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OLI Technology

  • Data Regression
  • Corrosion
  • Scale predictions

Technical Challenges

* Problems when importing ScaleChem Std files into Studio ScaleChem (pre-V9.2)

1) When importing a calculated Oil or Gas StudioSC automatically assumes Makeup species (CH4). This cause composition problems.

2) Saturating with NaHCO3 causes phase error in SC Std V4.1.11 AND SC V9.1.3. This is strictly a ScaleChem Std. problem, and there will be a new SC-Std release with these fixes

3) Saturating with NaHCO3 cause a calculation failure which was caused by a labeling error in SC V4.1.11. This is different from #2 above and is the same problem that Clare Johnson encountered). This will be fixed in the new SC release.

4) There are no warning in Studio SC that an oil analyses being imported did not contain a measured density – the default value of 1.000 is still in the density field). By contrast, Studio SC computes an oil density. This will cause the volume-mole relationship of the oil to differ in Studio SC. Therefore the oil mass in Studio SC will be in general, lower than oil mass computed in SC Std. We have known this for several years, but never included a warning to the user. Thus, a request was added that a warning be included when an imported file contains an oil. In this way, the user is aware of the potential mass/volume difference.

5) There is no warning/alert to the user that the standard temperature (15.56C) in Studio SC is different from the standard temperature (0C) in ScaleChem Std. The different temperature causes a 5% lower gas mass in Studio SC. I asked that a warning be included when an import contains a gas, so that the user is aware of the potential mass/pH/bubble point difference.


* ScaleChem Standard reporting wrong Scale Tendencies in pre-V9.1 Explanation of Problem

Two users from the same company reported separate discrepancies within ScaleChem V4.1. The first user reported that the software computed a scale tendency below one but a positive solids value. The second user observed an inconsistent correlation between the scale tendency and solids curve over a broad temperature range.

Diagnosis

AQSim and OLI initially tested the case looking to see if there were any speciation and thermodynamics issues associated with the database but did not find a problem. The numerical solver engineers then looked at how the calculations were being completed and identified the problem. The OLI Engine was exporting the scale tendency at a point in the solver process that was wrong under certain scenarios.

Who fixed it

Between December 2013 and March 2014, the OLI Numerical Solver engineers recoded the OLI Engine.

What was fixed

The OLI Engine’s Numerical solver is comprised of a series of subroutines which are used to converge every calculation to a solution. Convergence includes minimizing mass and energy balance errors and computing equilibrium speciation and phase existence. Periodically the software tests for above conditions and also tests solids saturation. At an iteration point that is just ahead of the final iteration, the Engine exports the scale tendency and then completes the phase equilibrium calculation. The point at which the Engine exported the scale tendency had to be revised.

Fixed Version and Implementation

AQSim studied the ScaleChem Standard calculations over a range of compositions and conditions. The ScaleChem versions studied included V4.1.11, V9.0.11, V9.1.1, and V9.1.2. The Studio ScaleChem versions studied included V9.0.14, V9.1.1, and V9.1.2. The conclusions are that ScaleChem Standard V9.1.2 and Studio ScaleChem V9.1.2 produce the same scale tendency and excess solute results. There are still differences between the two software predictions, but they are not associated with the solver. The remaining differences are associated with the oil density values and the temperature used for Standard conditions.

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