CO2 Foam Field Pilot Design and Initial Results

摘要

This paper presents the field design,monitoring program,and initial results from a CO2 foam pilot in EastSeminole Field,Permian Basin,USA.Tertiary miscible CO2 injection has suffered from poor areal sweepefficiency due to reservoir heterogeneity and an unfavorable mobility ratio between CO2 and reservoirfluids.A surfactant-stabilized foam was selected to reduce CO2 mobility for increasing oil recovery and CO2storage potential in an inverted 40-acre five spot well pattern.The foam system was designed to maximizethe success of foam generation through surfactant screening and optimizing surfactant concentration andfoam strength.Previous work identified a water-soluble,non-ionic surfactant at a concentration of 0.5weight percent(wt%)and 70% foam quality for the pilot.A surfactant-alternating-gas(SAG)injectionstrategy,consisting of 10 days of surfactant solution injection followed by 20 days of CO2,began in May2019.Baseline CO2 injection profiles,tracer tests,injection bottom hole pressures,and flow rates were collectedfor comparison to pilot surveys.The pilot monitoring program included repeat injection profiles,tracertests,three-phase production monitoring,and collection of downhole pressure data for evaluation ofreservoir response to foam injection.Produced fluids were also collected for chemical analysis to determinesurfactant breakthrough time.A field injection unit was designed to meet the requirements of surfactantdelivery,mixing,and storing.A methodology was also established to effectively validate foam formulationconsistency in the field.Initial results revealed that pilot CO2 injectivity was reduced by 70%,compared to baseline CO2injection,indicating reduced CO2 mobility after each surfactant slug.Baseline and pilot injection profilesshow increased flow into the reservoir interval and potential blockage of a high permeability streak.Thebaseline CO2 tracer test measured CO2 breakthrough in 22 days,in one of the pattern producers.Expectedbreakthrough,based upon simulation,is 66 days during the pilot,which will be verified by a repeat tracertest at the end of the pilot.Production response is not expected for another six to nine months due to thevolumes injected during the pilot.However,the early signs of sustained oil production despite less volumeinjected during the pilot indicate an initial positive response to foam.