The ability to increase the capacity of existing and planned crude oil pipelines with minimal capital expense has genuine appeal to midstream companies, producers and shippers alike. Enter drag reducing agents: special, long-chain polymers that are injected into crude oil pipelines to reduce turbulence, and thereby increase the pipes’ capacity, trim pumping costs or a combination of the two. DRAs are used extensively on refined products pipelines too. Today we continue our look at efforts to optimize pipeline efficiency and minimize capex through the expanded use of crude-oil and refined-product flow improvers.
During most of the Shale Era, the U.S. and Canadian midstream sectors have been playing a game of catch-up—building new pipelines, expanding capacity and/or reversing flows on existing pipes, even converting pipelines from one hydrocarbon to another, all with the aim of bringing the capabilities of North American pipeline networks in line with the fast-evolving needs of producers and shippers. That work is far from done, as evidenced (on the crude oil side of things) by the soon-to-open Dakota Access Pipeline (DAPL; see What a Difference a DAPL Makes) out of the Bakken and plans for new takeaway capacity out of the Permian Basin and the Alberta oil sands (What Is It? It’s EPIC and One Is the Loneliest Customer). But there’s also a lot of anxiety among midstream companies, producers and shippers—a fear (also common to a lot of guys in their twenties) of commitment, or more specifically a palpable wariness about committing to more pipeline capacity than may be needed three months (or three years) from now.
Drag reducing agents help to ease some of that, well, unease by adding a degree of flexibility to the carrying capacity of crude oil (and refined product) pipelines, and at a relatively modest cost. In Part 1 of this series, we explained that flows through crude and refined product pipelines operate within a “turbulent flow regime” in which fluid molecules move in a random manner, and where some of the energy applied to them by pumps and/or downhill gradients is wasted. Reducing that turbulence—and the “frictional pressure drop” or “drag” that it creates—is the aim of DRAs. To understand how DRAs work, you need to know that the turbulent flow regime has three parts: 1) a “turbulent core” that takes up most of the pipe’s internal diameter and accounts for the vast majority of the fluid flowing through the pipeline, 2) a “laminar sub-layer” along the pipe wall, and 3) a “buffer zone” between the turbulent core and the laminar sub-layer. Without DRAs, the flow along the pipe wall is in lateral sheets, slivers or “streaks” of which constantly slough off through the buffer zone into the turbulent core, making the flows more random, raucous and energy-wasting.