Transforming Challenges into Opportunities:First High Salinity PolymerInjection Deployment in a Sour Sandstone Heavy Oil Reservoir

摘要

This paper describes the design and implementation of a one-spot enhanced oil recovery(EOR)pilot usinghigh-salinity water(~166,000 ppm TDS)in a sour,sandstone,heavy-oil reservoir(~5 mol% hydrogensulfide)based on an extensive laboratory study involving different polymers and operating conditions.Inview of the results of this one-spot EOR pilot,a multi-well,high-salinity polymer-injection pilot is expectedto start in 2020 targeting the Umm Niqqa Lower Fars(UNLF)reservoir in Kuwait.Polymer flooding is normally carried out using low-to moderate-salinity water to maintain favorablepolymer solution viscosities in pursuit of maximum oil recovery.Nevertheless,low-to moderate-salinitywater sources such as seawater tend to be associated with a variety of logistical,operational,and commercialchallenges.For this study,laboratory experiments were conducted in conjunction with reservoir simulationto confirm the technical viability of polymer flooding using high-salinity water.Thereafter,a one-spot EORpilot was executed in the field using a well near the location of the planned multi-well pilot to confirm theperformance of the selected polymer vis-à-vis injectivity and oil desaturation.The one-spot EOR pilot described in this paper was successfully executed by performing two Single-WellChemical Tracer(SWCT)tests.For the first stage of the pilot,200 bbl of produced water(up to 166,000 ppmTDS)were injected into the test well in an attempt to displace mobile oil out of the investigated pore space.Following this produced water injection,an SWCT test(Test #1)was carried out and measured the remainingoil saturation to be 0.41 ± 0.03.This saturation measurement represents the fraction of oil remaining in thepore space of a cylindrical portion of the Lower Fars reservoir,measured from the wellbore out to a radiusof 3.02 feet,after produced water injection.After the completion of Test #1 and subsequent recovery of theinjected produced water,the same zone was treated with a 200-bbl injection of polymer solution.Followingthis 200-bbl polymer injection,a second SWCT test(Test #2)was performed and measured the remainingoil saturation to be 0.19 ± 0.03 out to a radius of 3.38 feet.These results indicate that polymer injection mayoffer considerable improvement to oil recovery over conventional waterflooding alone.Performing polymer flooding in a sour,heavy-oil reservoir using high-salinity water is a challenging andunprecedented undertaking worldwide.In addition to the improved incremental oil recovery demonstratedby this pilot,enabling the use high-salinity produced water for polymer flooding is expected to result insignificant benefits for cost-efficiency and operational ease by reducing or eliminating problems commonlyassociated with the sourcing,treatment,and handling of less saline water in the field.