Centralizers in the Drilling Industry.
In the drilling industries there are a number of ways in which contractors can play a key role in groundwater protection and management, namely;
- By preferencing non-corrosive construction materials where possible, and adopting effective grouting methods to ensure inter-aquifer connection and the potential for water contamination transfer between aquifers can be prevented.
- By providing a long-lasting seal to a tapped aquifer through the use of inert casing, to prevent contamination as well as aquifer depressurisation.
- By reducing the potential for cross-contamination of aquifers and sites, particularly in relation to inter-aquifer connection due to corrosion of steel casings.
The use of Centralizers assists to support the contractor’s role in groundwater protection and management by;
- Ensuring that the well casing is centred in the borehole during installation so that the required grouted annulus thickness can be achieved.
- Ensuring a uniform thickness of grout seal around the casing.
- Ensures that the Casing and stands off the wall of the borehole during the grouting or gravel packing process therefore reducing the potential for cross-contamination.
The use of Centralizers also assists the contractors to adhere to national or state requirements, license conditions or other applicable standards, guidelines or best practice methodologies that are applicable to water well construction where the use of centralizers is specified or considered best practice.
The National Groundwater Association (NGWA) Standard
NGWA-01-14 Water Well Construction includes a number of key references to Centralizers;
- For casing installation centralizers installed at maximum intervals of 40-foot (grouted and non-grouted casing) or at the top (below grade) and bottom of the casing if the casing is less than forty (40) feet.
- Centralizers uniformly spaced vertically to maintain the screen in the centre of the borehole.
- When utilizing bentonite chips or pellets as a grouting material, centralizers are critical in ensuring the adequate annual space is maintained to ensure the proper placement of chip or pellet bentonite.
The California Environmental Protection Agency guidance document – Well design and construction for monitoring groundwater at contaminated sites – June 2014 recommends the use of plastic or s/steel centralizers within the annular space at 10 to 20-foot intervals above the well screen to;
- Ensure that the well casing is centred in the borehole during installation of the filter pack, transition seal, and annular seal.
- Ensure the casing does not bow and make contact with the borehole wall affecting the integrity of the annular sealant and inhibiting bonding between the grout and the well casing, potentially resulting in cross-contamination.
- Ensure a straight well for effective installation of pumps, sampling tools, and other sensors to be deployed within the finished well.
Kwik-ZIP’s centralizers are manufactured from kwik-ZIP’s engineered thermoplastic blend and contain no metal parts and whose characteristics include high flexural strength, high temperature resistance, a low coefficient of friction, and a resistance to organic chemicals, oils and synthetic and corrosion.
Kwik-ZIP centralizers can be used for;
- Production wells
- Gravel packed well screens
- Pump torque arrestors
- Water well casing
- Coal seam methane casing
- Pump riser
- Submersible pump installation
- Down hole logging tools
- Waterwell casing within the borehole
- Drop pipe within waterwell casing
- Submersible pump within the waterwell casing