Thursday, September 26, 2019

Tight Oil Chapter 4

Success in extracting crude oil and natural gas from shale reservoirs depends largely on the hydraulic fracturing process (Speight, 2016b) that requires an understanding of the mechanical properties of the subject and confining formaitons. In hydraulic-fracturing design, Young's modulus is a criterion used to determine the most-appropriate fracturing fluid and other design considerations. Young's modulus provides an indication of the fracture conductivity that can be expected under the width and embedment considerations. Without adequate fracture conductivity, production from the hydraulic fracture will be minimal or nonexistent (Akrad et al., 2011). 

Typical of the crude oil from tight formations (tight oil- tight light oil and tight shale oil have been suggested as alternate terms) is the Bakken crude oil which is a light highly volatile crude oil. Briefly, Bakken crude oil is a light sweet (low-sulfur) crude oil that has a relatively high proportion of volatile constituents. The production of the oil also yields a significant amount of volatile gases (including propane and butane) and low-boiling liquids (such as pentane and natural gasoline), which are often referred to collectively as (low boiling or light) naphtha. 

By definition, natural gasoline (sometime also referred to as gas condensate) is a mixture of low-boiling liquid hydrocarbons isolate from crude oil and natural gas wells suitable for blending with light naphtha (light naphtha) can become extremely explosive, even at relatively low ambient-temperatures. 

Some of these gases may be burned off (flared) at the field well-head, but others remain in the liquid products extracted from the well (Speight, 2014a).

Bakken crude oil is considered to be a low-sulfur (sweet) crude oil and there have been increasing observations of elevated levels of hydrogen sulfide (H2S) in the oil. Hydrogen sulfide is a toxic, highly flammable, corrosive, explosive gas (hydrogen sulfide) and there have been increasing observations of elevated levels of hydrogen sulfide in Bakken oil. Thus, the liquids stream produced from the Bakken formation will include the crude oil, the low-boiling liquids, and gases that were not flared, along with the materials and byproducts of the hydraulic-fracturing process. 

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