Reservoir Engineering

Scorpion Plot

The Scorpion Plot: A Stinging Tool for Workover Analysis

In the oil and gas industry, workovers are crucial for rejuvenating aging wells, addressing production issues, and extending field life. However, deciding whether a workover is economically viable requires careful analysis. This is where the Scorpion Plot comes in, a powerful tool for visualizing and evaluating the economic impact of workovers.

What is a Scorpion Plot?

A Scorpion Plot is a graphical representation of the relationship between well production (typically oil or gas rate) and cost of operations, specifically focusing on the impact of workovers. The plot gets its name from its shape:

  • Tail: Represents the production performance of the well before the workover. This section typically shows a declining production trend.
  • Body: Represents the workover itself, depicting the initial cost incurred.
  • Stinger: Represents the post-workover production performance, showcasing the potential increase in production after the intervention.

Why is it Useful?

The Scorpion Plot offers a clear visual comparison of the cost and benefits of a workover, allowing for informed decision-making:

  • Economic Viability: The length of the stinger relative to the body of the scorpion indicates the profitability of the workover. A long, impactful stinger justifies the cost of the workover, while a short, ineffective stinger suggests the intervention was not financially worthwhile.
  • Workover Effectiveness: Comparing Scorpion Plots for different wells or different workover strategies highlights the relative effectiveness of each intervention.
  • Trend Identification: Analyzing the shape of the scorpion can reveal potential issues:
    • Flat stinger: May suggest the workover did not address the root cause of the production decline.
    • Rapidly declining stinger: May indicate short-term success but point to underlying problems.
    • Steeply rising body: Indicates a significant investment in the workover, requiring a substantial post-workover production increase to justify the cost.

Example:

Imagine two wells, both undergoing workovers. Well A experiences a significant post-workover production increase, resulting in a long, impactful stinger. Well B, on the other hand, shows a minimal production increase, leading to a short, weak stinger. The Scorpion Plot clearly demonstrates the superior economic viability of the workover performed on Well A.

Beyond the Graph:

While the Scorpion Plot provides a valuable visual representation, it's important to consider additional factors for comprehensive workover evaluation:

  • Well history: Understanding previous production trends and interventions is crucial for accurate analysis.
  • Field conditions: Factors like reservoir characteristics, well completion details, and regional production patterns influence workover effectiveness.
  • Cost breakdown: Analyzing the cost breakdown of the workover helps identify areas for potential optimization.

Conclusion:

The Scorpion Plot serves as a powerful tool for visualizing and evaluating workover performance, aiding in informed decision-making and maximizing economic value from aging wells. By understanding the cost-benefit relationship and analyzing production trends, this visual representation empowers operators to make strategic choices about workovers, ultimately contributing to the long-term success of oil and gas operations.


Test Your Knowledge

Scorpion Plot Quiz:

Instructions: Choose the best answer for each question.

1. What does the "tail" of a Scorpion Plot represent?

a) The cost of the workover b) The well's production after the workover c) The well's production before the workover d) The overall production decline of the well

Answer

c) The well's production before the workover

2. What does a long, impactful "stinger" in a Scorpion Plot indicate?

a) The workover was unsuccessful b) The workover was highly profitable c) The workover cost more than the production gains d) The well's production declined rapidly after the workover

Answer

b) The workover was highly profitable

3. Which of the following is NOT a factor to consider when evaluating a Scorpion Plot?

a) The well's production history b) The type of workover performed c) The oil price at the time of the workover d) The reservoir characteristics of the well

Answer

c) The oil price at the time of the workover

4. A Scorpion Plot with a "flat stinger" might suggest that:

a) The workover effectively addressed the production decline b) The workover was extremely expensive c) The workover did not address the root cause of the decline d) The well is nearing the end of its production life

Answer

c) The workover did not address the root cause of the decline

5. Why is the Scorpion Plot a valuable tool for workover analysis?

a) It simplifies the analysis of complex well data b) It visually displays the economic impact of a workover c) It predicts future production trends after a workover d) It eliminates the need for detailed well history analysis

Answer

b) It visually displays the economic impact of a workover

Scorpion Plot Exercise:

Scenario:

You are reviewing two Scorpion Plots for different wells that underwent workovers.

  • Well A: Shows a gradual decline in production before the workover (tail), a significant investment in the workover (body), and a steep increase in production immediately after the workover, followed by a gradual decline (stinger).
  • Well B: Shows a steep decline in production before the workover (tail), a moderate investment in the workover (body), and a slight increase in production after the workover, followed by a continued decline (stinger).

Task:

Analyze the two Scorpion Plots and answer the following questions:

  1. Which well experienced a more successful workover based on the Scorpion Plot?
  2. What insights can you draw about the potential causes of the production decline in each well before the workover?
  3. Which well would you recommend for further investment in workovers based on the Scorpion Plots?

Exercice Correction

1. **Well A** experienced a more successful workover as it shows a significant production increase following the workover, indicating that the intervention addressed the production decline effectively. 2. **Well A:** The gradual decline before the workover suggests a potential issue with natural reservoir depletion or gradual decline in well performance. **Well B:** The steep decline suggests a more rapid and severe production decline, potentially due to a sudden issue like wellbore damage, plugging, or a significant change in reservoir conditions. 3. **Well A** shows a more promising response to workover, justifying further investment to potentially extend the well's production life. Well B, despite a modest improvement, shows a less impactful workover and might require further evaluation and possibly a different intervention strategy.


Books

  • Petroleum Engineering Handbook: This comprehensive handbook likely includes a section on workover analysis and may touch upon Scorpion Plots.
  • Production Optimization of Oil and Gas Wells: Books focusing on production optimization techniques often cover workover evaluation methods like the Scorpion Plot.
  • Reservoir Engineering: Books on reservoir engineering may include discussions on production forecasting and workover strategies, potentially mentioning the Scorpion Plot.

Articles

  • "Workover Analysis using the Scorpion Plot" by [Author Name]: Search for articles specifically titled "Scorpion Plot" or "Workover Analysis" to find relevant content.
  • "A Comprehensive Guide to Workover Operations in the Oil and Gas Industry": Articles summarizing workover practices may include the Scorpion Plot as a decision-making tool.
  • Industry Journals: Publications like SPE Journal, Journal of Petroleum Technology, and other oil and gas journals might feature articles discussing workover evaluation techniques and potentially utilizing Scorpion Plots.

Online Resources

  • SPE (Society of Petroleum Engineers): The SPE website, including their online library and search engine, could contain resources on workover analysis and Scorpion Plots.
  • Google Scholar: Use Google Scholar to search for academic publications that mention "Scorpion Plot" or "Workover Analysis" in the context of oil and gas.
  • Oil and Gas Industry Websites: Websites of major oil and gas companies or industry organizations might have articles or presentations discussing workover evaluation methods.

Search Tips

  • Use specific keywords: "Scorpion Plot," "Workover Analysis," "Oil & Gas Production," "Economic Evaluation."
  • Combine keywords: Try phrases like "Scorpion Plot workover evaluation" or "economic analysis using Scorpion Plot."
  • Use advanced search operators:
    • "filetype:pdf" to find PDF documents
    • "site:spe.org" to search only within the SPE website
    • "related: [URL]" to find similar resources to a website you know

Techniques

Chapter 1: Techniques for Constructing Scorpion Plots

The Scorpion Plot, as described previously, is a valuable tool for workover analysis. This chapter delves into the specific techniques used to construct these insightful plots.

1. Data Gathering:

  • Production Data: Obtain historical production data for the well, including oil, gas, or water rates. This data should span a sufficient period before and after the workover.
  • Workover Costs: Collect a detailed breakdown of all costs associated with the workover, including labor, materials, equipment, and permits.
  • Time Stamps: Ensure accurate time stamps for both production data and workover costs, aligning them to provide a clear chronological representation.

2. Data Preparation:

  • Normalizing Production Data: Standardize production rates to a common unit (e.g., barrels of oil equivalent per day). This enables consistent comparison across different wells or workovers.
  • Cost Aggregation: Summarize the total workover cost into a single value representing the investment.
  • Data Visualization Software: Utilize suitable software (e.g., Excel, MATLAB, Python) to handle data manipulation, plotting, and visualization.

3. Plot Construction:

  • X-Axis: Represent time, spanning a period before and after the workover. This axis allows for the visualization of production trends over time.
  • Y-Axis: Plot production rate on the left y-axis, and cost on the right y-axis. Ensure consistent scaling for both axes.
  • Pre-Workover Tail: Plot production data prior to the workover, representing the well's declining performance.
  • Workover Body: Mark the workover time period on the x-axis. Represent the total workover cost as a vertical bar extending upwards from the x-axis.
  • Post-Workover Stinger: Plot production data post-workover, showcasing the impact of the intervention. The length and direction of this section reveal the workover's success.

4. Plot Interpretation:

  • Stinger Length: A long, upward-trending stinger indicates significant production improvement, justifying the workover cost.
  • Stinger Slope: A steep upward slope suggests a rapid production increase. A gradual slope suggests a slower recovery.
  • Body Height: A high body indicates a significant investment in the workover. It must be accompanied by a substantial production increase for profitability.
  • Flat Stinger: A flat stinger suggests the workover failed to address the production decline.
  • Declining Stinger: A rapidly declining stinger indicates a short-term improvement followed by further production loss, suggesting underlying issues.

5. Additional Considerations:

  • Data Quality: Ensure data accuracy and completeness. Poor data can lead to misleading plots and inaccurate conclusions.
  • Well Specifics: Consider factors like reservoir characteristics, well completion, and production history. This context helps interpret the plot effectively.
  • Sensitivity Analysis: Varying workover costs and production projections can assess the robustness of the economic decision.

Conclusion:

Constructing a Scorpion Plot requires careful data collection, preparation, and visualization. By mastering these techniques, operators gain valuable insights into workover performance, enabling informed decisions that maximize economic value.

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