A Unified Approach to Asphaltene Precipitation: Laboratory Measurement and Modeling
- D.J. MacMillan (Marathon Oil Company) | J.E. Tackett Jr. (Marathon Oil Company) | M.A. Jessee (Marathon Oil Company) | T.G. Monger-McClure (Marathon Oil Company)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- September 1995
- Document Type
- Journal Paper
- 788 - 793
- 1995. Society of Petroleum Engineers
- 5.5.8 History Matching, 3.1.6 Gas Lift, 5.2.2 Fluid Modeling, Equations of State, 5.4.7 Chemical Flooding Methods (e.g., Polymer, Solvent, Nitrogen, Immiscible CO2, Surfactant, Vapex), 4.1.9 Tanks and storage systems, 5.5 Reservoir Simulation, 1.8 Formation Damage, 4.2 Pipelines, Flowlines and Risers, 4.6 Natural Gas, 5.2 Reservoir Fluid Dynamics, 4.3.3 Aspaltenes
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A unified approach to evaluating asphaltene precipitation based onlaboratory measurement and modeling is presented. This approach used an organicdeposition cell for measuring asphaltene drop out onset conditions. Asphalteneprecipitation was detected by changes in optical fluorescence, electricalconductance, and visual observation. A series of experiments measured theeffects of changing pressure, temperature and composition on asphalteneprecipitation. A fully-compositional V-L-S mathematical model completed theanalysis by matching the experimental results. The model was then used toforecast asphaltene precipitation under a variety of production scenariosincluding response to gas-lift operations, and to evaluate the possiblelocation of a tar-mat.
An organic deposition cell (ODC) was developed to experimentally detectasphaltene drop out onset. Two different detection techniques were incorporatedinto the cell. Fluorescence spectrometry has been used to study aromaticcompounds. Fiber optics allowed application of this basic technique toasphaltene detection in the ODC. Conductance measurements were alsoincorporated into the ODC.
Thermodynamic models have been used to predict asphaltene precipitation fromreservoir crudes under a variety of conditions. Burke et al and others appliedpolymer solution theory to the prediction of asphaltene precipitation. Whilethis technique has been very successful, it is limited in its capability topredict the amount of asphaltene precipitate and varying precipitatecomposition. It was therefore decided to use the more rigorous approachpresented by Thomas et al to model asphaltene precipitation. This method isbased on an earlier wax deposition model which allows a fully compositionalrepresentation of the asphaltene phase.
The high-pressure (6000 psig) I high-temperature (250 F) ODC employed apiston to allow sample or chemical introduction and pressure/volume control(Figure 1). The piston was designed to minimize dead volume so that flashingduring sample introduction was reduced. Heating elements and cooling coils wereinstalled for temperature control. The sapphire window allowed limited visualinspection and the use of a flexible fiber optics probe for luminescencedetection. The cell was rocked to allow sample mixing and could be inverted sothe window was on top. Electrical conductance was measured between the cellwall and the conducting probe. The conductance values obtained included a highbackground contribution from the equipment.
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