Asphaltenes

Calsep offers evaluation of possible asphaltene problems in reservoirs and wells producing asphaltene-rich reservoir fluids.

Calsep’s services include: 

  • Asphaltene risk analysis
  • Asphaltene EoS modeling
  • Planning of experimental asphaltene studies
  • Tar mat analyses
  • Asphaltene seminars 

Calsep has state-of-the-art algorithms available for asphaltene modeling, which will give an overview of asphaltene precipitation pattern, not only in the reservoir, but also at surface conditions and even at refinery conditions. 

Simulated asphaltene phase diagram 


Asphaltene Risk Evaluation

Using well-established screening methods Calsep may carry out asphaltene risk analyses in the early stages of field development. If initial investigations show potential asphaltene problems, Calsep can plan an efficient experimental PVT campaign that will provide sufficient data to develop an EoS model for asphaltene precipitation.

De Boer asphaltene screening risk analysis.


Asphaltene Precipitation and EoS Modeling

Calsep has an in-depth understanding of asphaltene phase behavior and may include asphaltene precipitation as part of EoS modeling projects. Calsep has experience modeling asphaltene precipitation using both cubic equations of state and more complex equations as for example PC-SAFT. The below figure illustrates a case with no asphaltene precipitation at reservoir temperature, while asphaltene precipitation is seen at well temperature. Asphaltene precipitation may therefore potentially take place in the well.

Asphaltene phase diagram for a reservoir fluid that may precipitate asphaltenes at well conditions although no asphaltene precipitation is seen at reservoir conditions.


Gas Injection – EFFect on Asphaltene Precipitation

While an asphaltene rich oil may be produced by natural depletion without seeing any asphaltene precipitation, asphaltene precipitation must be taken into account when gas injection is considered as an EOR technique. Addition of gas will expand the pressure-temperature region where asphaltene precipitation takes place. Calsep can make EoS models matching the asphaltene onset at different amounts of injection gas, and rank tendency of different gases to precipitate asphaltenes.

Asphaltene Px phase diagram


Tar Mat Formation

The asphaltene concentration will increase with depth in a reservoir. Calsep can determine the asphaltene gradient considering the influence of gravity and a thermal gradient. Under certain conditions the increased asphaltene concentration may lead to the formation of a tar mat. Calsep may perform calculations to investigate the possibility of a tar mat existing in a given reservoir and define the reservoir depth in which the tar mat starts.

Oil column with tar mat. The tar mat starts at the depth in which the asphaltene onset pressure and the reservoir pressure become equal.


Asphaltene Seminars

Modeling of asphaltene precipitation is covered in Calsep’s PVT simulation courses. Calsep further offers asphaltene seminars (usually 1 day) that covers the asphaltene phase behavior, screening methods. experimental techniques, and asphaltene EoS modeling.


References

Agger, C.S. and Sørensen, H., “Algorithm for Constructing Complete Asphaltene PT and Px Phase Diagrams”, Industrial & Engineering Chemistry Research, 57 (1), 2018, pp. 392-402.

Boesen, R.R., Sørensen, H. and Pedersen, K.S., “Asphaltene Predictions Using Screening Meth- ods and Equations of State”, SPE 190401-MS, SPE EOR Conference at Oil and Gas West Asia, Muscat, Oman, 26-28 March 2018.

Hustad, O. S., Jia, N.J., Pedersen, K.S., Memon, A., Leekumjorn, S., “High Pressure Data and Modeling Results for Phase Behavior and Asphaltene Onsets of GoM Oil Mixed with Nitrogen”, SPE Reservoir Eval. Eng. 3, 2014, pp. 384-395.

Pedersen, K.S., Azeem, J. and Rasmussen, C.P., “1D Asphaltene Deposition Simulator for Reservoir Fluids Undergoing Gas Injection”, SPE-155447-PP, SPE EOR Conference at Oil and Gas West Asia, Muscat, Oman, 16–18 April 2012.

Rydahl, A., Pedersen, K.S., Hjermstad, H.P., “Modelling of Live Oil Asphaltene Precipita- tion”, AIChE Spring National Meeting, March 9-13, 1997, Houston, Tx, USA.