Chemical Technology April 2016

Processing light tight oil by Tim Olsen, Emerson Process Management

The refining industry has changed over the past few years with an ample supply of opportunity crude oils available.

O pportunity crudes have been around for many years, but not until recently has the abundance of these discounted crudes changed the behav- iour of refiners to shift away from their usual feedstocks. Tight oil, sometimes referred to as light tight oil or LTO, is also an opportunity crude oil from shales or other low permeability formations. Although most of the news about tight oil production is in the United States, tight oil is not unique to this region and is found throughout the world; see Figure 1 with the map of basins with assessed shale oil and shale gas formations, as of September 2015 (US Energy Information Administration, EIA). Production from tight oil formations requires the same hydraulic fracturing and often uses the same horizontal well technology used in the production of shale gas. The main challenges with processing opportunity crudes include: crude blending to match refiner’s configuration and processing capabilities, crude switch disturbances, fouling and accelerated fouling from incompatible crude blends, corrosion, and energy balancing across the crude unit pre-heat exchangers. In addition to the above mentioned issues, light tight oils also have challenges typically related to H 2 S (treated with amine-based H 2 S scavengers), paraffin waxes, significant quantities of filterable solids, variability in API gravity from the same source, and catalyst performance related to cold flow properties.

Heat exchanger fouling is one of the biggest challenges in refinery operations. Many refiners still use a spreadsheet with monthly calculations typically based on incomplete data to evaluate heat exchanger condition, with manual checks on individual bundles just prior to a turnaround to determine if cleaning is required. The traditional approach to monitor heat exchanger fouling through spreadsheets with manual entry of temperatures and pressures was usu- ally sufficient before the increase in crude blending from opportunity crudes such as tight oil. However, some crude oil blends are not compatible, leading to unanticipated accelerated fouling. Because tight oils tend to be lighter, they need to be blended with other crude oils to get the right balance for best utilisation of existing downstream units. Having a more consistent feed to the crude unit also allows for the oppor- tunity to optimise operation. If light tight oil feeds are not blended, the lighter oil can bottleneck the crude overhead and downstream naphtha processing units, and limit pro- duction for bottom of the barrel processing. Some refiners are blending more than two crudes to get the right balance of feed qualities which creates unknown issues with crude incompatibilities. When crudes are incompatible, acceler- ated fouling occurs in the crude unit pre-heat exchanger train due to asphaltene precipitation. Accelerated fouling can lead to additional energy costs with the crude unit fired

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Chemical Technology • April 2016