CSMGem

Sloan et al. (1986,1987)] with corrections by Song and Kobayashi (1994). Apre-diction scheme is discussed in Chapter 5 using the statistical thermodynamics method and included in the program CSMGem. 

Accuracy of CSMGem Compared to Commercial Hydrate Programs... 

The thesis of Ballard (2002) details this calculation method, which includes multiphase systems, solid phases including ice and salts, and thermodynamic inhibition. The CSMGem (the last three initials are the first letters of Gibbs energy minimization ) User s Manual, included in the CD in the endpapers, and the examples of hydrate calculation shown in the Appendix A, enable the reader to use the CD programs. 

The Gibbs energy minimization method allows for calculations of the formation conditions for any phase (including the hydrate). It also allows for the calculation of phases present at any T and P (whether hydrates are present or not). Therefore, included are the options to perform all thermodynamic calculations with every phase and not just the hydrate. The types of calculations, combined with plotting capability, included in CSMGem are... 

A comparison of predictions from CSMGem, the program included in the CD of this work, with the second edition s version (CSMHYD) and three commercial hydrate prediction programs, is given here for all recent hydrate data reported in literature. The five programs (with the last three commercial) compared in this work are... 

CSMGem—Colorado School of Mines (2007 edition) CSMHYD—Colorado School of Mines (1998 edition) DBRHydrate—DBRobinson Software Inc. (version 5.0) Multiflash—Infochem Computer Services Ltd. (version 3.0) PVTsim—Calsep A/S (version 11)... 

To test the predictions, experiments were carried out at the Delft University of Technology (TUD) (Ballard et al., 2001). In CSMGem, the pressure versus temperature phase diagram was generated using the model and then confirmed by experimental data. Figure 5.19 is the pressure versus temperature diagram for a 30/70 mixture of ethane and propane in contact with excess water. 

Avoidance of the hydrate formation thermodynamic conditions of temperature, pressure, or inhibitor concentration, makes it impossible for plugs to form. The calculations of thermodynamic conditions can be made with acceptable accuracy. Using the methods presented in Chapters 4 and 5 along with the CD program CSMGem provided with this book, the temperature, pressure, and inhibitor concentrations can be calculated respectively, to within 2°F, 10% in pressure and 3% of inhibitor concentration. Since the discovery of hydrate flowline plugs in 1934, such thermodynamic methods have served to provide the major method of flow assurance. 

Figure 8.14 Temperature changes as a result of depressurization (1) isenthalpic rapid expansion as through a valve, and (2) very slow depressurization, as in a large-volume pipeline. Note that for the rightmost case, a fluid system can be expanded into the hydrate region, as calculated by the methods in Section 4.2.1.1 and the programs of CSMGem on the CD accompanying this book.

CSMGem can also plot phase boundaries when used in conjunction with MS Excel. 

The authors acknowledge the Center for Hydrate Research Consortium members for the funding and data required for the development of CSMGem. Consortium members include BP, Chevron, ConocoPhillips, ExxonMobil, Halliburton, Petrobas, Schlumberger, Shell, Statoil. 

CSMGem predicts sll hydrate to form at a pressure of 166.97 psia (Figure A.2). Note If Advanced box is checked, the output for si and sH hydrates is P > P sll. This simply means that the calculation was only performed for sll and that it was internally determined that si and sH were not stable. 

CSMGem predicts sll hydrate to form at a temperature of 37.759°F (Figure A.3). 

Use the Plot tab on CSMGem to plot the isenthalpic expansion curve using MS Excel. Save this data under a different file name before continuing to plot-phase boundaries. The file will be overwritten if the name is not changed. 

Use the Plot tab on CSMGem (add intervals required) to plot the sll phase boundaries with and without methanol using MS Excel. After combining the calculated data, the final plot should look like Figure A.7. The solutions are the intersection of the expansion line and sll phase boundary lines. 

A 30 ft hydrate blockage occurs in a 12 in. diameter un-insulated pipeline. The upstream and downstream pressures are 780 and 180 psia, respectively. The Structure II equilibrium pressure is 200 psia (from CSMGem at the ambient temperature). 

Includes the software programs CSMGem, which supplies the most recent thermodynamic predictions, and CSMPlug, which provides the time required for hydrate plug removal from a pipeline... 

A new computer program CSMGem, for hydrate thermodynamic calculations... 

Appendices—Users Guide Examples for CSMGem and CSMPlug All sections All sections... 

CSMGem software (Sloan and Koh, 2007). The broken portion of these curves is where the acid gas liquefies and crosses the phase envelope. The steep portion is for the hydrate for the liquefied acid gas. 

All the experimental studies [18-24] for methane hydrates are in agreement that for a constant value of pressure, the methane solubility, under H-Lw equilibrium, decreases with decreasing temperature, whereas the trend is reversed under vapor-liquid water equilibrium. Similarly, for a constant value of temperature the methane solubihty, under H-L equilibrium, decreases with increasing pressure. This behavior is clearly depicted in the schematic of Figure 1. Shown with the black dashed line is the three-phase (H-Lw-V) equilibrium curve, as calculated with the CSMGem simulator [1]. The colored solid lines correspond to the two-phase (H-Lw) equilibrium calculations using the correlation reported by Lu et al., [18], for six isotherms. Lu et al., reported a correlation for their experimental data of the type ... 

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