PTQ Q2 2025 Issue

Thermodynamic solution for evaluating crude compatibility

Case studies emphasise the power of advanced analytical tools such as predective modelling in crude compatibility assessment and blend management

Asok Tharanivasan and Michelle Wicmandy KBC (A Yokogawa Company)

G lobal crude oil demand is projected to tip 103 million bpd in 2025, according to the International Energy Agency (IEA). As refiners aim to maximise output while keeping costs in check, many are turning to oppor- tunity crudes from various geographical locations through- out the world. This shift presents the refining industry with challenges in optimising crude oil blends driven by the growing demand for diverse crude sources, stringent environmental regulations, and economic pressures. While opportunity crudes are economically attractive, they are unpredictable – you never know what you are going to get in terms of composition and properties. One critical issue that refineries face when grap - pling with opportunity crudes is asphaltene stability. Specifically, this refers to how well the asphaltenes are dissolved in the crude oil at a given operating tempera- ture and pressure in refinery processes. Asphaltenes, the heavy and complex molecules in crude oil, can precipitate to either remain suspended or settle, depending on the conditions. The presence of precipitated asphaltenes can alter the physical properties of the fluid stream, leading to fouling and equipment damage, which causes significant operational inefficiencies and increased maintenance and repair costs.1 Problem Asphaltene precipitation, the precursor of asphaltene- related problems, is a thermodynamic phenomenon that depends on the fluid composition, temperature, and pres - sure. Additional factors such as the residence time, equip- ment configuration, chemical reactions, and high process temperatures can produce deposition in streamlines, pump plugging, and equipment fouling. Hence, asphaltene pre- cipitation is the primary trigger for these issues. Typically, refiners assess asphaltene precipitation in a particular crude oil using standardised titration tests. These tests determine the onset point, which represents the mini- mum amount of titrating solvent required to initiate asphal- tene precipitation. Usually, the onsets are reported in mL of solvent per g of oil. Alternatively, the onsets are also reported as P-Value (ASTM D71122, ASTM D82533), P-Ratio (ASTM D70604), and S-Value (ASTM D71575). Wiehe6 presents

the measured onsets in terms of solubility blending number (SBN) and the insolubility number (IN). The onset point indicates the severity of asphaltene precipitation; for instance, higher onset values indicate more stable crude oils. Crude oils containing precipitated asphaltenes are considered unstable, where the onset can- not be measured. Test conditions (pressure and tempera- ture) and titrants, typically n-heptane and n-hexadecane, vary by procedure, with most tests conducted at ambient conditions. Notably, onset values do not correlate to bulk asphaltene content of the crude oil. Blending crude oils from various sources is unavoidable during transportation, pre-refining, and refinery process - ing. Additionally, mixing processed fluid streams containing asphaltenes occurs during processing, and product streams are blended in certain scenarios during post-refining oper - ations. In all these cases, the source oils are incompatible when blending compositionally different stable source oils that lead to asphaltene precipitation. Consequently, using the correct proportion of source oils is crucial to avoid any unstable blends while ensuring compatibility. While onset tests assess blend compatibility, testing all possible blends is impractical and expensive. Simple aver - aging is unreliable, as asphaltene solubility depends on fluid composition. This underscores the need for a predic - tive tool to assess the compatibility of different source oils or streams. In today’s fast-paced environment, seamless integration of such a predictive tool into a process simulator is vital for efficient planning and operations. Solution To address the crude oil compatibility challenges, a Multiflash Crude Compatibility Tool (MFCCT) was developed and incorporated into KBC’s proprietary Petro-SIM pro- cess simulator. Adapted from KBC’s proprietary Multiflash asphaltene model, the MFCCT predicts asphaltene precip - itation onsets for blends, and it has been validated using data from several refineries. Its predictive capabilities elim - inate the need for extensive measurements in identifying the extent of compatibility of source oils or streams. Since the tool is based on the thermodynamic model, compati- bility assessments can be extended to changing operating conditions, providing a reliable and efficient solution for

PTQ Q2 2025