The multiple-contact calculation option is invoked by selecting Calculations|Multiple
Contacts or by selecting the MCM button on the options toolbar. Example data sets for this
option are mcm-condensing.dat, mcm-vaporizing-co2.dat, mcm-combined-H95-8lean- mmp.dat and mcm-Z12-5-mme.dat etc. The required data include the temperature, entered in the text box on Tab 1, Conditions and a pressure or alternatively a pressure range for the calculation. For calculation at a single pressure, enter the value in the text box Pressure. To specify a pressure range enter the minimum pressure, Pmin, in the text box labelled Pressure and enter a value for pressure step, Pstep, and the number of pressure steps, Nsteps. The maximum pressure, Pmax = Pmin + Pstep *Nsteps. The user needs to select one of the calculation methods: Cell-to-Cell simulation or Tie Line method. The other required data are the oil composition entered on the Composition form, the primary and make up gas compositions entered on Tab 2, Composition, the make up gas fraction or range of fractions and the pseudoization scheme for the ternary diagram entered on Tab 2, Composition as well. For calculation at a single solvent enrichment level, enter a value between 0.0 and 1.0 in the
Make-up gas fraction text box. The default value for the make-up gas fraction is zero,
implying the solvent composition equals the primary gas composition. In this case the make- up gas composition is not required and values of zero can be entered. To specify a range of make-up gas mole fractions, enter the minimum value in the Make-up gas fraction text box, enter a value for the Make-up gas fraction step and for the No. of make-up gas fraction
steps. If Cell-to-Cell simulation is selected, the pseudoization scheme need to have a value
of 1, 2 or 3 to group a given component into the first, second or third pseudo-component respectively. The pseudoization scheme is used in the post-processing step, which is just for ternary plots; the actual calculations are done with the full set of components.
Note that if a range of pressures is specified (MMP calculation), only one solvent
composition may be entered. That is the Make-up gas fraction step must be 0.0 and the No.
of make-up gas fraction steps must be 1. Similarly for the MME calculation where a range
of make-up gas fractions is specified, only one pressure value may be entered.
The following steps are used in the calculation (the points referred to by letter are shown on the diagram following step 4).
1. A solvent is first formed by mixing a primary gas (e.g. dry gas) with a specified mole fraction of make-up gas (e.g. LPG). The compositions of the primary and make-up gases, and the fraction of make-up gas are entered on Tab Composition. The oil composition is specified on the form Composition.
User's Guide WinProp Multiple Contact Miscibility Calculations • 107 2. Solvent is added to the oil such that the solvent to oil molar ratio increases by a
specified value for each mixture. This solvent increment ratio is entered on Tab
Conditions as Solvent increment ratio. The default value is 0.01. Flash
calculations are performed for a maximum of 100 mixtures of solvent and oil. If no two-phase region is detected, the process is judged to be first contact miscible and the calculations stop. In the event that a two-phase region is encountered, the calculation procedure proceeds to Steps 3 and 4.
3. Using the first point (A) in the two-phase region detected in Step 2, all liquid is removed. The remaining gas is combined with the original oil in the gas oil ratio RATIO:(1-RATIO) to form B1. The value of RATIO is entered on Tab Conditions as Equilibrium gas/original oil mixing ratio (default value: 0.10). A flash
calculation is performed, and the liquid is removed. The procedure is repeated. This simulates a vaporizing or extraction process, and generates the portion of the phase envelope marked B. A maximum of 50 flash calculations is performed. 4. Again, using the first point (A) in the two-phase region detected in Step 2, all
vapor is removed. The remaining liquid is combined with the original solvent in the solvent liquid ratio RATIO:(1-RATIO) to form C1. A flash calculation is performed, and the vapor is removed. The procedure is repeated until the oil cannot be enriched further or after a maximum of 50 flash calculations are performed. This process simulates a condensing gas drive process, and generates the portion of the phase envelope marked C.
C1 C2 A B1 B2 Heavy C B
Light Dry Gas Solvent Intermediate
Critical Point Oil
108 • Multiple Contact Miscibility Calculations User's Guide WinProp If Cell-to-Cell simulation is selected, the last column of the table on Tab Composition needs to have a value of 1, 2 or 3, which determines the grouping of components into three pseudo- components for the ternary diagram. In the following example:
N2 and C1 belong to Pseudo-Component 1; IC5, NC5, NC6 and FC20 belong to Pseudo- Component 3, while the remaining components belong to Pseudo-Component 2. The resulting ternary diagram from this multiple contact calculation is shown below, where the bottom left apex corresponds to Pseudo-Component 1, the bottom right apex corresponds to Pseudo-Component 2 and the top apex represents Pseudo-Component 3.
User's Guide WinProp Multiple Contact Miscibility Calculations • 109
Oil/Rich Solvent Multiple Contact Study Ternary Diagram 0 10 20 30 40 50 60 70 80 90 100 0 10 20 30 40 50 60 70 80 90 100
m ol % of pseudo com ponent 2
mol % of ps e u do c o mp on e n t 3
User's Guide WinProp Regression • 111
Regression
Overview
The regression feature of WinProp can be used to “tune” the equation of state to match experimental measurements. The parameters used in the regression are component properties and interaction coefficients. Most of the calculation options of WinProp allow experimental data to be entered for regression purposes.
WinProp uses the regression procedure of Agarwal et al. [2]. From the specified list of
parameters, the procedure orders the parameters such that the most sensitive parameters are used first. The regression is performed on a small number of parameters at a time. The default is to use a subset of 5 parameters, although this number can be modified. Once a parameter reaches the maximum or minimum value allowed or does not contribute any longer to improving the match, it is replaced by the next parameter that has not been used from the ordered list. Thus, a large set of parameters can be specified, and WinProp will regress on a small number of
parameters at a time, working from the most sensitive parameters to the least sensitive parameters.