continuous sheet bastianandoni

WELL AND PRODUCTION ENGINEERING EG551P

ASSIGNMENT 2

CONTINUOUS GAS LIFT DESIGN TUTORIAL 23 PROSPER MANUAL

GROUP: F2 NAME: BASTIAN ANDONI ID: 51448209 Instructions

a) Using the Prosper model provided, complete the following table and justify your choice of an optimal design option.

b) Submit the Prosper model saved as (Continuous_model_YourName) and this sheet saved as (Continuous_sheet_YourName)

Flow rate (STB/Day) Score (Leave blank) Water cut 0 8326.99 10 8341.79 20 8343.27 40 8304.05 60 8229.73 80 7980.73 100 3810.81 Gaslift gas injection rate (MMScf/D) 0 8315.14 2 8343.27 4 8324.03 6 8263.51 8 8108.11 10 8013.51 Flowing tubing head pressure (psi) 50 8343.27 100 8266.46 150 8164.86 200 7964.11

An optimum gas lift design has been done in a reservoir to produce liquid from a well using continuous gas lift method for several conditions. An IPR-VLP curve has been plotted as the most optimum design for the gas lift operation.

Based on given parameters from the assignment sheet, all cases for all certain parameters are plotted in a graph. The total simulation cases which have been run for this assignment are 210 cases. All of these plots can be seen on graph 1 below. From the graph, we can see that critical sand production rate is far below the system curve. So, it means that sand production is not critical for our system, no matter what the parameter is.

From plot of graphic below, the system will only work on intersection between IPR curve and VLP curve. To find the most optimum flow rate, we will only consider the curves inside the red circle only; all other curves can be cancelled out.

Graphic Plot 1 : Plot for all cases

A sensitivity plot will be made for each parameter to find how each of them affects the performance of IPR-VLP curve.

1. Water Cut

A sensitivity test has been completed for various water cut concentration, the result can be seen on graph 2 below. It can be seen that the changes in water cut will affect both the IPR and VLP curves, the higher the water cut, the IPR curves will be shifted up, and the VLP curves will be shifted down. The IPR curves is shifted up because water has higher mobility than oil because water is less viscous than oil, so it will be easier for fluid to flow in the reservoir at higher Water Cut, the TPR curves will be shifted down as increasing Water Cut because water has higher density than oil, so it means more pressure is required to push the fluid to the surface.

Graphic Plot 2 : Effect of Water Cut to IPR-VLP Curve

2. Gas lift Gas Injection Rate

A sensitivity test has been completed for various gas injection rates (see graph 3 below), changes in gas injection rates will affect VLP curves but will not affect IPR curves. From the plot of the curves, it can be seen that as the injection rate increases, the VLP curves will be shifted down, but at certain point, it will be shifted up, this happens because at lower rate, the gas will reduce the density of the liquid and will make the liquid easier to flow, but, at higher rate, the gas will form larger slug and prevent the liquid to flow and further will decrease the production capability.

Graphic Plot 3: Effect of Gas Injection Rate to VLP Curve

3. Flowing Tubing Head Pressure

A sensitivity test has been completed for various flowing tubing head pressure (see graph 4 below), changes in flowing tubing head pressure will affect VLP curves but will not affect IPR curves. From the plot of curves, it can be seen that as the Flowing Tubing Head Pressure decreases, the VLP curves will be shifted down. This is because the lower the wellhead pressure, the higher the pressure difference between reservoir pressure and the well head pressure, because pressure drop is proportional to the flow rate, then the flow rate itself will be increased.

Graphic Plot 4: Effect of Flowing Tubing Head Pressure to VLP

From those 3 sensitivity plot, it can be concluded that the optimum zone will be expected if we have low water cut, low top node pressure, and low gas injection rate. Based on this analysis, a new sensitivity plot is made and we get much better plot as can be seen on graph 5 below.

Graphic Plot 5: Plot of Sorted IPR-VLP Curve

To design the most optimum gas lift system, we will choose the most optimum injection rate and top node pressure. 5 cases have been run to see the effect of those parameters. Plots between liquid

rates versus gas injection rates have been done for different top node pressure (The result summary of these sensitivity tests can be found on the appendix). An analysis will be made based on how the gas injection rate will affect the liquid rate, the most optimum gas injection rate then will be chosen by selecting the injection rate that will give maximum liquid rate for any water cut concentration.

CASE 1: TOP NODE PRESSURE 50 PSIG

Graphic Plot 6 : Liq. Rate vs Gas Inj. Rate at Top Node Pressure 50 Psig


Graphic Plot 7: Liq. Rate vs Gas Inj. Rate at Top Node Pressure 100 Psig



From those five cases, it can be concluded that the most optimum gas lift gas injection rate is between 2 to 6 MMSCF/D, because if we increase the injection rate more than 6 MMSCF/D, the liquid rate will decrease.

From the graph 11 below, we can also see that the lower the top node pressure, the higher the liquid rate will be. This is because the pressure drop is larger, and makes the liquid rate will be larger too remembering that pressure drop is proportional to liquid rate. But, basically, the lower pressure drop means the shorter we can produce. In this case, we assume that to find the most optimum case we did not consider the production time, but we only consider the Top Node pressure that will give us the highest liquid rate. Based on the analysis, we choose top node pressure 50 psig as the design.

Graphic Plot 11: Liq. Rate vs Top Node Pressure

Summary:

The most optimum gas lift design for this well is reached by using parameter mentioned below. These parameters will give us liquid rate of:

Table 1: Liq. Flow Rate vs Water Cut

Water Cut

Gas Injection Rate (MMSCF/Day)

Top Node Pressure (psi) Liquid Rate (STB/Day)

0 2 50 8326.99 10 2 50 8341.79 20 2 50 8343.27 40 4 50 8304.05 60 4 50 8229.73 80 6 50 7980.73 100 4 50 3810.81

It can be seen from the table that as the water cut increases, we need to inject more gas in the future to maintain the production decline rate to be as low as possible. It is then recommended to build a compressor system that can achieve injection rate within 2 MMSCF/Day up to 6 MMSCF/Day.

The final IPR-VLP curve on initial condition (zero percent water cut) for the most optimum value can be given as the graph as shown below:

Graphic Plot 12: Initial IPR-VLP Curve for the Most Optimum Design

Bibliography:

1. Guo, Boyun, William C. Lyons, and Ali Ghalambor. Petroleum Production Engineering: A Computer Assisted Approach. Burlington: Gulf Professional, 2007. Print.

Appendix:

Sensitivity Test of Liquid Rate vs Gas Injection Rate for Top Node Pressure 50 psi

Water Cut

Liquid Rate (STB/Day)

Gas Injection Rate

(MMSCF/Day) 0 8315.14 0

8326.99 2 8224.83 4 8131.56 6 8016.07 8 7959.46 10

10 8300.34 0 8341.79 2 8312.18 4 8214.47 6 8050.13 8 7928.72 10

20 8260.36 0 8343.27 2 8324.03 4 8230.75 6 8070.85 8 7949.45 10

40 7949.95 0 8263.51. 2 8304.05 4 8263.51 6 8060.81 8 8013.51 10

60 7175.68 0 8033.78 2 8229.73 4 8202.7 6 8108.11 8 7898.65 10

80 4959.46 0 7506.76 2 7912.92 4 7980.73 6 7905.1 8 7765.03 10

100 0 0 3641.89 2 3810.81 4 3804.05 6

3797.03 8 3743.24 10


Water Cut


Gas Injection Rate

(MMscf/Day) 0 8219.43 0

8260.1 2 8224.51 4 8153.34 6 8060.45 8 7888 10

10 8182.57 0 8266.46 2 8243.58 4 8179 6

8083.43 8 7983.02 10

20 8091.06 0 8261.37 2 8251.21 4 8190.2 6 8102.5 8 7996 10

40 7680.53 0 8143.17 2 8223.24 4 8174.95 6 8089.79 8 7986.84 10

60 6740 0 7837.78 2 8083.92 4 8088.47 6 8009 8 7916 10

80 4178 0 7265 2

7736.67 4 7850.57 6 7818.02 8 7725.82 10

100 0 0 3495 2

3698 4 3763 6 3754 8

3713 10


Water Cut


Gas Injection Rate

(MMscf/Day) 0 8067.57 0

8164.86 2 8109.95 4 8046.15 6 7969.81 8 7884.37 10

10 7963.03 0 8131.57 2 8123.91 4 8064.71 6 7989.5 8 7903.14 10

20 7840.46 0 8098.14 2 8123.21 4 8070.98 6 7998.55 8 7913.59 10

40 7360 0 7927.79 2 8061.21 4 8042.13 6 7977.52 8 7893.83 10

60 6249.17 0 7589.5 2 7879.54 4 7930 6

7893.62 8 7809.14 10

80 3262.86 0 6979.33 2 7528.12 4 7680 6 7674 8

7597.58 10 100 0 0

3318.43 2

3547.67 4 3631.03 6 3651.87 8 3658.82 10


Water Cut


Gas Injection Rate

(MMscf/Day) 0 7816.52 0

7962.47 2 7957.55 4 7909.18 6 7846 8

7768.97 10 10 7718.95 0

7938 2 7964.11 4 7920.66 6 7858.34 8 7783.73 10

20 7570.54 0 7889.5 2 7950.99 4 7919.84 6 7859.98 8 7788.65 10

40 7021.76 0 7710.41 2 7857.97 4 7870.27 6 7818.02 8 7756.2 10

60 5836.49 0 7340.54 2 7671.62 4 7766.22 6 7728.38 8 7671.62 10

80 2164.32 0 6628.24 2 7291 4

7476.76 6 7501.35 8 7439.86 10

100 0 0 3182.15 2 3423.37 4 3505.94 6 3543.97 8 3558.1 10


Water Cut


Gas Injection Rate

(MMscf/Day) 0 6250 0

6709.46 2 6864.86 4 6885.14 6 6851.35 8 6743.24 10

10 5979.85 0 6580.77 2 6794.62 4 6828.83 6 6739.24 8 6711.21 10

20 5627 0

6465.29 2 6728.32 4 6786.06 6 6687.69 8 6666.31 10

40 4279.77 0 6120.53 2 6471.15 4 6547.85 6 6555.15 8 6540.54 10

60 0 0 5331.63 2 6186.57 4 6350.62 6 6368.88 8 6346.97 10

80 0 0 4634.04 2 5656.68 4 6021.91 6 6091.31 8 6094.96 10

100 0 0 2379.18 2 2661.1 4 2750.55 6 2810.55 8 2845.65 10

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