Pt. McIntyre: A Case Study of Gas Enrichment Above MME
- Timothy P. Moulds (BP plc) | Patrick L. McGuire (BP Exploration Alaska Inc.) | Gary Jerauld (BP) | Sheng-Tai Lee (BP plc) | Reinel Solano (BP plc)
- Document ID
- Society of Petroleum Engineers
- SPE Reservoir Evaluation & Engineering
- Publication Date
- June 2005
- Document Type
- Journal Paper
- 182 - 188
- 2005. Society of Petroleum Engineers
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- 470 since 2007
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Pt. McIntyre field operates an enriched-gas-injection scheme that displacesoil in a multicontact miscible (MCM) displacement achieved through a combinedcondensing/ vaporizing (C/V) mechanism. A range of miscible-injectant (MI)compositions, varying from the minimum miscible enrichment (MME) tosubstantially above the MME, is available to the project. Field-scalenumerical-simulation studies for the Pt. McIntyre field show that incrementaloil recovery is nearly doubled when using the richest available MIcomposition.
At the MME, dispersion can act to substantially reduce oil recovery byreducing the concentration of enriching components in the near-miscible zone.Increasing enrichment above the MME compensates for this action. Accuratepredictions of incremental oil depend on the numerical dispersion in asimulator being able to match the impact of physical dispersion. We show howcompositional core data from an MI-swept interval provide confirmation of theimpact of dispersion at field scale and demonstrate the appropriateness of thesimulation model. The benefit of enrichment appears to be robust to thevariation of reservoir description found at Pt. McIntyre and to whether the MIapplication targets incremental oil through liquid- or vapor-phaserecovery.
Previous studies into MI enrichment have reported that for a four-componentsystem, the mechanism changes from C/V to purely condensing as the enrichmentlevel approaches first-contact miscibility (FCM). We show that with theaddition of a small amount of heavy component, the C/V behavior is retainedwith increasing enrichment until transition into FCM. This makes it unlikelythat a transition to a purely condensing mechanism will occur in realreservoirs.
The Pt. McIntyre field, located on the north coast of Alaska, was discoveredin 1988 and contains an estimated 800 million bbl. Production began in 1993,and the current production rate is approximately 55,000 STB/D. The field has agas cap, and production is by gravity drainage in the region underlying the gascap and by waterflood in the wedge zone. From inception, it has been planned toincrease recovery from the waterflood region by means of an enriched-gas-driveflood. The field has been maintained at original pressure with voidagereplacement by water injection.
The productive interval in the Pt. McIntyre field is the Kuparuk formation.The reservoir has moderate permeability and typically is approximately 300 ftthick. The oil is 27 degrees API.
The Pt. McIntyre field is produced into a common export system, theTrans-Alaska Pipeline System, and is surrounded by several other producingfields. Although limited in the amount of enriching components available fromits own production, additional enriching components can be obtained byagreement with nearby fields. This provides greatly increased flexibility toselect the MI enrichment level that optimizes field performance.
Previous studies of MCM gas-injection schemes have reported results forfield-scale simulation models that show a significant increase in oil recoverywith enrichment above the MME. This is contrary to the much-studied 1Dlaboratory scale approach to miscibility that shows a negligible oil-recoveryincrease for enrichment above the MME. The difference between the impact ofenrichment at laboratory-scale and field-scale behavior is caused by thegreater dispersion in field-scale systems. Unfortunately, the magnitude offield-scale physical dispersion is uncertain. The concern exists thatfield-scale numerical-simulation results are reporting the impact of dispersioncaused by numerical truncation errors rather than physical effects and,consequently, may overstate the benefit of MI enriched above the MME. Here, weuse compositional core data to show that the dispersion assumptions in thefield-scale models are appropriate.
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