Flow Assurance & Process

Fluid properties and possible formation of solids must be taken into consideration in the design and operation of equipment for transportation and processing of reservoir fluid well streams. Water is often handled as an inert phase in reservoir simulation studies, but in flow assurance and process simulations it can be fatal to neglect the mutual solubility of water and hydrocarbons.

Calsep offers consulting services within:

  • (Acid) gases
  • Gas condensates
  • Near critical fluids
  • Volatile oils
  • Black oils
  • Heavy oils

Phase Distribution of Water and Inhibitors

Flow assurance and process engineers need a complete picture of the amount of free water and the amount of water dissolved in the hydrocarbon phases at conditions ranging from HT/HP reservoir conditions to standard conditions. This is for example required to:

1) Dose of the right amount of hydrate inhibitor for a subsea pipeline.

2) Assess the amount of free water present in a multiphase meter. The meters may not be reliable unless the amount of free water is known.

Calsep can solve these tasks using an extensive in-house knowledge about modeling of systems with water and other aqueous components (MeOH, NaCl, CaCl2, MEG, or TEG). Calsep has access to the most accurate thermodynamic models for handling aqueous components including Huron-Vidal and Cubic Plus Association (CPA). Calsep’s model parameters have been validated against an extensive experimental data material, allowing for an optimal model selection and assessment of the uncertainty on the simulation results.


Phase Distribution of Water and Inhibitors

Calsep undertakes evaluations of the hydrate formation and mitigation for pipeline systems, taking into account the:

  • Pressure drop
  • Heat exchange with the surroundings
  • Hydrate inhibition by salts and liquid inhibitors
  • Loss of inhibitor to hydrocarbon phases

Calsep has verified the hydrate model using extensive published experimental data, including data with up to 70 weight percent liquid inhibitor and saturated salt solutions as exemplified in the below figure. Validation reports are available.


Calsep’s experience with hydrate modeling dates back to the mid-1980s. Calsep has published several papers on hydrate modeling, hydrate kinetics, and loss of hydrate inhibitor to hydrocarbon phases. Most publications appear in peer-reviewed journals - a hallmark of Calsep model work.


Wax Deposition Evaluations

Calsep undertakes wax deposition simulations for wells and pipelines. The simulations are carried out using the fully compositional wax deposition flow simulator, DepoWax, which is an integral part of PVTsim Nova. With continued transport, the wax layer builds up and may eventually plug the pipeline if not mechanically removed. The simulation results include the development in thickness of the wax layer with time as illustrated in the below figure, and how the deposited wax influences the pressure drop. This may be used to decide on pigging frequency.

Wax layer profile after Time step 1 and 2.

It is possible to consider pipelines with multiple inlets and different sections of the pipeline may have different insulation (walls). The below figure illustrates how a varying GOR will result in different Wax PT curves, which will translate into differences in wax deposition in the pipeline. 

Saturation pressure and Wax PT curves for two different GOR’s


H2S Partitioning

Calsep can simulate the distribution of hydrogen sulfide (H2S) between gas, oil, and aqueous phases taking into account the dissociation of H2S in the water phase as determined by pH:

H2S<->HS- + H+

Calsep’s H2S technology has been used to quantify the concentration of H2S in the gas phase at atmospheric conditions for a leakage evaluation and for material selection in wells and other equipment handling production from fields with high H2S concentration.


References

Boesen, R.R., Herslund, P.J., and Sørensen, H.,”Loss of Monoethylene Glycol to CO2-and H2S-Rich Fluids: Modeled Using Soave–Redlich–Kwong with the Huron and Vidal Mixing Rule and Cubic-Plus-Association Equations of State”, Energy & Fuels 31, 2017, pp. 3417–3426

Madsen, J., Pedersen, K.S. and Michelsen, M.L., ”Modeling of Structure H Hydrates using a Langmuir Adsorption Model”, Ind. Eng. Chem. Res., 39, 2000, pp. 1111-1114.

Munck, J., Skjold-Jørgensen S. and Rasmussen, P. ”Computations of the Formation of Gas Hydrates”, Chem. Eng. Sci. 43, 1988, pp. 2661-2672.

Pedersen, K.S., “Prediction of Cloud Point Temperatures and Amount of Wax Precipitation”, SPE Production & Facilities, February 1995, pp. 46-49.

Pedersen, K.S., Michelsen, M.L., Fredheim, A.O. “Phase Equilibrium Calculations for Unprocessed Well Streams Containing Hydrate Inhibitors”, Fluid Phase Equilibria 126, 1996, pp. 13-28.

Pedersen, K.S. and Rønningsen, H.P., ”Effect of Precipitated Wax on Viscosity – A Model for Predicting Non-Newtonian Viscosity of Crude Oils”, Energy & Fuels, 14, 2000, pp. 43-51.

Pedersen, K.S. and Rønningsen, H.P., “Influence of Wax Inhibitors on Wax Appearance Temperature, Pour Point, and Viscosity of Waxy Crude Oils”, Energy & Fuels 17, 2003, pp. 321-328.

Rasmussen, C.P. and Pedersen, K.S., “Challenges in Modeling of Gas Hydrate Phase Equilibria”, 4th International Conference on Gas Hydrates Yokohama Japan, May 19 - 23, 2002.

Pedersen, K.S., Milter, J., Rasmussen, C.P. “Mutual Solubility of Water and a Reservoir Fluid at High Temperatures and Pressures. Experimental and Simulated data”, Fluid Phase Equilibria 189, 85-97, 2001.

Rønningsen, H. P., Sømme, B. and Pedersen, K.S., ”An Improved Thermodynamic Model for Wax Precipitation; Experimental Foundation and Application”, presented at 8th international conference on Multiphase 97, Cannes, France, 18-20 June, 1997.

Skovborg P., Ng, H.J., Rasmussen, P., Mohn, U.,, “Measurement of induction times for the formation of methane and ethane gas hydrates”, Chem. Eng. Sci. 48, 1993, pp. 445-453.
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Sørensen, H., Boesen, R.R., Leekumjorn S. and Herslund, P.J. “Peng-Robinson Equation of State Extended to Handle Aqueous Components Using CPA Concept”, Journal of Natural Gas Engineering, 3 (1), 2018, pp. 1-38.

Tybjerg, P., Pottayil, A., Pedersen K.S., ”Optimum Handling of Water and Methanol under Hydrate Inhibition for a Gas Condensate”, May 1, 2017, Proceedings, Indonesian Petroleum Association, Forty first Annual Convention & Exhibition.