32 nd Gas-Lift Workshop. Optimizing Subsea Well Kick-off Operations Case Study Using FlowLift2

Transcription

1 32 nd Gas-Lift Workshop The Hague, The Netherlands February 2-6, 2009 Optimizing Subsea Well Kick-off Operations Case Study Using FlowLift2 Denise Lima Artificial Lift Engineer Galileu de Oliveira Artificial Lift Engineer This presentation is the property of the author(s) and his/her/their company(ies). It may not be used for any purpose other than viewing by Workshop attendees without the expressed written permission of the author(s).

2 Summary Overview Premises Case Study Field A Scenarios RPSE Method FlowLift2 Transient Simulator Well, Fluid and Reservoir Data Simulation and Results Conclusions 2009 Gas-Lift Workshop 2

3 Overview This work presents a simplified approach for designing the kick-off operation for a subsea well, being the conclusion supported by numerical simulation, using the software FlowLift2. Prior Objective: optimization of the kick-off operation (aiming to anticipate the start up of production wells) by deciding about Make use of the Xmas tree cross-over valve (XO) Using one or two valves in the well Gas-Lift Workshop 3

4 Premises Of The Study Maximum well casing pressure = 250 kgf/cm 2 compression system upper limit One GL mandrel Comparison is made with an installation w/ 2 GLV Unloaded well No completion fluid in annulus and only reservoir fluid in the tubing Anticipation and feasibility of production deepening of GL valve 2009 Gas-Lift Workshop 4

5 Case Study Field A Scenario 1 Conventional well kick-off through the single GL valve 1.a) Estimate the mandrel depth using a simplified theoretical model (RPSE method) with just an operation valve; 1.b) Simulate (using FlowLift2) the kick off for comparison between the methods Gas-Lift Workshop 5

6 Case Study Field A Scenario 2 Well kick-off through the cross-over and a single GL valve: 2.a) Estimate the mandrel depth using a simplified theoretical model (RPSE method) with just one valve, however considering Pwh = flowing wellhead pressure; 2.b) Simulate the kick off for comparison between the methods Gas-Lift Workshop 6

7 RPSE Method A method for (among other things) determine the position of a kick off valve based on the fluids gradients. Static gradient in the gas lift line and annulus; Static or dynamic gradient, depending on the initial gas-liquid interface Gas-Lift Workshop 7

8 FlowLift2 FlowLift2 is a PETROBRAS in-house software, which models the transient one-phase/two-phase flow in a well. Allows for monitoring the relevant variables during the kick-off operation, such as pressure, velocities, temperature and volumetric fractions throughout the production system; Four fluids: oil+water, completion fluid, natural gas, nitrogen Gas-Lift Workshop 8

9 FlowLift 2009 Gas-Lift Workshop 9

10 Well data 2009 Gas-Lift Workshop 10

11 Water depth: m Tie back ~ m Tubing diameter: 6 5/8 Flowline diameter: 6 Well data Limited to 6, due to material restrictions for this water depth Reservoir depth: m 2009 Gas-Lift Workshop 11

12 Fluid data API = 27.7 o GOR = 229 m3/m3 dg (injection) = 0,75 dg (reservoir) = 0,85 Viscosity = 1,21 cp CO 2 in gas = 12 % Water cut (Early Life Production) = 0% Water cut (Late Life Production) = 70% 2009 Gas-Lift Workshop 12

13 Static pressure Reservoir data: early production life: 489 kgf/cm 2 late Production Life: 459 kgf/cm 2 Productivity index early production life: 12 (m 3 /d)/(kgf/cm 2 ) late production life: 9 (m 3 /d/kgf/cm 2 ) Bubble Pressure = 392,4 kgf/cm Gas-Lift Workshop 13

14 1) Kick off through the GL valve EARLY PRODUCTION LIFE 1.a) RPSE method Installation Depth = m Pressure X Vertical Depth (GLV depth = m) Kick off with just a GLV EARLY PRODUCTION LIFE Vertical Depth (m) Pressure (kgf/cm2) 0,0 100,0 200,0 300,0 400,0 500, Tubing Pressure Casing Pressure 2009 Gas-Lift Workshop 14

15 1) Kick off through the GL valve EARLY PRODUCTION LIFE 1.b) Simulation with FlowLift2 Installation Depth = m 2009 Gas-Lift Workshop 15

16 2) Kick off through the GL and XO valve - EARLY PRODUCTION LIFE 2.a) RPSE method Installation Depth = m 2009 Gas-Lift Workshop 16

17 2) Kick off through the GL and XO valves - EARLY PRODUCTION LIFE 2.b) Simulation with FlowLift2 Installation Depth = m 2009 Gas-Lift Workshop 17

18 Premises for the simulation: XO and M2 are opened simultaneously, just in the beginning of the operation (the best option); Opening/closing times for the XO e M2 valves = 60 s; Closing of the XO valve after 1 hour; Injection through de GL valve until the production stabilization. Finding the GLV depth making use of transient simulation, in all cases, was done such that the kick-off operation is not to slow Gas-Lift Workshop 18

19 Case Study results Early Production Life RESULTS for FlowLift2 Scenario 1 (1 GLV) GLV Depth: m Operation time: 5h 40min Scenario 2 (1 GLV + XO) GLV Depth: m Operation time: 2h 15min 2009 Gas-Lift Workshop 19

20 Case Study results Early Production Life RESULTS for FlowLift2 Natural Flowing well make the operation easier The production increment with the deepening the GL valve is not significant. That happens probably because of the high gravity of the injection gas, and also the relatively low PI 2009 Gas-Lift Workshop 20

21 1) Kick off through the GL valve LATE PRODUCTION LIFE 1.a RPSE Method Installation Depth = m 2009 Gas-Lift Workshop 21

22 1) Kick off through the GL valve LATE PRODUCTION LIFE 1.b) Simulation with FlowLift2 Installation Depth = m 2009 Gas-Lift Workshop 22

23 2) Kick off through the GL and XO valves - LATE PRODUCTION LIFE 2.a) RPSE method Installation Depth = m 2009 Gas-Lift Workshop 23

24 2) Kick off through the GL and XO valves - LATE PRODUCTION LIFE 2.b) Simulation with FlowLift2 Installation Depth = m 2009 Gas-Lift Workshop 24

25 Premises for the simulation: XO and M2 are opened simultaneously, just in the beginning of the operation (the best option); Opening/closing times for the XO e M2 valves = 60 s; Closing of the XO valve after 1.5 hour; Injection through de GL valve until the production stabilization. Finding the GLV depth making use of transient simulation, in all cases, was done such that the kick-off operation is not to slow Gas-Lift Workshop 25

26 Case Study results Late Production Life RESULTS for FlowLift2 Scenario 1 (1 GLV) GLV Depth: 3800 m Operation time: 5h 55min Scenario 2 (1 GLV + XO) GLV Depth: m Operation time: 3h 45min 2009 Gas-Lift Workshop 26

27 Case Study results Early Production Life RESULTS for FlowLift2 No longer a natural flowing well: GL is necessary to sustain a production ~ 1200 m 3 /d. Similarly to the case of early production live, the production increment with the deepening the GL valve is not significant. That happens probably because of the high gravity of the injection gas, and also the relatively low PI 2009 Gas-Lift Workshop 27

28 Late Production Life Using 2 GL valves: RPSE Method 2009 Gas-Lift Workshop 28

29 Late Production Life Using 2 GL valves: Simulation with FlowLift Gas-Lift Workshop 29

30 Premises for the simulation: The same as before, except for The second GL valve depth was placed at m (200 m above the top of the liner). The available casing pressure, at this depth, are still higher than the tubing pressure Closing of the XO valve after 1.5 hours The first valve is a bellows charged valve (IPO) 2009 Gas-Lift Workshop 30

31 Case Study results Late Production Life 2 GLV case RESULTS Scenario 1 (1 GLV) 1 st GLV Depth: 3800 m Operation time: 5h 55min Scenario 2 (1 GLV + XO) 1 st GLV Depth: m Operation time: 3h 45min 2009 Gas-Lift Workshop 31

32 Conclusions (1/3) The duration of kick-off operation in both moments of the production life are significantly affected by the method: injecting gas directly through de GL (more time consuming) first opening the XO (more efficient) The duration of kick-off operation using two GL valves (a charged bellows valve and an orifice valve), at the Late Production Life, is practically the same of that observed for the kick-off through the XO and GL valves; 2009 Gas-Lift Workshop 32

33 Conclusions (2/3) The increment of oil production by gas lift, compared with a natural flowing well, is significant with increasing water cut (above 40%). At the Late Life Production, when the water cut is 70%, the well only produces with artificial lift On the other hand, the increment of production due to the deepening of the GL (from m to m) valve is not significant similarly, the production increase by the use of two GL valves is not significant Gas-Lift Workshop 33

34 Conclusions (3/3) The kick-off operation through the XO and GL valve appears to be an efficient method to reduce the operation time, allowing the deepening of the GL valve. Deepening of the GLV is not advantageous for the present well, but that is not true in general for this field. These conclusions holds only for this case, and cannot be extended to other situations, even within the same field. Thus, the process summarized here should be repeated for every case, and it consists in Design with steady-state methods Check the results with transient simulation with and without making use of the XO valve Gas-Lift Workshop 34

35 2009 Gas-Lift Workshop Thank you for your attention! 2009 Gas-Lift Workshop 35

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