Underground gas and oil pipelines eventually reach the end of their service life. This creates a challenge – what to do with a former asset once it is decommissioned and/or abandoned to avoid unintended consequences. This has driven both the oil and gas industry and water/wastewater systems to look for solutions for safely and effectively abandoning pipelines.
One solution has been to excavate and remove the abandoned line – this is expensive and time consuming and carries its own environmental costs, in terms of disturbed ground, backfill material and access requirements. Another solution has been to fill the abandoned line with concrete or other flowable fills – this is also costly, as a lot of the pipelines are in remote areas with no access to ready mix facilities. Another difficulty is getting concrete to flow well enough to fill the large sections of the abandoned pipeline.
WSP is currently developing an alternative based on our long experience in the mining sector. We have well over 20 years of experience helping mining companies deal with a similar problem – the need to avoid collapse of their abandoned underground workings. Mining companies also need to deal with the problem of “mine water” – groundwater that flows through the mine, picking up contaminants along the way, which must then be treated before release.
WSP helps mining companies take the various waste products they produce on site e.g. waste rock, overburden, sand, etc. and engineer a recipe using the waste along with binder e.g. cement and other reagents, plus some water. The resulting “paste,” much like toothpaste in consistency, is pumped underground to fill the abandoned voids and tunnels. There, it cures with little to no change in volume and little to no water bleed, producing backfill strong enough to hold up the rock mass overhead. Backfilling the underground workings with paste also helps to solve the mine water problem as the water cannot easily penetrate through the paste mass.
Paste technology is mature, robust, and widely understood. The paste recipes are specific to each application and involve using locally available sources of material that meet the filling requirements e.g. strength and volume requirements.