Centre for Petroleum Fuels & Energy

1

Petroleum Fluids CHPR8531

Assignment 3 - HYSYS (Phase Behaviour)

Issued: Tuesday 20th April 2010 Due: 5:30 pm Tuesday 18th May 2010

Submit an electronic copy of your HYSYS PFD and an accompanying report containing your answers to all questions, through WebCT. Make sure you save a copy of your work in a reliable place, e.g. on a flash disk. Files saved onto the MCL computers are likely to be deleted.

PART 1 The purpose of the exercises in Part 1 is to give you some familiarity with HYSYS by calculating phase envelopes, and phase behaviour, using some of the Utility Packages. To do Part 1 you will need the reference article by K.R. Gammie which describes the processing strategy for the North Rankin A platform. Reference: Gammie, K.R. 1983, Process Selection and Optimisation Studies – North Rankin ‘A’, Woodside Petroleum Pty Ltd, Australia. EXERCISE 1 The following is a typical composition of a Gas Condensate reservoir fluid (for simplicity take C7+ as C7 and use the Peng-Robinson EOS):

Component GAS

CONDENSATE%Mole

N2 0.29 CO2 1.72 C1 79.14 C2 7.48 C3 3.29 iC4 0.51 nC4 1.25 iC5 0.36 nC5 0.55 C6 0.61

C7+ 4.80

1. Use HYSYS to plot the phase envelope for this fluid. Answer the following with

reference to {T,P,Q} conditions in the article by K.R. Gammie:

2

• At year 1 Flowing Conditions would this fluid be single phase or 2-phase? • At year 10 Flowing Conditions would this fluid be single phase or 2-phase?

As described in K.R. Gammie’s article, the gas condensate fluid now passes through a production cooler and into the production separator. It is now time to simulate this separator. 2. Enter the Simulation Environment and connect the stream through a cooler to a

separator. Set the separator conditions to the NRA process conditions (55°C and 11 MPa)

• Use the Envelope Utility and examine the phase envelope for each stream. Note that you can associate an envelope with each stream.

• Export the 3 phase envelopes (Feed, Gas, Liquid streams) to Excel and graph them on the one plot. (Paste the Excel plot into your written report as a figure.)

• Comment on the overlap and explain your observations. • Examine the gas and liquid outlet compositions. Do they make sense?

The Envelope Utility can also produce quality lines. 3. Take the feed to the production separator and get HYSYS to calculate some quality

lines. a. From your phase envelope and quality lines estimate the liquid/gas volume ratio.

The envelope utility can also calculate the Hydrate Formation Curve. While the prime purpose of the NRA platform is to dehydrate the gas stream, and dewater the condensate stream for anti-corrosion purposes, it is also essential to be outside the hydrate formation region. 4. Get HYSYS to plot the hydrate formation curve for the gas outlet from the separator

and answer the following: • Is hydrate formation a problem for pipeline transport to shore? • At what T would hydrates begin to form in the pipeline (if there was any water

around)? Export the quality line and hydrate curve calculations from HYSYS into Excel and combine these with the dew and bubble point curves to produce a comprehensive P-T phase diagram for the separator feed stream (by itself).

3

PART 2 The purpose of the Part 2 is to build on your capability to develop phase envelopes, and calculate phase behaviour, with HYSYS, and so reinforce your fundamental knowledge of how petroleum fluids behave. EXERCISE 2 The following table gives the typical compositions (in mole %) of various reservoir fluids:

Component DRY GAS GAS CONDENSATE

VOLATILE OIL BLACK OIL

N2 6.25 0.29 0.12 0.16 CO2 2.34 1.72 1.50 0.91 C1 81.13 79.14 66.59 36.47 C2 7.24 7.48 5.31 9.67 C3 2.35 3.29 4.22 6.95 iC4 0.22 0.51 0.85 1.44 nC4 0.35 1.25 1.76 3.93 iC5 0.09 0.36 0.67 1.44 nC5 0.03 0.55 1.12 1.41 C6 0.61 1.22 4.33

C7+ 4.80 16.64 33.29

5. Use HYSYS to plot the phase envelopes for each of the fluids. For simplicity take C7+

as C7 and use the Peng-Robinson EOS. 6. Tabulate the critical parameters (“real” and “pseudo”) as calculated by HYSYS.

Comment. (Consider the dependence of the critical parameters on composition) 7. Export the 4 phase envelopes to Excel and graph them on the one plot. Comment on the

variations of phase envelope from composition to composition. Is it what you expect? EXERCISE 3 Figure 1 (on page 5) shows the experimentally determined phase diagrams for various methane-ethane mixtures. Change the default units HYSYS uses for pressure and temperature to the units in Figure 1. Use the critical properties utility to obtain the critical parameters for each of the 10 mixtures. Tabulate these critical parameters (true and pseudo) in your report. Use HYSYS to generate the vapour pressure curves for pure methane and pure ethane, and to generate the phase envelopes for the binary mixtures 4, 6 and 8. Export all of this data to Excel, together with the critical parameters (true and pseudo) you calculated for all the mixtures. Generate a graph, with the same scale and units as Figure 1, which contains all of the information you exported from HYSYS. Your plot should contain the critical loci for this system, the pseudo critical parameters for these ten mixtures, the vapour pressure curves for the two pure components and the phase envelopes for the three mixtures.

4

Compare your HYSYS generated plot with Figure 1, which was generated from experimental data. Comment on the accuracy of HYSYS in predicting true-critical parameters, the inadequacy of Kay’s Rule, and the accuracy of phase behaviour calculations made with the PR EOS for this favourable case (neighbouring alkanes). EXERCISE 4 Figure 2 (on page 6) gives the critical loci for all n-paraffin binary mixtures up to C10 (n-decane). Generate your own version of Figure 2 (same scale & units) by exporting HYSYS calculations to Excel in a similar fashion to what you did in Exercise 2. You only need to consider pure methane and pure n-decane. Choose some (at least 4) compositions and use the Critical Properties (and Envelope) Utility to obtain the critical parameters (true and pseudo) for your mixtures. Use these parameters to produce the critical loci for C1 & C10 and compare this to Figure 2. You should find that HYSYS calculates some interesting/bizarre phase diagrams for this system! Export the phase envelope calculations for one of your C1-C10 mixtures that displays this bizarre behaviour. Generate an Excel plot and comment.

5

Figure 1: Phase Diagram of Methane-Ethane Mixtures

6

Figure 2: Critical loci of binary n-paraffin mixtures