Evaluation of Flare Gas and Flue Gas Injection for EOR

Evaluation of Flare Gas & Flue Gas Injection for EORTjokorde W. Samadhi, Stephanie L.U. Sutoko & Utjok W.R. Siagian*

Chemical Engineering Program*Petroleum Engineering ProgramBandung Institute of TechnologyFossil fuel trends in IndonesiaDecline in oil & gas productionIndonesia has become net oil importer since 2004Increasing demand for petroleum fuelFlare gas emissions from oil & gas production sector is very significantRanked 4th in total gas flaring volume in 2003

(Pallone, 2009)Miscible Gas Flooding EORMGF-EOR relies on the flooding of oil reservoir with an injection gas at high PDissolution of the gas in the oil increases oil mobilityUse of waste gases as injection gasopportunity to reduce gas flaring while increasing oil production!

(Ref.: Amarnath, 1999)BackgroundFeasibility of an MGF-EOR system is reflected upon its minimum miscibility pressure (MMP)Threshold value at which a complete, multiple-contact miscibility between injection gas & trapped oil is achievedPrevious study has highlighted the excessive MMP in flare gas injectionhigher compression costspotential damage to reservoir formationHigh methane content of flare gas inflates the MMPObjectives & ScopeEvaluates effect of adding flue gas to flare gas on the miscibility development of a model oilIncreased CO2 content from flue gas is expected to lower MMPEmploys a simulative approach using the multiple-mixing cell modelMaterial streams:Model oil: 45% n-C5H12 - 57% n-C16H34Model flare gas: 91% CH4 - 9% C2H6Model flue gas: 79% N2 21% CO2System temperature: 323.15 K

Multiple-mixing Cell ModelContact between injection gas & oil is represented by a series of equilibrium mixing cellsExcess fluid from a cell is transferred to the next cellEquilibrium tie lines are identified in each cell by P,T-flash calculation VLE compositions are calculated using Peng-Robinson EoSMMP computation package developed on Fortran platform

MMP DeterminationFor system with n components, gas miscibility is controlled by (n-1) key tie linesWhen P is increased, length of key tie lines decreasesAt MMP, one of the key tie lines becomes critical (approaching zero length)

Results Flare gas injection

3 key tie lines are identified as constant-length zonesshortest line (crossover TL) becomes critical as P is increasedMMP ~ 35.8 MPa

Tie line length vs. cell number computed for injection of flare gas (91% CH4 9% C2H6) to model oil (43% C5 57% C16) T = 323.15 K, P = 34 MPa

Results Flare-flue gas injection

C5-C16 model oil injection by 50/50% flare-flue gas mixture at 323.15K & 10 MPa

In mixed flare-flue gas injection, a crossover tie line is the critical tie lineAt 50/50% flare-flue gas composition, MMP~61.1 MPaCO2 enhancement of flare gasCO2 enhancement of flare gas attempted by mixing with flue gas & pure CO2flue gas addition dramatically increases MMP due to high N2 critical pressurecomputation failed at flue gas content > 50%flue gas is an unlikely source for CO2 enhancement of flare gas

Summary & AcknowledgmentCombining flare gas with flue gas for MGF-EOR injection gas produces unacceptably high MMPWhile flue gas does contain a substantial amount of CO2, the effect of high-critical pressure N2 predominatesThe feasibility of using flare gas as an injection gas is contingent upon the availability of a relatively pure CO2 to reduce MMP

This research has been funded by the Osaka Gas Foundation for International Cultural Exchange Research Grant 2012