Injectivity Index

Test Your Knowledge

Injectivity Index Quiz

Instructions: Choose the best answer for each question.

1. What does the Injectivity Index (II) represent?

a) The volume of fluid injected into the reservoir. b) The pressure difference between the injection well and the reservoir. c) The rate at which the injection rate changes with respect to injection pressure. d) The total amount of fluid injected over time.

2. Which of the following units is typically used to express the Injectivity Index?

a) Liters/second b) Barrels/day c) bbl/psi d) Degrees Celsius

3. What happens to the Injectivity Index if the permeability of the reservoir decreases?

a) It increases. b) It decreases. c) It remains constant. d) It becomes negative.

4. Why is monitoring changes in the Injectivity Index over time important?

a) To determine the volume of the reservoir. b) To track the movement of injected fluids in the reservoir. c) To detect changes in reservoir properties, such as damage or pressure increases. d) To calculate the total production from the reservoir.

5. Which of the following factors does NOT directly influence the Injectivity Index?

a) Wellbore radius b) Reservoir porosity c) Ambient air temperature d) Injection fluid viscosity

Injectivity Index Exercise

Scenario: An injection well has been experiencing a decline in its Injectivity Index over the past few months. The well is injecting water into a sandstone reservoir. The injection rate has decreased significantly, requiring higher injection pressures to maintain the desired flow rate.

Task:

• Identify at least three possible reasons for the decline in the Injectivity Index.
• For each reason, suggest a potential solution or mitigation strategy.

Techniques

Chapter 1: Techniques for Determining Injectivity Index

This chapter delves into the methods used to determine the Injectivity Index (II) of an injection well.

1.1. Injectivity Tests:

• Purpose: Injectivity tests are the primary means of determining II. They involve injecting fluid into the well at various rates and measuring the corresponding pressure response.
• Types:
  • Constant-rate test: In this test, the injection rate is held constant, and the pressure change over time is recorded.
  • Constant-pressure test: Here, the injection pressure is maintained constant, and the flow rate is measured.
• Data Analysis: Data from injectivity tests is analyzed using various methods, including:
  • IPR analysis: Inflow Performance Relationship (IPR) analysis is used to determine the II as the slope of the IPR curve.
  • Analytical solutions: Simplified analytical models can be employed to estimate II based on wellbore and reservoir properties.
• Limitations: Injectivity tests can be time-consuming and expensive. Also, they may not always accurately reflect the long-term behavior of the well.

1.2. Production Logging:

• Purpose: Production logging tools can be used to measure fluid flow rates and pressures at different points in the wellbore.
• Advantages: This technique allows for the assessment of injectivity along the wellbore, identifying potential flow restrictions.
• Limitations: Production logging is typically more expensive than injectivity tests and requires specialized equipment.

1.3. Modeling and Simulation:

• Purpose: Reservoir simulation models can be used to predict the II based on reservoir properties and wellbore conditions.
• Advantages: Models allow for investigating the impact of various factors on injectivity without conducting actual tests.
• Limitations: The accuracy of the II prediction depends on the accuracy of the reservoir model and input data.

1.4. Other Techniques:

• Transient Pressure Analysis: Analyzing pressure transients during injection can provide insights into wellbore and reservoir properties, contributing to the estimation of II.
• Nuclear Magnetic Resonance Logging: NMR logging can measure porosity and permeability, which are essential parameters for determining II.

1.5. Challenges and Considerations:

• Formation Damage: Damage to the formation near the wellbore can significantly reduce injectivity.
• Wellbore Conditions: The radius, skin factor, and presence of scale or corrosion can impact II.
• Fluid Properties: The viscosity and density of the injected fluid affect the flow rate and thus II.
• Data Quality: Accurate and reliable data are crucial for obtaining a meaningful II value.

Conclusion:

Choosing the appropriate technique for determining II depends on the specific application, available resources, and data quality. Combining different methods can improve the accuracy of II estimation and provide a comprehensive understanding of injection well performance.