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. 2023 Feb 16;8(8):7868–7873. doi: 10.1021/acsomega.2c07596

Modeling and Simulation of Autonomous Inflow Control Devices for Gas Exploitation

Junyu Yang †, Weiping Shi †,*, Yaohua Zhao ‡
PMCID: PMC9979313  PMID: 36873016

Abstract

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Horizontal well technology is an efficient method of oil and gas exploitation. The goal of increasing oil production and improving productivity can be achieved by increasing the contact area between the reservoir and the wellbore. The presence of bottom water cresting reduces the efficiency of oil and gas production significantly. Autonomous inflow control devices (AICDs) are widely used to delay the influx of water into the wellbore. Two kinds of AICDs are proposed to restrain the bottom water breakthrough during natural gas production. The fluid flows in the AICDs are simulated numerically. The pressure difference between the inlet and outlet is calculated to evaluate the ability of blocking the flow. A dual-inlet design can increase the flow rate of AICDs, thus enhancing the water blocking effect. Numerical simulations show that the devices can block water flowing into the wellbore effectively.

1. Introduction

Horizontal well technology is an efficient and widely used oil and gas exploitation method. It has most of the advantages of conventional wells, and it can also be used for unconventional exploitation of reservoirs with a high water content, low oil and gas content, and low permeability. It has the characteristics of long-distance penetration of the reservoir, wide oil exploitation area, and stable production. However, in the exploitation of oil and gas reservoirs with bottom water, there exists the “heel–toe effect”.1,2 The bottom water easily breaks through the upper oil–gas layer at the root and flows into the wellbore. This defect is more serious due to the heterogeneity of the reservoir and the existence of fractures, which extremely increases the water content in the production and sharply decreases the oil and gas contents. The service life of the horizontal well is seriously shortened, and the oil and gas exploitation efficiency is reduced.

To control the bottom water, prevent it from entering the wellbore too early, and maintain the horizontal well working normally, in the 1990s, the inflow control device (ICD) was designed for preventing the bottom water breakthrough.3 Traditionally, the first generation of ICDs aimed to balance the pressure between the horizontal well and reservoir, maintain a uniform flow in the whole exploitation area, delay the inflow of water, and maximize oil and gas production. Subsequently, ICDs were installed inside the horizontal wellbore.4 At present, ICDs include three types: spiral channel type, nozzle type, and their mixture type. The spiral channel-type ICDs were verified to keep the fluid flow in the wellbore uniform, so as to avoid large differential pressure, and could extend the lifetime of horizontal wells.5 In 2006, it was first confirmed that ICDs had the effect of stabilizing the fluid flow in the wellbore and delaying the bottom water breakthrough in the gravel layer.6 The nozzle-type ICD7 changed the spiral flow channel of the original ICD, generating a large pressure drop when the fluid passes through the nozzle. It could work well in increasing the friction resistance at the root of the wellbore where bottom water coning occurred, limiting the water flow into the wellbore and balancing the fluid pressure inside the wellbore. Later, a hybrid ICD8 was proposed. It had the advantages of both a spiral channel ICD and nozzle ICD, which kept the fluid flow in the wellbore more balanced and reduced the “heel–toe effect”. Another kind of hybrid ICDs used in the oil field of Manhara, India, has also proved that hybrid ICDs had a good effect in the well.9 By incorporating terrane characteristics into the design of ICDs, horizontal wells could lower the cost of construction and boost well production.10 The interior flows of ICDs were simulated numerically, and it has been verified that ICDs had water control capability.11

Autonomous inflow control devices (AICDs) have been applied in the industry due to their simple, low-cost, accurate, and automatic operation.12 AICDs could delay the water coning into the wellbore, and they do not need any accessory such as a cable or infrared ray. They could automatically separate the fluid according to the properties of the fluid itself, limiting the water flow into the wellbore. Moreover, AICDs have a wider scope of application, which was suitable not only for oil and gas fields without water but also for oil and gas fields with bottom water cresting or coning. The AICD is a practical technology with low risk and low cost. Crow et al.13 proposed a kind of AICD, which had a definite water control effect. However, the AICD is not widely used due to its complex structure, including moving parts and low reliability. The fixed AICD is mainly dependent on its special design. It could distinguish the fluid by its physical properties and guide the fluid into different flow paths. An AICD without moving parts has the advantages of water control ability, corrosion resistance, strong wear resistance, and low failure rate. A FD-AICD (fluid diode-type AICD)14 is composed of a Y-type splitting channel and external cyclone disk channel. The modified version15 and the phase selection controller (PSC)16 with a vortex disk have provided good results in the experiment. The fixed AICD has been applied in the Ginta oil field.17 Based on the numerical calculation, many researchers have improved the design of AICDs. Numerical simulation played an important role in the process of oil and gas exploitation.18,19 Stone et al. used numerical calculation methods to compare the application of mobile and fixed AICDs in the Ivar Aasen oil field and compared the oil production efficiencies of different AICDs in the application of the exploitation.20

2. Model Design

2.1. Mechanism of the AICD Blocking Water

Water has a larger density than that of natural gas. When water enters the AICD, the inertial force plays a major role in the flow, and the water rotates rapidly in the device, resulting in a large pressure difference between the inlet and outlet of the device. The Reynolds number of the natural gas flow is small. In a small-Reynolds number flow, when the fluid enters the device, it will flow along a short route, cannot rotate easily, and flows to the outlet directly.

2.2. Dual-Inlet Model I

The AICDs selectively limit the fluid flow inside themselves. As shown in Figure 1, the AICD consists of the following parts: inlet, main channel, branch channel, annular channel, asymptotic channel, inner annular channel, and outlet. When water and natural gas enter the device from the inlets and pass through Y-shaped channels (i.e., main channels and branch channels), annular channels, and inner annular channels, the AICD plays the role of water control due to its limiting effect. The 3D structure of the dual-inlet AICD is shown in Figure 2.

Figure 1.

Figure 1

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Dual-inlet AICD model I.

Figure 2.

Figure 2

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3D structure of model I.

2.3. Dual-Inlet Model II

The second model designed in this paper is shown in Figure 3. Unlike model I, this model changes the branch channel from the radial direction to the tangential direction. The diagram (Figure 3) and 3D structure (Figure 4) of the model II are shown.

Figure 3.

Figure 3

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Dual-inlet AICD model II.

Figure 4.

Figure 4

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3D structure of model II.

3. Numerical Simulation

3.1. Boundary Conditions

In this paper, computational fluid dynamics software is used to numerically calculate the fluid flow in the AICDs.

Boundary conditions: The boundary conditions at the inlet are set as the velocity inlet, and those at the outlet are set as the pressure outlet. The other boundary conditions are set as wall. The physical parameters of natural gas and water are shown in Table 1.

Table 1. Physical Parameters of Natural Gas and Water.

  density (kg/m3) viscosity (mPa/s–1)
natural gas 0.668 0.1087
water 998.2 1.0
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3.2. Numerical Simulation and Analysis of Model I

The flow rate is set as 5 m3/day. The flows of water and natural gas in the AICD are simulated. The pressure difference between the inlet and outlet of an AICD is an important indicator to evaluate the blocking effect of the device. Figure 5 shows the pressure contours of natural gas and water. The pressure of natural gas varies in the range of −6 to 22 Pa, while the pressure of water varies in the range of about −50,000 to 300,000 Pa. A portion of the fluid flows into the main channel, and the other part flows into the branch channel.

Figure 5.

Figure 5

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(a, b) Contours of natural gas and water pressure.

Table 2 shows the volume flow rates in the two channels. It can be seen that the flow rate of natural gas in the branch channel is large. The water flow rate in the branch channel is small. It shows that because of the large inertia of water, most of the water flows into the annular channel and rotates constantly. Under the action of pressure difference, most of the natural gas flows through the branch channel. It indicates that natural gas flows through the device directively, but water flows along a complicated trajectory. For model I, as shown in Figure 1, lines AB, CD, and EF are selected to analyze the profile of pressure and velocity along the line segments.

Table 2. Volume Flow Rates of Natural Gas and Water in Two Channels.

flow rate (m3/day) 1 5 10 15 20
natural gas in the main channel (m3/day) 0.44 2.89 5.81 9.03 13.56
water in the main channel (m3/day) 0.58 3.29 6.75 11.88 15.91
natural gas in the branch channel (m3/day) 0.56 2.11 4.19 5.97 6.44
water in the branch channel (m3/day) 0.42 1.71 3.25 3.12 4.09
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Figures 6–8 shows the pressure profile along the lines AB, CD, and EF, respectively. Figure 6a shows that the pressure of natural gas drops significantly at the initial stage and then increases. This is because the gas flow is bifurcated and the velocity in the main channel decreases, leading to an increase in pressure. As the fluid flows into the annular channel in the AB direction, the velocity increases, resulting in a decrease in pressure (see Figure 6a). Figure 6b shows that the water pressure profile also has a similar change. In contrast, the relative variation of pressure for natural gas is relatively large. It can be seen from Figures 7 and 8 that the flows of water and natural gas along the lines CD and EF are symmetric. The fluid rotates in the annular channel, and the pressure profiles are symmetric with respect to the centers.

Figure 6.

Figure 6

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(a, b) Pressure of natural gas and water along line AB.

Figure 8.

Figure 8

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(a, b) Pressure of natural gas and water along line EF.

Figure 7.

Figure 7

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(a, b) Pressure of natural gas and water along line CD.

Seven different flow rates are selected for calculating the pressure difference between the inlet and outlet and also the pressure difference ratio between water and natural gas. The calculation results are shown in Table 3. When the inlet flow rate is 5 m3/day, the ratio of water pressure difference to that of natural gas is 1373.3. The pressure difference of water is much greater than that of natural gas. Therefore, the AICD designed in this paper has a good water blocking effect.

Table 3. Pressure Difference between the Inlet and Outlet of Model I and the Ratio of Pressure Difference.

inlet flow (m3/day) 1 5 10 15 20 25 30
natural gas pressure difference (Pa) 2.28 45.8 402 987.7 1918 2825 4456
water pressure difference (Pa) 1927 62,898 256,265 583,057.6 1,058,418.2 1,630,250 2,389,164.5
ratio between water and gas pressure 845.2 1373.3 637.5 590.3 551.8 577.1 536.2
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Similar to the literature,21 it can be seen that the functional relationship between the pressure difference ΔP and flow rate q of the AICD is shown as follows

3.2. 1

Here, m and n are undetermined coefficients. The data in Table 3 are used to solve the undetermined coefficients by the function fitting method. For natural gas, the coefficients are mg = 2.668 and ng = 2.179. The pressure difference formula is

3.2. 2

For water, mw = 2394 and nw = 2.03. The pressure difference formula is

3.2. 3

The curves in Figure 9 represent the function of Δp–q. The upper curve in Figure 9 shows the pressure difference of water, and the curve at the bottom shows the pressure difference of natural gas. The “+” indicates the point of numerical values of Table 3.

Figure 9.

Figure 9

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Functional fitting of Δp–q of model I.

3.3. Numerical Simulation of Model II

The flow rates of natural gas and water are set as 10 m3/day, and the pressure contours of the flow field are obtained as shown in Figure 10. In the areas near the outlet, the pressure of natural gas has dropped to 200–220 Pa, while the pressure of water still fluctuates between 180,000 and 200,000 Pa. Only in the vicinity of the outlet does the water pressure begin to drop sharply, and the gradient of water pressure is steep near the outlet.

Figure 10.

Figure 10

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(a, b) Contours of natural gas and water pressure.

Figure 10 shows that the pressure variation range of natural gas is from −60 to 280 Pa, while the range of water is from −40,000 to 200,000 Pa. Obviously, when water passes through model II, the pressure difference of water is much higher than that of natural gas, which indicates that the device has the ability of blocking water.

We distinguish the flow into two parts, as shown in Figure 3, the main channel flow (labeled F1) and the branch channel flow (labeled F2), and calculate the flow rates in F1 and F2 channels.

Figure 11 shows the velocity contours of natural gas and water flows in the AICD at a flow rate of 10 m3/day. The velocity of natural gas at the connecting area of the main channel and annular channel is less than that of water at the same area. When the natural gas passes through the main channel and branch channel and then flows into the annular channel, it will collide with each other, resulting in its momentum loss and speed reduction. Here, Table 4 explains the reason for this phenomenon. Two flows from the main channel and branch channel flow into the annular channel at the opposite moment of momentum and lead to the decrease of the fluid velocity. The decrease of velocity in the annular channel is significant for natural gas. However, the decrease of velocity is small for water because water flows mainly in the main channel with Table 4.

Figure 11.

Figure 11

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(a, b) Contours of natural gas and water velocity.

Table 4. Flow Rates of Natural Gas and Water at Different Inlet Flow Rates of Model II.

inlet flow rate (m3/day) 1 5 10 15 20
natural gas in the main channel (m3/day) 0.61 3.18 6.51 10.38 14.12
water in the main channel (m3/day) 0.82 4.38 8.83 13.40 18.19
natural gas in the branch channel (m3/day) 0.39 1.82 3.49 4.62 5.88
water in the branch channel (m3/day) 0.18 0.62 1.17 1.60 1.81
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For evolution of the device blocking water ability, we simulate the flow in model II at seven different flow rates. Table 5 shows the pressure difference between the inlet and outlet. It shows that the ratio of water and gas pressure is large for low flow rates.

Table 5. Pressure Difference Between the Inlet and Outlet of Model II, and the Ratio of Pressure Difference.

inlet flow (m3/day) 1 5 10 15 20 25 30
natural gas pressure difference (Pa) 1.718 58.4 291.4 619 1472 1934 3312
water pressure difference (Pa) 1294 43,233.7 218,264.8 473,929.2 725,308 1,328,791.7 1,586,066
ratio between water and gas pressure 753.2 740.3 749 765.6 492.7 687.1 478.9
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According to the values in Table 5, similar to eqs 2 and 3, the fitting function of natural gas pressure difference is

3.3. 4

The fitting function of water pressure difference is

3.3. 5

The curves in Figure 12 represent the function of Δp–q. The upper curve of Figure 12 shows the pressure difference of water, and the curve below is for natural gas.

Figure 12.

Figure 12

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Functional fitting of Δp–q of model II.

Through numerical simulation, two types of dual-inlet devices can increase the flow rate. Two symmetrical inlets enhance the rotation of the fluid flow in AICDs, thus enhancing the water blocking effect of AICDs.

4. Conclusions

  • (1)

    The AICDs designed in this paper achieved the apparent effect for blocking water and limiting the water flow into the horizontal wellbore.

  • (2)

    Numerical simulations showed that the water pressure difference between the inlet and outlet is much greater than that of natural gas. It shows the ability of limiting the fluid flow selectively.

  • (3)

    Both types of AICDs have the apparent effect for blocking water, and model II is suitable for low flow rates.

Acknowledgments

This work was supported by the Natural Science Foundation of Jilin Province, China (Grant no. 20200201278JC).

The authors declare no competing financial interest.

Notes

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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