ABSTRACT
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Novel technologies such as horizontal drilling and hydraulic fracturing have enabled the economic exploration of natural gas from unconventional sources, such as shale gas, tight gas, tight oil, and coal seam gas (coalbed methane) [1]. Horizontal drilling increases the lateral exposed section length of the underground reservoir and allows more wellheads to be clustered into one surface location, which makes it easier and cheaper to complete and produce the wells. Hydraulic fracturing, also known as fracking, is a well-stimulation technology using hydraulically pressurized fluid or fracking fluid that usually contains proppants and chemical additives (discussed in detail later in this section). In fracking, the high-pressure fracking fluid is first injected into the wellbore, creating fissures in the deep-rock formations by the hydraulic pressure. Then, the pressure is reduced, allowing water and natural gas to flow back through the fissures (Figure 8.1 [2]). Thanks to these technologies, shale oil and gas production has dramatically increased in several regions of the world, including the United States, the United Kingdom, Poland, Ukraine, Australia, and Brazil.
