Simulation Study of Miscible Water-Alternating-Gas Injection in a Stratified Reservoir Model Input parameters based on literature data Jan Inge Nygård (author) Pål Østebø Andersen (supervisor) Kenny Walrond (co-supervisor)
1 WAG cycle WAG ratio Half-cycle of gas Injection rate (rm3/d) Duration (days) Volume of gas injected Half-cycle of water Volume of water Gas Water
𝑊𝐴𝐺 𝑐𝑦𝑐𝑙𝑒 𝑙𝑒𝑛𝑔𝑡ℎ= 𝐷𝑢𝑟𝑎𝑡𝑖𝑜𝑛 𝑤𝑎𝑡𝑒𝑟 + 𝐷𝑢𝑟𝑎𝑡𝑖𝑜𝑛 𝑔𝑎𝑠 1 WAG cycle WAG ratio Half-cycle of gas Injection rate (rm3/d) Duration (days) Volume of gas injected Half-cycle of water Volume of water For all scenarios studied in this work; WAG cycle length is 90 days Total volume injected per WAG cycle is also constant Injection occurs at miscible conditions What is the effect of changing injection rates and duration of half-cycles, while WAG ratio is kept constant? Is this effect present in different types of reservoirs? 𝑊𝐴𝐺 𝑟𝑎𝑡𝑖𝑜= 𝑉𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑤𝑎𝑡𝑒𝑟 𝑉𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑔𝑎𝑠 = (𝐼𝑛𝑗.𝑟𝑎𝑡𝑒∗𝐷𝑢𝑟𝑎𝑡𝑖𝑜𝑛) 𝑤𝑎𝑡𝑒𝑟 (𝐼𝑛𝑗.𝑟𝑎𝑡𝑒∗𝐷𝑢𝑟𝑎𝑡𝑖𝑜𝑛) 𝑔𝑎𝑠 = 𝑅 𝑤 ∗ 𝑇 𝑤 𝑅 𝑔 ∗ 𝑇 𝑔
Visual representation of WAG ratios We study WAG ratios 1:1, 1:2 and 2:1 Water Gas WAG ratio 1:2 Water Gas WAG ratio 1:1 Water Gas WAG ratio 2:1 Water Gas half-cycle Water half-cycle Water half-cycle Gas half-cycle One WAG cycle consists of one water half-cycle and one gas half-cycle
Waterflood vs Miscible WAG Sorw = 0.31 Residual oil saturation (Sor) after waterflood Soi = 0.81 Initial Oil In Place (IOIP) Sorg = 0.00 Residual oil saturation (Sor) after miscible gasflood Soi = 0.81 Initial Oil In Place (IOIP) Distribution of oil saturation at point of gas breakthrough Homogeneous model Case 82
Gasflood vs WAG Sorg = 0.00 Soi = 0.81 Residual oil saturation (Sor) after miscible gasflood Soi = 0.81 Initial Oil In Place (IOIP) Distribution of oil saturation at point of gas breakthrough Homogeneous model Case 82
Oil Recovery Efficiency Factor Gas- and waterflood vs WAG Gasflood WAG Waterflood Increased recovery Oil Recovery Efficiency Factor Time
Ranking of WAG cases A sample of the dataset Case Figure name WAG ratio Total simulation time (days) Oil Recovery Efficiency (FOE) FOE per year (%) Gas produced, cum (10^6 Sm3) Water produced, cum (10^6 Sm3) Gas-Oil-Ratio (GOR) PVs injected Performance Number of WAG cycles 102 w60-1500_g30-1500_h 2:1 5478 0,65755 4,38 1873,70 1,058 232 0,800 25,58 60 100 w45-2000_g45-1000_h 5844 0,65226 4,07 1919,92 1,004 240 0,810 23,47 64 101 w30-3000_g60-750_h 7121 0,64724 3,32 2167,25 0,875 273 0,860 17,98 79 82 w45-1500_g45-1500_h 1:1 6574 0,66027 3,67 2994,93 1,090 370 0,989 17,93 73 84 w60-1125_g30-2250_h 6847 0,65846 3,51 2795,54 1,088 346 1,028 16,85 76 83 w30-2250_g60-1125_h 7213 0,65323 3,31 2980,59 1,045 372 1,040 15,48 80 92 w30-1500_g60-1500_h 1:2 9496 0,68073 2,62 5451,92 1,095 653 1,435 8,16 105 93 w60-750_g30-3000_h 9586 0,66279 2,52 4951,60 1,092 609 1,446 7,96 106 91 w45-1000_g45-2000_h 9677 0,65923 2,49 4917,40 1,093 608 1,460 7,75 107 𝑃𝑒𝑟𝑓𝑜𝑟𝑚𝑎𝑛𝑐𝑒 𝑓𝑎𝑐𝑡𝑜𝑟= 𝐹𝑂𝐸+𝐹𝑂𝐸∗ 𝑃𝑉 𝑖𝑛𝑗𝑒𝑐𝑡𝑒𝑑 𝑑𝑎𝑦𝑠+𝑑𝑎𝑦𝑠∗( 𝑃𝑉 𝑖𝑛𝑗𝑒𝑐𝑡𝑒𝑑 −1) ∗ 10 5 − 𝑐𝑢𝑚𝑢𝑙𝑎𝑡𝑖𝑣𝑒 𝑔𝑎𝑠 𝑝𝑟𝑜𝑑𝑢𝑐𝑒𝑑 𝐹𝑂𝐸∗2000 The performance factor values oil recovery differently depending on Pore-volume (PV) size injected Number of days of simulation to reach given result Gas production Example: Same oil recovery achieved with a lower PV size is ranked higher
Homogeneous model Increasing up model Permeability ranges from 10 to 500 milli Darcy Kv/Kh = 0.5, ie. vertical permeability 50 % to that of horizontal permeability 30 % porosity Dimensions: 1050m*1050m*60m Variable model Increasing down model
Gas saturation distribution at gas breakthrough Homogeneous model Increasing up model Permeability ranges from 10 to 500 milli Darcy Here showcasing four different models at WAG ratio 1:1 500 mD 10 mD 250 mD Variable model Increasing down model 10 mD 500 mD 500 mD 100 mD 20 mD
Comparing all four models with WAG ratio 1:1 Cumulative gas production Oil Recovery Efficiency Factor Increasing down Models: Homogeneous Variable Increasing up Time Time
Oil Recovery Efficiency Factor Comparing performance impact of different WAG ratios Oil Recovery Efficiency Factor Increasing up model 2:1 1:1 1:2 Time
Oil Recovery Efficiency Factor Gas- and waterflooding compared to different WAG ratios Oil Recovery Efficiency Factor Increasing up model 2:1 1:1 1:2 Waterflood Gasflood Time
The effect of changing gas injection rate, for a WAG ratio of 1:1 Increasing up model The effect of changing gas injection rate, for a WAG ratio of 1:1 Water Gas WAG ratio 1:1 Cumulative gas production Oil Recovery Efficiency Factor Lower gas production Higher oil recovery Low gas rate High gas rate Low gas rate High gas rate Time Time
The effect of changing gas injection rate, for a WAG ratio of 1:2 Increasing up model The effect of changing gas injection rate, for a WAG ratio of 1:2 Cumulative gas production Oil Recovery Efficiency Factor Water Gas WAG ratio 1:2 Lower gas production Unchanged oil recovery Low gas rate High gas rate Low gas rate High gas rate Time Time
The effect of changing gas injection rate, for a WAG ratio of 2:1 Increasing up model The effect of changing gas injection rate, for a WAG ratio of 2:1 Water Gas WAG ratio 2:1 Lower gas production Higher oil recovery Faster production Cumulative gas production Oil Recovery Efficiency Factor Increasing gas rate Decreasing water rate Time Time
The effect of changing gas injection rate, for a WAG ratio of 1:1 Increasing down model The effect of changing gas injection rate, for a WAG ratio of 1:1 Water Gas WAG ratio 1:1 Cumulative gas production Oil Recovery Efficiency Factor Higher gas rate; Lower gas production Faster production Equal gas and water rate; Higher gas production Higher oil recovery Low gas rate Equal rates High gas rate Low gas rate Equal rates High gas rate Time Time
The effect of changing gas injection rate, for a WAG ratio of 1:2 Increasing down model The effect of changing gas injection rate, for a WAG ratio of 1:2 WAG ratio 1:2 Cumulative gas production Oil Recovery Efficiency Factor Water Gas Higher gas rate; Unchanged gas production Higher oil recovery Equal gas and water rate; Higher gas production Highest oil recovery Equal rates Low gas rate High gas rate Equal rates Low gas rate High gas rate Time Time
The effect of changing gas injection rate, for a WAG ratio of 2:1 Increasing down model The effect of changing gas injection rate, for a WAG ratio of 2:1 Cumulative gas production Oil Recovery Efficiency Factor Water Gas WAG ratio 2:1 Lower gas production Higher oil recovery Faster production Increasing gas rate Decreasing water rate Time Time
Conclusion part 1 of 2 For a fixed WAG ratio Injection scheme We have seen how changing injection rate and duration of half-cycles can alter production performance This means that it is important to consider how the WAG ratio is used This effect is strongest for WAG ratio 2:1 This effect is observed throughout all four reservoir models Injection scheme Optimal WAG ratio was not 1:1 Optimal WAG ratio was 2:1 and 1:2, when equal injection rates were used 2:1 Highest performance factor rating (ie. faster production over 5000 days) 1:2 Highest oil recovery efficiency factor (ie. slower production over 9000 days) Changing injection rate and duration of injection, while keeping the same WAG ratio, does affect the performance of Water-Alternating-Gas technique
Conclusion part 2 of 2 Performance factor Was developed by me to rank over 100 different injection schemes These are successfully ranked, considering: Oil recovery efficiency factor Pore-volume (PV) size injected Number of days of simulation Gas production Other factors may also be implemented in order to alter the rating behaviour Changing injection rate and duration of injection, while keeping the same WAG ratio, does affect the performance of Water-Alternating-Gas technique
References Eclipse Technical Description, version 2014.2 Fifth Comparative Solution Project (SPE 5), for PVT properties Data from pore-network simulation data of Skauge (2011), for relative permeability and capillary pressure curves
𝑊𝐴𝐺 𝑐𝑦𝑐𝑙𝑒 𝑙𝑒𝑛𝑔𝑡ℎ= 𝐷𝑢𝑟𝑎𝑡𝑖𝑜𝑛 𝑤𝑎𝑡𝑒𝑟 + 𝐷𝑢𝑟𝑎𝑡𝑖𝑜𝑛 𝑔𝑎𝑠 Backup 𝑊𝐴𝐺 𝑐𝑦𝑐𝑙𝑒 𝑙𝑒𝑛𝑔𝑡ℎ= 𝐷𝑢𝑟𝑎𝑡𝑖𝑜𝑛 𝑤𝑎𝑡𝑒𝑟 + 𝐷𝑢𝑟𝑎𝑡𝑖𝑜𝑛 𝑔𝑎𝑠 1 WAG cycle WAG ratio Half-cycle of gas Injection rate (rm3/d) Duration (days) Volume of gas injected Half-cycle of water Volume of water 𝐼𝑛𝑗.𝑟𝑎𝑡𝑒 𝑔𝑎𝑠 =1500 𝑟𝑚 3 /𝑑 𝐷𝑢𝑟𝑎𝑡𝑖𝑜𝑛 𝑔𝑎𝑠 =45 𝑑𝑎𝑦𝑠 (𝑑) 𝐼𝑛𝑗.𝑟𝑎𝑡𝑒 𝑤𝑎𝑡𝑒𝑟 =1500 𝑟𝑚 3 /𝑑 𝐷𝑢𝑟𝑎𝑡𝑖𝑜𝑛 𝑤𝑎𝑡𝑒𝑟 =45 𝑑𝑎𝑦𝑠 (𝑑) Example 1 𝑊𝐴𝐺 𝑟𝑎𝑡𝑖𝑜= 1500∗45 1500∗45 = 67 500 𝑟𝑚 3 67 500 𝑟𝑚 3 => 1:1 ratio 𝑊𝐴𝐺 𝑐𝑦𝑐𝑙𝑒 𝑙𝑒𝑛𝑔𝑡ℎ=45𝑑+45𝑑=90𝑑 𝐼𝑛𝑗.𝑟𝑎𝑡𝑒 𝑔𝑎𝑠 =1125 𝑟𝑚 3 /𝑑 𝐷𝑢𝑟𝑎𝑡𝑖𝑜𝑛 𝑔𝑎𝑠 =60 𝑑𝑎𝑦𝑠 (𝑑) 𝐼𝑛𝑗.𝑟𝑎𝑡𝑒 𝑤𝑎𝑡𝑒𝑟 =2250 𝑟𝑚 3 /𝑑 𝐷𝑢𝑟𝑎𝑡𝑖𝑜𝑛 𝑤𝑎𝑡𝑒𝑟 =30 𝑑𝑎𝑦𝑠 (𝑑) Example 2 𝑊𝐴𝐺 𝑟𝑎𝑡𝑖𝑜= 2250∗30 1125∗60 = 67 500 𝑟𝑚 3 67 500 𝑟𝑚 3 => 1:1 ratio 𝑊𝐴𝐺 𝑐𝑦𝑐𝑙𝑒 𝑙𝑒𝑛𝑔𝑡ℎ=30𝑑+60𝑑=90𝑑 𝑊𝐴𝐺 𝑟𝑎𝑡𝑖𝑜= 𝑉𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑤𝑎𝑡𝑒𝑟 𝑉𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑔𝑎𝑠 = (𝐼𝑛𝑗.𝑟𝑎𝑡𝑒∗𝐷𝑢𝑟𝑎𝑡𝑖𝑜𝑛) 𝑤𝑎𝑡𝑒𝑟 (𝐼𝑛𝑗.𝑟𝑎𝑡𝑒∗𝐷𝑢𝑟𝑎𝑡𝑖𝑜𝑛) 𝑔𝑎𝑠 = 𝑅 𝑤 ∗ 𝑇 𝑤 𝑅 𝑔 ∗ 𝑇 𝑔