PRIMARY RECOVERY MECHANISM

PRIMARY RECOVERY MECHANISM

1. PERFORMANCE CHARACTERISTICS

   • Ultimate recovery factor
   • Press decline rate
   • GOR
   • Water Production

2. Recover oil by natural drive mechanisms

3. Production of HC without add extra energy to reservoir

4. NATURAL DRIVES

   • COMPACTION DRIVE
     • rock & liquid expansion
     • materials present: crude oil, connate water, rock
     • as reser. press decr. -> rock& fluid expand due to their compressibilities-> grains expand-> bulk volume incr. -> reduce poro/pore V + fluid expand -> oil & water force out of pore space to wellbore
     • liquids & rock: slightly compressible -> can overcome the press drop due to production-> rapid press decline during production
     • constant GOR = gas solubility at bubble point press
     • least effective drive: only recover small % OIIP
   • DEPLETION DRIVE
     • As production, Press decr. < bubble Press -> gas form (GAS LIBERATION from oil)+ expand -> push oil to wellbore -> incr. oil production-> until reach critical press-> gas get inside wellbore instead of oil-> reduce oil production
     • also called SOLUTION GAS /DISSOLVED GAS/ INTERNAL GAS
     • press decr. rapidly & continuously. little/no water production. rapid inc. GOR . rapid incr. oil production until reach critical press at which rapid decr.
     • 5-30% recovery OIIP, best for secondary recovery
   • GAS CAP DRIVE
     • As press decr. during production -> gas cap expand (gas expand to occupied V loss by oil produced + gas liberate from oil) to maintain press -> push the oil to well bore
     • Develop wells positions: drills many wells at different depth -> determine GOR production from these wells -> shut down wells which produced excessive gas or use to re-inject gas back to reservoir
     • present of a gas cap with little/no water drive
     • Press fall slow, continuously. no/little water produce. GOR rise continuously
     • 20-40%,larger recovery than depletion drive
     • incr. size of gas cap, high vertical permeability, low oil viscosity -> greater Gas cap drive -> inc. recovery % OIIP
   • WATER DRIVE
     • as production, Press decr. & V of oil decr. -> water replace oil V (water move into pore space)-> maintain press -> push oil to wellbore
     • as compactivity of water < oil, water source in reser. need to connect to a large water body
     • At water invaded zone, polymers can be inject to inc. viscosity so the water can get through oil to wellbore
     • Gradual press decline (water maintain press drop). little change in GOR.
     • much higher recovery % OIIP than other drives. 35-75%
   • GRAVITY-DRAINAGE DRIVE
     • need a slow flowrate of production for gas to have time to move up to the gas cap
     • As production, press decr. -> gas lubricate from oil -> go up to gas cap due to gravity (gas density < oil density) -> opposite force push oil down & into wellbore
     • bigger gas cap -> greater gravity-drainage drive
     • occur as result of difference densities of reser. fluids
     • rapid press decr. Low GOR. form secondary gas cap in undersaturated reser. little/no water produce.
     • can excess 80% recovery OIIP
   • COMBINATION DRIVE
     • combination of different natural drives in one reservoir