Issue Date: August 4, 2014
Considering Safety Of Fracking Methods
As a researcher with a chemistry background who is working in an oil field, I am pleased to see articles like “A New Way of Fracking” that introduce new technologies in the oil industry (C&EN, May 12, page 31). The novel approach described in the article to fracture formations with LPG (liquefied propane gas) is fascinating. However, a few things need clarification or further discussion.
First, a water-based fracturing operation normally uses one of two approaches: fracturing with cross-linked fluids or with non-cross-linked slickwater. The former uses relatively low loading of natural or synthetic polymers, such as guar, and cross-links it to provide high viscosity even at high well temperature. This carries sand or ceramic proppants downhole and into the formation to prop open the fractures created in fracturing operations. This technology has been practiced for the past 60 years.
In many slickwater fracturing cases, no thickener is used; transportation and placement of proppant rely solely on the turbulence of the fluid. Therefore, it is not uncommon to see the pumping rate exceed 100 barrels per minute, which demands tremendous energy consumption. To save the horsepower, friction reducers are always used to lower friction (drag) pressure by up to 80%. Slickwater systems may deliver proppant only by velocity, but cross-linked, water-based fluid systems deliver proppant also by viscosity.
Second, the relatively new fracturing technique with LPG is very close to the “gelled oil” technology practiced since the early days of the oil industry some 100 years ago. It is still worth wondering about the advantage of LPG over gelled oil, which can use locally produced crude oil directly. Besides the cost factor, safety is a major concern with the LPG approach. Gelled oil is flammable, but LPG can be both flammable and explosive. A flash-fire incident of LPG was reported as recently as last January in Canada.
And last, key additives in LPG and gelled oil are similar: metal salt (cross-linker), phosphate ester (gelling agent), and gel breaker. It has been found that phosphate ester used in fracturing operations was responsible for refinery distillation tower plugging. When LPG is used in oil wells, such concerns also need to be addressed.
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