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The UK is actively looking at the potential production of shale gas and, as a result, the country's extractive minerals industry is looking at the role it can play in providing minerals that could be used in hydraulic fracturing (fracking). One such mineral is silica sand, which is used as a proppant, commonly referred to as "frac sand". Clive Mitchell, Industrial Minerals Specialist, provides an educated guess as to where this frac sand could come from in the UK.
By Clive Mitchell
Frac sand is composed mainly of quartz grains. It is used in the fracking process, hence the name "frac" sand. The sand is entrained in water and is pumped under great pressure into fractures created in the reservoir rock. The sand is packed tightly into the fractures and props them open, hence they are also referred to as "proppants". This forms a permeable pathway for the oil and gas to escape from otherwise impermeable rock formations, such as shale.
20/40 frac sand sources in Illinois, US.
Fairmount Santrol
Approximately 70% of the proppants used in fracking are naturally-occurring silica sand. Other types of proppants include resin-coated silica sand, and ceramic proppants, which are most commonly comprised of calcined bauxite or kaolin.
The current specification for proppants used in fracking in the UK is the British Standard (BS) European (EN) International Standards Organisation (ISO): 13503-2:2006 + A1:2009 petroleum and natural gas industries. Completion fluids and materials. Measurement of properties of proppants used in fracking and gravel-packing operations.
The standard covers the testing and specification of those properties that are important for a good quality proppant, such as frac sand. Table 1 shows a summary of the properties required for proppant material, as specified in the standard.
Table 1 also shows some typical particle size distributions for frac sand. One of the most commonly used is 20/40. The particle size distribution required is relatively narrow, which means that the particles need to be more or less the same size in order to maintain a high permeability so that oil and gas can readily flow into the borehole.
The sand particles must also have a relatively high degree of roundness and sphericity to ensure that they flow unhindered into the fractures. An average roundness and sphericity...