Reservoir Engineering

PT (well test)

PT (Well Test): Unlocking the Secrets of Subsurface Reservoirs

In the world of oil and gas exploration and production, PT (Well Test) plays a crucial role in understanding the characteristics of underground reservoirs. This process, often referred to as a "pressure test," involves carefully measuring the pressure and flow rate of fluids (oil, gas, or water) from a well.

Summary Description of a Pressure Test:

A pressure test involves intentionally opening a well to the surface and observing the behavior of the fluids within. This provides valuable insights into:

  • Reservoir Pressure: The initial pressure of the reservoir, which helps determine the potential productivity of the well.
  • Reservoir Permeability: How easily fluids flow through the reservoir rock, affecting the rate of production.
  • Reservoir Size: The volume of the reservoir, which influences the overall potential for oil and gas production.
  • Fluid Properties: The composition and properties of the fluids within the reservoir, such as viscosity and compressibility.

Types of Well Tests:

There are various types of well tests, each designed to gather specific data:

  • Drawdown Test: This involves gradually increasing the production rate of the well and monitoring the pressure response. It helps determine the productivity index and reservoir permeability.
  • Buildup Test: This involves shutting in the well after production and observing the pressure increase as the reservoir re-pressurizes. This provides insights into the reservoir pressure and permeability.
  • Interference Test: This involves monitoring the pressure response of multiple wells in a field during production, allowing for the assessment of reservoir connectivity and interference between wells.
  • Injection Test: This involves injecting fluids into the well and monitoring the pressure response. It helps determine the injectivity of the formation, crucial for enhanced oil recovery techniques.

Importance of PT (Well Tests):

Well tests are essential for making informed decisions regarding:

  • Well Completion and Production: The design of well completions and production strategies.
  • Reservoir Characterization: Building a detailed understanding of the reservoir's properties.
  • Field Development: Planning for the optimal development of the oil and gas field, including well placement and production optimization.
  • Reservoir Management: Monitoring the performance of the reservoir over time and implementing effective strategies for maximizing production and minimizing reservoir damage.

Conclusion:

PT (Well Tests) are powerful tools for understanding and managing underground reservoirs. By carefully analyzing the pressure and flow rate data obtained during these tests, engineers and geoscientists can unlock the secrets of these hidden resources, leading to more efficient and sustainable oil and gas production.


Test Your Knowledge

PT (Well Test) Quiz

Instructions: Choose the best answer for each question.

1. What is the primary purpose of a PT (Well Test)? (a) To determine the age of the reservoir. (b) To assess the characteristics of the underground reservoir. (c) To identify the type of rock formations present. (d) To measure the depth of the well.

Answer

(b) To assess the characteristics of the underground reservoir.

2. Which type of well test involves gradually increasing the production rate and monitoring the pressure response? (a) Buildup Test (b) Drawdown Test (c) Interference Test (d) Injection Test

Answer

(b) Drawdown Test

3. What information can a Buildup Test provide? (a) Reservoir pressure and permeability. (b) Fluid properties and reservoir size. (c) Well productivity index and injection rate. (d) Reservoir connectivity and interference between wells.

Answer

(a) Reservoir pressure and permeability.

4. How are PT (Well Tests) used in the context of reservoir management? (a) To predict future oil prices. (b) To identify new oil and gas fields. (c) To monitor reservoir performance and optimize production. (d) To analyze the environmental impact of drilling.

Answer

(c) To monitor reservoir performance and optimize production.

5. Which of the following is NOT a parameter typically measured during a PT (Well Test)? (a) Pressure (b) Flow rate (c) Well depth (d) Fluid composition

Answer

(c) Well depth

PT (Well Test) Exercise

Scenario:

An oil well has been producing for 6 months. During a recent drawdown test, the following data was recorded:

| Time (hours) | Pressure (psi) | Flow Rate (bbl/day) | |---|---|---| | 0 | 3000 | 1000 | | 1 | 2900 | 1200 | | 2 | 2800 | 1400 | | 3 | 2700 | 1600 |

Task:

Using the provided data, calculate the productivity index (PI) of the well.

Formula:

PI = Flow Rate / (Pressure Difference)

Instructions:

  1. Choose a time interval from the table (e.g., between 1 hour and 2 hours).
  2. Calculate the pressure difference between the two time points.
  3. Calculate the average flow rate during that time interval.
  4. Apply the PI formula to determine the well's productivity index.

Exercice Correction

Let's use the time interval between 1 hour and 2 hours.

1. Pressure difference: 2900 psi - 2800 psi = 100 psi

2. Average flow rate: (1200 bbl/day + 1400 bbl/day) / 2 = 1300 bbl/day

3. PI: 1300 bbl/day / 100 psi = 13 bbl/day/psi

Therefore, the well's productivity index is approximately 13 bbl/day/psi.


Books

  • "Well Test Analysis" by R.G. Matthews: A classic textbook covering the fundamentals of well test analysis and interpretation.
  • "Reservoir Engineering Handbook" by T.D. Matthews and J.F. Russell: A comprehensive resource on reservoir engineering, including chapters dedicated to well testing and analysis.
  • "Petroleum Engineering Handbook" by W.J. Skilling and H.J. Ramey: A practical guide to petroleum engineering, with sections on well test design and interpretation.
  • "Modern Well Test Analysis: A Computer-Aided Approach" by M.J. Economides and K.G. Nolte: A detailed book on advanced well test analysis techniques, including computer-based methods.

Articles

  • "Well Test Analysis: Fundamentals and Applications" by J.P. Spivey: A comprehensive overview of well test analysis principles and applications.
  • "Interpretation of Pressure Transient Tests in Gas Wells" by J.S. Agarwal: A detailed paper on analyzing pressure transient tests in gas wells.
  • "Analysis of Injection Tests" by H.J. Ramey: A classic paper on the interpretation of injection tests for reservoir characterization.

Online Resources

  • SPE (Society of Petroleum Engineers): The SPE website offers a vast library of technical papers, conference proceedings, and educational resources on well testing.
  • Petroleum Engineering Journal: A leading journal in the field of petroleum engineering, publishing articles on well test analysis and reservoir characterization.
  • Well Test Analysis Software: Several software packages are available for performing well test analysis, such as:
    • WellTest: A comprehensive well test analysis software developed by Schlumberger.
    • IPG Suite: Software for analyzing well tests and evaluating reservoir properties.
    • Petrel: A reservoir simulation software with advanced well test analysis capabilities.

Search Tips

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  • Combine keywords with specific well types: For example, "oil well test analysis," "gas well test analysis," or "horizontal well test analysis."
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