Glossary of Technical Terms Used in Drilling & Well Completion: Reserves, Probable

Reserves, Probable

Understanding Probable Reserves: A Key Concept in Resource Estimation

In the world of resource exploration and development, understanding reserve classifications is crucial for making informed decisions. While "proved reserves" represent the most certain quantities of recoverable resources, "probable reserves" represent a different category, adding a layer of uncertainty and potential. This article delves into the concept of probable reserves, providing a clear explanation and highlighting key characteristics.

What are Probable Reserves?

Probable reserves refer to those unproved reserves where geological and engineering data analysis suggests a more likely than not probability of recovery. This means that there's a greater than 50% chance that the actual recovered quantities will equal or exceed the estimated sum of proved plus probable reserves.

Key Characteristics and Examples:

  1. Step-Out Drilling: Areas with inadequate sub-surface control where reserves are anticipated to be proved by further drilling.
  2. Productive Formations with Limited Data: Formations showing potential based on well logs, but lacking core data or definitive tests, and not analogous to proven areas.
  3. Infill Drilling: Incremental reserves resulting from infill drilling, potentially classifiable as proved if closer spacing had been approved.
  4. Improved Recovery Methods: Reserves attributable to promising improved recovery techniques with successful pilot projects or favorable reservoir characteristics.
  5. Separated Formations: Reserves in formations separated from proven areas by faulting, but indicated to be structurally higher.
  6. Future Procedures: Incremental reserves anticipated from potential workovers, treatments, or equipment changes, even if their success hasn't been fully proven in similar reservoirs.
  7. Alternative Interpretations: Reserves in proven reservoirs where alternative interpretations of data suggest higher quantities than initially classified.

Importance of Probable Reserves:

  • Potential Upside: Probable reserves provide an indication of potential additional resources beyond proven reserves, offering valuable insights for future development plans.
  • Decision Making: They contribute to decision-making processes related to exploration, drilling, and development, helping to assess the overall value and viability of a project.
  • Investment Considerations: Probable reserves play a role in attracting investment, as they signal potential growth and long-term profitability.

The Role of Probabilistic Methods:

Probabilistic methods are crucial when estimating probable reserves. These methods, utilizing statistical tools and data analysis, quantify the uncertainty associated with resource recovery. They help ensure that the assigned probability reflects the likelihood of successfully extracting the estimated quantities.

Conclusion:

Probable reserves represent a valuable component of resource assessment, offering a crucial bridge between proven reserves and potential future discoveries. Understanding their characteristics and the role of probabilistic methods is essential for navigating the complexities of resource exploration and development.

Note: Probable reserves are often referred to as P2 in industry terminology, aligning with the Society of Petroleum Engineers (SPE) reserve classification system.


Test Your Knowledge

Probable Reserves Quiz

Instructions: Choose the best answer for each question.

1. Which of the following is NOT a key characteristic of probable reserves?

a) Areas with inadequate sub-surface control where reserves are anticipated to be proved by further drilling. b) Formations showing potential based on well logs, but lacking core data or definitive tests. c) Reserves already proven through extensive drilling and production data. d) Reserves attributable to promising improved recovery techniques with successful pilot projects.

Answer

c) Reserves already proven through extensive drilling and production data.

2. What does the "more likely than not" probability associated with probable reserves mean?

a) There's a 100% certainty that the estimated reserves will be recovered. b) There's a less than 50% chance of recovering the estimated reserves. c) There's a greater than 50% chance that the actual recovered quantities will equal or exceed the estimated sum of proved plus probable reserves. d) There's a 50% chance of recovering the estimated reserves.

Answer

c) There's a greater than 50% chance that the actual recovered quantities will equal or exceed the estimated sum of proved plus probable reserves.

3. What is the industry terminology often used to refer to probable reserves?

a) P1 b) P2 c) P3 d) P4

Answer

b) P2

4. How are probabilistic methods used in estimating probable reserves?

a) They eliminate all uncertainty related to resource recovery. b) They quantify the uncertainty associated with resource recovery. c) They guarantee the exact quantity of resources that will be recovered. d) They are not relevant for estimating probable reserves.

Answer

b) They quantify the uncertainty associated with resource recovery.

5. What is the primary importance of understanding probable reserves?

a) They provide an accurate estimate of the total amount of resources available. b) They help to assess the overall value and viability of a project. c) They eliminate all risk associated with resource development. d) They ensure that all reserves will be recovered.

Answer

b) They help to assess the overall value and viability of a project.

Probable Reserves Exercise

Scenario:

A company is evaluating a new oil field for potential development. They have identified a proven reserve of 5 million barrels of oil. Additionally, they have identified a potential probable reserve of 3 million barrels based on limited geological data and promising well logs.

Task:

  1. Explain the difference between the proven and probable reserves in this scenario, highlighting the uncertainty associated with each category.
  2. Discuss how the probable reserves can influence the company's decision-making regarding investment and development plans.
  3. Describe the role of probabilistic methods in this scenario and how they might be used to quantify the uncertainty associated with the probable reserves.

Exercice Correction

**1. Difference between Proven and Probable Reserves:** * **Proven Reserves:** These 5 million barrels represent a known and reliable quantity of oil that can be recovered with a high degree of certainty. Extensive drilling, production data, and reservoir analysis support this classification. * **Probable Reserves:** The 3 million barrels represent a potential resource, but with a higher degree of uncertainty. Limited geological data, well logs, and potential application of new recovery techniques are the basis for this classification. The likelihood of recovering this amount is greater than 50%, but not as certain as the proven reserves. **2. Influence on Decision-Making:** * **Investment:** The probable reserves add potential upside to the project, increasing the overall value proposition and potentially attracting investors. * **Development Plans:** The company might consider phased development, starting with the proven reserves and later incorporating the probable reserves if further data supports their existence and economic feasibility. * **Risk Assessment:** The company needs to carefully analyze the uncertainty associated with the probable reserves and consider potential downsides such as the risk of not recovering the estimated quantity. **3. Role of Probabilistic Methods:** * **Quantification of Uncertainty:** Probabilistic methods can be applied to the available data and geological models to quantify the likelihood of recovering the probable reserves. * **Range of Possibilities:** These methods can generate a range of possible outcomes for the probable reserves, allowing the company to make informed decisions based on various scenarios. * **Risk Mitigation:** Probabilistic methods can help identify potential risks associated with the probable reserves and inform strategies for mitigating those risks.


Books

  • Petroleum Resources Management System (PRMS): A Guide for Development, Implementation, and Use by SPE (Society of Petroleum Engineers): Provides a comprehensive overview of resource classification and reserve estimation, including detailed sections on probable reserves.
  • Petroleum Engineering Handbook by Jerry J. S. John: Offers in-depth coverage of various aspects of petroleum engineering, with chapters dedicated to reserve estimation and classification.
  • The Economics of Petroleum Exploration and Production by Robert M. Tiratsoo: Explores the economic principles underlying resource development, including the role of reserve classifications in financial decision-making.

Articles

  • "The Probabilistic Approach to Reserve Estimation" by the American Association of Petroleum Geologists (AAPG): Delves into the use of probabilistic methods for assessing reserves, including probable reserves.
  • "A Primer on Reserve Definitions" by the Canadian Association of Petroleum Producers (CAPP): Provides a clear explanation of different reserve categories, including probable reserves, with specific examples.
  • "Resource and Reserve Definitions - A Joint Statement by the Society of Petroleum Engineers, World Petroleum Council, American Association of Petroleum Geologists, Canadian Association of Petroleum Producers, Society of Petroleum Evaluation Engineers, and World Energy Council" (2010): Presents a unified framework for defining and classifying reserves, emphasizing the role of probable reserves.

Online Resources

  • Society of Petroleum Engineers (SPE): https://www.spe.org/ - Offers a wealth of information on reserve estimation, classification, and industry standards.
  • American Association of Petroleum Geologists (AAPG): https://www.aapg.org/ - Provides valuable resources for geological and reservoir characterization, including articles and data on probable reserves.
  • World Petroleum Council: https://www.worldpetroleum.org/ - Offers a global perspective on resource management and development, including standards and guidelines for reserve classification.

Search Tips

  • "Probable Reserves" + "Petroleum Engineering" - This search will return articles and documents specifically focused on probable reserves within the context of petroleum engineering.
  • "Reserve Classification" + "Oil & Gas" - This search will provide resources covering the overall framework of reserve classification, including the definition and significance of probable reserves.
  • "Probabilistic Reserve Estimation" + "Resource Assessment" - This search will lead you to articles and tools that focus on the use of statistical methods for estimating reserves, including probable reserves.
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