Process Intensification and Integration for Sustainable Design. Группа авторов

11.3 Haynesville LA and TX 11.0 Eagle Ford TX 7.1 Woodford OK 5.0 Barnett TX 4.4 Mississippian OK 3.8 Niobrara–Codell CO and WY 3.4 Bakken ND and MT 2.7 Fayetteville AR 2.3 Rest of the United States “shale” 4.0

Apart from US reserves, recoverable shale gas resources around the world have been found in countries such as China, Argentina, Algeria, Canada, Mexico, Australia, South Africa, and Russia [3,5]. Despite these discoveries, several factors such as geological aspects and the lack of the necessary infrastructure have curbed the development of the shale gas industry in those other countries [6,7]. Table 1.2 shows the production rates in 2018 for the six countries with more unproved technically recoverable shale gas resources.

Table 1.2 Recent shale gas reserves and production in for the six countries with more shale gas reserves.

      Source: From EIA 2015 [13].

Country	Unproved recoverable reserves by 2013 (Tcf)	Production in 2018 (Bcf/yr)	References
China	1115.20	353.15	[8]
Argentina	801.50	365.00	[9]
Algeria	706.90	No production	[10]
United States	662.50 (by 2015)	7079.62	[4]
Canada	572.90	182.80	[11]
Mexico	545.20	No production	[12]

1.3 Shale Gas Composition

One particular characteristic of shale gas is its varying composition. Shale gas composition depends heavily on the location of the sources, and it may variate even within wells in the same play. The primary component of shale gas is methane, but it also contains considerable quantities of natural gas liquids (NGLs) such as ethane and propane. Apart from these components, shale gas also contains acid gases such as CO₂, H₂S, and inorganic components such as nitrogen [5,14]. The separation of NGLs from methane has induced industries to look for alternatives to transform them into more valuable products, but at the same time the varying composition of shale gas represents a challenge for the treatment plants, which have to be robustly designed to handle such variations in the gas composition.

1.4 Shale Gas Effect on Natural Gas Prices

      The high availability of natural gas, generated as a result of the increasing production of shale gas, has caused a noticeable drop of its price in the United States. Moreover, the ability to extract natural gas from deposits that are not associated to crude oil reservoirs has uncoupled natural gas and crude oil prices [1]. These facts have contributed to what has been defined as the new era of cheap natural gas, in which it has been priced consistently under US$5 per million Btu for almost a decade in the United States [15]. In particular, natural gas prices in 2019 have shown a decrease from 3.18 at the beginning of the year to US$2.07 per million Btu in September [16]. Even more, in an extreme situation, producers at the Waha hub in the Permian basin in West Texas had to pay the pipeline to take the excess of gas, showing a negative US$9 in April, which contributed to an average price of only 73 cents per million Btu for the first eight months of 2019, compared with an average market price of US$2.10 in 2018 (which is also lower than the five year average from 2014 to 2018 of US$2.80) [17]. These trends create an opportunity for the development of technologies to transform shale/natural gas into value‐added chemicals. One additional point to consider is the increasing amount of liquefied natural gas that is being exported from the United States [18]. As this quantity grows, international natural gas prices may also get affected.

      The main consumers of natural gas are the electricity generation industry, the residential sector, the industrial sector, and the chemical industry. Low natural gas prices have incentivized the electric power plants to switch from coal to natural gas, with an impact not only on the economy of these systems but also on the environment by reducing the total greenhouse gas emissions [1].

Another sector that has shown interest in switching from oil‐based feedstocks, such as naphtha or crude oil, to natural gas is the chemical industry. The availability of inexpensive natural gas and NGLs has boosted the chemical industry to create new plants for the production of value‐added chemicals using methane and NGLs as feedstock [5,19].

1.5 Alternatives to Produce Chemicals from Shale Gas

      Due to the increasing availability of low‐cost natural gas, the chemical industry has started to invest in the research and development of chemical routes that can transform methane into value‐added chemicals. Some of the chemical compounds that have received special attention are methanol, ethylene, propylene, and liquid fuels obtained from syngas. Some of the processes to produce the aforementioned chemicals are discussed next.

1.6 Synthesis Gas

Synthesis gas is a mixture of carbon monoxide and hydrogen typically needed for the production of chemicals such as a methanol, ammonia, or gas‐to‐liquid (GTL) products. The production process for synthesis gas varies depending on the oxidizing agent selected for the reforming of the natural gas. The main reforming processes are steam reforming (SR), partial oxidation (POX), and dry reforming (DR) [20]. The characteristics of these processes are listed in Table 1.3.

Table 1.3 Reforming options and their characteristics.

      Source: Adapted from Noureldin et al. 2014 [20].

Reforming option	Oxidizing agent	Conditions	Chemistry	Type
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