Thursday, October 3, 2019

Tight Oil chapter 5

Oil from tight shale formation is characterized by low-asphaltene content, low-sulfur content, and a significant molecular weight distribution of the paraffinic wax content (Speight, 2014a, 2015a). Paraffin carbon chains of C10-C60 have been found, with some shale oils containing carbon chains up to C72. To control deposition and plugging in formations due to paraffins, the dispersants are commonly used. In upstream applications, these paraffin dispersants are applied as part of multifunctional additive packages where asphaltene stability and corrosion control are also addressed simultaneously (Speight, 2014). In addition, scale deposits of calcite (CaCo3), other carbonate minerals (minerals containing the carbonate ion, CO3 2-) and silicate minerals (minerals classified on the basis of the structure of the silicate group, which contains different rations of silicon and oxygen) must be controlled during production or plugging problem arise. 

A wide range of scale additives is available which can be highly effective when selected appropriately. Depending the nature of the well  and the operational conditions, a specific chemistry is recommended or blends of products are used to address scale deposition.

Another challenge encountered with oil from tight shale formations- many of which have been identified but undeveloped - is the general lack of transportation infrastructure. Rapid distribution of the crude oil to the refineries is necessary to maintain consistent refinery throughput- a necessary aspect of refinery design. 

Finally, the properties of tight oil are highly variable. Density and other properties can show wide variation, even within the same field. The Bakken crude is light and sweet with an API of 42 degrees and a sulfur content of 0.19% w/w. Similarly, Eagle Ford is a light sweet feed, with a sulfur content of approximately 0.1% w/w and with published API gravity between 40 and 62 degrees API.

Paraffin waxes are present in tight oil and remain on the walls of railcars, tank walls, and piping. The waxes are also known to foul the preheat sections of crude heat exchanger (before they are removed in the crude desalter). Paraffin waxes that stick to piping and vessel walls can trap amines against the wall which can create localized corrosion. 

 In many refineries, blending two or more crude oils as the refinery feedstock is now standard operating procedure which allows the refiner to achieve the right balance of feedstock qualities. However, the blending of the different crue oils may cause problems if the crude oils being mixed are incompatible (Speight,2014a). When crude oils are incompatible, there is increased deposition of the asphaltene constituents (Speight,2014a) which accelerates fouling in the heat exchanger train downstream of the crude desalter.


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