Productivity Index

Test Your Knowledge

Quiz: Productivity Index (PI)

Instructions: Choose the best answer for each question.

1. What does the Productivity Index (PI) measure in the oil and gas industry?

a) The volume of oil or gas produced per unit of time. b) The efficiency of a well's production at a specific pressure differential. c) The total amount of oil or gas extracted from a reservoir. d) The cost per barrel of oil or gas produced.

2. Which of the following is NOT a factor that can influence the Productivity Index (PI)?

a) Reservoir permeability. b) Wellbore damage. c) Market price of oil or gas. d) Stimulation techniques.

3. What does a higher Productivity Index (PI) indicate?

a) A less efficient well. b) A well producing more hydrocarbons at a given pressure drop. c) A well with a lower reservoir pressure. d) A well with a higher production cost.

4. How is the Productivity Index (PI) calculated?

a) PI = Q / (P_wf - P_res) b) PI = (P_wf - P_res) / Q c) PI = Q * (P_wf - P_res) d) PI = (P_wf + P_res) / Q

5. How can the Productivity Index (PI) be used as a diagnostic tool?

a) To determine the best drilling location for a new well. b) To assess the effectiveness of a completion design. c) To predict the future price of oil or gas. d) To measure the environmental impact of oil and gas production.

Exercise: Analyzing Well Performance

Scenario:

A new well has been completed in a reservoir. The following data is available:

• Flow rate (Q): 1000 barrels per day
• Wellhead flowing pressure (P_wf): 2000 psi
• Reservoir pressure (P_res): 3000 psi

Task:

1. Calculate the Productivity Index (PI) for this well.
2. Compare the PI to the ideal open hole scenario for the same reservoir, where the PI is known to be 2.5 barrels per day per psi.
3. What insights can you gain from this comparison?
4. Suggest potential reasons why the PI of the completed well is lower than the ideal open hole.

Techniques

Chapter 1: Techniques for Calculating the Productivity Index (PI)

This chapter focuses on various techniques employed in the oil and gas industry to calculate the Productivity Index (PI). These techniques vary depending on the specific conditions and data available for a given well.

1.1 Basic PI Calculation:

The most common and straightforward method for calculating PI is using the formula:

PI = Q / (P_wf - P_res)

Where:

• Q: Flow rate of oil or gas (measured in barrels per day or cubic feet per day)
• P_wf: Wellhead flowing pressure (measured in psi)
• P_res: Reservoir pressure (measured in psi)

This technique assumes a constant pressure drop across the wellbore and reservoir, which may not always be accurate in real-world scenarios.

1.2 Multiphase Flow Calculations:

When dealing with multiphase flow (oil, gas, and water), the PI calculation becomes more complex. Specialized software or analytical methods like the "Standing and Katz" method are used to account for the different pressures and flow rates of each phase.

1.3 Decline Curve Analysis (DCA):

DCA is a valuable technique to estimate future production based on historical flow rate data. This analysis can be used to derive the PI for different production periods and assess changes in well performance over time.

1.4 Well Test Analysis:

Well tests are designed to measure reservoir characteristics and flow behavior under controlled conditions. This data can be used to calculate PI and estimate the reservoir's maximum potential production.

1.5 Simulation Software:

Advanced reservoir simulation software can model the complex flow dynamics in a reservoir, including the impact of wellbore damage and production conditions. This allows engineers to accurately calculate PI and predict future well performance.

1.6 Importance of Data Quality:

Accurate PI calculation relies heavily on the quality of available data, including flow rate, pressure, and reservoir parameters. Ensuring data consistency and validation is crucial for obtaining reliable PI values.

1.7 Limitations of PI Calculation:

It's important to note that the PI is a simplified metric and does not account for all factors influencing well productivity. Factors such as reservoir heterogeneity, formation damage, and wellbore configuration can significantly affect PI and require specialized analysis.

1.8 Conclusion:

Selecting the appropriate PI calculation technique depends on the specific well conditions and available data. By considering these factors and employing appropriate methodologies, engineers can accurately assess and monitor well productivity, leading to more effective reservoir management and production optimization.