From Concept to Pilot to Full-Field Implementation: A New EOR Process for thePrudhoe Bay Field

摘要

The uppermost 200 ft of the main pay interval at Prudhoe Bayrnis a moderate permeability, high net-to-gross fluvial sandstonernwhich contains a number of thin, discontinuous shales. Mostrnof this interval is being produced by waterflood and misciblerngas WAG, but the updip third of Zone 4 has been produced byrngravity drainage since 1977 and is very mature.rnFullfield models and material balance estimates indicatedrngood recovery in the updip area. One Zone 4 core was taken inrnthe gravity drainage area and one was taken in thernwaterflood/WAG area. Both cores were history matched withrna reservoir simulator to determine the ultimate recoveryrnpotential of the process currently being employed. Detailedrnsimulations indicated that the gravity drainage process wasrnleaving high oil saturations behind the gas front which couldrnnot be produced economically because of excessive gas-oilrnratios (GORs). Both water injection and miscible gas injectionrnmobilized large volumes of oil and dramatically reduced thernGOR.rnThe Updip Zone 4 Injection Project (UZI) is designed tornmobilize and capture remaining oil trapped above the currentrngas-oil contact. In the updip area, both water and misciblerninjectant (MI) have been injected in Zone 4 while maintainingrngravity drainage in the lower intervals (Zones 2 and 3). UZIrnpatterns employ MI in a unique, highly efficient, single-slugrnoil swelling process rather than as a tertiary WAG. UZIrninjection has mobilized large volumes of oil and dramaticallyrnreduced GORs. The 14-01A pilot has produced roughly 2,000rnBOPD of additional oil for the last 5 years from MI injectionrninto a previously gassed-out producer. Total incremental oilrnfrom the MI pilot is approximately 3.5 MMBO.The 1-11 water injection pilot is another success, with fivernof the eight offset wells producing an incremental 960 BOPDrnand 35 MMscf/D less gas. This major reduction in gasrnproduction has allowed increased production of about 700rnBOPD from other Prudhoe Bay wells. A tracer program in thernwaterflood pilot has verified water containment within Zone 4.rnBased on this success, the Prudhoe Bay Unit has beenrnexpanding the UZI Project. Ten UZI patterns are alreadyrndeveloped in the Eileen West End area. In the mainfield area,rnfour patterns are currently on-line with another four patternsrnapproved.rnThis paper briefly reviews the core analysis data and thernreservoir simulation history match of the two Zone 4 cores andrnthe process comparison studies. Production data from thernupdip waterflood and miscible gas flood pilot tests isrnpresented, as is the performance of the early UZI patterns.