Global energy resources are depleting at an alarming rate. Conversely, energy requirements of developing economies are increasing at a rapid pace. Global focus on energy replenishment has shifted toward natural gas which is an environmentally friendly energy resource and also available in abundance. Natural gas extraction through hydraulic fracturing is economically viable as well as a popular technology around the globe. The relative permeability of shale rocks is extremely low; hence it produces very less volume of natural gas. Special extraction technology such as hydraulic fracturing is required to induce permeability in these rocks to produce natural gas. Foam based hydraulic fracturing fluids is a novel technology employed in tight shale gas reservoirs for the economically viable production and enhancement of natural gas. An effective foam based hydraulic fracturing operation depends on the type of foam used, additives used in the foam, and sub-surface formation properties.
There are generally three types of foam based hydraulic fracturing fluids. Most commonly used foam based hydraulic fracturing fluid in shale gas reservoirs is water based foam. Water based foams constitute water with foaming surfactant and nitrogen or carbon-di-oxide gas. Water based foams are suitable for low pressure shale formations as the foam becomes unstable with increasing underground pressure. Other foam based hydraulic fluids are acid based foam and alcohol based foam. Acid based foams constitute mild acid with foaming surfactant and nitrogen gas while alcohol based foam consists of methanol with foaming surfactant and nitrogen gas. Both acid and alcohol based foam are applied in water sensitive shale reservoirs. Nitrogen based foams are mostly used in fracturing fluids as they have better pressure and temperature stability. Most of the technological experiments for foam based hydraulic fracturing fluids have been conducted in shale gas reservoirs in the U.S. and Canada; hence, it is still a novel technology for most of the other countries in the world.
Extraction of shale gas is still a challenge around the globe despite its huge reserves as the gas is trapped in highly impervious shale rock formations and needs extremely modern and precise fracturing technology to extract the gas economically. Natural gas is captured in shale formations either by adsorption or by getting trapped in small pores or fractures of the formation; hence it is important to know the properties of the shale formation before selecting the foam type for fracturing. A significant amount of natural gas is stored as an adsorbed gas in the shale formation while very few shale reservoirs have natural gas trapped in pores or fractures. Surfactants are used to provide stability to the foam and also provide better bonding between the two phases of gas and fluid.
After the preparation of the foam, some amount of proppant is also added to it to keep the fracture open in the shale rock after fracturing is done. The type of surfactant also plays an important role in the stability and performance of the fracturing fluid. Typically, anionic or cationic surfactants are used in foam based hydraulic fluids according to the hydrophilic and hydrophobic property of the shale formation. Conventional water based hydraulic fracturing process involves the use of large quantities of water which results in high capital cost on water treatment. Water based fracturing also results in polluting of underground water reservoirs with harmful chemicals and heavy metals. On other hand, foam based hydraulic fracturing uses very less water as compared to the conventional water based fracturing process. Also, foam used in foam based hydraulic fracturing fluids can also be recovered back through the well after completion of the process. In addition, foam based hydraulic fluids reduces environmental damage to underground water aquifers and offers better transportation of proppant which makes them a superior choice for hydraulic fracturing in environmentally protected zones.
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Increase in hydro-fracturing, technological advancements, growing popularity of natural gas in the global energy mix, and huge global shale gas reserves around the globe are major factors driving the foam based hydraulic fracturing fluids for the shale gas market. North America is the leading producer of shale gas in the world followed by Europe and Asia Pacific. China has the largest reserves of shale gas in Asia Pacific, followed by Argentina and Algeria. Growing environmental concerns regarding hydraulic fracturing, sluggish economic growth in Europe and Latin America, and increase in prices of surfactants and chemicals are the major restraints of the foam based hydraulic fracturing fluids for the shale gas market around the globe.