

kwik-ZIP centralizer designs and materials are a quality alternative to metallic spacers. The kwik-ZIP centralizer range has integrated rubber pads which prevent movement on both steel and fibreglass CSG casing, which eliminates the need for stop collars.  This is imperative to the life of a fibreglass casing in particular.  

The diameter of each kwik-ZIP spacer is also adjustable. Unlike standard API 10D centralizers that have a fixed diameter, kwik-ZIP spacers are able to fit the varying diameters of composite casings. The kwik-ZIP range also includes various bow heights, allowing them to be used across a broad range of borehole combinations.

Corrosive-free spacers

Inert spacers must also be considered when it comes to dealing with corrosive groundwater or produced water used in re-injection wells.  As the kwik-ZIP range is made entirely from high impact thermoplastic, they will remain in-tact throughout the life of the well.