Unlocking Reservoir Secrets: The Power of the Horner Plot
The quest to understand the complexities of subterranean reservoirs drives the field of petroleum engineering. One vital tool in this pursuit is the Horner plot, a powerful graphical method used to analyze pressure buildup tests and extract crucial reservoir information.
Pressure Buildup Tests: A Glimpse into the Reservoir
Imagine injecting fluid into a well and then monitoring the pressure as it stabilizes. This pressure buildup test provides valuable data about the reservoir. The Horner plot analyzes this data, allowing engineers to:
- Predict the Virgin Reservoir Pressure (Pi): This represents the pressure within the reservoir before any production. Understanding Pi is crucial for determining the reservoir's energy potential and estimating production rates.
- Characterize Reservoir Properties: The plot reveals the permeability, skin factor, and wellbore storage coefficient, key parameters impacting production performance.
The Horner Plot: A Visual Tale of Pressure and Time
The Horner plot is a graphical representation of the pressure buildup data plotted against a specific time function. This function, known as the Horner time, is calculated using the time elapsed since the well shut-in and the time since the initial injection began.
Interpreting the Plot: Deciphering the Reservoir's Secrets
The beauty of the Horner plot lies in its ability to provide insights through visual analysis:
- Extrapolation to Zero Horner Time: The extrapolated line intersects the pressure axis at the virgin reservoir pressure (Pi).
- Slope (m) of the Extrapolated Line: The slope reveals the reservoir's properties:
- High Slope (m): Indicates high permeability or low wellbore storage.
- Low Slope (m): Indicates low permeability or high wellbore storage.
- Skin Effect: Deviations from the straight-line trend near the shut-in time indicate a skin effect, which can be caused by factors like damage or stimulation near the wellbore.
Beyond the Basics: Refining the Analysis
The basic Horner plot provides a valuable initial assessment. However, more sophisticated analysis techniques, such as the type curve matching method, can be used for:
- Accounting for Non-ideal Flow: The basic Horner plot assumes radial flow, which may not always be accurate. Type curves allow for analyzing different flow regimes, such as linear or elliptical flow, leading to more accurate results.
- Improving Accuracy: Type curve matching helps refine the determination of reservoir properties, providing a more precise estimate of Pi and other parameters.
The Horner Plot: An Essential Tool for Reservoir Characterization
The Horner plot is a powerful tool for analyzing pressure buildup tests, extracting key reservoir properties, and predicting virgin reservoir pressure. It empowers engineers to make informed decisions regarding production strategies and optimize reservoir development. As technology evolves, more sophisticated applications of the Horner plot continue to enhance our understanding of the complex world of subsurface reservoirs.
Test Your Knowledge
Quiz: Unlocking Reservoir Secrets with the Horner Plot
Instructions: Choose the best answer for each question.
1. The Horner plot is primarily used to analyze data from: a) Production logs b) Seismic surveys c) Pressure buildup tests d) Core samples
Answer
c) Pressure buildup tests
2. What does the extrapolated line on a Horner plot intersect at zero Horner time? a) Wellbore storage coefficient b) Skin factor c) Virgin reservoir pressure (Pi) d) Permeability
Answer
c) Virgin reservoir pressure (Pi)
3. A high slope (m) on a Horner plot typically indicates: a) Low permeability and high wellbore storage b) High permeability and low wellbore storage c) High permeability and high wellbore storage d) Low permeability and low wellbore storage
Answer
b) High permeability and low wellbore storage
4. Deviations from the straight-line trend on a Horner plot near the shut-in time could indicate: a) A perfectly homogeneous reservoir b) A lack of wellbore storage c) A skin effect d) A perfectly radial flow regime
Answer
c) A skin effect
5. The type curve matching method is used to: a) Determine the wellbore storage coefficient b) Account for non-ideal flow regimes c) Calculate the skin factor d) Estimate the virgin reservoir pressure (Pi)
Answer
b) Account for non-ideal flow regimes
Exercise: Applying the Horner Plot
Scenario:
A pressure buildup test was conducted on a well. The following data was recorded:
| Time (hours) | Pressure (psi) | |---|---| | 0 | 2000 | | 1 | 2200 | | 2 | 2300 | | 4 | 2400 | | 8 | 2500 |
Task:
- Plot the data on a Horner plot using Horner time (tH) as the x-axis and pressure (P) as the y-axis.
- Horner time (tH) = (ts + tp)/tp, where ts is the time since shut-in and tp is the time since the initial injection began.
- Extrapolate the straight line portion of the plot to zero Horner time.
- Determine the virgin reservoir pressure (Pi) from the intersection point.
- Comment on the slope of the extrapolated line and what it indicates about the reservoir.
Exercise Correction
**1. Horner Plot:** The data should be plotted on a graph with Horner time (tH) on the x-axis and pressure (P) on the y-axis. The Horner time values for each data point can be calculated as follows: | Time (hours) | ts (hours) | tp (hours) | tH | Pressure (psi) | |---|---|---|---|---| | 0 | 0 | 0 | N/A | 2000 | | 1 | 1 | 1 | 2 | 2200 | | 2 | 2 | 1 | 3 | 2300 | | 4 | 4 | 1 | 5 | 2400 | | 8 | 8 | 1 | 9 | 2500 | **2. Extrapolation:** The data points should show a roughly linear trend. Draw a straight line that best fits the data points and extrapolate it back to zero Horner time. **3. Virgin Reservoir Pressure (Pi):** The intersection of the extrapolated line with the y-axis (pressure axis) represents the virgin reservoir pressure (Pi). Based on the plot, the Pi should be approximately 2600 psi. **4. Slope:** The slope of the extrapolated line is an indication of the reservoir's permeability. A steeper slope suggests higher permeability, while a shallower slope indicates lower permeability. **Note:** Without more detailed information about the well and reservoir, a definitive interpretation of the slope is not possible.
Books
- "Petroleum Engineering Handbook" (2007) by Tarek Ahmed, edited by John Lee. Chapters on pressure transient analysis and well testing methods, including Horner plot.
- "Well Test Analysis" (1987) by R.G. Matthews and D.G. Russell. Comprehensive coverage of well testing techniques, including Horner plot analysis.
- "Modern Well Test Analysis: A Computer-Assisted Approach" (1989) by G.A. Matthews and D.G. Russell. Focuses on computer-based analysis of well test data, including Horner plots.
- "Production and Testing of Oil and Gas Wells" (2008) by Tarek Ahmed. Covers practical aspects of oil and gas production, including pressure transient analysis and Horner plot applications.
- "Applied Petroleum Reservoir Engineering" (2010) by J.P. Donaldson, M.J. Beckner, H.S. Fogler. Provides a general introduction to reservoir engineering and covers Horner plot analysis in the context of well testing.
Articles
- "A Practical Guide to Pressure Transient Analysis in Oil and Gas Wells" (2018) by J.P. Donaldson and M.J. Beckner. Provides a concise overview of pressure transient analysis, including Horner plot and type curve matching techniques.
- "Pressure Transient Analysis of Multi-Well Systems" (2008) by J.P. Donaldson and M.J. Beckner. Discusses the application of Horner plot and other methods for analyzing pressure transients in complex reservoir systems.
- "Horner Plot Analysis: A Practical Approach" (2004) by R.G. Matthews. Provides step-by-step instructions for applying Horner plot analysis to real-world well test data.
- "Type Curve Matching: A Powerful Tool for Well Test Analysis" (2012) by G.A. Matthews. Explains the principles of type curve matching and its application in conjunction with Horner plot analysis.
Online Resources
- SPE (Society of Petroleum Engineers) website: Extensive library of articles, technical papers, and presentations on well testing, pressure transient analysis, and Horner plot applications.
- Oil & Gas Journal: Industry publication with articles and resources related to oil and gas production, including well testing and reservoir characterization.
- Schlumberger's website: Information on well testing services and software, including tools for Horner plot analysis and type curve matching.
- Halliburton's website: Resources on well testing and reservoir characterization, including information on Horner plot analysis and its applications.
Search Tips
- Use specific keywords: Include "Horner plot," "pressure buildup test," "well testing," "reservoir characterization," "type curve matching," etc.
- Combine keywords: Use phrases like "Horner plot analysis," "applying Horner plot," "Horner plot example," etc.
- Include specific reservoir properties: Search for "Horner plot permeability," "Horner plot skin factor," "Horner plot wellbore storage," etc.
- Use quotation marks: Enclose specific terms in quotation marks to find exact matches, e.g., "Horner plot" or "type curve matching."
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