Nitrogen, on the other hand, raises the cricondenbar and decreases miscibility. It is sometimes used for pressure maintenance. There are also a few nitrogen miscible floods.<\/p>\n
In this TOTM, we will study the impact of CO2<\/sub>, H2<\/sub>S and N2<\/sub> on the phase behavior of different reservoir fluids such as black oil, volatile oil, and a rich gas. Computer simulated phase envelopes showing the quantitative effect are presented and discussed.<\/p>\n The Peng-Robinson (PR) [2] equation of state (EOS) option of ProMax [3] was used to perform all of the calculations in this study. In dealing with high content acid gases or nitrogen, care should be taken to verify the accuracy of an equation of state for handling these constituents. In general it is wise to assume the equations of state are inaccurate for modeling the thermodynamic properties and the phase behavior of systems containing high concentrations of non-hydrocarbon components like acid gases and nitrogen. Verification with experimental data is recommended before accepting results from equations of state.<\/p>\n Case Studies:<\/strong><\/p>\n Volatile Oil:<\/em> Figures 1, 2 and 3 present the impact of CO2<\/sub> and H2<\/sub>S and their mixture on the phase behavior of a volatile oil. The compositions of the light oil and the acid gas used to generate these two figures are shown in Table 1. For the properties (average normal boiling point, molecular weight and relative density of single carbon number (SCN), see Table 3.3 on page 64 of reference [1]. \u00a0Both CO2<\/sub> and H2<\/sub>S lower the cricondenbar of the volatile oil. These quantitative behaviors agree well with the qualitative ones shown in Figure 4.9 a and b. Figure 3 presents the impact of equal molar mixtures of CO2<\/sub> and H2<\/sub>S on the volatile oil phase envelope. The net effect is almost midway of the effect of CO2<\/sub> and H2<\/sub>S. In all three figures, the critical point of mixture shifts considerably to the left. The cricondentherm point also shifts to the left as the concentration of acid gases increase. The net effect is enhancing miscibility, shrinkage of the two phase region and expanding the liquid phase region. These are all desirable for enhanced oil recovery.<\/p>\n <\/p>\n Figure 1. The impact of CO2<\/sub> concentration on the volatile oil phase envelope<\/p>\n <\/p>\n Rich Gas:<\/em> The compositions of the rich gas and the non-hydrocarbons used to generate Figures 4, 5 and 6 are shown in Table 2. Figures 4, 5 and 6 present the impact of N2<\/sub>, CO2<\/sub> and H2<\/sub>S on the phase behavior of the rich gas, respectively. As shown in Figure 4, N2<\/sub> raises the cricondenbar of the rich gas. This quantitative behavior agrees well with the qualitative one shown in Figure 4.9 c. Nitrogen raises the cricondenbar, shifts the critical point to the left and decreases miscibility; therefore, it is best used for pressure maintenance. Miscibility can be attained only at very high pressures. Note for the case of 60 mole % in Figure 3, the bubble point curve and the critical point look abnormal which indicates that the equation of state and\/or the binary interaction parameters used are incapable of handling high concentrations of N2<\/sub><\/p>\n Figure 2. The impact of H2<\/sub>S concentration on the volatile oil phase envelope<\/p>\n \u00a0 Figure 3. The impact of acid gas (equal mole H2<\/sub>S and CO2<\/sub>) concentration on the volatile oil phase envelope.<\/p>\n \u00a0Figure 5 presents the impact of CO2<\/sub> concentration on the rich gas phase envelope. Like the case of the volatile oil, \u00a0CO2<\/sub> lowers the cricondenbar, \u00a0shifts the cricondentherm to the right but shifts the critical point to the left.<\/p>\n Figure 6 presents the impact of H2<\/sub>S concentration on the rich gas phase envelope. Both the critical and cricondentherm points shift to the right as H2<\/sub>S increases but the cricondenbar does not lower as it did for CO2<\/sub>.<\/p>\n Black Oil:<\/em> Figures 7 and 8 present the impact of CO2<\/sub> and H2<\/sub>S on the phase behavior of black oil. The compositions of the black oil and the acid gas used to generate these two figures are shown in Table 3.<\/p>\n As shown in Figure 7, contrary to the case of the volatile oil, the cricondenbar raises as the CO2<\/sub> content increases but both the critical and cricondentherm points shift to the left. Compared to Figure 1 for the volatile oil, the impact of CO2<\/sub> on the black oil phase envelope is much less.<\/p>\n \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Table 1. Composition of the volatile oil used to generate Figures 1, 2, and 3.<\/p>\n * Acid Gas = H2<\/sub>S, CO2<\/sub>, or equal molar mixture of H2<\/sub>S, CO2<\/sub>.<\/p>\n The impact of H2<\/sub>S on this black oil is similar to its impact on the volatile oil (Figure 2). As shown in Figure 8, H2<\/sub>S lowers the cricondenbar of this black oil. The critical point shifts considerably to the left. The cricondentherm point also shifts to the left as the concentration of H2<\/sub>S increases. The net effect is enhancing miscibility, shrinkage of the two-phase region and expanding the liquid phase region. The impact of H2<\/sub>S on the black oil is less compared to the volatile oil shown in Figure 2.<\/p>\n \u00a0 Figure 4. The impact of N2<\/sub> concentration on the rich gas phase envelope<\/p>\n \u00a0 Figure 5. The impact of CO2<\/sub> concentration on the rich gas phase envelope<\/p>\n \u00a0 Figure 6. The impact of H2<\/sub>S concentration on the rich gas phase envelope<\/p>\n \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Table 2. Composition of the rich gas used to generate Figure 4, 5, and 6.<\/p>\n * Non-Hydrocarbons = N2<\/sub>, H2<\/sub>S, or CO2<\/sub>,.<\/p>\n \u00a0 Figure 7. The impact of CO2<\/sub> concentration on the black oil phase envelope<\/p>\n Figure 8. The impact of H2<\/sub>S concentration on the black oil phase envelope<\/p>\n \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Table 3. Composition of the black oil used to generate Figures 7 and 8.<\/p>\n *<\/sup> For properties (average normal boiling point, molecular weight and relative density of single carbon number (SCN), see Table 3.3 page 64 of reference [1].<\/p>\n \u00a0<\/strong><\/p>\n Conclusions:<\/strong><\/p>\n The analysis of Figures 1 through 8 indicates that the impact of non-hydrocarbons on any reservoir fluids depends on the type\/nature and composition of the reservoir fluid. The type of non-hydrocarbon as well as its concentration also plays an important role. The injection of acid gases into a reservoir fluid changes the phase behavior and the thermodynamic properties of the reservoir fluids. Even though not discussed in this TOTM, CO2<\/sub> injection for the purpose of enhanced oil recovery may cause asphaltene deposition and blockage in the reservoir formation and the surface facilities. Depending on compositions, pressures and temperatures, much more complex phase behavior is possible. Multiple liquid phases (in addition to aqueous phase) and\/or solids may be present.<\/p>\n It is important to use the right tools and an accurate equation of state within simulation software to generate the correct phase envelope. It is recommended to check the accuracy of the thermodynamic models against field\/experimental data before generating any phase envelope. The equation of state should be tuned to match the laboratory measured vapor-liquid-equilibria data for a sample of the reservoir fluid before undertaking any practical study\/decision. The results shown in this TOTM are specific to the cases studied and have not been validated with actual data. These results should be used only as a guideline.<\/p>\n To learn more about similar cases and how to minimize operational problems, we suggest attending our G40 (Process\/Facility Fundamentals)<\/a>, G4 (Gas Conditioning and Processing)<\/a>, P81 (CO2<\/sub> Surface Facilities)<\/a>, and PF4 (Oil Production and Processing Facilities)<\/a> courses.<\/p>\n John M. Campbell Consulting (JMCC) offers consulting expertise on this subject and many others. For more information about the services JMCC provides, visit our website at\u00a0www.jmcampbellconsulting. <\/p>\n By: Dr. Mahmood Moshfeghian<\/em><\/strong><\/p>\n Reference:<\/strong><\/p>\n Hydrocarbons are frequently produced with non-hydrocarbon impurities. The most common include water, carbon dioxide, hydrogen sulfide and nitrogen. We have already discussed water-hydrocarbon phase behavior in detail in the October and November 2007 Tips of the Month (TOTM). Since water has a low vapor pressure and is virtually immiscible in the hydrocarbon liquid phase, it […]<\/p>\n","protected":false},"author":23,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"nf_dc_page":"","_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_feature_clip_id":0,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":false,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2},"jetpack_post_was_ever_published":false},"categories":[3,10],"tags":[],"coauthors":[15],"class_list":["post-1352","post","type-post","status-publish","format-standard","hentry","category-gas-processing","category-process-facilities"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_shortlink":"https:\/\/wp.me\/p1pQc4-lO","jetpack_sharing_enabled":true,"_links":{"self":[{"href":"http:\/\/www.jmcampbell.com\/tip-of-the-month\/wp-json\/wp\/v2\/posts\/1352","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/www.jmcampbell.com\/tip-of-the-month\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/www.jmcampbell.com\/tip-of-the-month\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/www.jmcampbell.com\/tip-of-the-month\/wp-json\/wp\/v2\/users\/23"}],"replies":[{"embeddable":true,"href":"http:\/\/www.jmcampbell.com\/tip-of-the-month\/wp-json\/wp\/v2\/comments?post=1352"}],"version-history":[{"count":2,"href":"http:\/\/www.jmcampbell.com\/tip-of-the-month\/wp-json\/wp\/v2\/posts\/1352\/revisions"}],"predecessor-version":[{"id":1471,"href":"http:\/\/www.jmcampbell.com\/tip-of-the-month\/wp-json\/wp\/v2\/posts\/1352\/revisions\/1471"}],"wp:attachment":[{"href":"http:\/\/www.jmcampbell.com\/tip-of-the-month\/wp-json\/wp\/v2\/media?parent=1352"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/www.jmcampbell.com\/tip-of-the-month\/wp-json\/wp\/v2\/categories?post=1352"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/www.jmcampbell.com\/tip-of-the-month\/wp-json\/wp\/v2\/tags?post=1352"},{"taxonomy":"author","embeddable":true,"href":"http:\/\/www.jmcampbell.com\/tip-of-the-month\/wp-json\/wp\/v2\/coauthors?post=1352"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}![\"\"](\"https:\/\/i0.wp.com\/www.jmcampbell.com\/tip-of-the-month\/wp-content\/uploads\/2012\/04\/1.png\" "\\"1\\"")
<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/strong><\/p>\n\n