lift Comparison gas based of deliquification deliquification methods

Transcription

1 lift Comparison gas based of deliquification lift gas based deliquification methods, Berend Brasjen, Stefan Belfroid (TNO) Kees Veeken, Frans Hollman (NAM)

2 2 Goal of Study Develop models for five methods that make use of HP (lift) gas Gas lift Wellhead eductor (jet pump) Downhole eductor Combination of wellhead eductor and gas lift Combination of wellhead and downhole eductor Compare ultimate recovery, production period and injection volume as function of Tubing size Inflow performance Water-gas ratio Maximum lift gas to reservoir gas ratio (economic limit)

3 3 System Model Reservoir model Tank Well model Darcy inflow model P res2 -FBHP 2 = A.Q Modified Gray outflow model THP = DTHP wet gas BHP (THP, ) P res, A DTHP= 15 bara Fixed pressure downstream of tubing head Wet gas with constant WGR from reservoir Dry gas for injection, available up to economic limit

4 4 System Parameters Tubing size: ID = Water-Gas Ratio: WGR = m 3 /10 6 Sm 3 Inflow performance: A = bar 2 /(10 3 Sm 3 /d) Economic limit: lift gas to reservoir gas ratio = 2 32

5 5 Base Case Input BHP vs, THP, WGR, CGR for 4.4 and 6.0 ID P res, GIIP, A For given THP, WGR, CGR Select BHP ( ) curve Calculate corresponding P res (P res ) From initial P res, GIP Interpolate (P res ) Update P res (GIP ) Iterate until too low to yield solution (a) BHP (b) P res, BHP (c) Q (d) P res, Q Q Q P res t

6 6 Gas Lift Lift gas injected downhole, mixed and transported with production gas THP = DTHP Q tot = + Q inj + Q inj DTHP= 15 bara P lift = 60 bara Available pressure: 60 bara + gravity head Gravity head If BHP > available pressure, wet + dry gas performance computed without gas lift BHP (THP, Q tot ) Q inj P res, A

7 7 Wellhead and Downhole Eductor Q tot = + Q inj DTHP= 15 bara Q tot = + Q inj DTHP= 15 bara THP (DTHP, Q inj ) Q inj P lift = 60 bara THP = DTHP P lift = 60 bara Gravity head wet gas wet + dry gas BHP (THP, ) P 2 (THP, Q tot ) Q inj P res, A BHP (P 2, Q inj ) P res, A

8 8 Combinations Q tot = + Q i1 + Q i2 WHP= 15 bara Q tot = + Q i1 + Q i2 WHP= 15 bara THP (WHP, Q i1 ) Q i1 P lift = 60 bara THP (WHP, Q i1 ) Q i1 P lift = 60 bara Gravity head Gravity head wet + dry gas wet + dry gas BHP (THP, +Q i2 ) Q i2 P 2 (THP, +Q i2 ) Q i2 P res, A P res, A BHP (P 2, Q i2 )

9 9 Deliquification Lift gas is dry lower WGR, CGR For same THP, interpolate BHP ( ) Wellhead eductor lowers THP For same WGR,CGR, THP from eductor model Interpolate BHP ( ) (a) BHP (b) P res, BHP (c) Q Q Downhole eductor lowers BHP and adds dry gas lower WGR, CGR even lower BHP For same THP, interpolate downstream BHP ( ) curve From eductor model, upstream BHP ( ) Q (d) Q P res t

10 10 Eductor Models a b ESDU constants vary linear with mass flow ratio injection DTHP q inj / q prod production Good agreement between ESDU and Caltec ESDU model more conservative on eductor benefit THP [bara] q inj = MSm 3 /d 1.0 MSm 3 /d 2.0 MSm 3 /d 3.0 MSm 3 /d q [10 6 Sm 3 /d] prod

11 11 Gas Lift Injecting dry gas lowers effective WGR Low lift gas rate: TPC shifts to left Higher lift gas rate Additional frictional pressure drop dominates TPC minimum beyond economic limit WGR [m 3 /(10 6 Sm 3 )] BHP [bara] q prod [10 6 Sm 3 /d] q prod [10 6 Sm 3 /d]

12 12 16 Wellhead Eductor Wellhead eductor lowers tubing head pressure no extra gas in well WGR remains unaltered Low injection rates: BHP significantly reduced High injection rates: economic limit prohibits eductor operation THP [bara] BHP [bara] q inj = MSm 3 /d 0.1 MSm 3 /d 0.25 MSm 3 /d 0.75 MSm 3 /d q prod [10 6 Sm 3 /d] Economic limit Increasing eductor rate q inj = MSm 3 /d 0.1 MSm 3 /d 0.25 MSm 3 /d 0.75 MSm 3 /d q prod [10 6 Sm 3 /d]

13 13 Downhole Eductor Downhole eductor lowers BHP and adds lift gas to well Pressure downstream of eductor determined by well flow (gas lift effect) Low injection rate: TPC shifts to left and down BHP [bara] q inj = MSm 3 /d 0.1 MSm 3 /d 0.25 MSm 3 /d 0.75 MSm 3 /d Increasing eductor rate More production from reservoir High injection rate Friction dominated q prod [10 6 Sm 3 /d]

14 14 Optimization Optimize ultimate recovery (UR) Simulate production evolution at constant injection rate Select injection rate with highest UR Optimize capacity and UR For each time step (here: 1 day) select injection rate with highest production for P res at that moment Same UR (since production terminated by loading) Shorter time (high injection boosts early-stage production) Larger cumulative injection rate

15 17 Optimize Deliquification [3] Wellhead eductor increases production but requires high injection volumes Downhole (DH) eductor only available for low production extends production time rather than increasing production, Q inj (10 6 Sm 3 /d) Economic limit ID = 4.4, WGR = 50, A = 10, EL = t (d) x 10 4, Q inj (10 6 Sm 3 /d) no deliquification, gas lift Q inj, gas lift, wh eductor Q inj, wh eductor, dh eductor Q inj, dh eductor, wh eductor+lift Q inj, wh eductor+lift, wh + dh eductor Q inj, wh+dh eductor

16 19 Deliquification Performance Method RF [%] RF Gain [%] Time [yr] Time Gain [yr] V inj [10 6 Sm 3 ] No deliquification Gas lift Wellhead eductor Downhole eductor WH eductor + Gas lift WH eductor + DH eductor

17 20 Deliquification Summary Gas lift requires comparatively small amount of HP lift gas Wellhead eductor attains UR comparatively quick Downhole eductor yields largest UR Wellhead eductor + gas lift Increases UR, production time and injection volume Wellhead eductor + downhole eductor UR same as for downhole eductor Shorter production time than downhole eductor Injection volume comparable to wellhead eductor (>> downhole)

18 21 Influence of Tubing ID Larger ID results in a lower UR (higher critical rate) Downhole eductor remains most effective strategy

19 22 Influence of WGR Increasing WGR decreasing UR (higher critical rate) Strategies with downhole dry lift gas (downhole eductor, gas lift) are less sensitive to WGR due to low effective WGR in tubing

20 23 Influence of Inflow A Factor UR decreases as A factor increases (higher drawdown pressure) Strategies with downhole dry lift gas are less sensitive as drawdown plays less of role Gas lift becomes more effective than wellhead eductor at higher A

21 25 Summary and Outlook Evaluated five methods that make use of HP lift gas i.e. gas lift, wellhead eductor, downhole eductor and combinations GL + WH ed. and WH ed. + DH ed. Downhole eductor achieves maximum recovery, surpassing combination of gas lift and wellhead eductor Gas lift requires lowest lift gas volume, achieving significant recovery Working towards DH gas eductor field implementation Interested in DH gas eductor hardware solutions