Evaluating 10 years of Foam Assisted Lift

Transcription

1 Gas Well Deliquification Workshop Sheraton Hotel, February 23 26, 2014 Evaluating 10 years of Foam Assisted Lift Kees Veeken and Gert de Vries Shell (NAM) Assen

2 Contents Intro Scope Results Conclusions & Recommendations 2

3 NAM Onshore (excluding Groningen) Gas fields ~100 Gas wells ~300 Production ~20e6 Sm 3 /d (700 MMscf/d) Liquid loading ~150 Foam assisted lift Review 10 years foam assisted lift (FAL) Batch foam ~1000 jobs in ~150 wells Continuous foam ~100 cap string years in ~30 wells plus trial only in ~20 wells 3

4 FAL Performance Review Establish success rate of batch and continuous foam Quantify reduction of critical rate achieved with foam Investigate dependency of foam performance on reservoir, well and foam application parameters 4

5 Parameters Reservoir Well Water to gas ratio (WGR), condensate to gas ratio (CGR), condendate to water ratio (CGR/WGR), H2S content Tubing ID, liner ID & length, depth of foam injection relative to producing interval, deviation at injection point, corrosion inhibition Foam* Batch: frequency, volume Continuous: injection rate * Foam chemical selection is not covered in this review 5

6 Batch Foam Performance 45 wells, 939 jobs, average 47 days between jobs Bullheaded total 46.6 m 3 foam resulting in total 236e6 Sm 3 (8.3 Bscf) incremental gas production: 5.1e3 Sm 3 (180 Mscf) per liter foam, 252e3 Sm 3 (8900 Mscf) per batch job 103e6 Sm 3 (3.6 Bscf) out of 236e6 Sm 3 (8.3 Bscf) associated with kicking off shut-in wells producing formation water or receiving batch corrosion inhibitor or fresh water soak treatments No gains in 24 out of 45 wells (53%) If it works it works well! 6

7 Batch Foam Success KOL E GGT1-FR Nm3/d KOL1-PR BARG /10/ :00: days KOL-100 Outlet KOL /11/ :00:00 Batch foam job enables kick-off after 800 L corrosion inhibitor batch job every 2 weeks hence safeguards ~75e3 Sm 3 /d (2600 Mscf/d) 7

8 Continuous Foam Performance 32 wells, 96 cap string years Injected total 657 m 3 foam resulting in total 808e6 Sm 3 (28.5 Bscf) incremental gas production: 1.2e3 Sm 3 (42 Mscf) per liter foam, 25e6 Sm 3 (0.9 Bscf) gain per well, 8.4e6 Sm 3 (0.3 Bscf) per foam-year No or insufficient gains in 14 out of 52 wells (27%) Most can be explained by non-foam related factors such as wells that were still producing stable or wells where inflow suffered from water breakthrough in the mean time Unexplained non-performance in 2 out of 52 wells (4%) It works well! 8

9 Continuous Foam Success Continuous foam safeguards ~230e3 Sm 3 /d (8100 Mscf/d) 9

10 Stable Rate with Foam / Minimum Rate Reduction of Critical Rate No Limit Limit Minimum-average-maximum = 30%-50%-70% 10

11 Gain (e6 Sm3/yr) Water-Gas Ratio (Continuous Foam) m 3 /e6sm 3 = 0.18 bbl/mmscf No clear trend i.e. No clear dependency on WGR Water-Gas Ratio (m3/e6sm3) 11

12 Gain (e6 Sm 3 /yr) Condensate-Gas Ratio (Continuous Foam) m 3 /e6sm 3 = 0.18 bbl/mmscf No clear trend i.e. No clear dependency on CGR Condensate-Gas Ratio (m3/e6sm 3 ) 12

13 Gain (e6 Sm 3 /yr) Condensate-Water Ratio (Continuous Foam) No clear CWR limit Foam effective at least up to CWR= CGR/WGR=CWR (-) 13

14 Gain (e6 Sm3/yr) Tubing Size (Continuous Foam) Larger gain for larger ID due to larger capacity! Tubing ID (in.) 14

15 Gain (e6 Sm 3 /yr) Liner Geometry (Continuous Foam) Long large liners do not limit foam application LinerLength*(LinerID-TubingID)/TubingID (m) 15

16 Gain (e6 Sm 3 /yr) Capillary String Injection Point % = Top, 100% = Bottom Default injection at top is OK N.B. intervals are typically 100 m TV % 0% 20% 40% 60% 80% 100% 120% Foam Injection Position Relative to Perforations 16

17 Gain (e6 Sm3/yr) Wellbore Injection Point Well deviation does not limit foam application Deviation at Injection Point (deg) 17

18 Monthly Gas Production (e3 Sm 3 ) Batch Foam Frequency Maximum 1x per week, average 1x per 7 weeks Assuming each foam batch lifts all liquid, optimum frequency depends on liquid produced (Q*WGR), tubing size (ID) and drawdown (DD) as following F ~ Q*WGR/(ID 2 *DD) Calculated optimum frequency is usually more than 1x per week, hence increase frequency as far as practical 3x per week is maximum frequency before continuous foam becomes more cost effective Gain proportional to 25 L batch foam frequency (1x-5x per month) Monthly Foam Consumption (L) 18

19 Batch Foam Volume Minimum 25 L, average 50 L, maximum 100 L Assuming foam volume represents 1% of liquid volume in wellbore, optimum volume depends on tubing size (ID) and drawdown (DD) as following V ~ ID 2 *DD Calculated optimum volume varies between 1 and 100 L, hence reduce as far as practical However, more foam may be required, see below Success rate 53% Due to inefficient mixing and agitation, and due to liquid stored near-wellbore that rushes into wellbore during kick-off Apply rocking and/or gurgling Apply multiple, larger and/or more frequent batches 19

20 Gas Rate (e3 Sm3/d), Foam Volume (L), Foam Rate (L/d) FTHP, FBHP (bar) Batch & Continuous Foam Success Theory: batch period 5 days, batch volume 1 L Actual: batch period 7 days, batch volume 50 L 20

21 Gas Rate (e3 Sm3/d) Foam Concentration L/d = 20,000 ppm Foam Injection Rate (L/d) 21

22 Gas Rate (e3 Sm 3 /d) Foam Concentration L/d = 650 ppm Foam Injection Rate (L/d) 22

23 Gain (e6 Sm3/yr) Foam Concentration Best results achieved below 1000 ppm ,000 20,000 30,000 40,000 50,000 60,000 70,000 Foam Concentration (ppm) 23

24 Continuous Foam Injection Rate Field data indicates that foam injection rate is often (much) too high, confirmed by observation that batch foam generates 4x as much gas per liter than continuous foam: 5.1e3 Sm 3 (180 Mscf) Vs 1.2e3 Sm 3 (42 Mscf) Reduce foam injection rate as far as practical Optimum foam injection rate will increase as gas rate decreases further below critical rate Success rate 73% Most failures are not directly related to foam, success rate of 3 out of 4 may be as good as it gets! 24

25 Conclusions & Recommendations [1] Reservoir parameters High WGR (up to 2000 m 3 /e6sm 3 ), high CGR (up to 100 m 3 /e6sm 3 ), high CWR (up to 1) and H 2 S (up to 4000 ppm) do not rule out foam Well parameters Larger tubing ID increases gains, related to larger capacity Long large liner, deviation (up to 60 deg) and corrosion inhibition do not rule out foam No reason exists to inject below top reservoir (up to 100 m TV interval) 25

26 Conclusions & Recommendations [2] Batch foam Frequency has been too low and should be increased Volume has been too high and could be decreased Economic alternative to continuous foam (up to 3x per week) Success rate has been modest (53%) and could be increased by rocking or gurgling to promote mixing and agitation Continuous foam Actually observed reduction of critical rate supports use of 30%- 50%-70% reduction for candidate screening Injection rates have been too high (up to 10x) and should be decreased Success rate has been reasonable (73%), no significant increase is expected from changing foam parameters 26

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