Asphaltene Precipitation and Deposition from Conventional Crude Oils

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Asphaltenes are the heaviest fraction of crude oils and can precipitate and sometimes form deposits upon a change in temperature, pressure, or composition. Asphaltene deposition in oilfield facilities leads to production losses and high treatment costs. Data and models for the precipitation and deposition process are required to avoid or mitigate deposition. This proposed research program targets two gaps in the available data and models that are of relevance for deeper reservoirs, such as those found offshore Newfoundland, and for carbon dioxide flooded reservoirs, some of which are found in Western Canada.*******Gap 1 - Precipitation Caused by Dissolved Gases: Asphaltene precipitation from depressurized conventional oils is strongly dependent on the dissolved gas content. However, the roles of the different dissolved gases, particularly methane and carbon dioxide, have not been systematically investigated. It is proposed to measure asphaltene precipitation for dead oils mixed with methane, carbon dioxide (and heptane if required to force precipitation) over a range of temperature and pressures. The data will be used to determine solubility parameters for the dissolved gases to be used as inputs for a phase behavior model. Existing phase behavior models will be adapted as required to represent the data. The deliverable is a data validated phase behavior model for asphaltene precipitation in all conventional oil applications.*******Gap 2 - Deposition in Open Flow at Elevated Temperature: Most asphaltene deposition studies have been performed at low temperature and deposition at the higher temperatures encountered in off-shore production (up to 130C) has not been rigorously investigated. Asphaltenes are commonly considered to precipitate as glassy particles that flocculate and potentially deposit. However, the particles are in fact an asphaltene-rich phase which becomes a liquid at higher temperatures. Hence, the deposition process will change at higher temperatures. It is proposed to design and commission an apparatus to investigate asphaltene deposition at deep reservoir temperatures and pressures. Deposition mechanisms will be proposed and tested against the data collected in this apparatus and the results will be incorporated into a deposition model.*******The proposed precipitation models will allow operators to avoid or plan for asphaltene precipitation to sustain production and potentially avoid or reduce treatment costs. The models will be of use to any operator of a deep or gas flooded reservoir. The proposed deposition research can be used to assess if and where a new off shore or gas flood development is likely to encounter deposition problems. This is the crucial first step in flow assurance and mitigation. The proposed research will also support two Ph.D. students who will receive background and training suitable for careers as research engineers in the oil industry and academia.**