January 2019, Vol. 246, No. 1
Features
Solutions to Liability Risks from Decommissioned Pipelines
By Sue Longo, Principal, Golder
Decommissioned pipelines form an environmental hazard with potential to impact the future success of pipeline operators.
This is because having the idea of obtaining and keeping social license to operate is increasingly important in the resource sectors. Without public acceptance of their plans, companies may find it difficult to gain the financial, regulatory and political support they need to move forward.
One way to gain that support is with a good reputation for managing the impacts of what they have in place right now – including their decommissioned pipelines, which are prone to long term corrosion and collapse.
Pipeline owners may find their plans opposed by the public if their existing decommissioned or abandoned pipelines allow groundwater to enter, which has potential to drain nearby water bodies. An empty, decommissioned or abandoned pipeline can carry water mixed with contaminants including fertilizer from farmers’ fields into environmentally sensitive areas such as wetlands.
Abandoned pipelines can also corrode and collapse, causing failures that may propagate to surface, distorting natural drainage patterns – as well as disrupting rail lines, roadways and building foundations.
This has caused the oil and gas industry to look for ways to effectively abandon pipelines, so that they do not become an environmental liability. There are two main priorities if environmental risks are to be managed well: to stop liquids such as groundwater from flowing through the abandoned pipeline, and to prevent collapse of the pipe.
One historic way to deal with the problem has been to excavate and remove the abandoned pipe. This can be expensive and time consuming – and it carries its own environmental costs in disturbed ground, access requirements and the need for backfill. Plus, there is the potential for disturbing still-active pipelines in the same right-of-way (ROW).
Another solution is to fill the abandoned line with concrete and other flowable fills, which can also be costly if much of the line is located far from ready-mix facilities. Another difficulty is getting concrete to flow well enough to fill the pipeline.
So what can a pipeline company do to protect the environment – and its reputation – from potential risks from its decommissioned pipelines?
Importing a Tried-and-True Solution from Mining
One solution that has shown good promise comes from re-applying technology that has been well tested and proven in another sector entirely – the world of hard-rock mining.
Two of the issues that the mining industry faces are similar to those involved in abandoned pipelines – filling long underground spaces to prevent their collapse, and stopping the flow of impacted groundwater. In mining, the underground spaces are the mine’s tunnels which have been abandoned after ore has been extracted. The water is “mine water” – groundwater that flows through the mine’s underground spaces, picking up metals and other contaminants along the way.
One solution to both problems is “Paste” technology. It starts with the tailings, which are the sand-like waste product from the mine’s mill after the ore has been ground up to allow extraction of the target mineral. The tailings are mixed with water and a carefully-engineered binder involving cement and other reagents to produce the paste, which is much like toothpaste in consistency.
The paste is pumped into the underground through pipelines to fill up the abandoned tunnels. There, it cures with little or no change in volume, and little or no water bleed. The paste is engineered to fulfill its two main tasks – supporting the underground workings so that they do not collapse, and solving the mine water problem as the water cannot penetrate the paste mass.
Paste technology as a solution has had decades to mature; it is robust and widely understood in the global mining sector.
So, we have a mining-industry technology ready and waiting to be applied to the oil and gas sector problem of decommissioned pipelines. How viable is it for preventing pipeline collapse and underground water transport?
Requirements for Decommissioned Pipelines
Although we have yet to make large-scale field applications of paste technology to decommissioned pipelines, tests to date are positive.
Key to this is understanding one of the chief advantages of paste – its adaptability. Paste recipes can be altered to suit each particular job, depending on factors such as slope of the pipeline, diameter, and the length of pipe to be filled, along with strength requirements and access points.
Paste meets the needs of the pipeline sector in several ways:
Preventing pipeline collapse: One of the chief environmental risks from decommissioned pipelines, particularly large trunk lines, is the possibility of pipeline collapses that propagate upwards to impact the surface.
Generally, the strengths required by the pipeline fill are not as substantial as they would be if they were, say, part of a building’s foundation. So, paste can be designed to produce cured strengths of 200 kPa – 2 MPa, which is a typical strength range for a paste recipe. This means that paste is able to solve the first of the two problems with abandoned lines – collapse of the pipe.
Preventing water inflows: Experience with paste in mining operations shows that it can be made impervious to water, so that the pipeline is no longer a conduit for contaminated runoff and groundwater to reach a sensitive receptor such as a wetland. So, paste solves the second problem as well – stopping the flow of liquids through the pipeline.
Able to reach long distances: One of the difficulties of using regular concrete as pipeline fill is that it can be hard to make the concrete flow well enough to fill the line. In mining, paste is routinely pumped for several kilometers or more, in a plug flow, to reach the point of deposition. This makes it practical to pump paste into a pipeline and have it flow for significant distances. This limits the number of access points that need to be opened along the line in order to pump in more fill. One difference is that in mining, the paste is intended to exit the far end of the pipeline for deposition; in an oil and gas line it would be pumped in to fill the pipe and then left there.
Suitable to linear properties: Another challenge of using concrete as fill has to do with the volume of materials that must be carried along the ROW to each access point along the pipeline. Given the flexibility of paste recipes and the long-established skills of the professionals involved, paste can be made using local sand, overburden or borrow material close to the pipeline access points. Therefore, the amount of material that must be transported to each site along the line is minimal. Even the water can often be sourced from water bodies and streams nearby, and the quality of that water does not need to be high.
Cost-effective: Being able to use local aggregate and soil, and perhaps water from near the pipeline helps to keep the cost affordable. The cement, binders and other additives can be brought along the ROW by truck, and the paste-making equipment as well, powered by diesel engines or generators.
Globally applicable: Paste technology is widely available through the world-wide mining industry. The technology is designed to be easily transported.
Temperature does not need to be a worry; we have had success in pumping paste into a worked-out mine in winter in Yellowknife, Northwest Territories, in northern Canada. Temperatures on site reached -61 degrees Fahrenheit (-52 Celsius) and, although it was challenging for the personnel involved, the paste flowed well.
To sum up, paste technology is robust and mature. It is a proven source of solutions to the kind of issues involved in remediating abandoned pipelines. Next step is to conduct further tests, possibly through an oil and gas industry association. P&GJ
Author: Sue Longo (P. Eng, MBA) is a principal in the Paste Engineering and Design division of Golder Associates, based in the company’s Calgary AB office.
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