Technical Ceramics and Shale Oil and Gas Recovery.
The past decade of increased oil and gas production, especially in the United States, is the product of innovations in drilling technology and hydraulic stimulation of wellbores known as hydraulic fracturing or “fracking”. This has been employed in so-called unconventional oil and gas reservoirs for fracturing shale rocks.
Such shales, previously regarded as impermeable using conventional production techniques, are fractured by pumping huge fluid volumes into the rock formation target below ground. This fluid consists of water, chemical additives and proppants. A proppant is a small solid pellet that used to be mostly fine sand and also glass and even mining tailings and walnut husks. These days, the proppants are mostly made of technical ceramics, which may be fused zircon, sintered bauxite, kaolin magnesium silicate or blends of these.
Fractures are created in the underground shale by pumping the fluid at a very high pressure, and these can extend for several hundred feet. Internal pressures in the fractured rock cause this fluid to flow back to the surface of the wellbore.
However, pressures underground can be 10,000 psi or higher, while sand is able only to withstand pressures up to about 6,000 psi. In the past this meant that such proppants would remain welded to the bottom of the fracture and impede the outflow of oil and gas from the shale.
Proppants made of Technical ceramics are able to withstand high pressures and are far more resistant to crushing underground. The pellets can also be manufactured in more uniform sizes than natural products. Typical sizes for proppants range between 8 to 140 mesh, or 106 micrometres to 2.3 millimetres.
Proppants made of technical ceramics also have a far higher chemical and thermal stability than sand or other products. The only downside is that the ceramic products are much more expensive than the natural products.
A solution has been to coat sand grains with a resin such as an epoxy resin, vinyl ester, polyurethane, polythene or furan. The most common coating is made from epoxy resin, as it has the best heat and chemical resistance among the coatings, as long as it is used at temperatures below 116 degrees Celsius. Although this process is cheaper than the ceramic product, it does not have the same high mechanical strength.
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