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Description
Shales are considered a highly promising source of oil and gas. Although they are abundant, shales are characterized by their low permeability, which restricts the flow of hydrocarbons trapped within the pores of this fine-grained sedimentary rock. This makes recovery technologies used in conventional reservoirs unsuitable for application in shale formations. From a production perspective, the development of horizontal drilling and hydraulic fracturing has made large quantities of unconventional oil and gas accessible. During hydraulic fracturing, permeability is increased by applying pressure through the injection of fluids. The high-pressure fluid is injected to create pathways within the reservoir so that oil and gas can flow to the wellbore.
On the other hand, shales contain solid organic matter known as kerogen. This material is insoluble and constitutes the most abundant fraction of the organic matter present in the rock. When subjected to thermal processes, specifically pyrolysis, kerogen decomposes into gaseous and liquid hydrocarbons. Pyrolysis of shale rock can be conducted either in situ or above ground (ex situ) in a process known as retorting. In situ retorting involves applying heat directly to the underground rocks. In ex situ retorting, oil shale is mined, crushed, and transported to a facility for processing in retorts. Oil can also be extracted from shale using supercritical fluids such as carbon dioxide, water, and organic solvents. Determining a suitable production or extraction process depends heavily on the geochemical and petrophysical characteristics of the shale.